cbracerx

It seems that the RS/RSR pistons are delivered from Mahle with a 1mm offset in the piston pin location. Some (maybe all) engine builders have found that running the pistons as delivered will produce a small difference in where TDC is achieved with on cylinder bank vs. the other. To counteract this, they machine the piston top to prevent interference with the intake valve, and then flip one bank of pistons "upside down" to match the offsets from side to side.

Not sure I got that exactly right, but what have the groups experience been?

Geoffrey

Leave the piston alone as the machining will lower the compression ratio and at that point, you might as well run a 3.6l piston/cylinder properly machined to get 11.3:1 compression. You'll be further ahead. The RSR pistons are really not designed properly and are not the best pistons from a design point of view.

cbracerx

Thanks Geoffrey,

Is there anything to the reported experience that the engine runs less smoothly and wears faster with the pin offset un-compensated for?

cbracerx

from another post from Geoffrey (just to keep everthing in this thread)

There is so little net dome volume in the RSR pistons that if you machine the exhaust valve pocket to the same size as the intake valve pocket so that you have the proper piston to valve clearance when rotating the piston 180 degrees you'll loose too much net dome volume and the associated compression ratio. I wouldn't do it.

The issue is not with reaching or not reaching TDC, it has to do with minimizing the piston rock in the bore with the short rod/stroke ratio the Porsche engine has.

Geoffrey

Remember that the RSR engines were not built to run 100k miles. They were 30 hour engines. Any 100 or 102mm bore engine will show signs of piston skirt and crown scuffing on the cylinder wall over time. The RSR piston has a "deaxised" wrist pin which helps minimize piston rock on 3 of the cylinders. It is a good idea that has been implemented poorly.