Valve seat pressure changing...

[bubbleguinea]

if you change how deep the valve is in the head, that changes the valve seat pressure, right?

 

i ask this cause ive got a P90 head with a few problems...

 

problem:

 

a. the valves are seated at two different heights

b. this causes me to use two different lash thickness

c. if i shave and shim the head, this would make me use over 3mm lash pad!!!

 

ive got two different length valves...

 

one is 4.530 inches the other is 4.570 inches, which means one is 1mm taller!

 

i think the pressures at lift are 210 and 250....

 

if the 250 is the one thats seated higher in the head, if i seat it say 1mm deeper, would it bring the seat pressure down around 210???

 

i know its kinda a confusing question.

[BRAAP]

Welcome the wonderful world of high performance cylinder head building. Valve train set up can be time consuming and for most, it can also be quite confusing.

 

If the valve seats were cut/ground deeper into the head, then yes, you would have less seat pressure. As for how much seat pressure you would loose for a given spring installed height change? Depends on the sprig rate itself. If your spring manufacture supplied that info, you could calculate the loss in seat pressure. For high end performance head work, it is always best to verify this using a spring tester. There are also many other things that need to verified as well such as over the nose pressure, retainer to stem seal clearance at full lift, coil bind with the cam being used, etc. etc. etc…

 

 

Here is a great thread on what is involved in building a custom L-series cylinder head with lots of pics and details of the tools and processes involved.

 

http://forums.hybridz.org/showthread.php?t=108398