79-85 Eldorado with 472/500 swap info from someone who did it

[CadVetteStang]

I put a 500 in a 82 Eldorado, then had do a swap because that 500 was bad. I then put in a 472.

I used the TBI injection and wanted to keep the lockup feature on my 4 speed tranny so I took all sensors off of the stock 4100 engine and adapted them to the 72 model 472. I used all of the factory smog equipment. I pulled the oil pan, brackets, pulleys and belts off of a 368. (I used the air pump from the 368, and the 472 I was using was a smog motor- it all bolted up except that I had to modify the 472 intake to accept a map sensor.

I used 500 Eldo exhaust manifolds. I had problems with the passenger side manifold contacting the A.C. box on the fire wall, so I had it re-clocked by a welding school so that the pipe mount bolts did not touch the box (I later found out that I may have had an odd manifold on that side because others who have done this swap have not had that clearance problem). My manifold keeps breaking due to a flaw in the metal of the manifold in that area. I’ll fix it either by having a different manifold welded, by removing the AC box, or by using a different style manifold. (right now the AC is fully hooked up- it just needs to be recharged). One option is to use a RWD manifold from the driver’s side turned upside down on the passenger side (Fan boat builders do this all the time and it works okay). The down pipe would then have to come up and curve over to connect.

Stay away from 425 manifolds if you can because they are more restrictive than the 500/472 manifolds. I had too close of a fit on the passenger’s side frame rail for my manifold, so I modified the frame with about 50 hits from a 4 lb. hammer.

My idea for headers is to use speed boat headers on the right side to clear the tranny and run the down pipe up over the fender well. I would then use a standard car tight fit header on the passenger side.

I had to make a bracket for the front of the engine to bolt to the front diff area of the TH325-4L overdrive tranny. I rigged a torque strap to the fraim rail with some steele cable to limit engine rock – giving it about 1” of play. At the time, I could not find a Chevy truck 670 CFM TBI, so I used a 500 CFM throttle body off of a Chevy 350 car. I used the idle control motor and throttle sensor from the stock 4100 TBI. I now have a Holly 670 TBI made for a car that will accept my idle control motor and will use it when I re-do the car. I mounted the TBI on a 4bbl to 2BBL carb adaptor that has a custom built plate on top (however 4bbl carb to 670 TBI adaptors are available. With a low rise breather on a small spacer, I could fit a 2.5” air filter, but can squeeze a 3” in when I get a flat top breather.

TBI or a carb? I wanted to keep TBI for MPG purposes. My engine worked fine with the swap because 82 – 85 does NOT have a knock sensor, but I think 80 is one of the years that does. If it does have a knock sensor, then the computer might interpret the internal sounds of the 500 as detonation and may then retard the timing on it – defeating the upgrade.

What was cool about the 82 up computer was that the 4100 is performance tuned from the factory, because it is a little motor tugging on a 3800 pound car. What is NOT cool about it, is that it wants to let the motor see high RPMs before shifting (however, that problem could have been because my temporary 500 CFM TBI and injectors could not deliver enough punch to feed it what it wanted… I’ll know more after I get the car running again with the bigger TBI.

A friend of mine put a 76 model 500 with the Eldo’s TH425 into a 79 Toronado and used the factory carb. He had no manifold clearance problems. His only two challenges were the CV shaft adaptors and a custom rear trans mount. (he made drawings and measurements and had a machine shop build them.) The CV mounts on the TH 425 diff are larger than the 79 – 85 CVs and require a metal disc with two sets of bolt holes. For a rear trans mount, he used 2” square tubing that connected to the stock 79 Toro trans mount location with a flat plate, ran up the back side of the TH425 Trans and across the top-back area where the chain drive cover bolts on. The mount was attached by using 3 or 4 longer bolts into the chain drive cover. Then the mount rand down the other side and connected to the other stock 79 Toro mount on the frame. It looked ugly, but worked well, cleared the firewall, and was very strong.

If I was going to drag race my car, that is the setup I would use. My application is a daily driver that sees 60 miles per day and will be used in autocross and rod runs. I will be looking for a high ratio front diff (which is already on the 80/81 model TH325. It is a 2.19 ratio which is perfect for highway driving on 26.6” or 27.1” tires (Stock tire is 27.1” ). It works out to be about the same as the taller tires on the old Eldos with 2.73 gears. That puts the torque where it is usable. Low gears are a waste and hurt performance on the 500. It will accelerate faster with 2.73 gears than it will with 4.11s. (IF we are talking about tires from 25” – 27” tall on a 3900 lb. or lighter car). It makes its power right off idle until 3600 RPMs. However a small block like a 350 needs to get past 2500 RPM to begin building power. So don’t let a small block Chevy “expert” talk you out of highway gears when you will be using a 500. Jeff Schwartz's Caddy that won the Real Street Eliminators used 2.73 gears and ran an 11.8 sec quarter mile on 25.7” tall C4 Corvette sized tires.

