72' 350 Comp Ratio

[Bill #33481]

I am rebuilding my 1972 350 engine. The engine is a CKW (200 Hp). I am reworking the engine to improve performance. I have planned to go back with a 10.2 CR forged piston in a 76CC head (487). Will this CR work reasonably well with pump gas? Last time I reworked engines, pump gas at 103 Octane (SUNOCO) was readily available. Recommendations / Comments.

Thanks, Bill #33481

[Joe L.]

Re: 72' 350 Comp Ratio

Bill-----

You might be ok with this compression ratio but you'd be at the ABSOLUTE highest that I'd recommend. In fact, I'd only recommend going this high if you plan to use a non-stock camshaft with considerably longer duration and overlap than your stock cam. The stock cam for your engine, GM #3896929, can be particularly pre-ignition prone with anything over 9.5:1 compression. Also, to achieve a 10.2:1 compression ratio with your 76 cc heads, you will need to use "pop-up" type pistons. These pistons also increase an engine's tendency to detonation.

[Robert C.]

Re: 72' 350 Comp Ratio

You might consider doing what GM did to your basic 350. Upgrade to an LT-1 combination of crank, pistons, cam, carb etc. A friend did this to his basic 200 hp. 72' with dramatic results.

[Joe L.]

Re: 72' 350 Comp Ratio

Bob-----

Yes, that could also be done. However, to do so requires changing just about every part of the engine except for the bare block. The existing cylinder heads can be used in the replica LT-1, but they will need to be completely reworked and modified for 2.02/1.60 valve size. Intake manifold, carburetor, crankshaft, connecting rods, pistons, camshaft, lifters and harmonic balancer also need to be changed.

[Duke W.]

Try an L-46/L-82 cam

Just putting an L-82 cam into a base 350 will make a world of difference. Because of the increased overlap you can run a bit more compression, maybe half a point, and the base engine quadrajet will probably work without major modificantion. As long as you keep peak occasional revs to 6000, the production bottom end should be sufficiently durable.

Duke