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Discussion Starter #1
I don't know if I'll ever do this, but I've been thinking about it again lately.

I have a 1979 federal emissions Sedan Deville, but I live in California. The car was originally sold in Washington I think. So, no smog pump!

But, I do still have to smog it, which, I don't mind really because I care enough about the environment to keep it legal, but I guess not enough to dump it and drive an EV or hybrid.

Anyway, so, I have a factory EFI setup, but I don't think I'll use it, because I would have to make too many mods to tune it to support whatever else I do, and then I'm pretty sure it would fail the smog test visually.

So, I'll just rebuild the quadrajet and make some invisible improvements to it.

Then, I have an intake off of a 500, which I think I could get away with using since it would still look stock, but what I would rather do is port the crap out of the aluminum 368 carb intake that I have and use that. I thought I would cut out the whole plenum area, and then match and blend the ports. If it doesn't work out, then I can always just use the 500 dual plane instead.

I would obviously port and do large valves on the heads, and get a slightly more aggressive roller cam.

Hopefully I could figure out a good way to boost compression to about 10:1.

The exhaust is pretty much set. I'm already running manifolds (with the EFE valve) from a 500, and I swapped the stock catalytic converter for a 3" magnaflow, which then goes into dual 2.5 the rest of the way back. I can't do true duals, but I think the single 3" to dual 2.5" is fine. I could probably upgrade the manifold to converter y-pipe in the future and that might help a little bit too.

My gut tells me that I would still pass tailpipe by keeping the converter and other smog equipment in place. My concern I guess is that I would need to run more timing than stock, and when I smog it, ignition timing has to be set to stock or they fail you. I don't think I'll mind changing it every two years, but I would just hope that it didn't run so bad that it caused suspicion.
 

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10:1 compression is probably overkill unless you plan to run unleaded race gas. True 9.0-to-9.5-ish would be adequate. Better to have full ignition advance, and a point less compression, than to have half-a-point too much compression and have to retard the timing. Get the quench/squish distance correct. NOT MORE than .045, and .035--.040 would be better. Which pretty-much means zero-decking the block 'cause I bet all the common head gaskets are right around .040.

I can't help with the intake manifold. What are the ports like in the 425 head? I thought they were small. Might have to hire a genuine expert to get flow from them.

The Q-Jet, properly calibrated, should work very well. Same deal with optimizing the distributor--find a stock one in good condition for emissions testing, and one that's been recurved for actual use in between tests. Swap distributors for the test, swap back to make it run right.
 

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If your Caddy is required to pass Calif. emissions for that same year, I believe you will need an EGR intake manifold and EGR heads with smog pump as EGR was what was required to sell that car in California. You could use a caddy 500 EGR manifold, with the factory EGR valve on your 425. Do your 425 heads have the smog rail and ports for EGR? I think only the California sold 425 motors had the smog rails and intake with EGR. These items should be available in California bone yards. I have a California emissioned 425 and it has the 425 EGR intake manifold, EGR valve, the giant mult-port vacuum switching valve on block near the water pump (to run the EGR) and smog ports and steel tube cross over manifold on the front of the 425 heads. It came with a Quadrajet with a California specific number, probably with different jetting for the EGR but I don't know the difference or metering changes.

On your build,
I would zero deck the block (if you are doing any machining, and also take 0.020 off the heads). You are going to be pretty limited on piston selection and compression ratio unless you go full custom piston. The 425 heads have the same size intake and exhaust ports as a 500 heads, but the intake port has a pretty bad short 90 degree turn right under the valve seat. Larger valves aren't the cure unless you can match it up with some pro level porting and re-radius the short turn. You can definitely help the factory intake manifold with some internal cleanup, radiusing, 1" carb spacer, and port matching. An Eldebrock is pretty, but won't perform much better.

In the heads, you can clean up the bowls, unshroud the valves, blend the bowls, narrow the guides, smooth the rough castings, etc., new 3 angle valve & seat grind. I would try not to remove much material in the combustion chamber as that will lower the compression ratio. If you want to go big hp, start with a 472 or 500. The 425 crank is a super lightweight version of the 472 crank and the horsepower limit to about 400 hp, before there are main bearing issues and cap walk. Haven't been there, but read about it.

