That's a hard question to answer because I did a complete rebuild motor exhaust transmission rear end gears all at the same time but under normal upgrades i would say more than likely about 30-45 hp total with long tubes y-pipe and cat back (with no cats) that's my opinion maybe another board member could give you a better answer.

 

Would I be better off (getting longtube regardless) getting a y pipe and 3 inch cat back, or just getting a exhaust shop to do duals?

 

I have custom true duals on my car. My headers have 3" exits, no cats, then it goes down to 2.5" pipe with a Magnaflow X-pipe, then it's 2.25" pipes over the the axle to the muffler, then 2.5" outlets. Headers were $285, I found the X-pipe off ebay for $75, O2 extensions were about $30 or so, and I think the rest of the work was somewhere around $600 or something like that.

 

this is the post from my project thread. The car has since gone back to the shop, where they installed the x-pipe and took care of some of the issues pictured.

A guy on LS1tech built his own true duals, and they turned out pretty sweet. This is what I gave the shop when I took the car back to get the exhaust fixed:

 

fyi- an off road y pipe deletes the cat.

Pacesetter ceramic coated long tubes
ORY
Magnaflow system

major benefits- you can change spark plugs a heck of a lot easier as well as drop the tranny without dealing with the exhaust.

yeh the added power is a plus but spark plug access is worth it.

 

so would it be cheaper to buy the set up and have a shop install it, or have them fab it?

 

the guy made this setup himself. If I were you, I would take these pictures to shops and get estimates on getting something similar built. If you want an X-pipe, I recommend looking around for one. A shop would get one directly from Magnaflow, which would cost $150+. I found mine on ebay for $75. The guy aborted his project and never used it.

 

I fount stainless long tubes on ebay with 3" y for just over $300.00.