Ronan,
The small end on the rod is easily handled. You just have it re-bushed and honed to 22mm with the new bushing to fit the S50 pin. Done!
If you don't change the crank then I see no need to use the GSR rods but they could run you in $300-$400 range. Shaving the piston, cutting reliefs and re-bushing the small end on the rod is minimal. Just talk to your machine shop that will do the work. If you're not going with the M47 crank then just change your pistons with minimal modifications and call it a day.
You definitely have to do your math!!
Here is an old post of mine I found with the math done for you. Just double check it and make sure I did it right!
M3 pistons are all S50 in the Mahle catalog. But you need to refer to them as US or Euro.
Euro wrist pins are 21mm. US are 22mm.
86.0mm S50B30 US compression height 32.8mm
86.4mm S52B32 US compression height 31.0mm
S52 is based off the M52
86.0mm S50B30 Euro compression height 31.6mm
86.4mm S50B32 Euro compression height 32.3mm
No matter what, all need to be decked and pocketed for the valves as well as dished for desired compression.
I think the M44 head gasket will allow for the 86.4mm piston.
Desired Compression Height = Block height - (Stroke/2) - rod length -piston protrusion out of block
Using stock rods and M44 crank:
DCH= 212-(83.5/2) - 140 -.15
DCH= 212-(41.75)-140-.15
DCH=30.1mm
So you can use any piston of your choice as long as you make the CH 30.1mm So if you go with the US 3.2L 31mm/CH 86.4mm piston you only need to shave off .9mm, then dish it and cut the pockets for the valves. Simple!
Just to give you an idea....for my stroker I used 3.0L US pistons and 138mm rods. I spoke with TEP racing when I was considering going with JE pistons and they said that even a 28.15mm CH was ok. NOW that is with a custom piston and stock rods at 140mm on a M47 crank. It all depends on how much meat you have at the top of the piston.
Compression Height of Stock S50 Piston is 32.8mm with Honda 1.8L VTEC B18C (GSR) 138mm rod
Desired Compression Height = Block height - (Stroke/2) - rod length
Desired Compression Height =212mm - (88mm/2) - ((138mm[Honda rod] - .15mm{protruding out of block}))
Desired Compression Height =212mm - 44mm - 137.85mm
Desired Compression Height =*30.15mm
The DCH is a desirable height.
30.15mm = 212mm - (88mm/2) - 138mm -.15mm*
This tells you that your target compression height is 30.15mm and we have enough meat to shave off 2.65mm from the 32.8mm :-P
Rod needs small end bushing to be drilled to fit 22mm S50 pin.
Again.....do all your math first and then buy your parts. Or use what you have and make it work. BUT I would never deck the head to make up any kind of distance when you have so many other variables such as the HG and pistons and rods. Just my .02
Cheers,
~Ralph
