could use some advice on a 454 -

[aaronkl84corvett]

car is a 70 Monte - original LS5 car, TH400, and 3.31 gears - the previous owner kept everything OE, but put speed pro flattops in it - with the stock 290 heads... no matter what I do, its just too low compression to make any power... from my math, its likely in the 7s.

anyhow - i'm having a set of closed chamber ovalports finished up now... they measure 94.2 CC - have 2.190 intake valves, and with 1.720 exhaust valves. I had hoped to get to about 10.5:1 compression and run the old L72/LS6 cam....

in fact, i had cliff ruggles calibrate the qjet for that very combo.... but after doing all the math (unless I'm missing something) i'm gonna wind up around 9.5:1 - i'm just not sure how happy that cam is gonna be in a lower compression, heavy car.

I suspect i'll have to go with a looser converter, but really - does anyone see any serious driveability problems, or should i scrap the LS6 cam all toghether

the car has the log type manifolds on it - and has a full exhaust of course - it is more of a restoration cruiser - but i certainly want it to run better than it did at 7.5:1 with the LS5 camshaft.... incidentally before sending these other closed chamber heads over to be rebuild, I tried using a Howards Hyd Roller cam - (spent a lil money - hoping i could get around the compression issue) - awful mistake and total waste of money - the car ran worse, that cam was 225-231, 567-578, 112 LSA - they said it'd be just fine wit 8:1 - but truely it wasn't - just don't want to make the same mistake.... and frankly, i really prefer the GM grinds as they just flat work with stock type heads/intake.

Any advice?
Cheers

[WILMASBOYL78]

I would say as a general rule the #143 cam would be better served with higher compression..at least 10.5 to 1 or better. Many of the original high horse motors ended up with less then the advertised 11 to 1, due to chamber volumes being inconsistent on the heads...so they can live with less. Your new set of heads are about 6cc's less than the factory spec 290's...so that should help. A thinner head gasket may also add a little to the equation.

Another interesting thing to consider are 1971 454/425hp motors...these had lower compression [9 to 1] and used the same camshaft. I believe these had open-chamber cylinder heads....so I guess the combo might work.

I assume you know the exact specs on the current pistons to help with CR calculations??

The engine gurus will likely add more to this discussion. If you can get the engine/cam issues sorted out...a looser convertor [2300-2500 stall] would probably help things...probably wouldn't go any higher without more rear gear or compression.
-wilma

[Salvatore]

9 to 1 is not bad. I think Crane and Comp Cams has what you need. Both are not bad camshafts. 4.10 gear helps too. Put a set of tubes on it also. Will help the motor breath better. Why do all this with stock manifolds?