I saw somewhere with a tune and longtubes alone added 13 rwhp. This was with a car that had a mid-pipe on the car also. So if you get longtubes and shorty mid-pipe with a tune, your gonna gain like 15-20rwhp.
I also have heard the stock exhaust manifolds are only restrictive at 350rwhp due to the bending at the passenger side or something.. Maybe it was driver side but the main thing is all shorty headers and stock exhaust manifolds have the bending that causes restrictive exhaust flow, and that only long tubes (re-design) fixes the bends. But don't quote me on that. Lol. Someone will chime in and correct me if I'm right or wrong I'm sure. 😜
But looking at my stock exhaust manifolds compared to my long tubes, my longtubes piping was way bigger. If anything definitely go long tubes. I see people do shorties turn around and get longtubes all the time, just cut the crap and get the longtube.
GT 5 Speed Full Bolt On 360rwhp 440rwtq