To me this seems to be a good idea, is it possible, what would be involved?

Huh....?:confused:

I think he means getting all the stuff from the 1981 368 V-8-6-4 and putting it on a 500 so you could cut it down to 4 cylinders wich crusing on the highway or something...

It would take mounting the rocker setup from a 368 on some 500 heads or using something custom. There might be material enough to drill the heads and mount them like that, otherwise it'll be a real pain...

Well I remember bbob saying something about an olds 455 w/ that setup but he didn't give much detail, I would think it could be done relatively easily and even running on 4 cyls a 500 should still have plenty of power, after all that is still 250 cu in

yeah but out of those 4 cylinders, only like 2.5 or so are being used to drive the car...

it isn't like have a 4.1L 4banger under the hood all of a sudden, it is still alot of work for the 4 remaining cylinders to be turning the whole enigne... that is one of the reasons when the NorthStar is in Limp Home mode, it can only go about 50mph.... thinking have half the cylinders, half the hp, you would have a 150hp 4banger... that dosn't work... lot of internal drag on the engine with those setups.

why would you want that setup anyways? it is my understanding that the V8-6-4 engines were quite flawed and that's one of the reasons cadillac came out with the ht 4100 engine...something doesn't seem right about that :hmm: .

fuel efficiency, the problems were mainly power related and an "unbalanced feeling" in 6 cyl mode, the 500 would take care of the first and bypassing the 6 cyl mode would solve the second problem.

To clarify a few items, the Northstar's limp home mode holds the valves open if memory serves. The 8-6-4 kept them closed, using that cylinder as an air spring. The problems with that setup stemmed from the inadequate computer technology to run such a system. If you were to controll it manually (with switches... they are just solenoids after all...) The system would probably work very well. If you also happen to have an electronic kickdown ala TH400, then you could even wire it up so it automatically switches to V8 when you floor it, so when you want to pass, you leave your manually controled toggle in 4 cyl, punch it, the car switches to 8 cyl, drops into passing gear and zips around the car your overtaking. Let up, and your back in crusing gear and in 4 cyl mode (or whatever your switches are set to)

the idea is really not a bad one, after all diamler chrysler and GM are both rehashing the idea, and they work similarly to the 8-6-4 and since the 368 and 500 are in the same engine family I would think the hardware would work.

Oh, and for those thinking otherwise, this is perfectly doable with a carburetor. The FI system on the cars equipped with this system factory were IIRC throttle body injection, no disabling of the injectors based on mode. With a carb, the metering is airflow based, so it will adapt to the demands of the engine. There wont be much stagnant mixture in the runners of the disabled cylinders, as there is no vacuum coming from that runner anymore.

having a V8 run as a V4..... woudln't that cause internal stress on the engine? the carnk isn't getting equal pressure across it, some pistons are being fired on while others are not etc... I just don't think it would be good for an engine... not to mention a performance engine...

the cyls being fired are puting no extra stress on the crank as the produce no more power than they would normally, in all likelyhood it puts less stress on the engine

I am a bit surprised that no one else has an opinion on this and bbob hasn't chimed in I got the feeling from a different thread that he liked the mod disp setup.

The modulated displacement setup worked great. There was absolutely no problem with the modulated displacement idea or hardware. The electronic controls of the day would not allow for "seemless" or "transparent" operation of the various displacment modes so there were driveability complaints from some people but most people thought it was fine once they understood the idea.

The displacement on demand system of today is exactly the same concept...just slightly different hardware.

Putting the V864 hardware on an old 500 cubic inch Cadillac motor is pretty simple. The hardware all bolts on and the solenoids are all 12 volts so you can just hook it up to a toggle switch. Run it with HEI and a carb and it would work fine.

The modulated displacement sytem closes both the valves so that what is trapped in the cylinder stays in the cylinder and what is compressed just pushes the piston back down like an air spring.

Contrary to opinions above an 8 liter V8 "modulated" to run on 4 cylinders as a 4 liter would have exactly the same power as an equivalent 4 liter... The deactivated cylinders take very very little to operate them...just the friction in the bearings and pistons. All the energy put into compressing the gases in the cylinder is returned when the compressed mixture pushes the piston back down.

The Northstar limp home mode is a COMPLETELY different phenomenon. In the limp home mode the valves operate as normal. They open and close just as they always do so the cylinder is still pumping air thru it and out the exhaust. The cylinder is deactivated by turning off the injector to that cylinder so it doesn't fire and doesn't make power. In 4 cylinder limp home mode the engine really does have only the power of about 2.5 cylinders.... The reason it looses so much power is the pumping losses of pumping air thru those 4 dead cylinders. So it is very weak but it can cool itself this way and protect itself in the event of a severe overheat event.

thanks bbob
what parts would be needed from an 8-6-4 to acomplish this and is there an overdrive tranny to comliment this setup the idea would be to have the ultimate full economy mode but be able to kick a$$ when you wanted.
what would be a good light weight vehicle to drop this into (firebird, camaro ect.)
this would be a project that I would like to do sometime in the future but was unsure if it was even possible.

it is possible to do the V864 setup on a performance built 500? or will those parts not be able to handle the extra power from the engine?

Now that it seems doable, I am really interested in this...

any idea what kind of power loss /mpg gain in 4 cyl mode on an otherwise stock 500?

If you can find an 81 V864 engine then get the rocker arms and the solenoids attached to the rocker arms on the deactivating cylinders. Also, get the valve covers as they are taller with clearance bumps for the solenoids. Probably get the pushrods also but I think that they were the same.

Pretty much should bolt onto a 500...just replace the original rocker arms with the V864 parts.

As long as the 'built" 500 was using the production rocker arms it could use the V864 mechanisms. Unless you are thinking of using pro-stock valve springs on that 500 the V864 mechanism will be fine. The engine power has no effect on it. Just the valve spring load and it is capable of handling the stock springs fine so I suspect that there is plenty of reserve load capability there.

Hard to predict fuel economy...the V864 was usually good for about a 20 % improvement if operated in 4 cylinder mode exclusively...so it can be worth quite a bit.

A camaro/firebird with a build Caddy 500 with the V864 setup would be cool. With a 4T80E w/overdrive or an overdrive manual trans and the right gears the car could have tons of power and cruise down the road loafing along in 4 cylinder mode. Neat.

what years of F body would work best, I am kinda partial to 2nd and 3rd gen myself

would a third gen camaro or trans am be able to handle the 500 (engine compartment,hood clearance,frame strength etc.) if so, what would be the ideal setup for one and how easy would it be to convert the wiring. would there be any other mods involved(suspension, brakes etc.)

bump

possible stupid question, isn't the 4t80e a transverse mounted tranny? and if not what vehicles would have one?

anyone?

Yes, it is a transverse mounted tranny.

Was found in Cadillac Seville, Cadillac De Ville and Oldsmobile Aurora.

A 2nd gen with a v864 500 would be awesome to see!

is there a rwd version of the 4t80e I know the 700r4 can't handle a 500 so what can?

