KCS

iTrader: (20)

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?

DeltaT

iTrader: (5)

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

helicoil

iTrader: (104)

When I see 30 degree seats I think of a low valve lift, Pontiacs, and John Deeres.

KCS

iTrader: (20)

I understand that it isn't ideal at higher lifts, hence the thinking that it may benefit the exhaust on a nitrous or boosted application rather than the intake side. Most of the exhaust flow occurs at "low" lifts and before BDC of the power stroke, especially on a nitrous engine where an early Exhaust Opening is common. Having more area for the exhaust to flow at early lifts when the cylinder pressure is highest, at least to me, makes sense.

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.