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Who is Bill Jenkins? He’s a guy that’s accomplished more than Smokey Yunick & David Vizard put together. If you can find a copy of his book, grab it, it is 10x more useful than the half dozen or so of Vizard’s books which I have.
I read the Vizard article. He says: “Most small-block Chevy engines have a static quench clearance of 0.055 to 0.065 inch. On a typical 400hp 350, cutting the quench clearance by 0.010 inch and holding the CR constant is worth about 3-4 lb-ft.” From the way he wrote that, we can assume that he has actually tested that part of the theory. That would mean going from .060” to .050” in a 120 cube B20 is worth 1 lb-ft. He then says: “This means decking the block (or using a skinny head gasket) to get the quench down to 0.030 inch is worth about 12 lb-ft.” This looks like he is simply jumping to a conclusion, but in a race engine, I'd go closer to .030" depending on how good my parts are, I just don't see how it could possibly be worth anything risking everything by shaving off another .006".
Did you read the rest of the article? There is way more power to be had by degreeing the cam & tuning the exhaust. Much greater bang for the buck in those parts of an engine. Notice what he says about what each lobe should be like too.
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.
What brand of pistons? Every stock one I’ve pulled apart has had the pistons .005” to .010” down + B20B & E have the same .028” crushed gasket, so I never take anything from a stock block.
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!"
So the only thing you did was deck the block & fit a thinner gasket? Nothing else was done at all? The head & cam were untouched, the carburettors & ignition were untouched, compression ratio was unaltered. What was the clearance before & after?
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