with my AFR165's, what is my compression ratio?

[rockin_rick]

I have a stock shortblock (well, really a FRPP shortblock assy made in 2000 (for the explorer) but I believe it's the same), AFR165s (58cc), Felpro 1011-2 head gaskets. What CR does this work out to? It's hard to compute since I don't really know the size of the eyebrows in the pistons and exactly how far up the bore the top of the piston is... Does anyone know for sure?

Thanks,
Rick

 

[Grn92LX]

Appx 9.3-9.4:1 should be close enough.

 

[rockin_rick]

Thanks- is this an educated guess, common belief, personally measured/calculated, or fact? No offense, just trying to judge your confidence level... (I have a calculation/formula which I need to supply the CR, and just want it as accurate as possible to prevent GIGO)

Rick

 

[S/CBlack95GT]

Appx 9.3-9.4:1 should be close enough.

A 9.4:1 with the 58cc heads would be very close.

 

[igotyofire]

A 9.4:1 with the 58cc heads would be very close.

good enough for 89 octane then right

 

[Pokageek]

Interesting. Having flat top pistons I am supposed to be at 10.5 :1 using the same heads. I wonder what the difference in HP would be as upposed to 9:1? They said I would be required to use 93 octane though.

 

[Mrgreen94gt]

I'm not entirely sure, but CHP uses flattops on their 302/306 and it gives near stock compression.

Also, those combustion chambers should be very detonation resistant. So, what kind of gas you use would depend more on your overall timing and A/F ratio as opposed to the bump in compression from the heads.