Skimmed pistons

[audiman]

Basically the top of a std piston is dished. If you flatten the pistons so the dish is gone, this is it. The volve pockets are still there, but no deeper than a normal piston. It does have any adverse effect of the engine with respect to how the engine runs. But it lowers the CR to about 8.6:1

[donce]

sorry for out of topic,but how deep are those holes for valves? and how many ccs is each?

[Audi Parts Guru]

Has anyone here had any experience on doing this? Im doing the rebuild on my car and want to lower the CR. I cant afford to buy new pistons etc, but would like to know if its possible to skim the pistons flat to reduce the CR, what sort of ratio would this give?

Many thanks

Tom, I would never consider this as you're asking for trouble, especially with the sort of boost that you're gonna be running. I would suggest a thicker head gasket. PM me as I might be able to help

[martinjs]

Eh, this threads nearly 2 years old, Tom did end up skimming his pistons and its been running ok ever since.

[audiman]

LOL, damn right, those pistons are OK too. Had the head off to chuck in a thicker gasket recently, and the pistons have no bad markings or burn marks at all. Been running 470ish BHP for a year or so, and also had some punishment when it ran 2.7bar boost for a bit

[audiman]

And as a final update, the car ran over 600bhp with the same pistons running 2.5bar of boost flat! No problems!

[4WheelDrifter]

That's good to know Tom. Thanks for letting us know.

[gnutz2]

And as a final update, the car ran over 600bhp with the same pistons running 2.5bar of boost flat! No problems!

Just intrested what turbo did you run to make 600+ @ 2.5 bar boost and what hot side A/R??

This is what i did to my std pistons Im running GT35R with .82 hot side (not running yet).

http://www.s2forum.com/forum/showthread.php?t=25254

[4WheelDrifter]

Just intrested what turbo did you run to make 600+ @ 2.5 bar boost and what hot side A/R??

This is what i did to my std pistons Im running GT35R with .82 hot side (not running yet).

Tom had the same turbo. GT3582R .82 hotside IIRC.

[Pirvu Eugen]

Hello!
I can make the pistons flat, or i can reduce the piston height with ~1mm from entire piston mantaining the squish area.
Is better than make the piston flat?(about the squish efect).
What do you think?
Thank You!
Eugen

[4WheelDrifter]

I did the same as Tom and had the pistons decked to the bottom of the dish.
I've got a set of stock 7A pistons that are just the same, flat. That tells you something about the importance of the squish area.

[Pirvu Eugen]

Thanks!
I calmed down now!
I will make them flat and use thicker head gasket!
Thanks!
I will calculate the cr after.
Thank You!
Eugen

[rash]

So if I understand this all right, i can skim my original RS2 Pistons for additional 1,4mm measurend in the middle of the Piston and a Diameter of 69mm to drop the CR to 8.5:1 with original RS2 Headgasket!?

right?