Well, whats the best way to drop the CR for a FI application? Through the pistons or the heads?

Currently i have a forged setup in my n/a 383 and want some boost. Is the best way to go about this through the piston dish or the combustion chambers?

I currently have ~55 cc chambers i believe and -15 cc dished pistons for a CR of about 10.8

I plan to get a set of AFR heads, and by using a CR calculator, it looks like i wont be able to get a big enough drop by the heads only.

A 74cc head and a 26 cc dish piston will net a 8.15 CR if i am right. and a 74 cc head with my current 15 cc dished pistons will only take me to 8.95

So, simply put, I will most likely be getting pistons specifically for boost apps. But where should I plan to take out the most CR from? What will give the best characteristics? I suppose i can always get a Cometic head gasket in any thickness to drop it some right?

What is the optimal combo here for a CR around 8?

 

I don't think it matters as long as the quench area (flat area on the piston that mates with the flat area on the head) remains the same. It's not advised, however, to install a thicker head gasket to get lower compression because it adversely affects the quench height (distance between piston and head at TDC). You want a quench height of .035" - .040". Since most aftermarket gaskets come in .039" - .041", it usually works well to deck the block to "zero deck height".

The engine I'm currently building uses AFR 68 cc heads and SRP 31 cc dish pistons in a "zero deck height" 383. The resulting compression ratio is 8.3/1. I'm actually scared that might be too low for 12 psi intercooled boost.

Mike

 

>I am using 35cc JE pistons , 0 deck height (I believe) , .040" Cometic head gaskets , AFR 64 cc heads , 3.875" DragonSlayer crank , 5,850" Oliver Rods . This should give me 8.5 c/r .
It won't be long now since the block is in the machine shop now (3 weeks is like forever ) .
I plan to use 12-15 psi on my T-trim aftercooled of course and a small shot of N2O .

 

If you can get it to 9:1 that will work. Listen to EngineerMike on the quench area comments.

I have a 9:1 383 I'm working on and will have around 23psi.

 

look more in depth to this

will the piston strength be compromised with a big dish?

I think i may just get a set of AFRs or the liking and use them.

What kinda CR should i be shooting for with 16psi of boost through a FMIC and small shot of nitrous later on? 8.7-8.8?

5.7 rods will work best for this? Keep the pin down low?

seems it would be best to take the CC out of the head instead of the piston?