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I've encountered two schools of thought among builders who believe in tight squish/quench on the first place (and a surprising number don't). One is that anything tighter than .040" doesn't accomplish anything. The other is that tighter is better, as long as there's no piston-to-head contact, and obviously that minimum safe static dimension will vary depending on the design and metallurgy of the specific pistons, running clearance, rods, redline, etc.
Smokey Yunick is often quoted as saying that .040" is about the minimum safe clearance -- I don't know what engine he was talking about, specifically -- but I can't see where he ever suggested that tighter wouldn't accomplish anything if it could be achieved without actual contact.
I find
this article to be a good overview, and it suggests much less than .040".
I've run .030" with forged pistons (Ross, they "grow" less than most other brands), .004" running clearance, and H-beam rods with no problems at 7500 RPM.
In any case, tight squish is NOT an internet myth, and decking a block is not a waste of money. It varies quite a bit, but factory B20s usually have the pistons a good .020" or .025" below the deck. Add a .035" carb head gasket (which is what the ones advertised as .030" actually crush to), and you end up with .055" or .060" clearance. Gaskets for injected heads crush to around .055", so you potentially have .080" clearance without decking. And then there are the .080" compression-lowering gaskets... which seem designed to guarantee more pinging and less power all at once.
I've had two cases where engines that already had good basic performance mods came to me, and all I did was deck the block. Both were completely transformed by this procedure -- same cams, same porting, same exhaust, same everything else. Even the exhaust tone became much crisper. Customer reaction upon returning from his first test drive: "Holy sh*t, Martha!"
Works for me...
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