The factory rocker assemblies and rods will need to be upgraded well before you get to 400 hp safely. All the money spent on this 425, could also be done to a 472 using the same parts with bigger results. The 425 is a great motor stock, or with mild mods, but if you want much over 300 horsepower on a 425 the bang for the buck is pretty low. The bang for the buck on a 472 is pretty good up to about 400 hp.

If it were me, I would find a complete caddy 472 or 500 with working EGR, EGR heads, HEI distrib, and working smog pump from an earlier caddy 1971 - 1976 caddy. Then swap on your 425 pan and oil pickup to match your chassis and swap it all in your '79. It would look almost identical, especially if you kept a 425 manifold on it. This is a pretty common swap and would look 100% factory. I doubt anybody at the emissions place could tell the difference, and it should pass '79 level emissions with a working cat and rebuilt carb. A 425 and 500 look identical on the outside, except the 500 has a dual plane manifold and a 425 has a single plane manifold.
 

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Discussion Starter #4
Although I live in California and the car is registered in California, I do not need the smog pump because the car was not originally sold in California. I've owned it for 18 years, all in California, and it's never been an issue.

If I zero deck the block and take 0.020 off the heads with stock pistons, you guys think that'll be in the 9.0 - 9.5 range? I'd be fine with that. I like the idea of the roller cam and upgraded valve-train.

Pretty sure I'd fail smog with the Edlebrock since it doesn't have EGR. The aluminum 368 intake does, so that's what I'd really like to try, and probably do the spacer. Should I cut out a lot of the stuff in the middle under the carb and try to blend that area into the runners nicely? Stock it just goes straight down and only leaves what looks like less than 1/2" of space between the floor. I guess that would help with velocity and mpg, but not flow. Can't have both I guess.

I really want to stick with the 425. I mean, thats so big already, it just seems silly to go bigger. I like that the 425 is lighter, and I don't know how well the stock 425 or 368 intakes would feed the bigger motors even if they were ported to the max. I think 250 - 300 hp would be fine, just something to get it into the 6 - 7 second 0-60 range to keep up with modern traffic a little better. 0 - 30 is great as is, but after that it pretty much starts to run out of breath, and I get nervous on uphill ramps getting on the freeway in this thing. On some hills you might get to 50 mph with the pedal on the floor, but it won't go any faster until the freeway levels out.
 

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That is good to know that your car passes Calif. regulations without the Calif. equipment. I know that modifying or removing existing working emission equipment is illegal no matter what state you are in. If you replace your "non working" ;) ;) old restrictive cat with a new high flow cat, can you pass inspection? Can you add headers and pass inspection?

It has been proven on a dyno that the stock cast iron 500 dual plane intake manifold, when improved with port clean up and radius, and adding a 1" carb spacer, only gives up a few horsepower over the Edelbrock at higher rpms but gives up nothing below this, see attached article. The stock manifold will allow you to keep your existing air conditioning compressor set up and still close the hood. The Edelbrock requires swapping and moving the compressor so the hood will shut. The stock dual plane 500 manifold will give you more torque down low over the 425 single plane intake which helps with acceleration. If you don't have heads with EGR passages, there is no reason to use an EGR intake as there is no way to get exhaust into the carb. If you find an EGR manifold I would tap the holes in the bottom floor (under the carb mount) and fill them with 3/8" NPT pipe plugs . You don't want fuel pooling there. If you find a cad 425 aluminum factory intake, make sure it is not for a 368, those have much smaller ports than a 425. I know that aluminum 425 intake manifolds exist, but I have never found one.

300 horsepower is very doable. Probably just a cam swap, valve springs, maybe a rocker upgrade, and some bowl cleanup and little valve un-shrouding in the heads will easily get you there. If you want run beyond 4500 rpms, upgrade rod bolts. I would pick a cam to try to make the 300 hp before 4500 rpms to avoid connecting rod upgrades and oiling upgrades.

