Originally Posted by TryHard

I go this from Dave Spashett.

Tryhard
The foam above the bladder increases pressure in the shock. This can help to make the car react quicker. One because it will allow you to use lighter oil and secondly because the shock will return quicker. I have used this on faster circuits and found it to work well. On carpet i prefer to use no foam and slightly more oil.
David

I'm going to try it myself tomorrow, one set of shocks with 50wt oil, 3 hole pistons, and the foam, and one set with 60wt, 3hole pistons, no foam. I'll let you know how it goes.
Ed