3.4L 930 Deck Height/Piston to head Clearance
 

Hello Everyone!

I’ve bored out a 1988 3.2L to a 3.4L with JE pistons which are domed. I went with the 10.5 to 1 compression and I’m wondering if with the higher compression, if the pistons will have a larger piston to head clearance

I used the solder method to measure and the clearance and those solders measured 1.76mm at the thinnest part. In Wayne’s book he calls this deck height measurement, and it mentions the thickness of that solder should be around 1.25 to 1.5mm with this method. I did not put the cylinder gasket (shims) in as that would add another 0.25mm pushing me well over the recommended 1.5mm. And I’m guessing not running cylinder gaskets isn’t a good idea.

Does he mean piston to head clearance instead of deck height? Im wondering with heat expansion and the higher compression if I need that extra 0.25mm to 0.5mm from the 1.5mm Wayne recommends. Worried that with the extra space I’m going to lose quench, or if I can still achieve that higher compression

You can machine the bottom sealing surface of each cylinder to achieve the exact piston to head clearance desired. I built (retired now) successful race engines and always ran them much closer than the 1.25mm minimum Wayne suggests. Since P-H clearance is determined by deck height, I'd say in this case the measurements are synonymous. Put the clearance where you want and don't worry about any clash.

I've seen builders here say that over 1.5 mm PTH clearance is undesirable, especially for high performance engines.