jwolf8604

Ok, I am NOT asking for preferences. I only want to know what the benifit of a custom 2.5 inch catback is. OUr stock piping is 2.5 correct? So I understand changing the muffler and tip, but is there a point to going custom "full catback"??? And my other question is how in the world does the gmpp 2.25 exhaust benefit us at all? How does smaller piping achieve more 12 more hp? I am trying to decide on which exhaust to go with but those are the questions that keep bugging me. Someone help.

aj_92rs

Mandrel bends would be the only real benefit. Crimped or 'pressed' bends cause the diameter of the pipe to become smaller inside causing a restriction in flow.

Based on what I learned when I worked HVAC, the best way to handle it would be increase the inside diameter through the turn. That's what they do in ductwork. The distance from the heel to the throat is larger than the inside of the straight duct, and sometime vanes are installed to help direct the airflow to keep the flow seamless, but that's not practical for the exhaust of a car.

I don't know if the GMPP exhaust is mandrel bent or not. I would hope so. But, for instance, if it is mandrel bent and a custom 2.5" system is press bent, then it will probably flow just as well, overall.

LopsidedJester

I believe GMPP keeps their resonator and muffler straight through or at least fast flowing, and i don't believe they have any neck-down points in the tubing. All mandrel bent ofcourse. Our stock piping necks down at a couple points equaling almost 2" and has a pretty restrictive muffler on the end. I guess its all relative since some people go by outer diameter and some by inner diameter, i'm willing to bet that GMPP is 2.25 I.D., i'm not fully sure though.

Onyxd04Redline

Our stock catback is 2.25". As for gains with the GMPP exhaust. I've never seen dyno proven gains with it.

ARKracing

Not everything comes from big piping mod.. This days, factory stock mods come with the all neccessary performance gains + parts. So far as aftermarket exhaust sytem, sometimes doesn't even increase hp, sometimes looses more. I seen other aftermarket exhaust system loosing hp from dyno test.

It is choice that you get right performance mods from your engine power and torque. Our estimate R&D choose 2.5" pipe because it is best gains come from 2.5" pipe.

3" : Somehow exhaust system sounds empty
2.5": WOW
2.25: hmmm...

Well... Just my opinion. btw, ARK offering special deal now an exhaust system.

https://www.cobaltss.net/forums/supporting-vendor-deals-group-purchases-133/

aj_92rs

There was someone that posted a 12 HP gain at the wheels with that system. I don't remember if it was the touring or sport though. A search may work.

EDIT:Here is the post.

Onyxd04Redline

If you gain 12whp with a 2.25" exhaust imagine what the gains will be with a 2.5"

aj_92rs

As I always say, there's only one way to find out.