Austarion

I did some quick calculations and taking one mm off the head will bring the compression up to 8.1:1, which should bring back some off-boost performance and make my car a little less slug-like off the line. What I want to know is whether anybody has done this and whether there are any problems with valve-to-piston clearance, water galleries in the head and/or retarding the valve timing. The engine and head are standard JA, Jet-valve head. Has anybody gone further than this (I'd like around 8.5:1 but that's nearly 2mm.

Cheers,
Duncan

I have had 2mm shaved off the previous head on my car to bring the compression well up. The current head has 1mm shaved off it with the compression up to just over 8.1:1. I have never had a problem with either. There is sufficient valve to piston clearance. I do, however, have everything else modified (ie ECU, MPI, cooler, turbo etc).

Were there any problems with cam timing due to the shortened tight side? I'm guessing it would amount to a degree or two retarded cam timing.
Did the increased compression help out off boost?

No problems with the cam timing as it is controlled via the ECU in my case. There was a definite improvement in off boost response.

NXTIME wrote:No problems with the cam timing as it is controlled via the ECU in my case.

Someone must be a magician

I guess you guys use a differant engine than us. The 2.6 typically needs about .035" removed just to clean it up and make it straight. That will retard the cam about 5 degress. So I make a cam gear that has 2 and 5 degree advance holes drilled into it. No it's not adjustable....you pick standard, 2 degrees or 5 degress advanced. But on ANY engine, if you lower the cam (head) you retard the cam timing. You can see a pic of the cam gear on the second addy below.

Does that mean the timing stencil on the Timing Belt cover 'B' is then wrong as soon as you shave your head LOL

flappa wrote: Someone must be a magician

haha, oops. Where did that adjustable cam gear go? :D

When you retard the cam, the valve comes down at a later point.. is that right? this plus 2mm off your head, would this not cause some piston/valve clearance issues?