94AWDcoupe

iTrader: (125)

I brought some 2.2 liter pistons from Norris Designs. Nobody in the states has any pistons made for the 94mm stroke. Actually the pistons were advertised in classifiesds on lancer register. I was disappointed when they came in today because they are used. No mension the pistons were used in the ad so I assumed they were new. Anyway look to be of good design. Bath tub shape dish. I quickly started to take some measurements to be sure they were for 94mm stroke. The pins should sit 3mm lower than a stock aftermarket piston. They only sit 2.4mm lower. This means that the piston is going to sit .6mm(.025) above the deck. With stock gasket at .050 piston to head clearance is only .025. I have always wondered how close is too close. I read an article were a supercharged engine was run on both stock .065 deck height. Then switched to .033 deck height. They were able to run 2psi added boost with the tigher quench area.

I brought this subjuct up before. The stock evo8 pistons dont really have a quench zone. The stock deck height is .170. Aftermarket pistons are always flush with the block deck. This gives gasket thickness as the deck height or about .050. I personally ran .040 on the last engine I built. I am a little weary of useing these pistons as is. .025 just seems alittle close to me. The burn pattern on the pistons looks real good. Simon should know what he is doing, so maybe he found maximizing the quench zone is a good thing? I also dont know for sure if these were run with stock gasket. They may have been run with a thicker gasket.

It may be a simple equation the tighter the quench zone the better the detonation resistance. I wish I knew for sure.

kjewer1

iTrader: (4)

It was found to be quite important on the DSMs, and Magnus' custom pistons have a large quench pad on them.

About the quench height, .025 does seem way to small for a high reving turbo motor. Last time I looked into this, most experience DSM engine builders were comfortable with 040, one guy ran 035. I would like to run it as tight as physically possible, but the chance that a mishsift could leave me with a lot more than just a loose flywheel makes me think twice about it for a daily driver. 040 seems to be the norm for poeple that pay any attention to it at all.