Which aftermarket pistons really have the correct dome for 885 heads?

[medgingt]

I am looking to buy pistons for my m20b25, and am wondering who actually gets the dome 100% correct? Top End claims JE does, has anyone verified? I take it the IE 2.9 Mahles do but I am staying stock stroke so they're unfortunately not an option.

If the highest duration cam I am considering is a 272, is higher compression worth it or would the OE Mahle +.5mm perform fine?

Thank you

[82eye]

If the highest duration cam I am considering is a 272, is higher compression worth it

i'd honestly run that cam stock. fwiw i went with the original pistons and a regrind cam.
there are other things to look at for gains as well. headers, porting, re-balance, stainless exhaust, chip, all of which i am doing. i'm building a mild street car, your goals may be more ambitious, but that's where i'd start.

or would the OE Mahle +.5mm perform fine?

Thank you

see above.


edit: i'd sure make sure to clay everything.

[digger]

I am looking to buy pistons for my m20b25, and am wondering who actually gets the dome 100% correct? Top End claims JE does, has anyone verified? I take it the IE 2.9 Mahles do but I am staying stock stroke so they're unfortunately not an option.

If the highest duration cam I am considering is a 272, is higher compression worth it or would the OE Mahle +.5mm perform fine?

Thank you

Topend had the OEM pistons 8.8/9.4/9.7:1 versions scanned so they are replica as they sell those for a local series here as permitted modifcations as some OE are NLA .
If the bore is larger than stock O/S 84.5mm they need to extrapolate the shape a tiny bit so it is not the same by definition. They cant massage the dish size you either get one of the three above versions and thats it, unless of course you give them a CAD model or they develop a different style.

for a street engine you could get a replica 4032 alloy 9.7:1 OE piston from topend (i think they do FSR style) instead of using the lower compression OE. There are various upgrades you could make as well e.g. rings, valve relief depths, skirt coating. It depends what the engine is for and if the OE pistons are new, used etc etc

[medgingt]

Topend had the OEM pistons 8.8/9.4/9.7:1 versions scanned so they are replica as they sell those for a local series here as permitted modifcations as some OE are NLA .
If the bore is larger than stock O/S 84.5mm they need to extrapolate the shape a tiny bit so it is not the same by definition. They cant massage the dish size you either get one of the three above versions and thats it, unless of course you give them a CAD model or they develop a different style.

for a street engine you could get a replica 4032 alloy 9.7:1 OE piston from topend (i think they do FSR style) instead of using the lower compression OE. There are various upgrades you could make as well e.g. rings, valve relief depths, skirt coating. It depends what the engine is for and if the OE pistons are new, used etc etc

Excellent info, thank you.
It is going to be a hot street engine. I haven't torn the engine down yet, but am planning on new pistons. The price that stock replacement Mahle's go for, I think it makes sense to go for the JEs, in 4032 as you mention. The plan is a fresh head, with a good 3 angle valve job, headers, and 272 cam. Nothing crazy.

[digger]

Ask for total seal conventional ( non gapless ) rings with Napier second ring to help scrape oil
get the 9.7 dish dome style and slightly deeper reliefs to future proof them. Full skirt style is ok probably save a few $$$.

[Andre3127]

Before I boosted my car I was running a rebuilt B25 with a 3 angle valve job, crank scraper, stock pistons, 3 angle valve job, polished ports, and long tube headers to a 2.5" stainless exhaust to a Magnaflow, a tune, and lighter S50 forged rods. Really simple build, sounded great, and definitely had enough power to get in trouble with. It screamed for a stock motor and loved RPM, but obviously you could get a lot more from it with higher compression and a cam. Just wasn't in my books.