I currently have 7" at idle (800 RPM) I have read a lot about 6 pack tuning, I don't think the car is making the power it should that maybe the carbs are not opening when they should (light yellow springs on the outboards) I have a Hydraulic Roller cam and roller upper end. Manual brakes....so the only thing requiring vacuum is the carbs and the PVC. This is a new engine (500 miles on it) manual transmission.....is 7" enough to do the job? I really wanted to stay with the 6 pack....but....