What size exhaust??

[fordeater]

I have read other exhaust threads, but I am unsure what to do for my truck.

Truck in question is a 1996 Chevy K3500 with a 7.4 big block. The motor is stock with the exception of larger injectors, and it will have a slight tune in a few weeks. It has stock manifolds with 3" exhaust leading into and out of dual cats. It was run back to a muffler with dual 3" inlet and single 3" outlet. The muffler went bad, and the exhaust is currently cut off.

So, I want dual exhaust, so my question is do I run 3" all the way back for a true dual, or do I have it taken down to a 2.5" system? I realize most people don't approve of my muffler choice, but I want to run glasspacks. I grew up with glasspacks on almost every vehicle I have owned, and I haven't quite grown up and out of the loud obnoxious sound yet.

I will be taking it to a shop that mostly speaks spanish, cause that seems to be how they are around here, so I want to know exactly what I want so I can just point and pay.

What should I do?

 

[sweetk30]

never step down if at all possible in pipe size that bad.

3" out back be fine.

and if going flow master get 50 delta or hd or suv for quiet mufflers in the cab and no drone sound harmonics on crusing highways.

 

[Cornfield creations]

2.5 inch tails is more than adequate. They ran 2.75" back on 7.4's and the 5.7's from 96-2000. The outlet's I believe are 2.5 inch out of the manifold on the 454, 2" on the 350. The reason they went with bigger pipes is for volume on the front side of the muffler. Not because they need 3" duals from front to back.

3" all the way back with duals will hurt the low end torque, kill velocity, and cause your engine to work harder to force the exhaust out the end of the tailpipe.
We always run 2.5" tails on them, and with those who have changed from 3" can tell a difference.

If you are running glasspacks I would personally want at least a H-pipe inserted before them to balance out the exhaust.

 

[fordeater]

I kind of thought 3" all the way out with duals would be too much. My thoughts were to leave it 3" to the cats, and then go down to 2.5" to the mufflers and tailpipes. Or, 3" from the cats to mufflers, and then cut it down to 2.5". I have no idea what I'm talking about, but it sounds good right?!

 

[big pappa b]

3" will be fine. Big blocks like to breathe

I run dual 3.5" on my Malibu but it's putting out 750hp

 

[sweetk30]

i had 2 mufflers on my old crew cab then went to single with 2in 2 out and loved that combo better than 2 mufflers.

less harmonic drone inside and better outside sound. but its up to you.

 

[Cornfield creations]

There are tons of people on here running a single 3" on a built 454 and it works great for them. Here are some Q&A for you, Magnaflow has a lot of them, but these seemed specific to your question. Also keep in mind, you are going from a single tail, to a dual tail, so the increase in combined pipe diameter is doubling.

http://www.magnaflow.com/07techtips/faq/question10.asp

http://www.magnaflow.com/07techtips/faq/question14.asp

 

[6.2Blazer]

I would be very surprised if you could feel the difference between 2.5" and 3" exhausts. With that said the only difference would be the sound and probably the cost. From my searching around recently it seems as if 2.5" mufflers and stuff are a good bit cheaper than 3" so that may be the deciding factor. The 2.5" would be fine.