Machining pistons

[whitneyd]

Hello All, I've noticed that a lot of people machine thier pistons to lower the compression but my question is does anyone know how much to take off to get to 8:1?

[dimma]

i got my 1.8 16v pistons done 6 years ago.bb tuning told me to take 1mm off the top of them.the car still works fine with this and i saved a fortune not having to buy forged pistons.

[whitneyd]

Was that from the top of the step or the middle?

[dimma]

mine was the 1.8 which are flat the whole way across.im not sure about the williams piston cause they have a risen lip on the out side.im sure there are a few guys on here that have done williams pistons. i would have thought what ever you take off the lip you have to take the same off the rest of the piston crown.maybe ktec raying might give you some info on it.

[whitneyd]

Thank you for the replies. I'm probably going to have to do this by trial and error. I'm not sure I want to go all the way to 8.1 yet but I deff don't want 10.1. I'll keep the forum up to date on what I'm going to do.

[Laine_16v]

A CR of 8:1 will be a dog to drive off boost.

[whitneyd]

It's being lowered for boost but I'll show you guys later whats up.

[Justin..]

Dont go any lower than 9:1 imo, I had 8.5:1 and it was ok but could have done with more poke off boost

[whitneyd]

I was thinking 9.1 also. I'm not going to be putting a lot of boost on it, and want it to be a good everyday car.