SBM Edelbrock/Speedmaster Head Data

Newbomb Turk said
I mean putting an angle on the margin of the valve to the face of the valve. So from the face of the valve to the margin.

Some guys call it “clipping” the valve.

It is supposed to (and does) shape the flow around the valve.

But it also makes the valve flow far better in reverse. At overlap you can end up with weird things happening if the intake port pressure is lower than chamber pressure. You get flow moving much better back up the port.

I’ve never really thought about what happens with EFI but I know with a carb the booster has no idea which way the air is moving.

So the air goes through the booster, down towards the valve. Then we get to overlap and the valve is much less an impediment to flow going the wrong way past the valve.

Now the air column, which already has fuel from its first trip down the carb now flows backwards through the booster. Once the system gets back in tune, that same air has now passed through the booster three times and you have 200% (roughly) more fuel than you should.

I know Yunik was big on top cutting the valves (I do a radius on the top of the exhaust valve) but after that I have not done it to another valve.

This was a Comp Eliminator deal and the car owner had money but he didn’t have enough to keep going down the rabbit hole.

We did all the flow testing with steel valves but never on the dyno. Once had a valve shape we wanted to test he would order the valves . At that time Ti intake valves were about 125 bucks each.

When you have 1k in 8 valves and it sucks buttermilk on the dyno you can only do that a couple of times until you get sick to your stomach.

If he has an unlimited budget (or at least more budget) I think he would have continued on testing.

Edit: I just read this post and I hope I’m explaining it correctly. I can’t even remember the angles I was trying but the cut goes from the combustion chamber face of the valve to the the margin.

You are essentially making the margin narrower from the opposite side of the seat.

I think it always flowed more in the forward direction and reverse. That’s usually bad.

I can’t see how that type of top angle would help flow in the proper direction at all. I can see how it promotes reversion.

I would like to play around with a small top angle between the seat cut and the margin. I’ve done it once with some mixed results, but never spent any real time on it. I think the general consensus in the industry is that this type of cut effectively reduces the valve diameter because the seat cut is now a smaller diameter.