Originally Posted by xspower
You should not need to remove a head shim from the engine it comes set for 16% from the factory. That is unless you are 1500 feet or more above sea level. You will find if you keep the head a bit high you will gain some top end out of the motor. "as if it needs it" and it will soften the punch a bit. The needles are set right that is the way the IDM and for that matter all the Picco based engines like to run. Using 20% will allow the engine to live a bit longer and you will get better fuel milage with no questions. The number 7 is also a good idea if it is hot or humid outside.
My crude crushed solder method of measuring deck height may be a bit off, but I believe mine was shipped with a clearance of 0.65mm and I was originally running 30%. I'll have to try the 0.65mm setting again (2 thin, 1 thick copper shim) with the 20% and try again next time my track is dry but this seems to be doing well already.
Texas has some wicked humidity, over 80% most race days..