HP or MPG and what would you do?
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500, 472, 425, 368 Discussion, HP or MPG and what would you do? in Cadillac Engine Technical Discussion; ok, so after my recent cross-country trip with the '79 http://www.cadillacforums.com/forums...617#post551617 I couldn't help but think about something the last ...
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    HP or MPG and what would you do?

    ok, so after my recent cross-country trip with the '79

    http://www.cadillacforums.com/forums...617#post551617

    I couldn't help but think about something the last parts of my trip.

    the car has an amazing running mostly stock 425 with 93,000 miles right now.

    I have been trying to get more power from it, the goal is to build up a nice 500 and have a super-sleeper, much like everyone else building up 500's in their classic Caddy's.

    The problem is, I do not have the money, time or means to do that, so I have been getting by with doing a little bit of work to the 425... but I quickly realie that the stock valve train is pretty much junk, and that is holding me back from doing much with the engine... and pulling the heads to upgrade the valve train is spending more time and money then I want to on the 425.

    So then I thought of the other extreme... something I never cared about before, and that is try to get high gas mileage out of my 425 in the '79

    It isn't as far fetched as I thought... first, yeah, I could drive a more fuel efficent car, but that isn't the thing, I don't want a smaller econobox, I want *this* car, read the other thread about my trip and you'll know why. Basically I can drive the thing across the country and hardly feel anything at all.... great for going back home to NY or visiting family in Texas or anything.. I love driving!

    So really, when the cruise is set at 70mph on the highway, you can have 1,000HP and it means nothing.

    Then I am thinking all the work I need to do to the '79 DeVille to make it "fast".... do lots and lots of work to the 425 or swap for a 500, get a shift kit in the tranny.... replace the whole rear end because the gearing sucks for performance etc... all this costs lots of money and plus, I live in an apartment now, I don't have the nice big driveway anymore to work on all my cars.

    Then I am thinking about the gas mileage thing... I have nearly everything I would need for a highway gas sipper of a Caddy.....

    '79 chassis is 1,000lbs lighter, and smaller size then '76 and eariler, yet is still a full size classic Cadillac that has all the same qualitys as before.

    The 425 is a whole lot smaller then the 472/500, yet still develops lots and lots of power for everyday use of the car.

    The 2.28 gears that suck for drag racing, are amazing for gas mileage, with them, over drive is not needed as it puts the RPM right in the engines peak torque....AKA best cruise RPM at my cruise speed.

    So I am thinking of what little work I would need, to get better mileage from it. I am not talking about 50mpg... but if I could get a solid 25mpg, up from ~16mpg it is now, that means I could get 500miles from a tank of gas (well, 20 gallons) and at, say $40/fill up.... that is a whole lotta driving in a whole lotta car for CHEAP!

    Now I have a modified '68 472 intake manifold on it, non-EGR. It did help on power alot. I am not sure what it would do for gas mileage though, I would probably keep it.

    Also, I probably would still want to swap on 500 exhaust manifolds (flow alot better) and get a nice 2-1/4" true dual exhaust, which would add power, and make it breathe better.... so it would have to help MPG.

    Really though, I would swap the cam... instead of a performance cam... for the cam I never thought I would get... the gas mileage cam! MTS #3 cam....

    3 Series Grinds-

    RPM Range: Idle-4000 / Advertised Duration Range: 250-255 / Duration @ .050 Range: 198-205 / Valve Lift Range: .470" - .480"

    These grinds are designed for maximum fuel economy. These work best in low compression engines. When tuned to run 92 octane fuel, the record is 22MPG from a 1976 500 cid in a full size Sedan DeVille. Great bottom end torque at the expense of top end performance. Power peak is earlier than stock cam. Theses cams are for those who enjoy trying to get Honda like MPG from their Caddy engine.
    The best thing is, since it brings the power band LOWER then stock, I don't have to do a damn thing to the valvetrain! which means that swapping to this cam is both easy and cheap.

    They say the record is 22mpg from a '76 DeVille... well, I have 1.2L of less engine, and 1,000lbs less weight, plus better highway gearing.... which mean that alone should make up 2-3mpg...

    THEN, I am even thinking about installing the V8-6-4 stuff on the 425. I already own all the needed stuff, and this would be later, after seeing the effects of the #3 cam swap. But if it isn't too hard, then shutting down 4 cylinders, so I can run on V4 mode on the highway would be freakin amazing... even if it only got me 2 or 3mpg more... that is still an extra 40-60 miles/tank....

    The best thing is, I already have nearly everything I would need to do this swap.

    Then atleast, I don't have to try to make the stock 425 something it isn't (hot rod) and I still have the car... I still have it for a later time when I do build up that massive 500 to dump in, but for now, have some fun with the 425 it has.

