Thread: compression ratios

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trying to calc. compression ratio on the 1971 460 with Dove c heads aprox 75.8 cc
bore 4.36 plus 30 over, and stroke 3.85. The pistons are dished .230. Any help would be appreciated.

the 460 with a stock crank with a 22cc dish would be 9.9

Thanks Pat. Was shooting between 9.5 to 10.0 so that will work just fine.

Your combo with L2404's (assuming) will get you at about 9.5:1 but with about 0.070" quench distance. Reduce that to about 0.040"-0.050" and detonation control will improve significantly.

Paul

Paul I talked with Casey in Wa. today. He said they bored it over.040 and got 200lbs compression on each cylinder, so I think it should be o.k. on 91 octane pump gas. Let me know what you think. Steve.

Originally Posted by stovens

Paul I talked with Casey in Wa. today. He said they bored it over.040 and got 200lbs compression on each cylinder, so I think it should be o.k. on 91 octane pump gas. Let me know what you think. Steve.

It's not the cylinder pressure he was talking about. It's the squish. (distance from the crown of the piston to the underside of the head with the piston at TDC)

The way I understand it, blocks before 1972 were cast and machined with a block deck height of 10.300". '72 and later blocks were cast and machined with a 10.320" block deck height.

With Silvolite 1143 pistons, your "stack" calculates to 10.290". If the block is 10.300, that leaves a piston deck height of 0.010". Combine that with a (guesstimate) 0.041" head gasket and you get a squish of 0.051".

The same stack, if used in a 10.320" block, would yield a squish of 0.071" which would be too wide to make an effective squish in the motor and it may have a tendency to detonate.

I think that's what Paul was getting at.