30 Degree Valve Seats
30 Degree Valve Seats Of course the norm is a 45 on street stuff and steeper on race engines, but Ken Sperry and David Vizard both made references on 30 degree seats lately and it got me thinking.
Theoretically, a 30 degree seat's advantage is more curtain or window area at lower lifts but the geometry limits throat area hurting flow at higher L/D ratios. Definetly not ideal for an intake seat, but what about on the exhaust for FI engines. I could see on those engines where the exhaust is more critical, having more area when that valve cracks open helping the blowdown phase.
D.V. has a cutter he recommends that I may end up trying one of these days:
45 x .020" top cut
30 x .034" seat cut
75 x .050-.100" bottom cut
Any comments, concerns, ideas?
Theoretically, a 30 degree seat's advantage is more curtain or window area at lower lifts but the geometry limits throat area hurting flow at higher L/D ratios. Definetly not ideal for an intake seat, but what about on the exhaust for FI engines. I could see on those engines where the exhaust is more critical, having more area when that valve cracks open helping the blowdown phase.
D.V. has a cutter he recommends that I may end up trying one of these days:
45 x .020" top cut
30 x .034" seat cut
75 x .050-.100" bottom cut
Any comments, concerns, ideas?
Read his charts carefully. The 30-degree seat only pays off on lower-lift cams, then becomes a detriment at higher, more modern lifts. I have a few of his books, and there's a lot of stuff that makes sense, but this only does on maybe an RV or tow truck, AFAICT.
Jim
Jim
Where I read, D.V stated that the valve job I just posted was the best balance of increasing low lift flow without hurting higher lifts as bad. At least on an asymetrical SBC port.
