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Re: Poly 318 Modification Questions

From: Hank Dozier
Remote Name:
Date: January 09, 2003
Time: 07:42:17


Kenny....Had a similar private correspondence with Bob O. regarding heads. If this is the first time in a while this engine is to be apart, you most likely need exhaust valve seats. Have the machinist look if he can get seats in that will take 1.60" exhaust valves. After that, evaluate how much material you have for a seat for the intakes, and enlarge to that. Your present valve diameter is about 1.84", and I think you can get 1.94" valves in those heads (Bob wants 2.02's, but that may run the intake seat margin inti your new exhaust valve seat). After the valve seats are installed and/or roughed in, then port blend the bowls to clean up any overhangs and stuff. Since you are using a carb, I would not massively port the heads (street anyway), but certainly you should gasket match the heads to the intake. As for compression ratio, unless you have access to inexpensive high octane fuel out there, I would stick with about 9.5:1 as a reasonable break between having to always use premium and spark knock if you don't.


Last changed: July 19, 2018