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post #23 of (permalink) Old 04-16-2019, 07:25 AM
Richard Jemison
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Join Date: Apr 2005
Location: Pensacola, Fl. U.S.A.
Posts: 6,870
Cam timing

I have never used "EFFECTIVE CAM CENTERS" that far advanced as it "would & should" bias the power band to lower RPM ranges (Which you might want for a street car)

Given: Jim`s head mods and intake designs and piston shapes are VERY different.
Most racers using my "race cams" typically find good results using my base line LCs of 104/104 or 104/106. Both of the engines in my two race cars are set at 103/106 now. A 104-105 LSA seems appropriate for the typical Alfa intake length. BUT, I`m using a shorter intake track length with very large raised ports (short custom manifold, 1" air horns in the cold air box) and 50mm DCO carbs. Hayes Flynn`s 230hp/215 hp (different RjR cams in same engine) and Ed`s use only a modified factory airbox (rounded 52mm openings to the 45 DCOE carbs I modified internally).
All these intake track differences have to be considered when choosing LCs of any cam, and the dyno adjustments are pretty much required to optimize the power band.

Key points of making real power are closing the intake valve "early" enough to limit the amount of reversion, and delaying the opening of the exhaust (and still get it closed before P to V issues) to lengthen the power stroke.

My newest Race intakes have total "off the seat duration (at .010" "lash" settings of 298* int. and 276* exh. Key points are durations at .050 are 265* int and 246* exhaust which is where "flow" really starts, and very high durations from there upward 125* int and 110* exh at 450 lift. (Total lifts are .525 int. and .495 exh)

Richard Jemison
RJR Racing

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Last edited by Alfar7; 04-16-2019 at 07:29 AM.
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