Another way to think of this task,

The stock 425 motor was rated at 180 hp and 320 ft lb torque, sound low but those are net ratings. With all drivetrain components on, including transmission. So as measured out of the transmission.
The stock 1976 cadillac 500 was rated at 190 hp and 360 ft lb torque net ratings.
If you compare this apples to apples, the 425 has about 89% net torque of the torque of the 500. Since torque is a real measurement not dependant of rpm, I would use this to scale the gross output of a 425 to a 500. The other drivetrain components are almost identical.
CAD Company tested a bone stock, rebuilt, low compression 500 (75-76 vintage) on the dyno (see their catalog) and got:
301.2 hp and 494 ft-lbs of torque measured at the crank.
If the 425 is about 89% of the output of a stock 500 (based on net power advertised), (assuming all other drivetrain components are the same, turbo 400 etc.) the 89% should also hold to gross power ratings since the rpms the hp and torque peak of each motor are not that far off from each other.
then the 425 should be around :
268 hp and 440 ft-lb stock as measured at the crank!
This is why the 425 is such a good motor stock: The torque of a 454 big block, but the economy of a small block! These 77 - 79 caddys with the 425 could get 18 mpg stock. GM had to downsize the 350 to a 305 to get stock mpg like this in the impala or caprice, (the chevy equivalent body style) and still meet emissions. The 425 is an excellent truck motor to swap in.
Gaining 30 hp will not be a problem with better cam, intake, exhaust (better breathing) I would also recurve the HEI distributor to get the emission strangle choke out of it.

I think most of your acceleration problems are the stock very numerically low rear gear 2.28 that came in that year for gas mileage improvements. That 2:28 rear gear in a heavy car will be a dog in almost any motor even a mild built 500. If you can find a caddy limo or hearse of the same vintage in a junkyard swap the rear end since these came with a 3.08 rear gear. Other GM full size rear ends of that vintage may swap in as well, but may require fabbing up or swapping spring perches and attachment points. Getting your 4200# boat into 6 to 7 second land (to 60 mph) will require a locker or traction control and good tires, so if that is your wish look for a rear end that either has a posi, limited slip, or has aftermarket support to add a locker or posi. Of course, swapping to a 3:08 will take a hit on cruising gas mileage on long trips. Lots of rear ends could work. Olds, Pontiacs, Buicks, anything with a tow package should have the higher gear ratios. If you want in the 6s, swap in a higher rpm converter too, and add a shift kit to the turbo 400.

Are you sure your transmission kick down is functioning? You should be in second gear on a hard acceleration from a stop or merging in traffic on the freeway. Try manually shifting it into 2nd and keeping it there and see it that helps. Your transmission kickdown switch may be bad.
 

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Discussion Starter #6
I already swapped the cat to a magnaflow 3" one, and it passes inspection. I felt a difference too. I don't think headers would pass, but I do have manifolds off of a 500, and no one has said anything, so I'm passing with those.

I would think all 425 heads would have EGR ports. I mean, the engine has EGR, so, I can't imagine them not being there, and that needs to be left intact to pass smog.

I'd like to get 300 net horsepower if I can, so based on what you're saying, that may not be as doable.

I haven't heard of an aluminum 425 intake before. I have heard of aluminum 77-79 hoods, and I got one of those a few years ago. I think all 368 intakes are aluminum, and I've never seen one with cast iron anyway. But I already have one, so, I might as well try to use it.

I like my low highway rpms, so I don't know if I wanna loose that. I had looked at getting a built 200-4r at one point. It has a lower 1st, and if I also switched to the 3:08s, then I would probably be close to the same on the highway with the OD, but it also seems like a pain to do. I guess the drive-shaft would still be the right length, but the shift linkage change seems like a headache, and then there's some kind of throttle cable that you have to hook up or something.
 

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Discussion Starter #7
Been doing some more research. IIRC, when my shift linkage once came loose, the the shifter on the column just moved freely, so maybe switching to the 200-4R wouldn't be that big of a deal there. Of course I would be missing a drive mode indicator. The TV cable doesn't seem like that big of a deal either, and there are also ways to control the converter lockup with engine vacuum.

Now I've started researching CCC Quadrajets and Rhoads lifters.

This guy (Performance Olds 307) has a ton of cool info about souping up Olds 307s with CCC systems, and more info on 200-4Rs too. Got me thinking those same tricks could be applied to a Cadillac engine if you added the CCC and 200-4R trans to it. Then perhaps one could run Rhoads lifters with maybe one of those #10 cams, making life a little easier on the CCC system at lower rpms, but still having the benefits of the #10 higher up.

