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Stude292

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  1. Old post, I know. Here is my opinion: I hope folks are not following the advice to utilize thick i.e. ~.038"-.042" multi-layer head gaskets here- a common mistake. These heads provide significant quench which quickly becomes ineffective as piston to head clearance increases, and is likely mostly gone if the multi-layer gasket is used in a stock-decked 289 block at performance-oriented compression ratios. Thus detonation is much more likely to occur. The way to eliminate detonation (besides cool air, proper AFR, correct timing etc) is to MAXIMIZE QUENCH. My R1 motor uses hypereutectic (John Erb) pistons in a block decked to achieve .030" quench using, of course, the steel shim gasket, (the closest I felt I could safely go with a 6k redline; other cylinders vary due to the crank tolerances up to ~.010") with heads significantly milled to recover cylinder pressure (the pistons are dished and I was this able to achieve enough valve-piston clearance over the range of cam timings I wanted to try). The cranking pressure measures 195 psi, with some variation due to crankshaft tolerances mentioned. No detonation with 93 pump gas. I can achieve ~200 psi by increasing the intake valve clearances from .018" to .023" (a JE long-furation "special" cam that we were curious about which I advanced by 7 deg,) but decided I didn't like the added noise. Still no detonation....Note that the reduced thermal losses in these pistons should, according to John, add ~.5 compression point during operation to my computed (based upon actual volume measurements) of ~10.3:1. A last note about compression testing: Expect variations due to valve timing and varying piston height from these cranks. A leak-down test will determine the truth regarding, well, leaks... The motor runs quite well in my hot rod: 13.02@103.5 with 3:50 gears, street tires, 87deg ambient and a computed altitude of ~1900-ft..
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