The Stovebolt Site Forums The Shop Area Engine Shop Looking for 261 .080 over Pistons

This is part of an email answer i received from a fellow I know. He is currently building Street rods and track racing machines. Even his "more modern" ideas are similar to my "old days" ideas and practices.

"You are correct in saying that thinner walls cannot dissipate the heat as fast. Metal transfers heat much faster than water and anti-freeze, and the tops of the bores run the hottest. If the bores are thin, there is less metal to dissipate the heat. When too much heat is in one place, coolant can boil and form steam pockets, which is probably what caused problems in your 235. A nice thick cylinder wall acts as a better "heat sink" and pulls some of that heat down to the cooler lower portion of the engine. In other words, it's not as concentrated. People tell me all the time, " If the coolant flows too fast, it wont pick up the heat in the block and you'll have problems." That is not true at all. Faster flowing coolant is better, providing the pump does not cavitate and there is enough block pressure. Faster flowing coolant reduces steam pockets and helps even out engine temps. Coolant boils when it picks up too much heat. When it flows slower, it picks up more heat. Flow the coolant twice as fast and it can only pick up 1/2 the heat, then when it gets to the radiator, there is 1/2 the heat to get rid of, so it can do that twice as fast also. By doing this the coolant is only picking up 1/2 as much heat in the block, but doing it twice as fast. So where back to the same amount of total heat transferred, but we're reducing the chance of steam pockets by evening out the temps some.

There is also many other things that happen to the bores under heat and pressure that have a lot to do with bore thickness and consistency. Core shift can really mess up the works, it's bad enough that the bores flex (which they all do), it's even worse with the flex out of round due to walls being thicker on one side. That's another long story.

IMO, the old 6 Chevy's had pretty thick walls. 0.080" should still leave plenty of metal for good cooling, I wouldn't want to go any higher than that. I personally like to have at least 0.200" thick walls for any kind of performance engine, but the thicker the better. Joe"

I hope he has explained it better then I have.