MrNuke

I am trying to find out what kind of piston design is in the '85 stock engine.
Are they flat top, or not? I knwo they are forged and stock compression is supposed to be 9.5, but that's about it.

Thanks.

jburnett

Yes...It's an OEM 4013 design sourced from TRW by GM. Flat-top with 4 valve reliefs and heavy as lead!
-Jeb

Bluevette85

The 85 pistons are forged flat top with one long relief across the top not four. I'll post a picture tonight.

MrNuke

Thanks guys, Trying to figure out what sort of compression I would have switching to new heads.
Anyone know how to figure it out?
If I went to 58cc, 64cc, 67cc, 72cc, 76cc?
I know the stock heads are 82cc.

neverendingproject

:iagree: i have 8 of em sitting in my storage room right now, 1 long valve relief.

b.t.w. are the x rods worth anything?


[Modified by neverendingproject, 5:11 PM 9/18/2003]

Bluevette85

The stock 85 heads are 76cc and compression is 9.0:1.

When I put on the 113 aluminum heads (58cc) and a 0.05" head gasket, my compression went to 10.6:1.

Pete Pulos

Pi x Radius squared = area of circle
area of circle x stroke = cc of cylinder

Convert the bore and stroke to centimeters 1" = 2.54 centimerter
Pi is 3.14

Figure the maximum volume of the block at bottom stroke and add the cc of the head

Divide max volume by minimum volume
you will also need to calculate the head gasket volume the same way and add it to the equation

okinawa86vette

When I took the heads off my old '85 parts car, they were flat with one long relief.

There's some really good compression calculators on the internet that take into consideration everything from heads, pistons, all the way down to the head gasket thickness. I should have a couple bookmarked at home, so when I get home tonight, I'll see if I still have them and I'll post their links.

Chris

Bluevette85

Picture as promised:





[Modified by Bluevette85, 10:38 PM 9/18/2003]