Bought the Flowmaster 40 (currently in the mail). Running single in dual out. It's 3" in (offset) 2.5" out (dual), also bought 3" tips for it. Was wondering if I should open up the entire outlet pipe to 3" and do full 3" pipes or keep the 2.5" outlets. Will I lose backpressure if I run 3" all the way?

 

I run 3 inch exhaust on my 3.0L V6 Nissan 300zx...so I don't think it would be a problem with a V8 truck lol

 

But is your Z the twin turbo, turbo vehicles run much better with less back pressure. I had a 2005 Subaru Impreza 2.5RS which is the N/A Impreza 2.5" was the biggest to go on that vehicle the car would have still ran fine 3" but would have lost the low end torque that boxer engines are known for. I then traded it in for a 2005 Subaru Impreza STi and I put a 3" exhaust on it and helped immensely but it is turbo and some people ran 3.5"-4" piping and no cats to get as little back pressure on the STi as possible. Now as that is said I don't know what would be the best for a v-8 but would think its the same as 4 cyl. na engine and 2.5" would be the biggest I would go.

 

Back pressure on these motors dont really help alot since these motors run better in the higher RPM's. The older 5.7 liter vortec's did need it for more low end torque but they would shift around 5000 RPM's. So you will be ok with 3". No less than 2.5". That is what I have in mine but I'm gonna go with 3" since I am puttin in a good size cam.

 

Hmm true, I'm used to older vehicles. Especially my 96 Blazer where it was all low end torque and nothing but. The torque curve dropped off earlier and had terrible passing. I want to go 3" for better sound, so should I go 3" over 2.5"?

 

The 3" will give it more deeper tone and flow more. I would.

 

Yep that what I'm aiming for. Thanks!

 

No problem!