Bottom End
Connecting Rods
There are two revisions for the Connecting Rods offered by GM. The 02-05 rods are pictured below (left). They featured a 0.905" pin. The 06-09 (right) rods featured a 0.925" pin. Note the much larger small end of the 06-09 rod.Â
The step in the side of the 06-09 rod is a piston oil squirter which bleeds oil off of the rod bearing.
Here are the weights on the 02-05 rod. Note that the bearings are installed.
Pistons
GM offered two revision on the pistons. The 02-05 obviously featured a 0.905" pin. The 06-09 pistons obviously featured a 0.927" pin. Here are the weights:
Forged Rods and Pistons
There are a few ways to go with this.
If you go Molnar rods, you either need a custom piston. I am working with Mahle to develop an off the shelf option (See below).
MAHLE Pistons
These are the specs we are working on with Mahle.
Wiseco Subaru Pistons
We recently used some Wiseco Subaru Pistons. They are very close to working on a 4200. They just need 0.040 inch cut off them.
JE Pistons
Another Option are these JE Pistons that Race Rant had spec'd out.
Other Options
Another route is custom rods, and custom pistons. Racetec piston #1003628 is setup for stock bore with a 6 inch rod and a 0.927" pin. Those pistons can be paired with Crower B93913B rods. Be sure to ask for 7/16 rod bolts as the part number given comes with 3/8 rod bolts.
Another route is to have the rod journal machined down to a Small Block Chevy 2.100" size. You could also reduce the stroke a bit. as well, and try to line it up to a 6.000" rod. This would be ideal because 6.000" rods are cheap and widely available. You will need a custom piston. The other part that I don't like about this solution is it reduces the strength of the crank, and would likely cause even more likely hood of failure from harmonics issues.