Yes...it is called the 4L80E. It would easily handle a 500 Cadillac. Check any of the hot rod magazines for ads for transmission shops for an idea.

at one time i had a 472 in my 2nd gen. it was a nice fit with a rear sump pan. bbc headers w/ caddy flanges bolted right in. i got as far as starting fitting a 472 in my 85 iroc and found not much room between the strut towers for exhaust manifolds. i never got as far as trying to fit manifolds or headers cause i found the car had been wrecked and was not structurally sound, so that got scrapped.

the 4L80-e would be beautiful behind a big cad motor, however they are $$$$$ trannies(i've seen cores go for close to a grand). and they require an expensive stand-alone controller to control them, as they are ECM controlled and the shifting is done via electronic solenoids. a built 700r4 would do the job if you use good parts. all the updated parts that went into the 4L60-e(rear planetary set and other things), aftermarket hardened sun shell, good clutches and band, 13 vane pump.

would 3rd gen stock suspension be able to handle the extra weight? and w/ the 8-6-4 hardware would there be any clearance issues w/ an otherwise stock 500

would 3rd gen stock suspension be able to handle the extra weight? and w/ the 8-6-4 hardware would there be any clearance issues w/ an otherwise stock 500
Would you really want stock suspension with this kind of mod? I would think you might consider an Eibach setup for the Camaro or Firebird, you have a bit more weight with the larger engine. With a Camaro/Firebird scenario have you considered an aftermarket glass tilt front end? This would help with weight and also make it easier to change plugs later on the beast. If it is done properly I think it might be hard to tell from stock. It seems to me that, along with extended economy while cruising, there is a nice little 'Sleeper' potential here, eh? :yup:

Kev

and they require an expensive stand-alone controller to control them, as they are ECM controlled and the shifting is done via electronic solenoids.

I've heard that the 4L80E was used in some diesel trucks and had a seperate controller that can be pulled from a junkyard for cheap and used.

question...

is the 4L80E a Turbo 400 with OD? (as I have heard before)

It is its own transmission, although it uses a lot of TH400 components. It's a very solid tranny, it even weighs in 100 pounds heavier than a 400 which is no lightweight.

If you can find an 81 V864 engine then get the rocker arms and the solenoids attached to the rocker arms on the deactivating cylinders. Also, get the valve covers as they are taller with clearance bumps for the solenoids. Probably get the pushrods also but I think that they were the same.

Pretty much should bolt onto a 500...just replace the original rocker arms with the V864 parts.

As long as the 'built" 500 was using the production rocker arms it could use the V864 mechanisms. Unless you are thinking of using pro-stock valve springs on that 500 the V864 mechanism will be fine. The engine power has no effect on it. Just the valve spring load and it is capable of handling the stock springs fine so I suspect that there is plenty of reserve load capability there.

Hard to predict fuel economy...the V864 was usually good for about a 20 % improvement if operated in 4 cylinder mode exclusively...so it can be worth quite a bit.

A camaro/firebird with a build Caddy 500 with the V864 setup would be cool. With a 4T80E w/overdrive or an overdrive manual trans and the right gears the car could have tons of power and cruise down the road loafing along in 4 cylinder mode. Neat.

I am going to the junkyard tomorrow... if it isn't raining that bad. From the '81 Fleetwood I will remove the valve covers, take those....... then take all the rocker arms? this is all I should get from that car (to make this work)

Is there anything I should get from the 368 that could be of use to me in my '79 or the 425.... there is no damage to the car, so nothing is broke (accident etc...)

if the front passenger side wheel opening molding is the same as your 79 could you snag it for me if its not bent? i'll pay for it and shipping. i cant find it anywhere around here.

I do not understand what you need....

you mean the plastic wheel well piece?

those are always around and at junkyards... but to ship thing thing would be a PITA..... maybe get a picture of the dirver side... or where it goes on the passenger side etc....

ok guys i have a question! i ve got a new project which is a 74' 26ft gmc motorhome.
originally it powered by olds455 v-8/th425/3.07 axle ratio ("toro set up). same style r.v used in stripes movie with bill murray.. well the engine was replaced with an olds 307. which i fill wont have the power of cucumber water . id like to install a cadillac v864 set up with a carburator.. ive owned the 81 eldo but i dont think the stock 368 would have sufficient torque to move the r.v which ways 11,000lbs. would i get better power by using a 368 and having the heads shaved .030 should bump compression up from 8.25 to 8.75 . i have access now to a 425 caddy v-8 but im not sure of what it would take to installl the solinoids . its been a while since ive had the valve covers off to see how it allbolts 2 gether .. is it possible to put the 368 modulated solinoid heads on a 425 or 500 caddy v-8 this may be an off the wall idea but i feel the caddy engines would pull the truck as well as the 455 olds ever did but im thinking with modulated set up it will get better fuel economy on the highway.. the sad thing is i have an olds 455 rocket v-8 to build for the truck now, but this idea of the v864 set up just came 2 mind and though an uncle of mind says it will not work i kinda wanna prove him wrong ..all replys will be most appreciated ..

That's what this entire thread was about. Please re-read it.

You really have to think about what you are asking of your extreemy high rod angle engine. This worked just barely in the 368, in the 500, I bet you'd snap a rod in 100 miles.

what you're asking of the engine in modulated displacement mode is no more than what you're asking of it any other time it is running. The valves simply stay closed, and the pistons compress and expand the same mixture over and over again. How this would be any harder than compressing a fresh mixture, I have no idea.

Also, Caddy engines have been very well proven as reliable tow motors by many, many people. They're up to it.
IMO, the whole rod angle thing seems pretty overblown for a street engine. There are both gains and benefits to both long and short rod engines, but if it is well assembled and maintained, either will provide plenty of reliable power on the street.

Well, I am bringing this thread back for a good reason....

I bought the stuff needed to convert my 425 to V8-6-4 :)

So, from that 1981 Fleetwood, I removed both valve covers, I saw the selonoids, so I got them, and I got the rocker arms *ONLY* on the 4 selonoids... for the other 4 "normal" cylinders, I left them... my my stock rocker arms be ok?

I then spliced the wire harnesses as far back as I could on all 4 of the selonoids.

So I have 4 sets of rocker arms, 4 selonoids, 2 valve covers and a few misc. parts.

Then I bought Fel-Pro rubber valve cover gaskets, and a 3 position toggle switch (center off, up and down both on) and some 18gauge wire to rig it all up...

Now here is the question... when I pull the valve cover off the 425, do I just put all this stuff in like it came out of the 368? so 2 center cylinders on the left bank and 2 outter cylinders on the right bank?

So to wire them up for 6/4 cylinder mode, which 2 are a pair? the 2 cylinders that can be deactivated in the front, and the 2 in the back?

Then the next question is, what is the best way to wire it up to the switch? It is a simple 3 position rocker switch, ont he back are 6 terminals.... how I take it, the selonoids act as if they weren't there when no power is sent, so when they get power, that is when they deactiveate the cylinder? in that case, "center" on the switch will be 8 cylinder mode ("off") up will be 6 cylinder mode (wire only 2 selonoids to the terminals) and down will be 4 cylinder mode (wire all 4 to the terminals) Will this work?

