I just bought my heads for my 383 build. They are afr 195's with straight plugs and 76cc chambers.

I know that the bigger chamber generally lowers CR, but where should I plan on it being with flat top pistons and 5.7" rods?

If it's too low, would upgrading to 6" rods be a good correction?

 

Since compression is the total volume of the cylinder/chamber when the piston is at bottom dead center divided by the total volume when the piston is at top dead center, any increase in displacement for a given chamber size/piston crown volume will increase the CR.

6 inch rods will stick the piston tops out of the cylinders approximately .3" - not the proper way to raise compression. To use 6" rods, you need to get pistons made for them.

CR is modified/finalized by properly choosing pistons, head gaskets, and possibly machining such as shaving the heads (to reduce chamber volume) and block zero-decking.

 

So with a chamber that large, to get my CR to someplace useful, I am probably going to want to look at a domed piston?

 

Or supercharge it...I like that idea better

 

Or shave the heads to reduce the chambers to 70-72cc or so. That's pretty typical for 383/400's.