One issue you will have in this swap is the shift linkage. I solved the problem by converting my tranny to cable shift using parts from an 80s Toronado. (This will require trans pan removal.) You could then use the Toronado column or modify the Eldo column to fit the cable. I skipped the collum and used a floor shifter and console out of a 90 Eldo when I put bucket seats in it. This gave me two problems: 1. the shifter action was reverse of the tranny. If I remember, I flipped the tranny linkage upside to solve that problem (had to take the trans pan off again) but the cable wasn’t long enough. I mated the 90 Eldo and 80s Toro cable together and that never worked just right because my homemade bracket and linkage joint had some give. Also, the two shifters had different throw lengths. I plan to solve that by hooking the Toro cabe to the column and then running the 90 Eldo cable to the column as well. This will cause the floor shifter to move the detent indicator under the speedo and will return the operation of my neutral safety switch. The Eldo column also communicates with the computer to tell it what gear the car is in - at least that is what it says in the manual. I can mount the two cables in different locations on the column lever to “gear” the throw of the 90 Eldo shifter to the right length. (Sounds complicated without a picture to look at- but it is easier than it sounds.)

80-81 Eldo torsion bars are already stiff enough to handle the 500 if it came stock with a 368 because engine weight won’t change too much. However, putting the big block cast iron Caddy in place of the aluminum 4100 lowered my car a lot- which was good except that it made my 4” exhaust hit the ground went I went over a small dip in the road. I plan to use the torsion bars from a full size 5,000 lb. 77 or 78 Eldo (only 3/8” longer) to make up the difference and add level cornering. When this mod is done, the torsion keys have to be ground down, because the thicker bars raise the ride height of the car a few inches. Or I’ll adapt Chevy ¾ ton torsion bars into it and use a Ford torsion key to turn the ride height down instead of up. That should make it feel like an 84 Vette with the Z51 handling pkg. (My goal is to beat the Vettes in autocross – not feel like I am floating in a cloud when driving)

I also intend to use 12” C4 Vette rear rotors on all four wheels to upgrade from the stock 10.5” rotors and adapt C4 or C5 Vette calipers onto custom brackets (when budget and time allow). I’ll also ditch the factory body bushings and put in solid aluminum ones (or use washers).

For more information about my car, here is a copy of the info from my album that I loaded two days ago:

I bought the 82 Eldorado to fulfill the need for immediate transportation while the 72 Mustang was down. I got a good deal on it because it needed a front cap. My son and I did the repair and I sent it to get a cheap paint job.

It had a good 4100 engine with low miles. I drove it 52,000 miles that year getting just over 25 MPG as a traveling salesman. I have heard some reports of the 4100 powered Eldos getting 32 MPG, but I averaged 80 MPH on the interstate and Arkansas has a lot of hills in the rural areas.

With the light 4100 engine and a 4 wheel independent suspension, this car already handled better than the 72 Mustang and with 4 wheel disc breaks it stopped quicker as well. When I upgraded to the thicker sway bars from an 85Eldorado touring coupe, I was driving a car that handled better than a 1978 Z28 Camaro and almost as good as the 70 Elorado.

However, the 82’s springs were too soft in back, and the torsion bars were so weak in the front, it was more like flying a hover craft than driving a car; Despite the good handling, I knew there was room for much improvement. I swapped the rear springs with some from a 70 Malibu Station wagon and that helped the car to start cornering flat like a late model Camaro.

I was still doing research for the front torsion bars hoping to find something stiffer than the 80/81 touring bars when trouble began to happen. At some point, the transmission quit shifting into fourth gear, but the engine was so quiet and the shifts so smooth, I did not notice anything but a dramatic drop in gas mileage. Not realizing I was buzzing the motor hundreds of miles a day with the 3.15 front gear ratio, the 4100 soon began to suffer from the upper end knock that they were known for. Since I had already discovered that with several more upgrades, this 3,680 lb. car had the potential to handle in a Corvette-like manor and was in the same weight class, I was already thinking about doing a big block Caddy swap. (understanding that weight would go up 100-150 pounds).

Since the big block Caddy engine only weighs 35 lbs. heavier than the 350 Chevy, cranks out more power then the 454 Chevy, I had the potential of bettering the power to weight ratio of a C5 Corvette Z06. Not to mention that with fuel injection, the 472/500 engines can be built to get gas mileage close to that of a GM 3800 V-6 of the mid- 90s, (17 city/26 interstate). I could still drive hundreds of miles a day with no big drop in gas mileage from the 4100 IF the MPG tune was right and I avoided the temptation to put in a performance cam.

The 82 Eldorado used a TBI injection system like the one used in the Chevy 454 SS truck, so a throttle body and sensor swap would allow the use of the existing OBD 2 engine management system with salvage yard parts.