Also, how exactly do they deactiveate the cylinders? I was holding the selonoids in my hand and moving the thing back and fourth, and I really didn't see anything going on to disable the rocker arm or anything....

hopefully with any luck, I'll get a start on it tomorrow night.... my 425 may not be the fastest around, but it'll sure be the most cool, and fuel efficent :)

I have been doing some more reading about this now....

Some say that the 368 rocker arms will not bolt up to the 425 heads? I kept all the bolts from the 368 that I removed.... Will this be a simple swap?

Also, Bbob was mentioning that in 6 cylinder mode it would run very rough, so my question is, should I just forget about 6 cylinder mode? return the 3 posistion switch for a simple on/off switch? it would make wiring it up a whole bunch better.... as it would get rid of all the guess work involved, and also the switch for on/off would look alot better then the one I have now.

But the main issue is, will the rocker arms bolt on? I don't wanna bring the Caddy in the shop and start tearing it down only to find that I am not able to move the car for a while now.

*The more I think about it, the more I want to return the switch and make it V8 or V4 mode only.... just get rid of the V6 mode.... I think the stock 425 has the power to drive around in 4 cylinder mode, not to mention I will be doing some work to get a little more out of it too...

I don't know, but it doesn't take long to pull a valve cover. You could probably look at it and be able to tell if the rockers will fit. Probably better to wait a couple days in case someone knows for sure though.

yeah, but I don't want to pull the valve cover, then put it back on only to have it leak.... so I figured when I do it, I'll do it all in one shot, and install the new gaskets too....

I thought the 425 uses the t-pedastal rockers, which would mean that the V864 rockers are not a bolt-in.

If your rockers are not interchangable, what you'll need to do is buy a stud mount rocker conversion kit from one of the places that sells them and mount the V864 rockers to that. Of course, then you might want the other four rocker assemblies, plus the 368's rockers are a much better design than those crappy t-pedastals anyways.
This is what I am planning to do on my 472 some year. I think I've worked out almost all the little issues in my head...

I would only rig it up as a V8-4 setup. I have heard that one of the problems with the V864 was engine roughness in the V6 mode. 4 cylinders leaves you with 213ci, which would be more than enough on the highway, or even around town if you're not accelerating.

yeah, I bought a switch for on/off, only 8 or 4, much more simple this way....

So these things are not a direct bolt in?

How much trouble exactly am I gonna be going thru to get the thing to work? Should I go back to the yard and pull the other 4 rockers from that 368?

Not sure, I am not familiar with the 425. I am only really familiar with the 472ci motor which uses the T-pedastals. The pedastals use one bolt between the two rockers to hold the whole thing down, as opposed to the two bolts used by the 368 motor, and there's not enough room, at least not on 472 heads to drill and tap holes for the 368's rockers. The 368's setup also seems ALOT more stable than the pedastals which have problems with higher RPM's.
Personally, I grabbed all of the assemblies when I pulled the stuff off a V864 motor. That way they'll all be the same, they are newer than my current rockers, and should be more reliable in the long run.

As for fitting them onto a head that came with pedastals, I forget which company had them (do a search for another thread on here about V864's, there's a link there I think) but there is a kit out there to convert the pedastal rockers to stud rockers. You do have to remove the heads, and have a machine shop mill down the pedastal mounts. Then, bolt a metal plate onto the holes that the pedastals used to use. This plate has holes drilled and tapped for the rocker studs.
A few changes would be needed to the conversion kit for these though. First, you'd need to use countersunk bolts to hold down the plate so it doesn't interfere with the base of the 368's rocker setup. You'd also have to make sure the holes for the studs aren't too big for the 368's rocker bolts, or ask them to drill and tap the plate for the right size bolt.

I guess it depends how much work you want to put into it. The idea of even getting 20mpg highway I think is worth it. Plus, I have a few broken exhaust manifold studs so I have to pull the heads at some point anyways... I figure I'll go all out; port the heads, install bigger valves, add headers and the modulated displacement system all in one go. Should be fun. The way money and time are shaping up though, it probably won't be untill next summer though.

well, when I go back to the junkyard (wasn't planning on it for awhile though) I will snag the other 4 sets of rocker arms, I should have got them there, but oh well...

I know what you mean now... honestly, I do not know, I *THINK* they use the pedistal-type supports, I guess the only way to find out besides someone telling me, so to pull the covers and look.

If it really requires what you are talking about, then I am going to forget it... as it is right now, I have a strict "no head removeal" policy, not only for the work involved, down time of the car etc.... but if I get the heads removed, I will want to get them ported and polished, then I will want to change the cam, and a whole other host of stuff.... IOW alot more then I want to do with the 425, I am saving all the major hot-rodding for a 472/500 in the future.

Well, worst comes to worst, I don't install it yet, and I have the parts laying around... can't beat that, I mean these things are getting rare now, so having them around waiting for me is nice, they have a nice coating of (semi-gunky) oil on them so they wont rust.... the only thing is I paid about $25 for valve cover gaskets I will not use.... eh, never know though, if I ever need to remove the covers, or pull them off to paint them (rusty) I will be all set...

Yes your 425 has the T pedistal PiecesOS. If one of you ever gets around to doing this, by all means take some pics of the process. I doubt I'll ever do it since I won't care about mileage in the 75 since it's just weekend car which will be propane fired anyway, but someone else might.

I have wondered how good a 425 would be on gas in V4 mode, with the fuel milage cam from MTS, and either stock stock TH400/2.28 gears or an overdrive setup....

Obviosuly it wouldn't be a race car, but for someone that is doing alot of highway driving, your 7.0L BB V8 would move the car around pretty well, but you may get something like 30mpg on the highway?!?

Really, if all that work is involved, when I will pass.... oh well, atleast I have the things. Maybe in the future when I build up a 472/500 I will use it, only thing is it would make the engine look ugly with the valve covers....

Still... there is no other way besides pulling the heads to do all the above mentioned work?... the light at the end of the tunnel is slowly fadding.... :(

Well, I haven't thought of a better way to get them in there. I had a T pedastal right next to a rocker assembley from the 368. The height from the mounting base to the rocker pivot is the same for each, so the base of the 368 rockers would have to rest right where the pedastals mount. Since the T's use a single bolt in the center, and the 368's use two bolts, I don't see a better plan without going to a really wierd way of mounting it.

I'll probably get around to it sometime with my student aid money :D Heads need to come off to fix the broken exhaust manifold bolts anyways. I don't mind 10city/15hwy too much except that I'd like to take a real roadtrip in this beast. Like 900 miles one way down to my fiances parents in California. Start working out the gas bill on that one! Then going from 15 to the low 20's (?) starts to really sound nice... If GM's claims from back in the day of the cylinder deactivation being better than overdrive for economy are true, the gain should be very noticable.

Rick
could you just machine a hole in the 368 rocker mount at the proper location?

