I chose the z22yh pisons because of the higher compression ratio and the improved design of the skirts for less friction.
PLEASE NOTE: The z22yh pistons here are 0.5mm oversized ones, and thus 86.5mm diameter and not 86mm, so the mass reported here will be slightly higher than standard ones.
z22se piston:
You can see a flat ring around the piston and then a slight dish. That is there to create squish at TDC and bring more of the charge into the middle of the combustion chamber.
Skirt shot:
Gudgeon pin boss shot:
Piston mass:
Gudgeon pin mass:
Combined piston and pin mass. Please note the pin locking clips are not present in this mass - the pistons will be revisited in another thread once they are modified and balanced, so i'll do it then as a final mass.
z22yh piston skirt shot. Notice the black coating. This is a screen printed anti-friction coating. This works in two ways - the coating will wear quickly in high spots in the bore and create a conformed coating for the piston, so making the skirt smooth and it also gives better cold start (pre-oils pressures) properties.
Gudgeon pin boss shot:
Piston mass.
You can see the raised dome on the piston here. This added material in the combustion chamber raises the compression ratio. You can see a little rebated 'tongue' shape at the back - the z22yh has direct injection and this helps with the injection and injector. Sadly I won't get this benefit as these are going in a port injected engine But it does let you know quickly if you have put the pistons in the wrong way!
Gedgeon pin shot. The pin is shorter and thinner than the z22se item, but appears to be the result of a more advanced stress analysis, as the waisting inside the pin is smoother, and/or better quality material.
Because of the smaller gudgeon pin the total mass of the piston and pin is 387.8g, so just under 2g lighter than an z22se piston and pin. Thats a benefit to reciprocating mass. Again, please note the piston clips are not here.
The pistons and their pins. You can see the z22yh pin in shorter.
The wall thickenss of the z22yh (left) is significantly reduced from the z22se.
z22se pin; 20mm:
z22yh pin; 20mm also.
You can see the length difference in the pins:
And thats because the gudgeon pin bosses are closer together in the z22yh.
The design of the z22yh is more like that you'd see in an aftermarket piston of the time period these engines came out in, and that's because the shape dosn't need to support such a wide skirt. The upshot being that you can use a lighter, shorter gudegon pin.
