Thoughts on stroker kits

I would agree with Jeremy that modifying the pistons on a stroker kit would not be necessary if the stroker kit was designed properly, ie.. it has the correct spacer thickness.

The idea is to get the “DECK HEIGHT”at ZERO. The outside shoulders of the piston are flat, and you want these to be absolute flush with the top of the edge of the block when the piston is at absolute Top dead center. Any amount the piston is down in the hole at TDC or above the block at TDC dictates + or – deck height. Now, the “Compressed thickness of the Head Gasket”, will determine how far away the pistons are from hitting the head. In the case of the Kawasaki, the compressed thickness of the stock head gasket is .030 inch. This means your squish or piston to head clearance is .030 if your deck height is ZERO. I don’t know how much deck height or squish Jeremy designs into his kits. This also effects your compression ratio.

If when building a motor, stroker or not, and the pistons stick up above the edge of the block, then you have that amount to subtract from the head gasket thickness. If the pistons stick up say .005 above the block you have only .025 squish or piston to head clearance. If the pistons fall .005 from making it to the top, you have a squish or piston to head clearance of .035.

Now what is good. Because pistons have some “ROCK” at Top dead center, I feel that .030 is to tight. I build all my motors with a minimum of .035 or .038 if 14,000rpm.

Now get this, most ZX7s come from the factory with only .035-.040 all ready. I had to replace a liner once and milled .005 off the top of the block for a perfect deck surface. I later found that only gave me .030 of squish.

The Wiseco pistons I installed, I later discovered were slightly kissing the head on the exhaust side as the piston rocked at TDC.

I could tell this because Wiseco puts a arrow on the exhaust side of the piston to indicate direction. You could easily see this arrow stamped ever so slightly in the head.

In my opinion, .030 is too tight.

I once heard a NASCAR engine builder say that when pistons are slightly kissing the head is when you make the power. I say that is nonsense.

Some people measure do this by doing a MOCK build up with a used head gasket and by placing strips of solder on the pistons at 3,6,9,12 o’clock. Then rotating the crank by hand 3 or 4 turns. This mashes the solder, sorta like plastigauge. Then measuring the solder is your squish or head clearance. I do not do this. I use a precision machined gauge for measuring my deck height accurately on all 4 cylinders

Cometic makes varying thickness of base gaskets to raise the block to adjust the squish.

I later learned the compression height on the wiseco pistons were .005 larger than stock. The compression height is the distance from the center of the wriston pin to the deck height surface. This would equate to a Stock Piston to head clearance of about .040. Not much margin for error.

UNLIKE SUZUKIS, there is no metal to “SKIM” off the heads of these sevens. Actually less than .003 inch. Not 1mm or.040 like on Suzukis.

I DO NOT SEE HOW “REMOVING” MATERIAL FROM A PISTON {“RAISES”} COMPRESSION, this would reduce.

To sum this up, I DO NOT KNOW, how much deck height or Piston to head clearance Jeremy builds in to his kits, BASED ON HIS SPACER THICKNESS, but I do agree that a stroker kit properly thought out does not require machining the pistons’, (UNLESS), you are going to HIGH lift long duration cams and will have a PISTON TO VALVE clearance problem, then the tops of the pistons will need fly cut for additional valve to piston clearance.

BOTH OF THE ABOVE CHECKS ARE VITAL IN ANY ENGINE BUILD.

Kenneth H20s

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