The way I would explain the horsepower loss is something like this.
Now I'm a big guy and can push with my shoulder quite a bit of weight with my legs against a wall. If the wall is too close (restrictive) and I barley fit then I cant use my legs and loose power. If the wall is too far away (open) and I can only use my ankles, I loose power.
Somewhere in the center there is a sweet spot and its called tunned exhaust.

Is the rest of the exhaust stock and all you did was take the mufflers off or what? Also, what all is done to the engine. The stock mufflers flow very well, so I doubt you lost much backpressure at all pulling them off. (the stock mufflers flow well enough to get well into the 11'*) You have to remember there is one single 2.25" pipe running through the cat & resonator and then that pipe splits into 2 2" pipes with the mufflers on it, so those mufflers would have to be very restrictive to have more backpressure than the cat, u-bend, resonator, and 2.25" pipe.

I don't think the car lost any power, its possible, but knowing how the exhaust is set up, I highly doubt it.

Shawn

Stock pipes, and we just cut out of mufflers........ He is running a k&N conical on the stock intake hose.

Cutouts.......If I were running one, I'd leave it closed to get off the line, then at about 1/8, I'd open it to gain the high end hp.

that'* actually pretty clever.

about the performance, I can put it down to 3/4'* now and only have it chirp whereas before it would spin. All in all it feels like it pulls a bitch more harder.

The science behind it: http://web.tampabay.rr.com/redroby/3liter/exhaust.html

Usually stock V8'* have trouble breathing when they are made. Opening the exhaust on those help a lot. That'* why the F-body and Stang owners get a lot of power after adding an exhaust

The 4.6L Northstars are the same way. They gain like 25hp from just an exhaust!

Shawn

I know with V-8s atleast, with a good manifold and exhaust, each cylinder is actually helping the others, and too big or little backpressure hurts that.

This is why X pipe dual exhaust setups have more power the true dual.

I think ZZP/Intense did a little test on a L67 Regal with backpressure, found that no muffler was bad for it, you made more hp with a muffler on there.