Competition 3-angle valve grind specs?

[JGK]

My searches in the forums find several posts where a 3-angle valve grind is recommended for performance. But no where have I found specifics on the how the grinding should be done. Can anyone provide the specs? This is for a 12-valve head.



I know that a 45° face and seat are typically used on both the intake and exhaust on gas engines, but the 12-valve CTD uses a 30° face and seat angle on the intake. Is that maintained on a 3-angle performance grind or is that changed?



The other 2 angles on a gas engine are generally about 15° on the chamber side and 60° on the port side. What about the angles on the CTD? Also, about a 35° back cut is sometimes done on the back side of the intake valve head on a gas engine, but no such back cut is done on the exhaust valve. Same on our CTD?



Is any grinding recommended at the outer edge of the valve face on the chamber side?



All these questions are in anticipation of doing an o-ring job and as long as the head is off and getting decked, the valves will be inspected and serviced if needed. So I might as well have this done if the cost isn’t bad.



Thanks in advance.

-Jay

 

[Todd T]

the only thing i can add is get a good 3 angle job on the valves matching them to the seats, back cutting them 30* and trying to get the depths the same--around 0. 052" to 0. 055" from the valve surface to the deck surface



so match the seat angle to the seats and backcut the seats 30* and radius face to margin area (10*+/-) to increase low lift flow.



might be what you're looking for

 

[JGK]

Thanks, Todd. That helps.



But I still want to know what the 3 angles should be on both the intake and exhaust.



Nobody else? Lots of folks talk about it but no numbers? Is it because we really don't know the numbers, or are they closely guarded secrets?



-Jay

 

[Todd T]

I dont think its anything guarded. when i did my head a few months ago they did just that. matched the angles to that what was already there and backcut the seats 30* like i had asked for.



On my last 12V'er I did the same, but in-between machining and assembly I radiused the faces and cleaned up the head by rounding off the edges and some bowl work to just smooth em out a bit. I also did the regular porting/polishing to that head.



Calls PDR they will tell you all you need to know.