Really not much I can do with my exhaust set up to increase HP. It breathes about as good as it can get, especially now with what little fiberglass was in the side pipes originally has pretty well vanished. It means for some careful baby'ing when driving in town, as it does have a bit of a growl. Scares dogs and makes babies cry..
A few builders have actually gone with the Street Cobra theme and run an undercar exhaust, exiting at the rear. With such limited ground clearance on these cars, you'd really have to build a custom system to get it to fit. Here's a fine example..