Valve Seat Angles???

[my_mad_z]

Hi fellow Z enthusiasts,

Does anyone know the valve seat angles for the P90 head? I was curious to know if they have a three angle grind from factory as there appears to be three different angles on the valves/valve seats out of my P90.

I tried to find information regarding the valves in the P90 but I had no luck. The Haynes manual only has the listing for the L24 and L26, no L28....

Are there a specific angles I should aim for (turbo application)?

Any information would be greatly appreciated.

Thanks in advance.

Marc.

[Arne]

My factory service manual shows a three angle seat cut as standard for the '70-71 L24. That (plus other things I have read) leads me to believe that ALL L-series heads used three angle seats.

[Phred]

Marc,

I cut high perf. seats on a daily basis. There is literally a catalog of available seat designs, angles, and widths. Generally speaking, a three angle seat has a 45 degree contact area, with a 30 degree angle on top, and a 60 degree angle on the bottom. Note: air flowing across a surface will "separate" if forced to change directions more than 15 degrees, causing turbulance, or loss of flow. That is why a three angle valve job increases air flow. The other general air flow trick is to grind a small 30 degree angle on the inside of the 45degree angle of the intake valve. Again, to help smooth air flow across the back of the valve. All this results in what the tech. people call volumetric efficiency. So you get more horsepower out of what you already have. Seat widths vary depending on application, valve material, and length of required service life. Example: a race engine with steel valves can use a 1mm wide intake seat, and a 1.5mm exh. seat. A high perf. street car would have a longer life expectancy with a 1.5mm int. and a 2mm exh. seat, with only a small reduction in flow. Seats also have another function. Heat transfer. For this reason, turbocharged engines will frequently have a wider exhaust seat, (3mm or more) All this is a general overview to show how valves and seats should be designed around your specific engine.

Phred

[my_mad_z]

Thanks for the feedback, appreciate your help!

I'll pass the info on the the guy reconditioning my head and see how it goes.

Thanks again.

Marc.