Rick
could you just machine a hole in the 368 rocker mount at the proper location?

No, there are 2 seperate bolts running the length of the whole setup.... it woudln't work...

I'll have to get some pics of it all... kinda disapointing right now, but ah well....

search for 'V864 findings'. It's a thread I posted after I picked up my set, should have pics in there.
Yeah, it was diasppointing for me as well. I was figuring to bring them home and bolt them on, have variable displacement in a day or two... Oh well.
Oh, if you're still wanting to do it, another part you might want is the spacer that goes between the throttle body and aircleaner on the V864 engine. It spaces the cleaner up so the snorkel clears the valvecovers. A more vertical path to the carb is also better for power.

search for 'V864 findings'. It's a thread I posted after I picked up my set, should have pics in there.
Yeah, it was diasppointing for me as well. I was figuring to bring them home and bolt them on, have variable displacement in a day or two... Oh well.
Oh, if you're still wanting to do it, another part you might want is the spacer that goes between the throttle body and aircleaner on the V864 engine. It spaces the cleaner up so the snorkel clears the valvecovers. A more vertical path to the carb is also better for power.

Yeah, I saw that spacer there, the air cleaner was off of it though...

I use a 14" Edelbrock open element, and I have a total of 1.5" of spacers to clear the AC compressor....

I have read all the threads on the subject, including that one..... it is a sad day for me...

could someone get me a picture of those 425 heads?

Can this please be stickied? right under my cheap power improvements to 425 thread?

Not sure if this is a 425 head or a 472/500, but since the two interchange and use pedastal rockers, it should be close at least (the 425 just has smaller ports and different headgaskets)
The bolt centers for the 368 rocker assembley come in on either side of that pedastal mount.

Yes, this thread should definately be sticky. I think the swap is entirely do-able if you have the time to put into it.

Someone with some money should try the MTS economy cam, overdrive, and cylinder deactivation... Maybe toss EFI on top to boot. That'd be a dang sweet setup, and you could just look at Hondas and laugh :histeric:

not sure from the picture you provided but I don't see any difference b/w that head and the 368 picture in my 1981 factory service manual.......hmmm:hmm:

They might have used the wrong pic in the manual. The difference is in the mounting pads for the rocker setups.

not sure from the picture you provided but I don't see any difference b/w that head and the 368 picture in my 1981 factory service manual.......hmmm:hmm:
Would it be possible for you to post that picture? Then we'll know for sure and it won't keep me awake for a week! :coffee:

I was engineering a modified intake manifold that would take care of this for the 472 in the 69 limo... Which, by the way, gets back Friday with new paint!

The basic premise was that if you put valves (butterflies or something) inside the manifold (hell you could even open/close them with a lever/cable from inside the car)on top of cylinders 2,3,5, and 8, you'd have an even firing order of 1-6-4-7 every 90 degress on the crank - since it switches cylinder banks as well as front/rear firing positions, it should run smooth. If you just cut off air supply to those cylinders the spark could fire all it wanted to, but nothing woul dhappen because it wouldn't be getting any fuel. You might pull/push some exhaust fumes in through the exhaust valve because there would be a partial vacuum at the bottom of the combustion stroke, but you wouldn't move even 1/3 of the air you normally would since the only time the engine would be open to air would be during the exhaust stroke, pushing out whatever came in to fill the vacuum... The carburetor wouldn't know the difference - It would act just like the engine was spinning half as fast...

The only reason I haven't done this with the 472 is that the engine has 90k original miles and runs great, and the last thing I want to do before a 5k mile road trip is start taking apart a perfectly running engine...

Interesting ping pong game. You might notice that Cadillac didn't try to use modulated displacement until they had a feedback fuel system with ECM controlled EGR. I can't see a carbureted 8/6/4 doing much besides making a huge pinging noise when the idle cylinders are activated. Heck, you might find the piston skirts laying in the oil pan someday. The carbureted intake manifold is carefully designed to work into 8 pulses. Kind of like the way exhaust headers scavenge the cylinders using existing flow. 4 dead passages might confuse all those little atomized gas-o-particles.
The whole thing could be quite worthwile with decent fuel injection as they were back when Regan was the most powerful person on earth. The 8/6/4 cars were pretty darned good to grab for a song when they were a few years old and the owners started to believe the stupidity which was accepted as fact concerning that engine's reputation.

Putting valves in the manifold is not an effecient way to do it. You're still having the engine pull vacuum against the runner, which costs energy. With both valves deactivated, the trapped charge is simple compressed and expanded over and over, like pushing a spring. You get out the same energy you put in, more or less. You still have ring drag, but there's no way around that.

Ape, remember that the V864 motors were TBI. The manifold is pretty much the same as the carb manifold. The fuel will only be going where the air is, and with the intake valves not opening, the air simply won't be going there.
It should work out well with the dual plane manifold and every other cylinder deactivated. That way, one side of the carb sees no vacuum, and the other sees the same as normal. Since the fuel circuits for each side follow independent paths, you shouldn't have any fuel coming out on the inactive side.
Why do you think the inactive cylinders would start pinging when they are reactivated? The valves would open, and they would simply draw in a fresh charge.

Putting valves in the manifold is not an effecient way to do it. You're still having the engine pull vacuum against the runner, which costs energy. With both valves deactivated, the trapped charge is simple compressed and expanded over and over, like pushing a spring. You get out the same energy you put in, more or less. You still have ring drag, but there's no way around that.

Ape, remember that the V864 motors were TBI. The manifold is pretty much the same as the carb manifold. The fuel will only be going where the air is, and with the intake valves not opening, the air simply won't be going there.
It should work out well with the dual plane manifold and every other cylinder deactivated. That way, one side of the carb sees no vacuum, and the other sees the same as normal. Since the fuel circuits for each side follow independent paths, you shouldn't have any fuel coming out on the inactive side.
Why do you think the inactive cylinders would start pinging when they are reactivated? The valves would open, and they would simply draw in a fresh charge.

The 368 TBI intake is not really all that similar to a 425 or 472/500 intake. The ports are smaller and it is busier inside with some mouse maze looking areas. On top of that the TBI system has got to atomize fuel a whole lot easier than a carbonator. The fuel is being sprayed out under pressure verses being pulled out at much less than atmosphere.
Activated cylinders will hammer for a little while even with the factory 8/6/4. Ask anyone who has one on the road. My guess is that the ECM is programmed to provide a little extra EGR to keep that to a minimum.
If a carburetor were smart enough for this application then why didn't someone come out with 8/6/4 before the DEFI?

Actually, having the fuel pulled by vacuum is an advantage to the carburetor. Remember, the engine doesn't burn liquid fuel, it burns gasoline vapors. The lower pressure the fuel is at, the better it will vaporize.
EFI does benefit from more precise fuel metering with the O2 sensor and all, but a well tuned carb, particularly in a basically stock application does very well.

