Don Terrill’s Speed-Talk

here is a picture of a Harley Davidson twin cam with offset valve seat. they work quite well

Pictures of the cylinder head

Machining offset seat

Interesting application of an age old speed "secret" of moving valve center(s) and or angles to gain performance. It still works if the application is happy with the change.

First did it in 1961 on a Studebaker V8. It worked. Many happy years followed.

I have done this many times, moved valve centerlines.
Why to the hd twin cam? Is it because of valve overlap?

On the Stude V8 which direction did you move the valve? EX or INT?

This is different. He just moved the throat. The seat and guide are located stock

No remove the stock seat. And then bore new seat pocket offset.

OK I get it, guide and valve are still unchanged however.

Ok. This is a very common way to make a seat by hand porting after seat job. It takes a couple of minute to do that move.

Ok, for the stupid like me....How do you move a valve seat without moving the guide? You are talking lateral moves and not in or out ?

I can see the valve seat is moved but don't understand what it accomplishes?? The valve has not moved
In relation to the port.

The throat or venturi is not round after offset portning. Short side radius is better after that move. I do this every time, for every head when porting.

Thanks I get the concept. It seems that it would add a lot of dollars to the porting job for 8 off set intake seats and
8 exhaust seats. What is the return on investment in terms of CFM and torque.

Good question, I would be more interested in hp and tq with a back to back test. Added flow does not always equal more of either