Hi
I bought these pistons from someone on cobaltss.net who had them custom made by diamond
They are 9:1 compression, have valve cutaways, and have a large 'ringland' area. Bore size is identical to that of the wiseco's (oversize ones) - I've attached spec sheet
Due to this large ringland, the rings are mounted lower (but the pin is not) and the pin impedes on the space that would normally be for the oil ring. Because of this, these pistons use "oil ring support rails".
They include pins, clips and a set of mahle rings. The oil ring in this set is the wrong size for these pistons, they need the wiseco-style higher ones (I believe wiseco oil rings are a direct fit from my measurements although don't take my word). The support rails that are included are the wrong size also (some screw-up by diamond) - there are also some other discrepencies on the spec sheet and measuring these for yourself is essential!
I overlooked this fact when I came to build the engine and was suddenly stuck when I came to build it, so in the end I bought a set of wisecos so I could just get it built.
I believe these pistons use the better grade aluminium which ppl have talked about on here quite a bit.
Due to the fact that they need oil rings and oil ring support rails (probably USA sourced), I've priced them accordingly £230 incl postage to normal UK address (will post international but will costs a bit more)
Please let me know if you have any questions and I will try to answer 🙂
CUSTOM
JOB# 18504 FORCED FABRICATION
GM I4
BORE = 3.400
COMPRESSION HEIGHT = 1.062
EFFECTIVE VOLUME = -7.4CC
VALVE DEPTH: INTAKE: .120 EXHAUST .125
TOP RING: 1.2MM
2ND RING: 1.5MM
OIL RING 2.5MM
SUPPORT RAIL 01-9001-810
LOCK RING DESCRIPTION: ROUNDWIRE
LOCK RING PART# 01-5126
OFF SET PIN: YES
WRIST PIN DIAMETER: .787
WRIST PIN LENGTH: 2.400
PISTON WEIGHT: 324 GRAMS