I think they didn't do anything like this earlier because fuel mileage was not as much of a concern. They had EFI for several years before trying the V864 idea. When the EFI alone wasn't enough to meet emissions and fuel economy needs they first downsized the engine to 425, then 368 before finally doing cylinder deactivation. High fuel economy simply wasn't a concern in the days of the 472 and 500 engines. The public as a whole doesn't care about fuel economy even today. Cylinder deactivation has only returned for the same reason that it came about in the first place - CAFE standards, and emissions regs.
Another interesting fuel economy car way back when was the Oldsmobile 'Turnpike Cruiser'. It got around 20 highway, and in the 8 second range for 0-60, not bad. Why don't we ever hear about it? The public preferred the Olds 442. Nobody cared that it got 15mpg at best - it was faster, and with no reason to keep a car around just for good mileage, Olds tanked the cruiser...

Actually, having the fuel pulled by vacuum is an advantage to the carburetor. Remember, the engine doesn't burn liquid fuel, it burns gasoline vapors. The lower pressure the fuel is at, the better it will vaporize.
EFI does benefit from more precise fuel metering with the O2 sensor and all, but a well tuned carb, particularly in a basically stock application does very well.

I think they didn't do anything like this earlier because fuel mileage was not as much of a concern. They had EFI for several years before trying the V864 idea. When the EFI alone wasn't enough to meet emissions and fuel economy needs they first downsized the engine to 425, then 368 before finally doing cylinder deactivation. High fuel economy simply wasn't a concern in the days of the 472 and 500 engines. The public as a whole doesn't care about fuel economy even today. Cylinder deactivation has only returned for the same reason that it came about in the first place - CAFE standards, and emissions regs.
Another interesting fuel economy car way back when was the Oldsmobile 'Turnpike Cruiser'. It got around 20 highway, and in the 8 second range for 0-60, not bad. Why don't we ever hear about it? The public preferred the Olds 442. Nobody cared that it got 15mpg at best - it was faster, and with no reason to keep a car around just for good mileage, Olds tanked the cruiser...

So you are saying that a TBI system will not atomize fuel as well as a carburetor?

I currently own a car with a carburetor that works so well it's hard to believe. It's still basically a toilet bowl filled with gasoline. Works great. I'd stil rather have fuel injection.

Fuel mileage was not a concern until CAFE? What were you doing in the 70's?

No matter how you slice it, the modulated displacement system alone is not going to buy a whole lot of extra gas mileage. It just isn't that simple. A good lockup 4 speed transmission and with a good choice of rear axle gears is a better route to put time and money into.

It might not. You've gotta distinguish between atomization, and vaporization though. Atomization simply referrs to little particles of liquid fuel. It encourages vaporization, but is not the same. Vaporization is when the fuel evaporates. Fuel also only burns in a vapor state.
TBI has an advantage over point injection with the injectors being further from the engine giving the fuel more time to vaporize.
This is actually one of the ways I've read of racers making the same power from EFI and carb - the EFI might give the same fuel to each cylinder, but the carb can vaporize it better. Of course, EFI can kick butt in a street application because of the problems of running a huge carb on the street, while a 2000cfm throttle body would be easy, and the better throttle response of EFI.
Don't put the carb down, especially a Q-jet is not at all a toilet bowl. There are alot of intracite systems that go into getting that fuel well mixed with air and put into the engine. The carb actually starts mixing the fuel with air before it even leaves the venturis, those air bleeds mix everything so that the venturis are actually spitting out a frothy air fuel mix. Tripple venturis on a Q-jet give excellent booster response as well as providing much reduced pressure at the outlet. As I mentioned, this reduced pressure encourages the fuel to vaporize (not just atomize) in the same way that water boils at a lower pressure at higher altitude, due to less pressure.
The downfall of carbs was emissions. Without that, I doubt EFI would be where it is today. Carbs biggest fault is the overly rich mixture needed during cold engine operation, not ideal fuel mixtures during transision periods, and of course it is not entirely maintenance free.
I have three vehicles we drive regularly with Rochesters, and from the drivers seat you wouldn't know that they aren't EFI. Response is right now, never a bog or sag. They just don't start as simply as my EFI cars.

Maybe the public was concerned about fuel mileage, but obviously the OEM's weren't. Why was Cadillac selling 500ci motors in some of their heaviest cars ever? Chevy extended their small block from 350 to 400ci during the 70's and was selling it in trucks and huge Caprices. The Camaro saw it's top-selling years in the late 70's, with V8's (305's and 350's) topping the list. Heck, Pontiac kept selling the Firebird with their SD455 engine untill what '77? '78? Didn't they also sell Corvettes with 454's back then? Fuel economy obviously wasn't the top on everyones minds...
Sadly, it also takes alot to change the direction of a car company. Gov't regulations can do it easily, but they don't listen to the bottom line it seems untill things are crashing well into the red.

As for the mileage, I am going on the comments of a GM engineer in an article about the V864 system from back when. They reported bigger gains with the modulated displacement than from an overdrive.
There's only one lockup OD tranny to really put behind a healthy 472, and that's a 4L80E. Talk about expensive, and then you've gotta buy the trans controller.
A gearvendors OD to bolt on costs around $2k as well, and doesn't have lockup.
Those are the only two options I'd really consider for overdrive in the Caddy.
For the other OD tranny options, 200-4R and 700-R4, those trannies I think would be a bit overburdened in such a heavy vehicle/high torque application. I know the 200-4R has been taken through 9-sec runs by the Turbo Buick guys, but when I think about pulling a long grade out here in a 5500# car, I dunno. We're talking 6-7 miles at nearly WOT for 'The Hill', as we call it, when I take the Caddy up (need all 8 going up that). That's alot more stress than a quick 1/4 mile run.
Plus, I'd like to try both in the long run...

It might not. You've gotta distinguish between atomization, and vaporization though. Atomization simply referrs to little particles of liquid fuel. It encourages vaporization, but is not the same. Vaporization is when the fuel evaporates. Fuel also only burns in a vapor state.
TBI has an advantage over point injection with the injectors being further from the engine giving the fuel more time to vaporize.
This is actually one of the ways I've read of racers making the same power from EFI and carb - the EFI might give the same fuel to each cylinder, but the carb can vaporize it better. Of course, EFI can kick butt in a street application because of the problems of running a huge carb on the street, while a 2000cfm throttle body would be easy, and the better throttle response of EFI.
Don't put the carb down, especially a Q-jet is not at all a toilet bowl. There are alot of intracite systems that go into getting that fuel well mixed with air and put into the engine. The carb actually starts mixing the fuel with air before it even leaves the venturis, those air bleeds mix everything so that the venturis are actually spitting out a frothy air fuel mix. Tripple venturis on a Q-jet give excellent booster response as well as providing much reduced pressure at the outlet. As I mentioned, this reduced pressure encourages the fuel to vaporize (not just atomize) in the same way that water boils at a lower pressure at higher altitude, due to less pressure.
The downfall of carbs was emissions. Without that, I doubt EFI would be where it is today. Carbs biggest fault is the overly rich mixture needed during cold engine operation, not ideal fuel mixtures during transision periods, and of course it is not entirely maintenance free.
I have three vehicles we drive regularly with Rochesters, and from the drivers seat you wouldn't know that they aren't EFI. Response is right now, never a bog or sag. They just don't start as simply as my EFI cars.