    I figure, if between all the above mentioned, if I can get a solid 25mpg highway from the 425 and TH400, that would really make this car amazing on the highway. I would then add a nice CD player, new 6x9 speakers, and do something about a sub.... basically, I would build up a kickass budget sound system in this car (since the '93 Coupe has all the really nice stuff) which means that on my cross contry trips I now have a great sound system to listen to music on, good gas mileage, and most of all, a sweet, comfortable car to ride in with lots and lots of luggage space... or room for other people!

    What is everyones opinion? I am just pondering it... figure $120 for a regrind #3 cam, with new lifters and push rods that puts me right around $200 when all said and done.... it would require no more parts after that, just my time to do the swap.... I could bang it out in a full Saturday and have time on Sunday to leave to any errors.

    Plus, they say it is amazing for low end torque but bad for high RPM HP.... well, that is pretty much what it is now, never sees above 2,000RPM in everyday use unless I put it to the floor and open the secondaires... not something I do every day because then it starts to inhale the gas. So with the 2.28 gears, a lower torque peak would actually make the car faster around town... in effect, making the car atleast seem a whole bunch faster then by moving the power band up (with a bigger cam) and the stock gears.

    My only question is, stock torque peak is 2,000RPM, which is what it is at, at 70mph... with this new cam, if that lowers the power band, it would now be above the torque peak, which that be bad for my mileage or kinda offset the effects of anything right now?

    Yeah, it was long and I rambled, but I am definitly interested in this and may be doing it in the near future... I just want to here from people supporting it or have anything against it....

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    Re: HP or MPG and what would you do?

    In order of what is will cost:
    EGR helps fuel economy. You will be able to run more timing with it.
    Consider headers instead of manifolds. Properly sized headers and some tuning would be another advantage.
    25 MPG with a TH-400 in a 4000 Lb car is a very tall order at cruise speeds higher than 60. An overdrive trans with lockup and the right axle gear would be good for a few less drops of gasoline. With overdrive the 8/6/4 thing becomes useless as the engine will not be able to make enough power to cruise in 4 cyl mode.
    Now for the iceing on the cake, carburetor disciples may want to stop reading. F U E L I N J E C T I O N. Looks good on an emblem written like that!

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    Re: HP or MPG and what would you do?

    Yeah, the EGR thing would have to be thought out... it is basically put the stock 425 manifold back on to get EGR back (may as well buy a new EGR valve) or keep the modified 472 intake... I will probably just end up keeping the modified 472 intake simply because it took so long for me to get it and it does help alot.

    The problem with this car is, none of the BB Cad headers will fit the chassis without clearance problems, plus thats alot of money..... used 500 manifolds from the junkyard are cheap.

    I do not want to give up the TH400, especially for fuel mileage.

    MTS said someone got 22mpg in a '76 Sedan DeVille with the 500...dunno what trans tho, probably the 400

    I do not want fuel injection on this car either, I like the Q-Jet.... again, more work and money then I want to spend to make this a fuel efficent car....

    I am simply thinking about swapping out the cam, instead of going performance, going for better highway mileage... swap the trans more OD, install FI, all that.... I don't want to do.

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    Re: HP or MPG and what would you do?

    Yup. You land up spending a lot of money in the name of saving a few bux in gas. That's the whole problem. EGR would work much better with the factory valve on top of a '73-'76 intake. Your intake modification is likely hurting fuel mileage too.

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    Re: HP or MPG and what would you do?

    I have heard that the intake mod will cut back on low end torque, but greatly increases the mid and top end range air flow... which is where the engine needs help.

    Really, I guess I just want to know what kind of benifit I would get form swapping to that fuel mileage cam, the main reason why I really like that idea is, my car has everything I would need/want to make it good on gas, but to make it a hot rod, I would have to replace all the stuff... including the rear end and all that...yes, I want to do it, but not at this time.

    Since I do want to have some fun with the 425.... I *do not* want to remove the heads... then it starts the snow ball effect of what to do. Without removing the heads means I want to keep the stock whimpy value train, which also means I gotta be really careful with cam options.

    *IF* I didn't go with the #3 gas saver cam I think I would want this:

    #5 Series Grinds-

    RPM Range: 1000-4500 / Advertised Duration Range 258-266 / Duration @ .050 Range: 208-215/ Valve Lift Range: .495"- .510"

    Excellent choice to replace 1974 and newer smog control factory cam. The #5 grinds are an updated version of the "hottest" cam grind used by Cadillac. The 1973 Cadillac engines came stock with specs in this range. These cams run more lift and duration than 1968-1971 and 1974-1979 original cams. This cam provides a stock type idle. Excellent economy with a good gain over the stock smog cam. Works excellent with stock TH400 transmission shift points. Just leave it in drive, smash the gas and let the trans shift by itself. Peak cruise RPM for efficiency 2200-2500.
    Yeah it isn't a wild cam, but I think that in the stock 425 would be a pretty nice overall engine, and most of all, I would be pretty safe with the stock valve train.