I found another discussion somewhere too where some guys were discussing the flow of the 425 heads. Most agreed that the runners themselves flow about 10% less than 472/500 heads, and the main limitation is the smaller valves and un-shrouding them. There was some concern about adding the bigger valves and creating a detonation nightmare though, especially if you wanted to add compression.

My biggest worry with adding the CCC system is whether or not a smog tech would notice. They haven't noticed my 500 exhaust manifolds yet, and I've had those on for like 8 years. Maybe I could get away with it, but they do tend to look at the distributor to make sure the vacuum advance is there, and with CCC, I'd need to use the electronic advance distributor instead. I guess I could attach a fake vacuum module to it?
 

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The 425 heads use the same exact valves as the large chamber 472/500 heads. The runners are really close in size with the intake ports barely smaller. The 425 heads have decent flow for low lift, but the sharp 90 degree short side turn on the intake runner doesn't flow well for high performance, high rpm, high lift situations.

The 425 chamber chamber is the same size as a 472/500 but since the bore of the 425 cylinder is only 4.06" you can't unshroud the heads as much as the 472/500 heads which have the 4.30" bore, since you can't do any work past the cylinder walls if you are going to get fire ring on the head gasket to seal. The 425 chamber runs almost the full width of the cylinder bore, where the 500 has an extra 0.13" room on each side of the chamber to unshroud the intake and exhaust valve near the cylinder wall. Adding bigger valves would not help much since they will be even more jammed up against the cylinder wall from the bigger diameter, so there may not be any gains. You can unshroad the 425 heads some, just not as much as the 472/500 heads.

If you put 425 heads on a 472/500 you could unshroud them about the same, but if you did you could not use them again on a 425 block since the fire ring of the head gasket would be exposed where you unshrouded the 425 head to the 4.3" bore.

What do you need the electronic advance for?
 

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Discussion Starter #9 (Edited)
I see. Can the 90 degree turn be ground down a little bit?

The electronic advance would only be needed if I run a CCC feedback quadrajet system instead of the regular, original non-feedback one. I think the electronic advance distributor has a sensor inside that the computer needs, and the system probably works best when the computer can control the advance too, I would guess.
 

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Discussion Starter #10 (Edited)
More revisions!

After speaking to a gentleman at cadillacperformance.com, the following suggestions were made:

1. Leave bottom end completely stock.
2. Use their CTA 205 RV cam for low compression engines. I assume it's similar to the #5 cam that MTS sells.
3. Use the 2.11 size valves, since 2.19 might be too big.
4. Open up the port around the valves, and then I think they said smooth out the 90 degree angle, but also try to add a little bit of angle somewhere else. I'll have to get more clarification on that when the time comes.
5. Use the dual plane intake from a low compression 500/472. Fortunately I've collected several intakes and I have one of those.
6. Use the stage one rockers.
7. Use some sort of rev limiter set to about 5,200 rpm so I don't bend a rod.

And that's basically it! They claimed I should get 25% more power, and the total in parts looks to be about $2k. So maybe 225 HP / 400 LBS/FT? I'd be happy with that I think.

Way cheaper than an E-Rod LS3 swap, for almost as much torque.

Then maybe later I would go to EFI, and I've been looking at the MSD Atomic EFI system since it's 50 state legal. I think then I would try with the ported 368 intake since it's single plane. I'll just port the ever living crap out of it, and if I mess it up, no big deal. Any thoughts on that system?

After that I would also add an MSD 6AL ignition, which appears to allow you to disable the mechanical advance, and work with the EFI.

Obviously I would love it if I could use the actual factory EFI parts with this, but then I think it would technically be an engine swap, and I don't think I would be allowed to use a more modern, tunable EFI computer with that system.
 

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More revisions!

