Don't be afrriad to try revving it pasr peak HP RPMs, my 518(4.300 stroke with BB Chevy rod sizes) low deck six pak motor made peak HP at 5800 RPM and peak torque at 4500 RPM. I ended up finding out the car will run the fastest by shifting it at 7300 RPM I agree on the headers the rear gear ratio and the chip, get rid of the chip and shift it higher in 1st gear and see what happens