offset valve seats

sbcharlie · Post by **sbcharlie** » Thu Jan 16, 2020 1:43 pm

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

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sbcharlie · Post by **sbcharlie** » Thu Jan 16, 2020 3:03 pm

Pictures of the cylinder head

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sbcharlie · Post by **sbcharlie** » Fri Jan 17, 2020 4:35 pm

Machining offset seat

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Sparksalot · Post by **Sparksalot** » Sat Jan 18, 2020 3:10 am

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.

jarmoyp · Post by **jarmoyp** » Sat Jan 18, 2020 7:17 am

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

Post by **gordon** » Sat Jan 18, 2020 1:58 pm

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

HDBD · Post by **HDBD** » Sat Jan 18, 2020 3:08 pm

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

sbcharlie · Post by **sbcharlie** » Sat Jan 18, 2020 3:30 pm

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

HDBD · Post by **HDBD** » Sat Jan 18, 2020 7:23 pm

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

jarmoyp · Post by **jarmoyp** » Sun Jan 19, 2020 10:32 pm

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.

Truckedup · Post by **Truckedup** » Mon Jan 20, 2020 7:36 am

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 ?

Post by **jed** » Mon Jan 20, 2020 9:13 am

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.

jarmoyp · Post by **jarmoyp** » Mon Jan 20, 2020 9:24 am

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.

Post by **jed** » Mon Jan 20, 2020 9:50 am

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.

HDBD · Post by **HDBD** » Mon Jan 20, 2020 11:33 am

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

Don Terrill’s Speed-Talk

offset valve seats

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