After speaking to a gentleman at cadillacperformance.com, the following suggestions were made:

1. Leave bottom end completely stock. I agree, but if motor is out of car I would inspect the main and rod bearings and replace if they show copper or out of clearance spec using plasti-gauge.
2. Use their CTA 205 RV cam for low compression engines. I assume it's similar to the #5 cam that MTS sells.That would be a good choice with the stock rear end and make more torque and power.
3. Use the 2.11 size valves, since 2.19 might be too big. A 2.19" intake and 1.88" exhaust together are bigger than the 4.06" bore of your cylinders and are too big for a 425. I think you can hit your goal with the stock valves with a 3 angle valve job and bowl blending. Or try the 2.11" and 1.77" valves and try to unshroud them best you can to the 4.06" bore. The problem with bigger valves is that the edge of the bigger valves get very close to the cylinder wall which makes it harder for air/fuel/exhaust gases to enter/exist. So larger valves do not always flow better than smaller valves unless they have good unshrouding. The 4.06" bore doesn't leave much area for unshrouding even for stock valves. I just did this to my 425 heads.
4. Open up the port around the valves, and then I think they said smooth out the 90 degree angle, but also try to add a little bit of angle somewhere else. I'll have to get more clarification on that when the time comes. Unshroud the valves using the head gasket as a template to scribe the cylinder to the head. It would take somebody with experience with porting the 425 heads to make appreciable gains with the short turn 90. If I were to do it, I would get an extra head to cut up to see how far I could radius out the 90 degree short turn before I hit the water jacket. I think a bowl blending, improving the push rod pinch some, and removing casting flash, smoothing the guide, would be enough to get your extra 25%.
5. Use the dual plane intake from a low compression 500/472. Fortunately I've collected several intakes and I have one of those.You can improve the stock dual plane and single plane considerably with some porting and a 1" spacer. With your stock rear gear, the dual plane will probably be better. For the dual plane, remove the four holes to make one big one with a low walled divider, there are posts on how to do that. If your 425 has EGR and valve you should use a dual plane with EGR or you could get flagged at emissions.
6. Use the stage one rockers. Yes, if you plan on running the motor over 4,500 rpm the stock rockers got to go. You will need new valve springs also.
7. Use some sort of rev limiter set to about 5,200 rpm so I don't bend a rod. A tach will be enough, that 205 cam will fall short and stop pulling starting below 5,000 rpms so there is no reason to run it any higher. Its going to want to pull like crazy at 2,500 rpms, not so at 5,000 rpms so you would shift before 5,000 rpms unless you go to a bigger cam. Are you sure you want to keep that rear gear? It will take quite a distance to get to 5,200 rpms in first and second, and you will never see close to that rpm in 3rd. I wonder what 5,200 rpms would be in 2nd? 90 mph?

And that's basically it! They claimed I should get 25% more power, and the total in parts looks to be about $2k. Save some more money for machining (valves, heads), maybe new bearings, and replace the stock timing gear and chain with real one, then pull all the nylon teeth out of the oil pan from the old set. I would plane off as much as possible of the heads to try to bump up compression. So maybe 225 HP / 400 LBS/FT? I'd be happy with that I think.I think you could have that HP at the wheels with just cam and head work. The flat torque starting at 1,000 rpms is what is going to move that car. Chasing peak horsepower or a peak number is just bragging rights.

You could also hit those +30% power numbers by dropping a stock late model 500 in with the same cam, a 425 single plane manifold, and the 425 pulleys. I seriously doubt anyone would know it was not a 425 at the emissions place. The blocks are very very similar from the outside. That cam would idle like stock. The biggest visual difference between a 425 and a 500 is the single plane intake and pulleys, and the old 500s don't have HEI. Swap these items and how would anybody know it wasn't a 425?


Way cheaper than an E-Rod LS3 swap, for almost as much torque. The LS3 swap has its place, like getting more than 500 hp on the cheap, or max. gas mileage, but IMO not in a heavy car that already has the right motor in it, that just needs a few upgrades.

Then maybe later I would go to EFI, and I've been looking at the MSD Atomic EFI system since it's 50 state legal. I think then I would try with the ported 368 intake since it's single plane. I'll just port the ever living crap out of it, and if I mess it up, no big deal. Any thoughts on that system? I think the 368 manifolds have smaller ports, if so I wouldn't use them. EFI will not make you any more power than a correctly set up quadrajet. You might get an extra 1 mpg with EFI at cruise but that is a lot of money and work. If mpg is super important, than go LS3 with a 4E60, but swap the rear too. Those LS3 combo set ups usually came in a car or truck with a 3.72 or 4:11 gear

