Piston work on M42 turbo

[naikaFR]

Hi Guys

I wonder what would be the best option on an M42 turbo:
- Piston work to lower the compression ratio
- Swapping other model pistons to drop the CR

Have any of you done this?
I am considering an MLS Cometic HG but would rather work on the pistons instead if possible

Thank you for your input

[naikaFR]

Any one has advice on this?
I read that pistons are approximately 3/8" thick which seems enough to me to remove some and lose some CR, have any of you experienced?

Thanks
Franck

[wazzu70]

Not the best solution. Typically turbo pistons have a thicker crown thickness! More engine power = more heat.

I would rather use a thicker MLS gasket than shaving pistons. Best solution is new custom pistons, but MLS is the best cheapo route.

[thebrelon]

Salut franck!

so your touring is not powerfull enough?

to reply your questions we need to know your power goal/car use/budget, as you already know.
from the info I gathered I think that you're safe on stock internals up to 12PSi, which brings you around 200WHP with a turbo, less with a supercharger.
if that is enough for you then you don't have much to do. skimming the pistons is optional IF you use a good engine management with knock detection/control. for cost reasons I would use a thicker HG and while at it ARP studs.

you can also use pistons from M20/M50/M52 as they're all 84mm bore, you may find one with the correct compression height and avoid piston machining. you may also use pistons from S50/S52 and re-bore to 86/86.4mm for additional power...

so what are your expectations powerwise?

[fumstoo]

Power goal?


CP pistons from vac arent too expensive now a days. then youre bottom end would be solid.

[naikaFR]

Thanks for your input guys

TheBrelon, I didn't know you were hanging around here

The goal is to be able to boost 10 to 15PSI and reach in the 220-230HP, therefore I'm thinking it will be either using other pistons with an identical bore, or using an MLS headgasket.
ARP studs are planned as well.

I'm thinking that using the right HG to drop the CR to 9:1 or so should allow a good boost while keeping a decent performance at low RPM.

Anyone know of pistons in an 84mm bore that would drop the CR? maybe ETA pistons?

[romkasponka]

10:1 compression ratio is good for turbo these days and there is no need to lower it. Check what compression ratio new cars have now.... The only thing you need is arp studs and MLS gasket.

One of the successful projects in Lithuania with setup in the end.... http://www.youtube.com/watch?v=sptsXGSRkDY
Later he was boosting  more than 2 bars with E85 fuel during competitions... Stock pistons are good enough for turbo.

[thebrelon]

TheBrelon, I didn't know you were hanging around here

here and on all others like r3v, e30tech, etc...

[wazzu70]

TheBrelon, I didn't know you were hanging around here

here and on all others like r3v, e30tech, etc...

Agreed. There is no point really in switching pistons to remain at 84mm bore. If you want to drop compression slightly, use a slightly thicker gasket that goves around 9:1 compression. At the power level you want though, I wouldnt even bother lowering compression.

[naikaFR]

Alright, so I guess it's going to be an MLS gasket to slightly drop the CR and be safe.
What thickness would you recommend to be closer to 9:1 CR?

Thanks again for all your input

[romkasponka]

Make ir 10:1. It is not 80's...