We selected JE's asymmetrical FSR pistons in 87mm or 1mm oversize from stock for the bottom end. The FSR is a strut type piston meaning that it has a reduced slipper skirt profile. In the past slipper skirts meant light weight and low friction, but lots of noise and sometimes rapid wear. Not so with FSR pistons. JE has the piston design and barrel profile down and we have found FSR pistons to run quietly when we have used them, great for street engines. The JE FSR pistons' asymmetrical skirt has a larger area on the more heavily loaded thrust side and a reduced profile on the non thrust side for less friction and weight. The strut type design also means minimal weight as there is no excess material, unlike fully skirted pistons.
We chose a moderate 9:1 compression ratio for our turbo motor since out motor will be run on E85, this is somewhat conservative. The lower compression is apparent when you see the dish in the piston. As we said previously, the JE FSR pistons are made from low silicon 2618 alloy. 2618 is very ductile and tough, properties which are appropriate with detonation prone high boost turbo motors. 2618 expands more with heat and needs to run a wider piston to wall clearance than higher silicon alloys, typically about 0.002-0.003″ more. In the past, this meant a more noisy engine and many builders would spec a higher silicone but more brittle alloy like 4032. JE's advanced skirt profiles have reduced the piston slap and the engines run quiet even with wider clearances.
As you can see here, the piston pin is set high on the piston to make us for the long stroke crank. A lot of this is also because the compression ring grooves have been moved down from the stock position for strength and detonation resistance, important in a turbo engine. We are not running compression ring pressure ports as on a boosted street engine, they could shorten ring life and we didn't think that the trade off for improved sealing would be worth it on this longish stroke and high piston speed engine.
We used straight wall, thick piston pins. On a turbo motor with high cylinder pressures, trick lightweight tapered tool steel pins can flex and spin the small end bushing out of the rod. This can result in rod failure.
Our piston pins are retained by round wire Cosworth style locks. Although they don't look as substantial as things like spiro locks, they are very positive, wedging tighter under load and are much easier to install and disassemble.