After that I would also add an MSD 6AL ignition, which appears to allow you to disable the mechanical advance, and work with the EFI. I don't think anything will disable mechanical advance besides removing the weights on the advance mechanism inside the distrib. or swapping distributors. It is a fully mechanical system. You can remove the vacuum advance by just plugging the line at the carb. This car was available new in Calif. with the HEI distributor and Quadrajet carb. I don't see why you couldn't make it carb/HEI and fly through emissions This would let you reach your goal. The california models came with California only model carb & HEI, so it might be a little harder to find the carb with the right Calif. number if your car is a California model. You can still run an MSD 6AL using your stock HEI distrib. You can set up your advance curve on the HEI to make the best power and gas mileage, very easy to do. A HEI recurve kit is like $35.

Obviously I would love it if I could use the actual factory EFI parts with this, but then I think it would technically be an engine swap, and I don't think I would be allowed to use a more modern, tunable EFI computer with that system. That is a good question. I don't see why you couldn't use a modern EFI that has better emissions. Only EGR was required for this year, as long as you retained the working EGR system with smog pump.
 

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Discussion Starter #12
2.28 rear doesn't have to stay. The thing is, if I change it, and I want to add posi, it looks like all the aftermarket 12 bolt posi units need 30 spline axle shafts, and to my knowledge, we have 28 splines, so I would have to get new axle shafts, so then I figure I'm looking at another $1,500+ for that whole setup. I'd like to do it one day. Then I would also add a built 200-4R to get my highway rpms back down.

I know I could pass with a 500, I just, don't want to. I figure a 425 is big enough, and I have it. There's an emotional connection to it being the original engine.

I don't need high rpms. My main goal is just to be able to outrun idiots on freeway on-ramps, and eventually I may do some light towing. Stock, the thing pulls hard to 35 mpg, and then it's fairly slow from there to 70.

EFI I would mainly do for drive-ability and mpg second, emissions third. but it's a mod that would be further out.

It's a Federal Emissions car, so no smog pump, but of course EGR, and the dual plane I have has EGR. So that would be part of phase one. Dual plane with the quadrajet.

I guess my main concern with using a modern computer on the old factory EFI setup, is that it would require extra sensors and other hardware that the smog techs may or may not notice. Then I think with EFI, you don't need the EFE valve anymore, and that would just add to the confusion.
 

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I did some looking at rear ends available in that body style (77 - 90) that it looks like they would be the same width and rear coil suspension for an easy swap.

The 77-80 had the 2:28 rear, but there was an 2:73 and 3:08 option. Those might have been the Fleetwoods and commercial chassis. So maybe looking for hen's teeth at the junkyard.
Starting in '82 when they ditched the 368 they went to a 3:42 rear gear for the wheezy 4100 motors. Those had 4 speed autos. That 3:42 would put some serious pick up in your on ramp speed.

Top speed in each gear with your 2:28 per Cad specs says 64 mph 1st, 108 mph 2nd, and 159 mph in 3rd at stock redline That is way too tall for acceleration, as you are stuck in 1st gear trying to merge and make peak torque and power from 0-60 mph. You would have to manually shift to 1 st gear before the on ramp to get it to stay in first.

Top speed in each gear with a 3:42 rear is 42 mph, 1st, 74 mph in 2nd, and 116 in 3rd. Now we are talking, so you could nail it and let it shift up in 2nd and be near peak power at 60 mph for merging. Your mpg will suffer a bit with 3:42 without a four speed. Yes you could also swap in the 200R4 tranny off of the same donor car, but that is another topic and it would take $1500 to beef up this tranny so it would live on a mild 425. So lets look at some 3:08 gears. Specs say the 3:08s are found in Cadillacs in the late 80s early 90s running the chevy 305/turbo 400, or 350/turbo 400. They might also be found in the olds 350 combos or years but I didn't check every year and model. This ratio seems like a good compromise

If you look at older deville models like '75 -76 rearends, the standard ratio was 2:73. That is 56 mph 1st, 94 mph 2nd, and 139 mph 3rd top speeds at the stock redline. This would still be way better than 2:28 but fuel economy would not suffer too much. There was a 3:08 option probably standard in the commerical chassis or Fleetwoods

Limited slip was an option for about every year, if you can find a stock caddy rear with a 2:73 or 3:08 with limited slip, this seems like the way to go on the cheap. Easiest way to check at the junkyard, is to spin one rear wheel and hope the other wheel spins in the same direction, or look at the option codes, or decode the tag on the pumpkin. Unfortunately the cars that typically had the limited slip were in the northern states and succumbed to the road salt.

