Originally Posted by Maximo

I see ! well a modded race .21 is always going to have the advantage over any of the Mach engines...The Mach's are not bad of course, but they are definitely outgunned against some of the higher end race engines...You probably can squeeze a little more out of the Mach with head clearance, but unfortunately its not going to be the silver bullet I think you are looking for...My best advice is to slowly reduce your head clearance in small increments and test the performance........lower it down by 0.05 mm at a time if you have the shim options...... what you will see is when the engine hits the sweet spot the engine will run crisper at lower temps and idle down very clean...if your too tight the engine will start being picky to tune, high idling being one of the first signs......If your too loose the engine will run decent, but tend to load up easier and need to run at higher temps to make good power......