Mr.Classic

If I wanted to use the Edelbrock performer cam, performer manifold and 650 4 barrel carb, on a Oldsmobile 350 with 8:1 comperssion what is a cheep way to incress comperssion? The engine has 60,000 original miles on it. Not looking to rebuild it right now,,,, Money is tight right now. It's a 1971 Cutlass with AC.

Charlie Jones

There is no " cheep " way to increase compression on an Olds 350.
The compression ratio is determined by the depth of the " dish" in the piston top.
Increasing compression involves replacing the deep dish '71 pistons with shallower dish or even flat tops.
Ten to one or maybe a little more is about the most for 93 octane premium.
Any more than that will require race fuel.
My advice would be to spend your money on a re-build first. Get 10 to one pistons.
Include your new cam in the re-build.
Then when you get some more money, buy the manifold and carb.
That manifold, carb and cam won't do you any good without a substantial increase in compression.

Vintage Chief

I read one or two of your other posts in which you stated it was mostly a highway car but you wanted a little something extra, or something like that. Here you've stated you're thinking of increasing compression but on the cheap. Everyone has their own range of measuring what cheap equates to, but have you considered dropping in a set of headers?

Fun71

As said, the 71-72 engines have pistons with a HUGH 25cc dish. There’s really no way to increase compression with those pistons since all the “good” small block heads have the same combustion chamber volume, so you can’t just swap heads and increase compression. And keep in mind that with that low compression it is extremely easy to overcam the engine and create a situation that is worse than before. Too large of a cam will kill low RPM torque and make daily driving unpleasant. The factory cam has a short duration with an early intake closing that helps build cylinder pressure - if you put in a cam with a later intake closing event, the cylinder pressure will drop along with power / torque / driveability.


If you want more power, swap in a 4bbl intake and a QuadraJet carburetor (those are 750 cfm), install dual exhaust (factory specs show 20 hp gain over single exhaust) and ensure everything is tuned to factory specs.

Mr.Classic

Thank you for all your thoughts. I wasn't sure,,, some spoke to me about changing heads to a smaller cc to maybe increase cylinder pressure. I guess for now I will just do the aluminum manifold new carb and HEI? One question though,,,, is a Edelbrock 650 AVS different than a 750 Rochester? What are the pros and cons? Thank you for your time

Fun71

As for heads, there aren’t any with smaller combustion chambers than your original 1972 heads. Those should be 7 A (small capital letter). That carb should work well but is smaller than the OEM carb. May not feel any different in daily driving, though. I once had a Holley 600 cdm and after a lot of tuning it ran as well as the original QJet. I eventually put the QJet back on as I got better mileage with it.

Olds64

^^^THIS^^^

An OE 4 barrel Quadrjet and intake manifold will have the greatest effect on your butt-dyno.
​​​​​​

olds 307 and 403

As said, the big dish pistons leave the compression low. Good part is, there is multiple choices for replacement pistons to boost compression including two in a 4.065" hone to fit size, CP and Mahle, if your block has little wear. A Performer manifold and 650 carb, at least go with the AVS2, will gain nothing and need a wideband to match a factory 4 barrel carb and intake for proper tune. Another option to boost power is full length headers and dual exhaust, should be around 30 HP over single exhaust. Good luck.

BangScreech4-4-2

No need for an aluminum manifold, "cheepest" way to go will be to use factory manifold and Q-Jet takeoffs from somebody else who "upgraded". As already pointed out, there is no alternative head you can use to increase cylinder pressure; that is accomplished with pistons. There are also no performance benefits to be had from HEI -- it's largely used just for easier maintenance.

If I was in your situation, I'd just drive it as is for now, and save money for a rebuild that would get me what I really want.

BillK

In that case just leave it alone and enjoy it. None of the things you have mentioned will make any noticeable improvement in performance.

Mr.Classic

Again thank you all. I know a rebuild is best. Guess I need to just save money and do it right.

BangScreech4-4-2

Now you're thinkin'!