Maybe the public was concerned about fuel mileage, but obviously the OEM's weren't. Why was Cadillac selling 500ci motors in some of their heaviest cars ever? Chevy extended their small block from 350 to 400ci during the 70's and was selling it in trucks and huge Caprices. The Camaro saw it's top-selling years in the late 70's, with V8's (305's and 350's) topping the list. Heck, Pontiac kept selling the Firebird with their SD455 engine untill what '77? '78? Didn't they also sell Corvettes with 454's back then? Fuel economy obviously wasn't the top on everyones minds...
Sadly, it also takes alot to change the direction of a car company. Gov't regulations can do it easily, but they don't listen to the bottom line it seems untill things are crashing well into the red.

As for the mileage, I am going on the comments of a GM engineer in an article about the V864 system from back when. They reported bigger gains with the modulated displacement than from an overdrive.
There's only one lockup OD tranny to really put behind a healthy 472, and that's a 4L80E. Talk about expensive, and then you've gotta buy the trans controller.
A gearvendors OD to bolt on costs around $2k as well, and doesn't have lockup.
Those are the only two options I'd really consider for overdrive in the Caddy.
For the other OD tranny options, 200-4R and 700-R4, those trannies I think would be a bit overburdened in such a heavy vehicle/high torque application. I know the 200-4R has been taken through 9-sec runs by the Turbo Buick guys, but when I think about pulling a long grade out here in a 5500# car, I dunno. We're talking 6-7 miles at nearly WOT for 'The Hill', as we call it, when I take the Caddy up (need all 8 going up that). That's alot more stress than a quick 1/4 mile run.
Plus, I'd like to try both in the long run...

Great discussion. It's nice to be able to get past the stage where one is not comfortable with fuel injection systems. It takes correct information and maybe a little support from others sometimes. Getting past simple fuel systems does take a little study. BTW, I used to rebuild carburetors for several local garages. Made a whole lot of money doing that. A few foreign car specialist shop owners used to make fun of American technology at that time. Looking back, they were mostly correct. The invasion of foreign (whatever happened to that word?) automobiles was awful for our economy but it sure got American manufactures to offer a much better product in the long run.

I'd like to see any engineering article concerning the Cadillac 8/6/4 results. Maybe you can post the link. The idea was developed by Ford Mo Co so maybe it is sitting on a Ford interest site.

On the subject of fuel economy, the Cadillac engines do have a larger displacement than the competition. Remember, displacement does not always mean less economy. The camshaft profiles on the '68-85 series engines was very fuel stingy. This combined with low numeric axle ratios provided better economy than anything else made with the same set of restrictions. Those restrictions being: Unleaded lower octane fuels, 3 speed automatic transmissions, relatively lower exhaust and evaporative emissions limits than older vehicles, Reasonable performance and drivetrain reliability.
Most lux cars of the early to late 70's were expected to get awful mileage. It was not widely known that the Cadillacs did very well on gas if driven conservatively. This fact seems to have been lost among those who were not Cadillac owners at that time. One reason is today's highway cruising speeds have increased quite a bit since the national 55 MPH limit. Having actually owned and driven many 8/6/4 cars leaves me with the impression that the factory system would not be of much use when attempting to cruise at 70 instead of a couple of MPH over 55. To put it another way, the engine would switch into 4 cylinders and stay there only on a steady almost flat highway roll at 55-60 miler per hour. In order to get it to work at today's 65-70 cruising speed something else would be needed. The increase in displacement from the original 6 litre to an experimental 7 litre 8/6/4 might be enough if the 7 litre had every advantage available including a fuel system conceived in the 20th century.

Whatever Pontiac selling cars with 455's has to do with this discussion is not obvious to me. Put a 1976 CDV next to a 1977 CDV and tell me that Cadillac didn't care about fuel economy.


Yup a 4L80-E is not cheap. The prices on controllers might come down with more competition. Let's hope. These transmissions are starting to show up at reasonable prices ($500.00) now. The alternatives are all compromises. A 2004R can be set up to live behind a 425 or 500 though. Just takes someone with a little knowledge of the black art of transmission modification. The world is full of 700R4's that survived in light truck applications also. Yes, plenty of these needed to be replaced every 30,000 miles.

The point about the 455 is that the OEM's didn't care too much about fuel economy untill CAFE, and hence didn't have any motivation to do a V864 untill after that when they had to get even more economy. CAFE standards started in '78. Cadillac downsized its cars in '77, hmmm? They sold more cars in '77 than in '76, and even more in '78 because the public liked it, but the feds gave them the first push. Also, '76 was also a record-setting year for Caddy sales (best since '74), so they didn't have any pressing need to downsize the cars except for the federal regs.

The article I referr to isn't exactly an engineering article. Okay, not at all.
http://www.sfu.ca/~ajgee/mags/864.html
But, to quote Cadillacs chief engineer at the time "that would mean a 4 to 5 mpg improvement, better than if we had overdrive". He was talking about steady cruising on flat ground with 4 cylinders though. Middle of the second page to read it in context.

I'll bet the V4 mode could cruise on level ground plenty fast. 3 litres? Even a 3L V6 back then could have cruised at 75 without having to use super heavy throttle.
The programing probably causes problems though. GM wants to keep people happy with superior V8 acceleration, so enough throttle to keep up 75 might have been where they felt drivers wanted to feel that torque come on...

I have thought about the 200-R4's, but the price of a fully built one is close on par with a gearvendors unit.
I do not accept having a tranny that needs replacement every 30K on anything other than a racecar or similar. The Caddy is a driver. The tranny should have a life expectancy as long as the engine and the rest of the driveline...
For the 4L80E, I'd try and find a controller from a diesel. Probably has about the right shift points for a mostly stock 472 anyways. $500 for a good tranny, or a core? Places I've seen are 2-3x that for something pulled from a truck and just have to take their word that it works.

4L80-E. Not always one available but the price is typical for a working pull. I've been stalking these for the last year.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=7979864643

1977 Cadillacs were on the drawing board in 1973. First '77's were built on or before 9/76 and Detroit had about a 3 year design to manufacture time unless it was a special project. That's 5 years before you said Coprorate Average Fuel Economy standards went into effect.

I've seen that magizine article quoted several times before. If you read it very carefully you might notice that the same GM engineer quoted a less than 10% fuel savings would be reflected in the EPA figures. I'd take any unofficial figures with several grains of salt. Now we have the benifit of a lot more road testing. Ask someone who drove an 8/6/4 long enough to wear it out.

You have a valid point about the ECM programming changing back to 8 cyls.