I upgraded the radiator to a Chevy truck 4 row, put in a salvage yard Caddy 500 and added an exhaust that consisted of dual 2.5” header pipes that joined into a single 4” pipe in the tunnel, then back into dual 2.5” pipes and turbo mufflers. The first salvage yard 500 Caddy engine was bad, and then I pulled a 472 from a 1972 Lemo rated at 535 lbs. of toque @ 3200 RPMs (after hearing that it had been rebuilt by the former owner.) That engine had been painted in a way that suggested it had been taken apart.

I did the swap and began driving the car to see if I could get the transmission to start shifting into overdrive. I was also looking for a taller front diff to swap in. However, when doing some drive testing with “the Cadinator,” I found that even WITHOUT 4th gear and with the 3.15 low diff, I was getting 20 MPG at 50 MPH. Better gears and fixing 4th gear, would have yielded the same or better MPG results at my 80 MPH normal avearage driving speed, and even better results at the 70 MPH speed. Unless aerodynamics is that much of an issue, 25+ MPG (goal is 27) should be possible at 75MPH since I will be turning less than 1700 RPMs.

It turned out that the 472 was not a rebuild - or it was a bad rebuild. It started knocking 212 miles after I started driving and the car was parked before it was finished and all the buggs were worked out. I am now doing a budget for the re-do of this car. It has been sitting in a field for the last five years and needs a lot of work.

I want to run the 2.19 ratio because I will have Corvette 17 X 9.5 wheels and 275/40 ZR 17s under the fenders. They will be only 25.7" tall. I still need to find out if the lockup converter will work if I have the detent in the 3rd gear position and only use overdrive for above 65MPH driving. The 60 mile round trip I drive every day to work on the interstate will make use of overdrive and the engine will have more than enough torque at 1450 RPMs to keep the car comfortable at 75MPH. The 2.19 will also help me in the autocross because I should be able to see 50 MPH in first gear depending on tranny slippage. Top speed will be limited by aerodynamics and the 670 CFM of the TBI. I don't think I will try to find top speed, because it would probably get airborne somewhere above 170MPH. I also do NOT plan to drag race the car; if that was my goal, then I would use a carb and the stronger tranny TH425 from a 68-78 Eldo/Toro with the 2.73 front diff. The 3.07 front diff would be a torque waste with short tires. (And it would be turning 3091 RPM at 75 MPH)

Hope this helps,
Cody G. Carson

[CadVetteStang]

For those who would want to use the stronger TH425, I found the post and pictures from my friend who put a TH425 into a 79 Tornado. This was originally posted in another forum. I tried to link to it, but this site wouild not allow it.

I had just made a post about my 82 Eldorado and these were some of the replies:


REPLY from DARIUS:
Reminds me of my 1979 Olds Tornado that received a Caddy 500 mated to a 425 Turbo Hydra-Matic. That was my daily driver for several years and it was a sweet swap. Best mileage was 17 MPG with 2.73 gears and the vehicle was dead on reliable. However, it looked like hell. I bought the body, minus engine and transmission, from an impound lot. Paid $50 for the car. Those who saw it said I overpaid.
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Not difficult putting the larger transaxle in. Just used two left side halfshafts (eliminating the flex joint that was standard on the passenger side shaft). Had to "clearance" the tunnel area with a BFH but there was no cutting or welding required.



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Reply from 73Eldovert: 2 left side shafts? From the 325? So the new shafts (vs. old) were the same as far as splines, flanges, and length? I thought there were more differences between the shafts and that was one of the pita's of the swap.

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REPLY from DARIUS:
My bad. Not halfshafts but outer CV joint housings. Those housings were from the stock E-bodies and adapters were machined to mate those smaller halfshafts to the larger 425 transaxle.

So, to be clear:

425 trans was used

Stock '79 E-body halfshafts - with the right side CV housing replaced with one from another car's left side (these are the housings that the "tulips" of the CV joint fit into)

Custom adapters to mate the halfshafts to the flanges of the TH425

Custom rear mount from bell housing to frame mounts (see picture)

Use of stock Eldo front center mount to crossmember

Caddy 500 engine

Radiator from 75-76 Caddy


Sorry for the confusion.
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Reply from CadVetteStang:
Which passenger side exhaust manifold did you use?
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REPLY from Darius:
Stock Eldorado passenger side manifold. There were no problems. Things were a bit tight at the rear, making spark plug access a slow process, but all in all, no problems. It "may" have required a bit of shaving of one of the "ears" where the bolts go through, but I can't remember for sure. Been too long ago.
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NOTE from CadVetteStang: I’m thinking about building another 79-85 Eldo as more of a rough duty hotrod than the mild daily driver “Cadinator” pictured above. If I do, it will have a TH425 mounted like Darius’ and it will be carbureted and cammed for dragstrip use. Sfter doing some research on those cars, the only “core” body I would want, would be the Touring Coupe because it has a lot of the performance suspension upgrades already installed.

[CadVetteStang]

Now that I am able to post pictures, here are some from my swap: