Hello,
is there a big difference in the performance of a low compression 1973 472 engine an a hight compression 1970 472 engine?
I kown the 1973 has only 220 hp but this net hp and the 1970 has brake hp.
Thanks
Patrick

I want to say I have heard it is really only about 20-25 horses real difference.

the biggest thing is the lack of all emmissions junk... AIR pump, cat. cov. etc.... and the compression.... 8.2:1 or so to 10:1... IIRC heads were also changed....

the biggest of all engines being the 400hp/550ft-lbs tq. 500 in the 1970 Eldo.... but, again, those were rated differently...

I *think* someone said that the "true" numbers on a 1970 500 are 300hp and 450ft-lbs tq.... don't hold me to it.... still, that is very good for today... and even better in it's day....

These numbers come from Flash when they dyno'ed 2 stock rebuilt 500s.

10:1 - 323hp and 504 ft.lbs.
8:1 - 302.1hp@3600, 493.5@2600 (keep in mind this is a bit lower than stock compression, everything else was essentially stock)

When I get my 1968 overhauled (10.5:1 compression ratio) I'll try to get it dyno'd and post the results.

Other things that make a real difference:

- Dual Exhaust - really helps
- any cam other than the stock cam specs even a "series 0 or 1" will help, but at the expense of some sommthness at idle
- head porting can really help, but only if you have dual exhaust, otherwise there's too much backpressure
- oversized valves - ditto above

I'm considering all these in my overhaul

For the record, early 472s had AIR pumps. In 70, they didnt curiosuly enough. CadillacMike, how does yours behave on regular gas? Does it have octane creep like mine? I can tell just by listening to it wether or not it has the right fuel in it as soon as im driving it. Between the relatively high compression and the years of carbon buildup, they tend to require 93. I have dual on my 68, and a Edelbrock carb. While I will admit the mileage has gone down some, The Edelbrock is loads easier to tune, especially when it comes to idle mixture. I just gotta actually get to tuning it and up the mileage a bit. You have the posi?

For the record, early 472s had AIR pumps. In 70, they didnt curiosuly enough. CadillacMike, how does yours behave on regular gas? Does it have octane creep like mine? I can tell just by listening to it wether or not it has the right fuel in it as soon as im driving it. Between the relatively high compression and the years of carbon buildup, they tend to require 93. I have dual on my 68, and a Edelbrock carb. While I will admit the mileage has gone down some, The Edelbrock is loads easier to tune, especially when it comes to idle mixture. I just gotta actually get to tuning it and up the mileage a bit. You have the posi?

Mine won't run on anything less than premium, terrible knocking. I'm going to have the AIR pump removed and go to a 3 belt setup like the 1970 when its overhauled (I ahd a 1970 Fleetwood brougham in my earlier days). It's a cleaner engine compartment and the AIR was a POS item anyway. I'm going to have it dual exhausted, but am going to stay with the Rochester QuadraJet. There's also some crossovers in the intake manifold that routes hot exhaust gasses under the carb and forces all exhaust out the right side until the car is "warmed up" I'm thinking of having the crossovers welded shut and the rt side exhaust manifold either permanently opened or replaced with one that doesn't have this "feature".

I don't have the limited slip differential (at least I don't think so - can't tell without taking it apart). I'm in FL so no snow and no hills, so it's not really needed.

You should be able to tell via the gas pedal. :coolgleam

You should be able to tell via the gas pedal. :coolgleam

True, but i don't want to blow a hole in one of these tired old pistons. :lildevil:

While the gas pedal method is by far my favorite (I check from time to time, make sure its still there of course... ;) ) You should have a sticker in the trunk across from the jacking instructions sticker, (its called a Controlled Differental) or look for a metal tag on the fill plug. If both are missing, the only other way to be sure would be to jack the car up in park, (both wheels off ground) and try to spin the tire. If it is really difficult/impossible to turn (btw, really difficult but can still turn by hand = smoked posi) you have the "Controlled Differental" If the wheel spins easily you probably don't have it. The wheel on the other side will also turn in the opposite direction from the one your turning.

True, but i don't want to blow a hole in one of these tired old pistons. :lildevil:

Don't worry, those old high-compression 472s are tough engines. They can take it. My family's former '70 CDV and '69 CDV were given a workout once in a while and there was no complaint from the engine!

Don't worry, those old high-compression 472s are tough engines. They can take it. My family's former '70 CDV and '69 CDV were given a workout once in a while and there was no complaint from the engine!

Yeah, but my engine is real tired. It has some weak connecting rod bearings, and a bad # 7 cylinder.

But it still goes 95+ MPH with the top down! :lildevil:

I'm going to get it overhauled as soon as I get back from Ft Benning. (I'lkl be making that good colonels pay, etc.)

Here's how to tell what differential you have.

Ok I was looking a little deeper in my service manual and came up with this regarding the diff. and the two types in 1969.

http://images5.theimagehosting.com/Diff.02.jpg
http://images5.theimagehosting.com/Diff.jpg

and also this regarding the fluid change.
http://images5.theimagehosting.com/Diff.01.jpg

Hope this helps others with the same question. My car is a 698 series. Commercial Chassis. Thanks.