mill heads or change pistons?

[vx355]

I have a 93 3.1 out of my beretta that I am building. I have the cam and the other parts worked out, now I am wondering if I should have the heads shaved .020 or change to 3100 pistons. Anyone have some suggestions of ideas? Thanks

[geoffinbc]

Shaving the heads will raise compression

3100 pistons will lower it ALOT

So whats your goal? More or less compression?

[GPXSS]

Shaving the heads will raise compression

3100 pistons will lower it ALOT

How do you figure 3100 pistons will lower compression?

Personally id shave the heads only as a last resort.. you throw off alot of specs by doing that and make the head more prone to warping.

[Compufreek]

I thought the bottom end was the same on the 3100 and 3.1. I have shave .015 off my 3100 heads and noticed a difference. How can I tell how much my CR is raised?

[robby1870]

You should have done a compression test before and after the milling after it, you should have gotten a higher reading on the guage

[geoffinbc]

Shaving the heads will raise compression

3100 pistons will lower it ALOT

How do you figure 3100 pistons will lower compression?

Personally id shave the heads only as a last resort.. you throw off alot of specs by doing that and make the head more prone to warping.

LOL sorry.. Im in iron head world here. 3100 pistons wont chage compression cuz you already have al heads.

Using an iron head, head gasket will raise compression

[RidgeRunner]

LOL sorry.. Im in iron head world here. 3100 pistons wont chage compression cuz you already have al heads.

Using an iron head, head gasket will raise compression

So what makes up the difference in compression ratio from the old 3.1 and the 3100? I thought it was pistons.

[geoffinbc]

Ahh Touché

Indeed the pistons do make the difference. But was it not also combined wih other things?

[vx355]

Is it the depth the piston sits in the hole? I am thinking due to the relation of the piston rod height in the 2 different pistons. Anyone ever done a measurement in this? If not, I have both so I could take a measurement for those interested.

[robby1870]

I thought it was the piston dish that changed. I may have some specs, I'll have to search around on my computer.

EDIT: According to my info a 3.1L has a piston dish of 26.4 cc's and a 3100 has a piston dish of 24.6cc's And a 3.1L has a piston compression distance of 1.45in and a 3100 has a distance of 1.47in. Those should make up for the .6 difference in compression

[Rhedalert]

9.6-8.8= .8

[robby1870]

Brian + pointing out dumb shit = FAG!!!!!!!!!!!!!!1

[RidgeRunner]

9.6-8.8= .8

But is the 3x00 really 9.6:1, or is it 9.5:1? And is the oldskool 3.1 8.8:1, or is it 8.9:1? So it could be .6, .7, or .8 difference.

[robby1870]

My info shows 3.1L has 8.9 (no turbo) and 3100 has 9.6

[Rhedalert]

WTF? Forget it.