    Still though, I am interested in the gas saver cam..... it is amazing what the 1,400 mile trip will do to ya, I mean, even if it was only 22mpg, and I put 19 gallons in it when I fill up (3 gallons left in tank) that would be 418 miles..... compared to the ~310 miles I am getting now. Thats an extra 100 miles... free.... even getting ~400 miles to a tank of gas on the '79 would be great for long highway trips.... basically I could go to Texas or NY and it would only cost $120 each way in gas.... in a '79 DeVille, I like that... because I love driving, highway driving is fun.... as long as I have a way to listen to my music, I couldn't ask for anything else...so saving some money on gas in the process would be great.

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    Re: HP or MPG and what would you do?

    Make some headers lol

    Basically, I think you should go with the good mpg plan, but only to a certain extent. Keep the budget on the cheap, get better mpg, and save for your built 500. Just my 2 cents

    EDIT: What is up with all of MTS cams having a lift "range"? Do they not know what lift they are actually grinding?

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    Re: HP or MPG and what would you do?

    25MPG in a 4200lb car with a 7.0 Liter 4bbl and a 3 speed tranny???????

    My grandfather got 26mpg on a trip out to Nevada in his '92 Roadmaster Limited Sedan with the TBI 350 and a 4L60-E. That car was rated at 16/25 IIRC. Your deVille stock is rated at like 13/18 (?)
    I think it would be quite hard to do even with some modifications like you have, but I have heard of people getting surprisingly good mileage on the freeway.
    For instance you have gotten 32 mpg in your Oldsmobile, when its rated at 19/28 (?) And I have heard of people getting 30 mpg in the 91-93 deVilles when they are rated at 25mpg.

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    Re: HP or MPG and what would you do?

    Yes, I think 25mpg isn't too far fetched of an idea....

    ~23 I think would be easy... maybe with the cam alone... then the V8-6-4 stuff would be good for the rest, but require alot of work....

    I think I would be happy with just the cam for now.

    That cam is designed for low-end torque, which would actually help with the 2.28 gears, if I keep the speed under 75 on the highway, I don't see why low-mid 20's woudln't be possible.

    Yeah, the Oldsmobile was a freakin beast when it came to gas... on every single highway trip I took it never got less then 30mpg.... 32-34mpg was the normal.... NY to NJ and back with plenty of gas left... over 400 miles to a tank (18 gal tank...not ran empty) on my 25 min. each way trip to work.... hell in stop and goo town driving I got atleast 22mpg with that thing...

    My fathers '99 Grand Prix GTP, lightly modded gets about 33mpg on the highway too... low-mid 20's around town. It really is amazing what kind of mileage that engine gets.

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    Re: HP or MPG and what would you do?

    wait, you're gonna put a V-8-6-4 on a 425???

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    Re: HP or MPG and what would you do?

    Just the needed parts to be able to switch between V8/V4 mode.

    I already own all the stuff, pulled them from a V8-6-4 at the junkyard. The problem is the rocker system is different, but from what I know someone over at CB7 is making it work... if the rockers will fit then its a go.

    On the same note if I had an Oldsmobile 455, it would be a direct swap... too bad I don't have an Olds....

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    Re: HP or MPG and what would you do?

    wait, whats CB7??

    Will the 425 w/ 8-6-4 have the reliabilty problems the original motor had??

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    Re: HP or MPG and what would you do?

    Quote Originally Posted by I~LUV~Caddys8792
    wait, whats CB7??

    Will the 425 w/ 8-6-4 have the reliabilty problems the original motor had??
    The original 8/6/4 had no reliability problems due to modulated displacement. They DID have problems. Each problem still existed in later years where the same DEFI system was still in use.

    There is little worry as to what would happen with the 8/6/4 on other Cadillac engines because none exist and most likely never will. If and when they do they will be unhooked long before stuff breaks.

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    Re: HP or MPG and what would you do?

    wasnt the major problem on the 8-6-4's due to the engine heat wrecking the solenoids

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    Re: HP or MPG and what would you do?

    Nope.

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    Re: HP or MPG and what would you do?

    Quote Originally Posted by I~LUV~Caddys8792
    wait, whats CB7??

    Will the 425 w/ 8-6-4 have the reliabilty problems the original motor had??
    The reliability problems you mention have nothing at all to do with the actual cylinder deactivation system. The selonoids hardly ever fail.

    I would set it up with a simple on/off toggle switch in the car... V8 or V4. No V6 which was part of the problem. Then *I* would choose when I want to cut it back to V4 (ex. on the highway with cruise set) That would eliminate the rest of the "problem" the origanal setup had.

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