If your car pulls hard only to 35 mph, the shift to second is probably killing the acceleration at 35 mph +. You can mess with the transmission governor to increase the rpms it shifts up from 1st to 2nd at full throttle. Raising this shift point to 50 mph at full throttle would help on ramp acceleration quite a bit. This would also raise the shift point of 2nd to 3rd at full throttle, which would only be a problem getting into 3rd at full throttle before 100 mph. It should still shift normally at part throttle. Or you can buy the $100 Turbo 400 valve body reprogram kit that allows for full manual shifts up or down. Which gives you the best performance and ability to hold any rpm in any gear, but you loose the fully automatic shifting feature and now have a clutchless three speed.
 

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Discussion Starter #14
So I'd basically have to get a whole axle and swap it in. I guess I could do that. The HT4100 cars use a smaller rear end though. I don't think it's a 7.5, but it might be an 8.2, and probably not as strong as the 8.75 is. The limo/commercial rear end is beefier, but also probably somewhat heavier. The 2.73 with limited slip and disc brakes sounds like the way to go if I can ever find one, or maybe an 8.5 3.08 limited slip from a 9C1, although it might be wider.

Anyway, back to the engine. I'm wondering if I could modify the Edlebrock intake and add an EGR mount to it that would actually work. It has the exhaust passthrough ports for EFE. Then just grind off the Edlebrock and performer text and paint it blue. Smog techs might not notice.
 

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There are also tons of 8.8 and 9" Ford rear ends that could work. You would have to get axles with the GM wheel pattern or run wheels with the dual bolt pattern. This swap is done all the time. The 8.8 rears are very cheap and plentiful if you can find them in the right width to work with your car. They are found on all the light duty trucks and explorers, expeditions, mustangs, broncos, crown vics, t-birds, lincolns, etc. of the 80s and 90s and some 2000s. Many are limited slip, later ones are disc brakes, and limited slip ones can be beefed up with better clutches for cheap. The 8.8 and 9" are very strong. The 8.8 are usually found in 2:73, 3:08, 3:27, 3:54, and 3:73 ratios. There is a huge aftermarket support for them since this is what the mustang guys run with. Since your rear is coil spring, it might be easiest to find an 8.8 with coil spring rear and modify the perches and link connectors to fit. I know the lincolns and crown vics used a coil spring rear, and I think the T-birds did.

Modifying an Edlebrock to add EGR would probably be illegal in your state, and would look very suspicious. You have to connect the internal exhaust port of the manifold to the EGR valve and get it back into the plenum below the carburetor to function. Since there are not internal passages in the Edlebrock to do this, it would all have to be externally plumbed. It would look very unusual, even if it worked. The Edlebrock doesn't really add any gains over a ported stock manifold until you are over 4,500 rpms and the gains are slim. The Edlebrock will actually loose some power down low. You would also loose your air conditioning compressor, since it will not be able to mount on top of the motor anymore. The biggest reason people use the Edlebrock is for looks and weight savings. If I had to run EGR, I would use a center section ported stock dual plane EGR manifold with a 1" open spacer and run it with the stock EGR valve. Then bury the motor with the stock vacuum lines everywhere to make it look stock. The EGR system doesn't rob that much power but it certainly clutters up an engine.
 

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1979 Sedan Deville
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Discussion Starter #16 (Edited)
Alright, I'll just stick with the stock dual plane that I collected. I thought I could just weld a tube from the exhaust passthrough to the back, cut the EGR mount out of 368 manifold, and then weld that up so it looks stock, and the tube would be on the bottom, so they couldn't see it.

For the rear, I don't want to go to that much trouble. I'd rather just wait and see if I can find a tow package 77-81 Fleetwood and pull the rear from that, or just go ahead and drop the $1,500 to put posi, new gears, and 30 spline axles in my existing axle. Or! Get a 2004-06 GTO rear subframe and put a 9" housing on that!
 
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