998 with 12G940: Choice of pistons
Turbo Mini Forums

Hi,
after lots of research I could not make up my mind what piston to use for a high boost 998 with 12G940.
Flattops (AE, Calver, Hypatec) are not strong enough for 9cc dish.
Dished are only the 20773s or the 500£-Omegas (to expensive) available, I'm I right ?
What pistons would you choose ?

(This engine will not be build for the next two years, I'm still troubled with injection on my 1098, but I'm gathering parts :))

I'm looking at the Calver ST ones, and having a 28cc head. Still gives a rough CR of 8.8:1.

even a 2cc dish in the pistons would bring it down to below 8.5:1 though

http://www.turbominis.co.uk/forums/index.p...tid=469104&fr=0

I have used the Minisport aus dished (6cc) pistons with lots of boost.

They are basically the 20773 in a more modern material as far as I can tell.

If you mean really high boost though, save your pennies for the forged ones.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

The calver flat tops don't have much meat on them, to machine a decent size dish. Well my +80's didn't.

Edited by gr4h4m on 30th May, 2013.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Grüß Dich Max, wusste nicht, dass Du auch nen Turbo baust!-Wasn´t aware, you building a Turbo now!


Maybe try Mahle and ask them about a matching piston. They also produce them to Your needs. We once payed 1500€ excl. VAt for a set of 12 pistons. Hope this helps.

@mike Yes, I would do the same if I was going 12G295

@wil_h 16psi is high enough for me. The rest of the power has to come from revs.
btw: Thank you for all the reports in this forum, I learned a lot from your posts.

@graham Yes, but 10cc seems a lot to ask from a flat top. What size are yours ?

@enne Yes, I'm planing on going turbo since 2009, but I don't want to use a carb (despite most of the forum here) and I never mastered fuel injection...yet. Tryouts will continue again tomorrow.


I bought today a set of 20773s, based on the experience of wil_h.
But I don't feel overall optimistic because of its 4 ring design. Pmax should be 7100rpm.

I measured mine and decided that they would have ended up thinner than a std piston so I left them as they were. I have the Russell engineering +80 from Keith calver

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

I would say there is only one choice and that's Wil's recommendation

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

I think mike ment a 28cc 940 head rather than a 295

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis

The calver pistons will take around 3cc and last.

I put 6cc in some and they failed eventually.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk