OK, we all know that longtubes add a pretty significant amount of HP, as well as make the car sound great, but I'm curious about a couple other factors:

1) Is there any amount of weight savings to be had by going with longtubes and an off-road H / X - pipe? I'm assuming there would be, as catalytic converters weigh a TON, whereas a straight pipe weighs next to nothing. Do the headers themselves (in general) weight less than the stock exhaust manifolds? Anyone have any concrete numbers as to the weight savings?

2) Since the exhaust gases are being moved away from the engine more efficiently, is there any increase in gas mileage after installation and a tune? I'm sure that MPG is the last thing on someone's mind when installing headers, but it never hurts to increase your efficiency, right? Even 1 MPG would help with today's gas prices.

3) Anything else I'm not thinking of?

 

I'm not 100% sure on the weight savings, but after lugging the old cats and rusty boats back to the garage, compared to the LTs when I lifted them out of the car, there is a definite difference in weight. Probably nothing you can noticably feel though.

As for gas mileage? I have run my car on the highway, and have reached a high of 31.2 mpg on the highway ONLY, with the car in 5th gear, doing exactly 65 mph. My routine mpg are around 17.5/18.5 around town, and between 25.2/27.5 or so, on the highway. And this is with a custom tune for ALOT more power!!!

 

No true numbers on weight saving but like the post before me just picking the stock manifolds and cats up verses the longtubes I'd guess the longtubes are a few pounds lighter but not enough to make a difference.
I noticed no change in my gas mileage at all. Most of my driving is at 45-60 mph. I am averaging 19 mpg. But when on the highway for a long trip I get 24 mpg about. And that is with cams.
There is really only 2 reasons to do longtubes IMO..The HP gain and the sound improvement.

 

I've only had my LT's on for about a week, all I can say is it now sounds like a proper muscle car!

 

I've had my LT's on since Dec.07, no difference in the milage. I average around 20/21 combined. My best has been 27 on a trip. I drive alot of highway on my work commute.
Weight savings; I'm guessing around 20lbs when you factor in the stock manifolds,cats & H-pipe.Not really enough to make any difference.

Mine was strictly a performance mod.