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

To clarify my previous post- The engine I was refering to was a Corvette 235 and it was almost 40 years ago, so things are a little foggy but not "that bad"-LOL

When you bore an engine oversize you decrease the ability of the cylinder wall to dissipate the heat. You also, when boring past .060 over, get the chance of compromising bore strength and getting bore distortion. If you (for what ever reason) figure you need to bore your engine past .030 over I would suggest that you have it "Sonic" tested. Of 235's bored past .060 over about 95% will fail this test. A prefered thickness of cylinder wall is 0.200" thick and I like 0.2500" better. Talk to your machinist and then talk to some other machinsts. Let "logic" dictate which way and what you will do. If still in doubt- get ahold of me, what I don't know- I know a couple of good machinists that do know.

As to the over heating issue- I will lay this out as I see it. The cooling systems on these old trucks are barely adequate, at best, and when they aren't maintained properly (as Tony does his) then they are prone to failure. When you increase the size of the firing chamber (generating more heat) and simultaneously decrease the ability of the cylinder wall to dissipate heat, you need to increase the ability of your cooling system. But, here is the draw back- When you increase your cooling system you will need to use power from your engine to operate the increased cooling and thereby reducing your ultimate horsepower output. Sometimes "bigger doesn't equal better".

There are better ways of increasing the output of the I-6 then overboring it to a large extent.

FTyler, I wouldn't be extremely concerned about a 292 bored 0.060" over unless you have a poor cooling system. Or, unless you are making it into an experimental racing engine. Now if you were talking a 235 (261?) bored 0.060" and were going to be turning it at 4-5,000+rpm then there would be other concerns to think about.