Hello,

I just completed my engine build and payed more attention to my static compression ratio than my dynamic compression ratio. Anyhow, I am now concerned my dynamic is too high. I already planned on running 93 octane gas.

Static = 10.29:1
Dynamic = 9.56:1 (Based on 4 different calculators)

My quench is .041
AFR heads


Is this too high? What problems may I run into?

 

With 10.3 static, I seriously doubt your dynamic is that high. Post all the relevant specs.

 

I hope you are right! Any help would put me at ease because I am going to put in the engine tomorrow morning.

Bore: 4.04
Stroke: 3.48
Rods: 5.7
Zero decked
Gasket: .041 (compressed)
Cam specs (213/219) 112LSA (Spec Sheet Attached)
Combustion chamber: 65CC
Head gasket bore: 4.10
Valve reliefs: 5CC

 

I get 8.24 DCR using Kelleys which I believe gives a more accurate number because it uses the seat figures ;
not a made up duration number ( 0.050 + 15 ) like some of the other calculators

http://members.uia.net/pkelley2/DynamicCR.html

http://cochise.uia.net/pkelley2/dcr.zip

Used the 264/270 @.006 figures
Why are you using a 4.100 gasket , not a 4.060 ?

 

Thanks for the help! I think I was using an incorrect value. I used the 4.10 gasket because that is what AFR recommended for the heads. Will the extra hurt anything?

 

There's no problem with a gasket bore that's only .04" too large. In fact, sometimes it's necessary to make sure it matches the combustion chambers. If it's running well, don't go taking it apart just to install new gaskets that may not match the heads. The 8.24:1 dynamic sounds about right. But that's only correct if your block was zero-decked, because if it wasn't, then your static isn't 10.266758:1

 

Yeah, I think in my tiredness I mistakenly used the wrong value. I should have used the seat value.

The block is definitely zero decked. The piston is exactly level with the top of the bore.

Thanks for everyones help! Wish me luck this week as I plan to fire the engine on Wednesday evening.