I'm surprised at how small the resonator's inside diameter is. That is probably why our exhausts are quite a bit quieter than some of the unresonated systems. I would imagine the resonator to be similar on my HKS exhaust since the muffler size and sound levels are close to each other.

I don't think the neck downs will hurt performance much under 400whp. I have an RS*R exhaust on my 2g, which necks down to 2.25" ID at the muffler. People have run 11s @ 120+ mph with this exhaust, so it is definitely not restrictive. It is also super quiet too. I'm willing to sacrifice a few top end hp, for a quieter setup.

I also felt my HKS was a little too loud after I first installed it. It took a little getting used to, but now I think the exhaust sounds matches the car since the EVO isn't necessarily a comfort car.

Thanks for document pic. I'm going to make one for my HKS exhaust.