LeonardZ

O.K. I am not seeing too many prices for 3.3 pistons and fewer for the 3.4
I wanted to buy just pistons to raise the C/R on my current 3.3 but then thought about 3.4s. I have seen references to 3.5 but have not seen others using these or where to buy or how much?
Questions:
1. Will new Pistons ( with higher C/R) seat in old cylinders after cross hatching the walls, or is there another method?
2. Is it worth the extra $ to go 3.4 or 3.5 if the 3.5 actually do exist.

Thoughts?

125shifter

The old cylinders would probably have to be replated since they're probably not round anymore.

The original cylinders are not fully finned so it's best to replace them if possible.

Since the best plan is to replace the cylinders to get fully finned, you might as well go to 3.4 (98mm). There may be 3.5, but it's not recommended for turbo cars.

I would NOT buy them from Motor Miester in case you come across their fancy ad.

sand_man

3.4 should be all you need. I'm not sure if the 3.5s are even a "drop-in" cylinder...I.E. does the case need to be machined to accept them? Try Imagine Auto, EBS, Supertec, etc. they all cary what you need. Imagine Auto can get you ANYTHING you desire. Because the ORIGINAL 3.3 930 cylinders lack the cooling fins on top, even replacing with the 3.3 cylinders found on the 965 (964 Turbo), which were/are fully finned would be an improvement.

sand_man

EBS also can take a 3.2L Carerra cylinder and bore it out to 3.4L specs and replate it it with Nikasil. I believe the package comes with JE pistons.

Steve Weiner-Rennsport Systems

Leonard:

You cannot buy Mahle pistons by themselves,...only in piston & cylinder sets.

You can buy a JE piston in whatever configuration you want but your cylinders need to be in perfect condition (and round) and if you are planning a performance upgrade, I'd not use the half-finned 97mm versions if I could help it. These are not known for staying round when hot and that means excessive blowby. One can see this by watching how quickly your oil darkens,.....

Soooo,....with that said, on to your questions:

1) If your stock Mahle cylinders are in really good shape and still nice and round (youll need a dial-bore guage to confirm this), you can measure the bores and have a JE made specifically for that bore size in whatever CR you wish.

2) 3.4 (98mm) P/C's offer a tad more compression and a bit more displacement to give additional off-boost torque and a bit more HP depending on how the rest of your engine is configured. I would not use the Mahle 100mm (3.5 litre) P/C's in turbo applications due to their inability to remain round after a bit of running. These cylinders are too thin and unstable for forced induction. The case spigots must be machined for the 100's, as well.

We now use a custom aluminum cylinder with a forged steel sleeve for big-bore turbo applications since these stay round and have FAR better leakdown figures over time. These can be used with a JE or Mahle piston.

Hope this helps,

LeonardZ

Thank you Steve, sandman, and 125 for the help. Sounds like I need to go the 3.4 route, and probably pass on using the original cylinders with new pistons.
I wasn't sure about line boring the case for 3.5 but would rather skip that unless it was really worth it.

I will do some research on all of the suggestions. Thank you all!!

Any other input is welcome.

Leonard