silent running

I'd thought that the standard valve seat angles were 30-45-60 but looking at a Subaru workshop manual it appears that the top-cut is 15 degrees, not 30 and there are more than three discrete angles there i.e. two different throat cuts?

My STi3/4 heads are off to have the seats and valves cut to spec, but should I ask for them to be kept at 15-45 for the top cut and contact angles, or get it recut to 30-45-60 if possible? Is there any advantage in one way or the other?

dazdavies

iTrader: (22)

I've never bothered with that. I've always just reground the valves into current seats.

silent running

Well I think they've done the cutting now, so we'll soon see, when I go to collect them. Next problem is equalising the chamber volumes and getting the skim depth right, but that's for another thread!

JohnD

iTrader: (5)

Is the technique of hairline valve seats still used on inlet valves? (higher seating pressure for a given spring force)

JohnD

silent running

Well the contact widths are 1mm inlet and 1.5mm exhaust so no, not hairline. I suppose they go as narrow as they can whilst still being able to shed valve heat effectively.