Alright,
So i've been reading a lot this morning about CR. Im trying to figure out what mine is going to be. Can someone explain to me how to get it.
4.030 Bore
6.125 Rod
-3.2 Piston
64cc Chamber
3.622 Stroke
Not sure on gasket bore or compression thickness(GM MLS).
Also confused about deck height.

It'd be pretty sweet if someone could explain it to.

Thanks.

 

Well, we need to know exactly what motor this is.

Also need to find out the head gasket thickness for us as well as how far the pistons are down in the hole.

But looking at your sig, and IF this motor is said 6.0 and your using 64cc heads on it, Id say 11:1 is in the ballpark.

 

Yes. This is the 6.0
I believe the headgasket is 0.057
And I'm not sure of piston to deck clearance.

 

If you dont have the heads on the motor yet, you can turn the motor over until you get a piston up as far as it will go, to the point right before it starts dropping back down. Then you measure how far the piston comes out of the cylinder. So measure from the top of the block the the top of the piston.I think the average is anywhere from .005-.012 out of the hole. Havent seen that many that are down in the hole.

 

Connecting rod length, center to center, 6.125 + 1/2 stroke, 3.622/2 = 1.811 plus the compresssion height of the replacement piston. For this calculation, I will assume you are using Wiseco K398X3, a 4.030 forged flat top piston with a compression height of 1.304. Adding up all these numbers, 6.125 + 1.811+ 1.304 = 9.24 inches. All this means is this particular piston I chose should be flush (zero deck), as long as the block measures to its intended spec. If you calculate compression with a zero deck and a .040 head gasket and your figures in post, I come up with 11.02:1 compression. Hope this helps. Steve

 

What would the CR be on a -8cc piston?
On a 64cc and 59cc head.

Thanks guys.

 

Around 11.15:1 with the 64cc head and 11.88 with the 59 given a .040 HG thickness.
Bores size of the HG will matter as well but those numbers are close.

 

sweet. thanks.

 

blanco... i'm getting 10.42:1 with the -8's and a 64cc chamber and 11.05:1 with 59cc chambers. those #s make sense because the 8cc's would drop the CR using the same chamber volume.

My calcs were right on with smask using the original #s.