: 540 into a '79 Coupe

06-16-10, 11:11 AM
My '68 Eldo project is going pretty well now. I had some ideas about adding some engine performance mods but I think besides an HEI and the sway bars I'll just keep it a good driver.

Gonna have to strip and get rid of the two '68 eldo parts cars soon.

The main reason for the switch is that my brother owed me some money and gave me a '79 Coupe to settle up. The coupe has a rebuilt motor and trans, very nice interior but needs paint - all the trim is currently off the car.

My idea with this car is to turn it into the car Cadillac should have made. I hope to keep all the desirable caddy characteristics like smooth low-end quiet torque and a smooth ride, but with increased capabilities.

An off-set ground crank stroker 500 in the 540 or over range with stock intake but with headers and quiet duals. A 10 or 15 level cam (the operating range has to be close to stock as I will keep the stock trans, torque converter and rear gear set. Yep, I'll sell the rebuilt 425.

Additional missing body/frame mounts. I already have the Impala SS springs an a 2nd gen front sway bar. Still need a rear bar and probably new shocks.

My '96 9C1 car had the Impala SS 17" wheels and they had a nice sidewall cushion. But the brakes on a stock '79 Coupe Deville are marginal, so if I step up to the C5 conversion I'll have to do 18s. 19s and above on b/d cars just look too goofy to me.

Drum rears are OK with me - I actually like the pedal better. Wish there was a cheap ABS retro kit; I'll miss those 9C1 brakes.

And not much more than that; juts a decent Coupe, a little lower than stock, that handles well and still has a nice ride and has excellent torque in the factory rpm range.

I know, I know, I'm giveing up fuel economy and probably some longevity to the engine and drive train. I'm OK with that.

Using the stock block and crank and off the shelf rods and pistons and stock heads should make great torque at a very reasonable price. I realize my redline would be 4000 or so and I'm OK with that too.

Using used suspension parts and other low cost mods will make this car one of the lowest cost and best performing street cars ever - for me. Its a heavy car so it will never be that fast or handle that well, but I like bigger cars and I'm OK with that too.


06-16-10, 01:18 PM
You should go with a #5 cam, I have a #10 cam and I think the torque band is a little high for the weight of the car. You should grab the Big Inch book cause it shows the measurements on a stroker using off the shelf pistons. It also shows the measurements the crank grinder will need. And if you have an extra power steering pump for a great price, let me know.

06-16-10, 05:13 PM
If you're going to go with all that trouble, I'd do a little port work on the manifold and heads while you're at it.

Also, you're going to want to swap out the rear end for something with a little bit lower gear and posi. Stock they came with a 2.28 rear gear, something like a 3.08, 2.93, 3.23 would let you still cruise at a decent RPM but really wake up the car. Something to mull over.

Also, have you thought about just rebuilding the 500 to stock 1970 Eldorado specs with some headers and true duals??? You got 400hp/550lb-ft torque stock. I know its rated in gross hp, but maybe with headers/true duals you'd be looking at around 350hp net, with more torque than you'd know what to do with. It would also idle and have the same street manners as a stock Cadillac.

07-18-10, 02:00 PM
I tend to agree with your thoughts on the '5' level of cam. The goal is to increase the torque in close the stock operating range.

I did get a book from MTS, 'Big Inch Cadillac', but the Ross pistons the author used were custom pistons from Ross. The advantages to a modern pistons seem to be worth the cost.

The chevy rods the author chose are relatively inexpensive but require a fair amount of additional crank cutting to work. With the low, close to stock rpm operating range, I think there may be other rod choices that don't require the additional crank work that are still affordable.

I also like you idea about there being an off the shelf piston that would work and still be affordable.

I have also been thinking about the 425 with the same stroker crank, rods and pistons. The 425 block was lightened by Cadillac from the 500 block and looks like it might be an interesting block to use. Of course the 425 starts with a smaller bore - I wonder how much boring the block would take...?

I'm not done with scavanging parts from the two '68 Eldos for the '68 Eldo project car but I'll be sure to send you a message if I end up with an extra steering pump. About the '68 Eldo... the brakes have taken a LOT longer to sort out than expected. Multiple problems with similar symptoms can be a challenge - we have these old cars because we like them right?

07-18-10, 02:14 PM
Trouble? I mess with these cars because its interesting and I like to drive them. At least thats what I tell the wife. No trouble, but older cars can cause a grey hair or two.

I agree with you about port matching the intake and heads and maybe even some basic pocket porting. The big inch book has some ideas about updating the fragile valve train system. But if its not simple, inexpensive and very effective I'll just stick with the stock valve train. Lunati has some very interesting VooDoo cams for the Caddy.

I may have to swap out the rear end when it breaks but the tall stock gears are exactly what a low RPM high torque engine needs with a TH400 trans and stock converter. The late 70s B/D body was also 700 or 800 lbs lighter than ealier caddys making taller gears more usable too.

I also very much agree with your thoughts on headers and true duals for the '68 Eldo. The stock exhaust system is buzzing and banging at the rear of the car. I only reacently knew about this since I got the brakes done and could drive it some miles. Since it seems ehaust work is in the near future headers and duals make good sense.