I'm currently rebuilding my motor in my ASP STI. I'm on my 2nd ring land failure and want to replace the pistons for forged units as per the rules. I've bolded the rules below.
The big thing I'm finding is that the weight of the forged material VS the Cast is showing to be a problem to match(forged being lighter than the cast). so if the pistons are 100% identical, dish, dome shape etc.. how can the 2 materials be matched weight wise. For this reason, I'm thinking that the wrist pin and piston must be the same weight between the 2 combined. This way there is no lightening in the overall mass of the assembly.
If anyone has specific insight on this, please advise. I'm talking with various piston makers and so far they are all asking about the pin and piston combo meeting the weight.
S. Cylinders may be rebored to no more than 0.0472 in. over standard
bore and the appropriate standard oversize piston may be substituted.
This overbore dimension is an absolute limit; no additional tolerance
is permitted to accommodate wear. Cast or forged, non-stock
pistons of the same dimensions and configuration as original equipment
pistons may be used. Additionally the replacement pistons must
be of the same weight or greater as the original equipment pistons.
Replacement pistons must match OE piston configuration exactly including
quench area. The allowance for the use of aftermarket forgings
vs. OE castings does not permit alternate piston dome designs.
This allowance does not permit alternative ring configurations.
T. Rotating and reciprocating parts may be balanced but not lightened.