4g63 under cut valve?

[Gst18]

I dont know if this is a good idea but do any of you guys who build 4g63's undercut stock valves at 30 degrees?
I heard it would cause you to burn valves extremely fast because of there being much less material left... am i right? not right?

Any suggestions welcome!

thank you

 

[Big Woo]

The term you are refering to is know as back cutting. It is when a second cut is made on the valve seat surface, up to the point where the valve actually seats. Basicaly it smooths the corner for air flow.

As far as back cutting making valve more likely to burn. If the tune is good, and there is suffucuent valve seat width for proper valve cooling, back cutting will make no difference.

A crummy tune with valves back cut too far, so that the back cutting effectivly reduces seat width, sure, maybe.