: Inexpensive performance

The Bif
02-26-05, 10:33 AM
Some might think it's sacrilige, but I'm looking into hot-rodding the hell out of my '71 Coupe Deville. I was wondering if anyone had any advice as to what would give me the greatest increase in performance without killing reliability and at a low to moderate cost. Any ideas?

02-26-05, 11:09 AM
Hmmm, sounds fun to me! Low buck?

1. dual exhaust if it doesn't already
2. Add a harmonic balancer bolt, Cadillacs used a cork and an interference fit. Check with CMD performance on torque. Cadillacs really never were intended to rev over 4500 rpm.
3. See if a Chevy full size car rear end bolts in, chevies are typicaly torquless compared to your 472, so they will have better gearing.
4. Get an HEI out of a 75-7x 500 or 425 (I think the 425 interchanged) Tweak timing, readj mech adv to be faster. Look for a site called DAPA, look for Jim Hand's timing article. It is excellent. I think it is DAPA.org, but it is the Dallas Area Pontiac Association. Great tech on Pontiacs, much can be applied to Cadillacs of the era.
5. Go with full time vacuum advance on the distributor, not ported, there is likely the TCS, Transmission Controlled Spark on it, which killed vacuum advance till you are in 3rd gear.
6. Get some 70 heads, they are higher compression.
7. Get some sort of ram air, for ever 7 degrees drop in intake air temp is 1% HP increase. Don't suck underhood air! The factory aircleaner is made to maintain roughly 100 degrees F intake temp. "fix" it... Take a look at the gnttype.org website for the under bumper ram air for those cars, it is a good setup and doesn't attract attention.
8. Build your own dual snorkel air cleaner. I did one for my 85 Cutlas that looked factory stock. Just get 1 aircleaner and cut the snorkel off, leaving a flange , so you cut it at the base. Then cut a smaller slot out of the new one and pop rivet it in. Paint the rivets black and you have a cool looking factory appearing air cleaner.
9. Shorter tires are the same as shorter gears, so a set of 295 50 15's are shorter than the tall tires and have more traction. Might want to lower it some then too.
10. Set the alignment to have the max caster you can, and then around -1 degree camber, this is will help handling. Unless you are dragging it, then keep the caster high and set the alignment to be zero camber and zero toe at the height you expect the nose at while you are at the end of the 1/4 mile. use a floor jack to adjust.
11. Lose the weight, losing car weight is the same as adding HP. So, ditch the things that you don't need, PW, PL, spare tire, whatever you can think of. AC even is like 100lbs when you get EVERYthing out.
12. Build up a THM350 to replace the THM400, it can be built to take it.
13. Get a built THM 700 R4 and get OD for economy and have a 3.06 first gear. But it needs to be built and it will cost $$ to do it.
14. Get a Chevy torque converter, for same reasons as above on gearing. Get one for the weakest car that has a THM350. Like a Nova with a 307 or something. You don't want these holeshot converters, factory ones are less stall. THM350 converters are typically 11inches, THM400's are 12inch. less rotational mass....
15. B&M used to make a good shift kit for the THM350, most people like TransGo now. But check out a good shift kit. But an old trans make not live long with it.

Well, there is a start, I am sure there is plenty more to do.


02-26-05, 11:14 AM
MSD ignition and coil for starters. Put an MSD on my buddies 66 Cutlass w/70 455 and it knocked 5/10's second off his 1/8th mile times. He was using the stock points distributor. Thats a huge difference, almost unbelievable. Put one on my 67 455 Cutlass shortly thereafter and knocked 2 tenths off my times but I had already installed an HEI distributor. Other than that I'd go with headers, dual exhaust w/high flow mufflers, intake, carb(or rebuilt stock Q Jet), cam, performance built transmission, gears and a small stall convertor. Improving performance is not sacrilege. You should be able to knock off low 14's without incredible expense out of the 472/500 in that big boat. Dont forget things like K&N filter, any hp helps.

02-26-05, 03:37 PM
First upgrade to an HEI distributor from a 74/75 - 81 or so non computer controlled Caddy. Just hit the junkyard and then buy an advance kit and adjustable vacuum advance and use them. Since this is on the cheap, HEI is definately the way to go.

I think if you take 70s monte carlo headers and weld on cadillac flanges they'll fit your deville. Followed up with dual exhaust of course.

For what you're doing the Edelbrock performer 2115 intake will do great. Rebuild the Q-Jet if it needs it and use it.

Cadillac ready reckoner lists 10:1 compression, Cadillac history lists 8.8:1, I don't really know which it is. But they both should have 76cc heads so a head swap from 70 would be completely useless.

A small cam will do a lot of good, don't get one that makes power above 5000 or so since you'll be keeping the stock rockers and T pedistals.

What the hell would adding a harmonic balancer bolt do for performance? The cork is just there to keep the threads in tact and free of grease and dirt.

I'd trust the stock TH400 as is unless it's got a billion miles on it, they're tough. Putting in a TH350 would save a few pounds and waste a good thousand bucks if you want it to live behind 500+ foot pounds. If your car got the posi "controlled differential" you should be in business, otherwise you'll need to get ahold of a posi rear with gearing close to 3:1 - these engines don't rev high if you stick a 3.73 in back there you better not want to take it on the freeway.

Your car's almost 4700 pounds, power window motors and lock solenoids won't do much good and it's a Caddy - it's supposed to have these things. Take the spare out and if it's not to hot where you live the AC and call it good.

Anyway, cam, intake, HEI, headers & duals could have you in the high 14s. Then stick a 150 or 200 shot of nitrous on there and real high 12s might be in your future.

02-26-05, 07:20 PM
What the hell would adding a harmonic balancer bolt do for performance? The cork is just there to keep the threads in tact and free of grease and dirt..

Pure and simple, you are going to run it hard, the balancer WILL be coming loose, and you WILL damage the engine due to vibration. Note I did not say it will fall off.. It will be looser than it is designed to be (remember Cad's only revved to around 4500 rpm) and the harmonics will get worse which will caust harmonic vibrations up and down the crank, which will cause it to fail at a much younger age than it should.If you will never see over 4500, then leave the cork to do its job.

Call CMD and ASK them why they put the bolt in every engine they sell. And the first thing they tell you to do on a Cad buildup is to install it.

Why do you think GM, Ford, ChryCo and every other car maker HAS the bolt in when they could just not machine it and interence fit everyone of them? It is adding cost, and they don't do it for nothing.

Another thing, change the valvesprings. They are designed with a light load for low rpm engines, so they will float the valves at a low rpm. Do that with your cam swap if you do one.

02-27-05, 12:23 AM
Well, that should keep The Bif busy for a few ....YEARS!

Man, you guys have that system down pat!

02-27-05, 03:52 PM
Hell Cads didn't even rev to 4500 but I didn't think it would be a problem under about 5k or so. And it's just a bolt so it's not like it's all expensive or something so it couldn't hurt.