Hi Guys

Need some help..

I have a 20v running on Std ECU, mild cams and recently did 82mm pistons.

I have tried the OEM valves, the 2 of the inlets on the 3rd cylinder suck into the head (This was a STD head that was Gas flowed), then decided to use another head.

This head was overskimmed, so compression is over 12.0:1 (Possibly 12.3:1), on this application we used the Ferrea valves along with the toda valve springs, however, same thing happened with the most damage occuring on the 1st cylinder.

Any ideas on why the valves are mushrooming?

Here is what one web site says....



Distortion
Result: Cupping or tuliping of the valve head.
Cause: Very high seating forces. Excessive combustion temperature and pressure.
Contributing Factors:
a) Engine overload.
b) Pre-ignition.
c) Detonation.
d) Excessive valve spring pressure.
e) Improper compression ratio.
f) Improper air-fuel mixture.
g) Difference in angle between the valve seat and the valve face.

Considering that the valve head has changed shape, and that valves have to get
seriously hot to become soft enough to change shape, I think that the cause as
stated above pretty much covers the situation.

For a second opinion you can read this....
http://www.engineaustralia.com.au/~engine/sites/default/files/SB018.pdf

Cheers... jondee86

any photos of the valve seats? How wide is the contact between the valve and the seat? If the seat is too thin, and out at the edge of the valve, AND you are running LEAN(HOT).... between heat and spring pressure they can "tulip".

Thanks for the response guys..

unfortunately I havent take any pix

RXi20 wrote:Hi Guys

Need some help..

I have a 20v running on Std ECU, mild cams and recently did 82mm pistons.

I have tried the OEM valves, the 2 of the inlets on the 3rd cylinder suck into the head (This was a STD head that was Gas flowed), then decided to use another head.

This head was overskimmed, so compression is over 12.0:1 (Possibly 12.3:1), on this application we used the Ferrea valves along with the toda valve springs, however, same thing happened with the most damage occuring on the 1st cylinder.

Any ideas on why the valves are mushrooming?

Do you have any specs on the pistons and cams you are running?

If I had to guess , you comp is too high and your using pump gas? Likely pre ignition/knock?

Did you cc the head after it was skimmed?

Also what timing are you running and Cam duration ?