HKS installed, but having a loss of power???
 

I have 2 gen2's. One with a ApexiN1 Universal and one with a HKS Universal setup. Both are cat-back with straight pipe at 2.25" and no scuba or resonators. The ApexiN1 system has more low-end power (pick-up) and gets better gas mileage than the HKS system!! Does anybody have any idea as to why this is??? I am thinking that it's because the HKS muffler has a larger inlet and outlet, but can that really make for that much of a difference?? Please advise.

yes i think, because you are losing back pressure for having a larger inlet/outlet.

It's all in your head. Unless you have any real numbers, it's all placebo effect and guessing. Changing one muffler, especially ones that have the same design (straight-through can), will do almost nothing for performance (especially because the only difference in this case is at the end of the exhaust system, for about 10-12 inches. That's nothing).

Less backpressure does not mean less low-end torque.

Intersting comment Old, but not true in my case. Running tusdo duals with Weapon R ram intake. Tusdo trumpets installed gained 1.75hp & 2.23 ft. lbs at 3000 RPM on dyno. Love the sound with trumpets removed but want the power gains more right now

Gains so little hardly prove your case. Infact are mostly just dyno variance as one dyno run will never be identical to another.

I agree with Old. Having a little difference in the inlet/outlet at such a small area in the end of an exhaust system will not have any effect.

What's your baseline? Stock vs intake/tsudo exhaust, or intake vs intake/tsudo exhaust? Even then, 2 HP is nothing. I dynoed a car three times and it had more variation than what you had.

Baseline was everything idential except trumps. I love the sound without them but was concerned about back pressure/performance. Yes dyno runs do vary mainly because of engine heat etc. Base was with just warmed engine to temp. Next 2 runs with and without trumpets followed. 1st without, 2nd with