The 4-1 header makes more peak power than the 4-2-1, and more power in the upper rpm. If you wanted midrange power, you should have gotten a 4-2-1. You can still make high RPM power on an LS motor, you just need the right combo of parts. You might notice a little loss in the low end due to decreased backpressure, but I didn't really notice any loss. I did notice a small top end gain, but I have a much freer flowing exhaust than you. Like Snoopy said, don't expect to make more than a few hp from a mass produced header, when you aren't making much power to begin with.