Replacement Pistons - Legal?

#1

[quote]9.3.1.2.2. All pistons, including aftermarket replacements, shall be factory replacement spec
and match factory dome, dish, valve relief depth, ring groove placement, weight and
wrist pin height; compression shall meet factory replacement specifications. The
maximum allowable overbore is limited to the largest available factory replacement
piston, not to exceed .020 inch.[/quote]

I’m doing research on what is legal and what is not. Mahle has replacement pistons for the m20b25 models but there are three different version. I am certain the one of those three are not legal; due to it is a European model replacement, however there are two different compression ratios. 8.8 and 9.4 are the two options. The 9.4CR states 87-88 and the 8.8CR is from 87-90.

http://www.bmwccn.no/rogaland/Mahle_m20.html

and another site comparing early to late CR; http://gevans.info/m20/enginecalc.php

Any comments? Did I just open up a can of worms?

#2

As far as I can determine, only engines with 8.8:1 were shipped to to the US. There is a change in pistons during the product life of the M20B25 in an E30 that occured in 6/88. According to realoem.com pistons from 6/88 are “weight improved”.

So I’d say that only the 8.8:1 Mahle piston is legal.

#3

I think you’d also want to look at a factory service manual to see what various pistons are discussed.
bruce