Help! Can I use these pistons?

[berni29]

Hi There

I have been asking about Mahle piston part numbers in a different thread, but now I have some further information and need some advice.

My car is a 1994 non varioram. The pistons from the car are Mahle with the part number 100P45. I have bought a low mile set of Mahle pistons and cylinders off this forum and they bear the part number 100P47.

I have read many engine rebuild posts and articles and have not read anything about the engines being different between varioram and non varioram. I thought the differences were in the induction system.

However the Mahle site list the 100P45 as being non varioram, and the 100P47 varioram.

The 100P47 are listed with the same dimensions but a higher compression ratio of 12,3:1 vs the earlier 100P45 11,3:1

I have examined the pistons, and although they look the same the later pistons have a narrower depression on the crown.

Can I use these pistons and cylinders as direct replacements for my existing ones? What are the implications if I do?

I am going to post this in the 993 Rennlist forum also.

Many thanks

Berni

[Eagledriver]

I'm not an expert on 993 engines but here are some thoughts: They should fit fine. Typically the stated compression numbers are optimistic by about .5, so you'd probably measure about 11.8 compression. Higher compression means more power. The worry would be that you might have too much compression and get spark knock. I'd check with Steve Wong (911 chip guy) to see what he thinks. He might be able to make a custom chip for you to accept the higher compression pistons. If your engine has a knock sensor you might be ok with the stock chip. You could always run a little race fuel for track days.


-Andy