Don Terrill’s Speed-Talk

I've been looking at different 45-degree intake valve seat configurations done by various cylinder head shops & manufacturers and am curious about what the "head guys" have seen that influences whether they cut a more typical 30/45/60/75 seat or use more and/or different angles.

Because I've seen the same heads prepped w/ various seat configurations depending upon the shop doing the work, questions like these came to mind:

- Have you found different flow results?

- Are you trying to present the air/fuel mixture w/ additional sharp edges to help keep the mix in suspension?

- Does a particular configuration seem more effective depending upon the valve diameter?

Thanks,
Brad

I've seen a 10 to 15 CFM difference between various intake valve cutters. My favorite 45 degree intake cutter is the Sunnen #17258. It's on page 17 of the catalog given below:

http://www.sunnen.com/graphics/assets/d ... 4e8040.pdf

It's a 35,45,60,75,82 cutter. If you use a 82 degree bowl cutter and extend the 82 degree cut deep into the long side of the bowl, you can usually pick up another 3 to 5 CFM across the board. The best cut on the valve I've found is a .100" wide 45 degree cut with the widest 30 degree cut you can get away with above that (.100" max). Usually there's not much space left on the valve face after you cut a .100" wide 45 degree cut on the valve. I find the wide 45 valve cut gets the air turner sooner around the valve.

The best seat is the seat that helps the air go to a place where it can diffuse well, so changes with every head configuration / chamber.

Besides, for smaller valves like 32mm (1.25") or less, if you're running a 90% throat and 1.6mm wide seats (exhaust) you have no angles left under the seat. The throat becomes your seat inner diameter. A 25mm / 1" Yamaha bike valve at 90% throat can't have a seat wider than 1.25 / 0.050" if it wants any angle under the seat at all.

In fact, some of the most powerful heads I have made has a 45º intake seat and a 38-32º top angle, no underseat angles at all. The angle from the seat to the chamber walls/ceiling is more important anyway, IMHO.

SWR wrote:The best seat is the seat that helps the air go to a place where it can diffuse well, so changes with every head configuration / chamber.

Besides, for smaller valves like 32mm (1.25") or less, if you're running a 90% throat and 1.6mm wide seats (exhaust) you have no angles left under the seat. The throat becomes your seat inner diameter. A 25mm / 1" Yamaha bike valve at 90% throat can't have a seat wider than 1.25 / 0.050" if it wants any angle under the seat at all.

In fact, some of the most powerful heads I have made has a 45º intake seat and a 38-32º top angle, no underseat angles at all. The angle from the seat to the chamber walls/ceiling is more important anyway, IMHO.

Do you mean by this 90*(throat) below the 45* ? Which kind of head is this? 4valve cylinder I guess.

Amilcar wrote:

SWR wrote:The best seat is the seat that helps the air go to a place where it can diffuse well, so changes with every head configuration / chamber.

Besides, for smaller valves like 32mm (1.25") or less, if you're running a 90% throat and 1.6mm wide seats (exhaust) you have no angles left under the seat. The throat becomes your seat inner diameter. A 25mm / 1" Yamaha bike valve at 90% throat can't have a seat wider than 1.25 / 0.050" if it wants any angle under the seat at all.

In fact, some of the most powerful heads I have made has a 45º intake seat and a 38-32º top angle, no underseat angles at all. The angle from the seat to the chamber walls/ceiling is more important anyway, IMHO.

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Do you mean by this 90*(throat) below the 45* ? Which kind of head is this? 4valve cylinder I guess.

Several different types, but I'm talking of 4 and 5-valve heads, yes. Don't know of many 2-valve heads with single 35mm valves..

In my case the stuff I run would have intake valves in the 2.14 to 2.25 inch range...

BradH wrote:In my case the stuff I run would have intake valves in the 2.14 to 2.25 inch range...

which head?
i believe port shape, chamber shape, and the lifts used, also play a role as to which angles the head likes and doesn't like.

wil8115 wrote:

BradH wrote:In my case the stuff I run would have intake valves in the 2.14 to 2.25 inch range...

which head?
i believe port shape, chamber shape, and the lifts used, also play a role as to which angles the head likes and doesn't like.

I work on big-block Mopar stuff (hobby), so we're talking typical aftermarket standard- or Max Wedge-sized port replacement heads.

The MAX Wedge program I have has a Serdi 610 intake and 604 exhaust.

I assume you mean Serdi 604 (Angle profile) Intake and Serdi 610 (Radius profile) Exhaust.

http://www.serdi.com/cust/bitsnew.aspx? ... 195&lg=ENG

http://www.serdi.com/cust/bitsnew.aspx? ... 207&lg=ENG

Interesting that the Sunnen 17258 and the Serdi 604 (intake), and the Sunnen 17536 and the Serdi 610 (exhaust) are exactly alike. Wonder who got it first for bragging rights?