I've read and read everything I can about DCR on this forum, used the calculators, and can't quite figure it out. I want to build a 383, more than likely the eagle motorsports kit with 5.75" rods and 28cc dished pistons, thinking about getting the trickflow heads with 64cc combustion chambers, and I want to run a relatively mild cam with more lift. The stoker kit shows an 8.7:1 compression ratio with 64cc heads. I have a Vortech S-trim in stock form was getting 9lbs of boost. I want to run the same pulley setup, but I don't know what the new boost will be. Every time I try calculating DCR with a relatively mild cam, the DCR is too high with boost (9.5 - 10.5), runs about 5.9 to 6.9 without boost. Do I really need to drop the CR below 8.7:1 for this to work or am I missing something?

Added: And also, if the crank is internally balanced, does it still need to be balanced with the flywheel and damper?

 

You have your terms kind of confused, which is understandable as "dynamic compression ratio" is used in (at least) two different ways. The generally accepted definition is based on calculating the CR based on the position of the piston at the point of intake valve closing. This is the DCR referred to as in the context of aiming for 8-8.5:1. Some people use the term "dynamic compression ratio" to refer to some sort of a "compression ratio equivalent" which takes boost into account. I don't think there is any standard way of wither calculating or interpreting this latter use of the term.

Your combo sounds in line in most boosted EFI cars.

Rich

 

Thanks. I kinda figured the calculator was guessing the DCR with boost applied, I just wanted to make sure I was understanding it correctly.