It's not like congress sprung CAFE on the automakers in '78 with no warning. The bill was passed in '75.
You can read about it here: http://www.nhtsa.dot.gov/cars/rules/cafe/overview.htm

I still think that if the automakers had truly cared about fuel economy, they would have done something sooner. Why keep making Caddys with 500's, when the 472 was a proven engine they could have dropped in for a bit of savings? Why did other manufacturers and GM brands persist in putting in larger engines when they could have done the same thing?
Anyways, that's not the point...

You said that V864 cars would ping for a bit when reactivating cylinders. Any ideas why? Possibly a slow response on the part of the EFI?
I would think that as soon as the rockers start moving again, the carb would see the regular vacuum signal and begin dispensing fuel as normal very quickly.

All the comments I have read on this board about the V864 cars have been pretty positive, especially about the mileage.

You said that V864 cars would ping for a bit when reactivating cylinders. Any ideas why? Possibly a slow response on the part of the EFI?
I would think that as soon as the rockers start moving again, the carb would see the regular vacuum signal and begin dispensing fuel as normal very quickly.

All the comments I have read on this board about the V864 cars have been pretty positive, especially about the mileage.

That CAFE stuff is quite interesting. It shows how out government unwittingly gave a boost to the sales of "Sport Utility Vehicles" (just what does that mean anyway) while trying to reduce our dependence on oil.

Dunno for sure why the 8/6/4's hammer a little when going from 4 back to 8. They do it only for a second. Add that to the list of things these cars did that might make the original owners worry. I've torn down a couple of very high mileage 6.0 MD engines and the bores were typical Cadillac round with cross hatch marks still visable. The pistons had some skuffing in the skirt area. Overall very low wear especially compared to other brands.
The reason I brought up the pinging is that it would be an idea to bring in some EGR when switching cylinders on. Again, the factory setup may very well have done exactly that.

I've only seen 2 quotes concerning 8/6/4 mileage here. Maybe I missed them. One was from someone looking at the MPG display on the dash. Did someone actually post data calculated from a fill up or 2?

Who ever said anything bad about 8/6/4's here? They were certainly maligned by plenty of ignorant people over the years. That worked out well for quite a few who were able to buy those cars second hand for a song. What could be better? Well the HT-4100 might have been a little better as that made plenty of clean 80's Cadillac bodys available to the mechanically inclined.

So I have 4 sets of rocker arms, 4 selonoids, 2 valve covers and a few misc. parts.

...hopefully with any luck, I'll get a start on it tomorrow night.... my 425 may not be the fastest around, but it'll sure be the most cool, and fuel efficent :)

Can you post some pictures of the solenoids? I would like to see the setup.

Also, my opinion is forget 6 cyl mode, get 4 and 8 working. 6 is just too odd and rough.

1 - 8 - 4 - 3 - 6 - 5 - 7 - 2 -----8 cyl mode

1 - x - 4 - x - 6 - x - 7 - x -----4 cyl mode

...Pontiac kept selling the Firebird with their SD455 engine untill what '77? '78? Didn't they also sell Corvettes with 454's back then? Fuel economy obviously wasn't the top on everyones minds...

The Pontiac 455 was std on the T/A from 72-75, 76 was optional. The 455's lifespan was 1970 - 1976. The SD455 was very limited production in T/A and Forumlas in 1973 and 1974. Only around 1000-1500 ever made. Maybe 2000 on the high end. 455's were in all car lines except the X body as an option, and standard in the GrandVille.

Corvette got the 454 from 1970 to 1974. All 455's died in 1976, Olds living the longest from 1968 to 1976. All Olds BB's died in 76, the 403 was a SB. The 400 Olds (there were 2 variations) were BB's.

As for fuel economy? Big engines aren't always the culprit. The 1976 Olds Delta 88 with a 350 was EPA rated at 13 city and 17 highway. The 455 was 12 city and 18 highway. So the 455 was the economy engine. All this with a 4860 lb car. Anyone know the EPA ratings on the 500 in 1976? Dealer Brouchures have it.

Can't say a 472 and 500 would have any fuel economy differences, but honestly, it probably saved Cadillac money by dropping the 472 in favor of the 500 in all cars. Less tooling costs.

I think more importantly is having the engine at peak torque or near peak at cruise rpm. Those big beasts did just that. Imagine, if a 455 got 18 highway in a 4860 lb car with a Q-Jet. Imagine with OD and EFI! But it would be like low to mid 20's highway and 12-15 city. I don't know too many people who would turn that down!

The 8100 V8 (496 BBC) is rated at 11 city and 15 highway in a 6000 lb Suburban. Not bad for 345 hp and 455 lb ft torque NET. And I would bet that is with 4.10 gears. A friend of mine has a 96 Suburban 454 and gets an average of 14 city. Drive gently and it isn't so bad. Punch it, and regret it at the pump....

Yes, for every engine rotation there is friction, and fuel used per rotation. Reducing that rotation will save fuel. But if BSFC goes up, you may easily negate the fuel savings with more fuel burned at that rpm. Emissions is easy, fuel economy is hard while trying to meet good emissions. They are often inversely proportional.

12-15 city. I don't know too many people who would turn that down!

The 8100 V8 (496 BBC) is rated at 11 city and 15 highway in a 6000 lb Suburban. Not bad for 345 hp and 455 lb ft torque NET. And I would bet that is with 4.10 gears. A friend of mine has a 96 Suburban 454 and gets an average of 14 city. Drive gently and it isn't so bad. Punch it, and regret it at the pump....


But can you run an 8877 with it?:coolgleam

Look here for pics of the solenoid setup: http://www.cadillacforums.com/forums/showthread.php?t=37682&highlight=v864+findings
Also has a link to the guys who make the stud mount rocker conversion. I plan to either buy the plate from them, or make my own out of a piece of steel since I don't want the rocker setup they sell with it.

Yes, definately eliminate the 6 mode. Never heard anything good about it, and it would make wiring easier. Didn't GM also go with just 4/8 in their new V8's with cylinder deactivation?

I would try EGR when switching, but my '70 has no EGR at all. Maybe swap a manifold later. hmmm. Have to get some kind of vacuum solenoid to controll it then.

Good lowend torque does help alot with fuel economy, but low RPM's are probably equally as important. Lowering cruise RPM's, just like decreasing engine displacement causes one to need a larger throttle opening to maintain a specific speed. The larger throttle opening reduces pumping losses on the intake side (lower vacuum) and increases combustion pressure in the engine, leading to better combustion. Basically, engines are more efficient in terms of BSFC at higher throttle openings.
GM uses this in their current V8-4 engines by eliminating the throttle cable, and having the ECM controll the throttle body. This way, the driver still thinks they are just lightly brushing the gas, while the engine is actually working in 4 cylinder mode at a higher throttle opening.

possible stupid idea, would the 368 heads swap directly onto the 425 I realize that it would increase compression but by how much and would it cause the piston to hit the head?

possible stupid idea, would the 368 heads swap directly onto the 425 I realize that it would increase compression but by how much and would it cause the piston to hit the head?

Way smaller intake and exhaust ports. You'd be better off bolting them back onto a 368.

