1redta

I have an 08 Sierra with a 5.3 and BTR truck 2 cam. The engine has flat tops, 243 heads, nnbs intake, Texas Speed 1 3/4” headers and y pipe no cats, 4l60e and 3.73s.
I am currently using the stock exhaust with a Hooker maxflow in place of the OE muffler. the truck has a street tune by Weeks and runs pretty well.
I’m thinking the stock 2.75exhaust is restrictive? I’d like a 3.5” from a truck with the 6.0 or 6.2 would that be worth the hassle for more power? is the stock cat back to restrictive for my set up?


thanks Art

FFDP

iTrader: (2)

Probably less restrictive than you think, that combo isn't making a lot of power.

You already have the stock muffler gone, so that is helpful.

imma_stocker

iTrader: (19)

Do you want more performance or more loud? If performance is the goal, what do you want your powerband to look like and where do you want peak torque?

I doubt your exhaust is restricting anything at this point unless you're also running nitrous. Honestly you could add resonators and high flow cats without losing noticeable power.

1redta

I was thinking about 400ish flywheel is what that combo makes, I’d like to add a 28” bodied magnaflow to quiet things down, I was just wandering if a 3.5 takeoff would be an improvement

dantheman1540

There are a lot of guys running stock take offs. I have some stock 3in cat back from a NNBS on my RCSB to keep it sounding stock when the cutout is closed. It's as quiet as my buddies all stock 2500 and I don't notice much difference with my butt dyno between cutout open and full 3in factory exhaust. But maybe that's because it's being force fed with a blower.

My new combo with a bigger motor and more boost will probably end up getting a 3.5 cat back like your talking about.

ZO6Ted

I read on Corvette Forum where the quickest C7 ZO6 in the country doesn't have headers or at least didn't when it was written. He said NA Vettes definitely benefited 30 hp or so but blown it didn't do anything except make it sound better. Seems to agree with what you've experienced. Interesting to say the least.

1redta

If someone is using a 3” pipe on a blown setup they are limiting themselves.

here is a great article

http://www.chevyhardcore.com/tech-st...-up-the-power/

1redta

here is another


http://www.dynomax.com/downloads/pro...ion_secure.pdf

dantheman1540

I totally agree that it was probably hurting a little. Just not enough for me to tell with my butt dyno. Somewhere I read a long time ago that unless the mod makes a 10% or more difference you likely want be able to feel it. Since the old combo probably made around 400 to the tires (total guess) then the 3in catback would have to hurt 40whp or more to be noticeable on the street.

I even tried to do comparisons on how much boost I would see cutout open/straight headers compared to cutout closed/full OEM catback. Sometimes I would see 1psi more with the cutout closed and sometimes I wouldn't but it's difficult to say that's the only changed variable when making pulls in a street with belt slip and changes in ambient temps.

1redta

I took the stock stuff off from the y pipe and replaced with a 4 foot piece of 3” stainless and a huge magnaflow muffler that I think it is two feet long itself. It’s sounds much better now and isn’t nearly as obnoxious