The advertised compression ratios were just that,advertised, more often than not,at least 1/2 point lower in reality to allow for fuel and production variances.
And you always have to consider the piston height at TDC.On the engines with standard size GM pistons,the piston is about .010 below the block deck at TDC.On all the stock type oversize replacement pistons I've seen,the piston is as much as .040 below the deck.
Raising compression within reason improves throttle response,torque and fuel mileage and increases the feeling of engine vibration.
I had a modified 261 in my 37 truck,an 848 head milled .030,the block decked .030 with flat top pistons .010 below the deck height.Actual compression was about 9-1.With a hotter cam ,headers and some other hot rod tricks it ran real well.
Then I dropped in a 302 GMC built about the same way as the 261,I'll never bother spending money on hot rodding 235/261's again
It's all in the head,and the 235/261's are limited by a poor head design.
