I'm looking to buy some flat top pistons to achieve a higher compression ratio.
Based on other forum posts it appears that a compression ratio of around 10:1 is what I should be aiming for as a weekend driver with a mild cam.
Doing abit of calculations, the compression ratio of an L26 with an E88 and N42 head are roughly the same. All else remaining the same, a stock L26 should have 8.3:1 compression. If you get some flat-tops this will yield 9.3:1 compression. If you want to go higher, you can get 0.8mm and 1mm head gaskets which will up the compression to 9.5:1 and 9.6:1 compression respectively.
If you're budget conscious, go with the flat-tops and potentially a new head gasket and be done with it.
One engine shop is stating that they have fitted L20 pistons to achieve this.
Given the L26 stock bore is 83 mm, and L20 bore is 85 mm, this is a 1 mm or 40 thou" oversize.
Has this been done by anyone else?
What compression ratio is achieved with the L20 pistons?
I am assuming that gudgeon pin size is compatable also.
Anything can be done if the geometry is right. The L20 and L26 pin heights and diameters are the same so you're fine there. The bores are different and depending on the piston head design as well the piston dish volume will be different as well.
A bored out to 85mm L26 with L20 pistons will yield 8:1 compression. If you manage to get some L20 flat-tops you're looking at 9.6:1 compression.
If my calculations are correct, just go with the L26 flat-top pistons, your life will be so much easier.