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B20E 140-160

uid 4846's pic
posted by  JohnMc on  Mon Jun 29 12:07 CST 2009
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last visit: Thu Oct 23 07:42 CST 2014
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Ruins the squish, and it will make it ping worse.

Actually, 10.8:1 isn't *that* bad with modern 93 octane pump premium as long as you build it with nice tight squish. Get a good measurement on the deck height of the pistons at TDC, then get a gasket (Cometic MLS or copper) of the right thickness for a tight .032" clearance to the head. The piston *almost* touching those flat sides of the head rather violently snaps the air into the combustion chamber area, which creates a lot of swirl that helps prevent detonation.

Alternatives include enlarging the combustion chamber. One no brainer is to take the sides out to match the bore. Then make a little more clearance around the intake (unshrouding). Possibly shrink the island around the plug some, but bear in mind that those flat shelves are there specifically to promote squish.

Here's what I did to an R-sport head I got on eBay. It came to me ridiculously shaved down, to something around 12.5:1 on top of a 2.0L bottom end, even worse on my 2.1L. I enlarged the chambers as much as I felt I could, and even then had to team it up with dished pistons (B21FT) that gave me another 12cc. Ended up in the mid 10's CR. With a nice tight squish it doesn't want to ping at all on 93 octane. With 87 octane regular, it will ping some.
--
'63 PV544 rat rod, '93 Classic #1141 245 +t






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