I thoutht the ports were the same b/w the 425 and 368 but were both smaller than the 472/500 , but the question is would it work, my primary mission is to increase specific cyl power output for the 864 system when running on 4 cyls and not loose gas mileage in the process so the high performance question is secondary, if the ports are smaller I could possibly live w/ it as long as it works properly, if it would work wich head gasket would you have to use

I would bet the smaller ports would make a better driving engine overall, sure, you will lose some peak power, but the gains due to higher port velocity will make you wonder why more don't do it. Again, you will lose PEAK power, but this isn't a strip engine, it is a daily driver, and fuel economy (with Chicago at $2.41 last tuesday) is important. As well as the thoughts of mod displacement will help greatly in overall gains.

So if you do any porting, find someone who knows Cad ports well, and have them give you recommendations to bolster low end torque and port velocity, not overall flow. Else, don't port them. Way too many people think that they need high flow numbers to make good power, but in reality the importance of port velocity is actually far more important. Sure, you can get overkill, like putting 7A Olds heads on a 455, and it will have killer velocity and fall flat on its face at 3000 rpm.
Consider you don't see over 5000 rpm, and spend 90% of your time below 2200 rpm, (unless you have changed gearing), you should worry about the power downstairs, like any good Cadillac V8!

If the ports match, use them. If they can be or ported to match, still, go that way. Go to the parts store and see if you can take a look at the gaskets and see for yourself. You may need to buy both sets to do some porting work. It is ok to have a larger head port to a smaller intake port, this does help some reversion and does not significantly affect overall flow, but it does mess up some port velocity.

Possibly take it in 2 phases, an initial, and then a later phase.

I have been doing some studying on this. GM has some interesting patents on this system, as well as ChryCo. Most, if not all, are with a turbo that works on the 4cyl mode. And not with the V8 mode. Pretty interesting stuff!! Personally? I think the Turbo should be in both, one for each bank that is operating. So 1 for 4cyl mode, and the other for V8 mode. Maybe even a larger one for the other bank, allowing for even more boost! On a 500? YEAH! Can we say 750-800 hp @ 5000 rpm? And oh, maybe 1000 lb ft torque @ 3500 rpm? Here little CTS-V..... Come to grandpa....

grrrr

Should I pull those heads from that 368, if the car is even still there?

It seems like someone with a '77-'79 deville would be a great car for this gas mileage thing, it is smaller and lighter then cars before, but still has the Caddy big block, just get the cam, engine, mod displacement and gearing and get like 35mpg! with still power to move the car around good.... interesting....

I suppose what i want to know is would it be mechanically safe/sound to just slap some 81 368 heads on a 77-79 425 w/out any machining or other work.

also what kind of compression increase would there be

i also plan on building computer control into it

The 76 500 (Fleetwood), 77-79 425 (Fleetwood) all share exhaust gaskets.

The 81 368 has it's own exhaust gasket.

Each have unique intake and head gaskets.

But, you all knew that, right?

Now, what is different on them? Are they interchangeable still?

Is the 368 the same deck height as a 425, 500 and 472?

I suppose what i want to know is would it be mechanically safe/sound to just slap some 81 368 heads on a 77-79 425 w/out any machining or other work.

also what kind of compression increase would there be

anyone have any idea on this?

Just what would be the point?

That's just what I want, a dash full of toggle switches from Radio Shack, one labeled "turn off cylinders" and the other "engage overdrive". Why not another for, "I'm trying a 25-year old idea all over again."?

Better yet, why not convert an olds 350 diesel to be an 8-6-4 engine?

How about turbocharging cylinders 1,3,5,7 and pulling a vacuum on 2,4,6,8?

Better yet, put two Vega engines under the hood. Start one for normal driving and start the second for acceleration.

Install a third for better performance.

If you don't want to do it, then don't do it and be quiet. If people want to try to get better mileage on the highway via cyl deactivation (kinda like GM and Chrysler are doing now) let them be.

anyone have any idea on this?

OK, this is all I can say on the subject...my best guess, if nothing else.
Many people have installed 425 heads on low compression 500s, this gets them about 1.5-2.0 points more compression ratio the difference between 425 heads and late 500 heads is about 20-30 cc. The difference between 425 heads and 368 heads (I think) is nearly 40 cc, but since the displacement is smaller the compression ratio will probably still be increased by about 1.5-2.5 points.(around 10:1)
Now, as for head gaskets, the 425 has a larger bore than the 368, so you would have to use the 425 gasket. There are water jacket differences between the 472/500 and the 425, so, likely there are water jacket differences between the 425 and 368, you may need to punch some extra holes in the gaskets and/or drill some holes in the deck surface of the block.
A 368 intake would probably be best to use with the heads, also.

Bringing up the compression is a good thing, better thermal efficiency. Cam profiles have come a LONG way since 1981, and we aren't so concerned about emissions.

I would look at getting a cam optimized for the gearing in the car, talk to a cam company (whoever might be grinding now for a Cad) and see what they think of the idea of dropping off 4 cyls at cruise and optimize cam for that mode. The rest will fall into place. The engine will not be optimized for 1/4mile, don't built it to be. If you are building for economy, keep these things in mind.

An earlier 500 or 472 cam might be a good cam, if they are still around. One that was meant for the compression you are targeting with the 368 heads.

I don't have a 368/425/472/500 to look at, but reverse cooling like the LT1's and old Pontiac V8's (1955-1958) might be a viable option to allow for the higher compression and run pump gas. I have some plans that I need some time that I can do it on a modern Pontiac V8, the Cad V8 shouldn't be too much harder.

If anyone has a dead 368/425/472/500 block (with water pump and front cover), heads and intake that they need to go away, that would give me something to work with, and all info would be shared with the members of the forum. It would be returned when done.

9.5:1 to 10:1 is streetable with a reverse cooling system on 87 octane, around 12:1 with 92 octane and reverse cooling. Else, you are limited to 8.5:1 with 87 and std cooling and 9:1, maybe 9.5 with 93 octane. And that is with fighting timing and cam requirements. So on a 425 with the V864 heads, or even a 500 with it, reverse cooled, that would be a great combo.

Just what would be the point?

That's just what I want, a dash full of toggle switches from Radio Shack, one labeled "turn off cylinders" and the other "engage overdrive". Why not another for, "I'm trying a 25-year old idea all over again."?

Better yet, why not convert an olds 350 diesel to be an 8-6-4 engine?

How about turbocharging cylinders 1,3,5,7 and pulling a vacuum on 2,4,6,8?

Better yet, put two Vega engines under the hood. Start one for normal driving and start the second for acceleration.

Install a third for better performance.

:helpless:

9.5:1 to 10:1 is streetable with a reverse cooling system on 87 octane, around 12:1 with 92 octane and reverse cooling. Else, you are limited to 8.5:1 with 87 and std cooling and 9:1, maybe 9.5 with 93 octane. And that is with fighting timing and cam requirements. So on a 425 with the V864 heads, or even a 500 with it, reverse cooled, that would be a great combo.

12:1 on any iron head on pump gas is just not gonna happen.

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