[trond]

I had my heads cut back 0.25mm and used thicker 0.5mm gaskets. Unfortunately the machine shop made them all different height. I managed by playing around with head/barrell combinations to get combined height variation within tolerance. In other words the new Mahle Motorsports cylinders (new set of 6, all stamped with height group5) were NOT the same height either. Both cylinders and heads are hard to measure for an amateur without all the tools. If you have parts machined you don't be a dummy as I was but 1) use a shop with good reputation for aircooled 911 work 2) Make a real effort to have heads and cylinders accurately checked by a third party.