GMC Sierra Exhaust

[jkool725]

Hello fellow truck nuts,

I am new to the forums and have a few questions about my exhuast on my truck, so please bear with me!

Ok, I have a 2006 GMC Sierra 5.3L V8, and I want to do the exhuast on it. I already have a Flowmaster super 44 on it but I'm looking to make it louder. I was thinking about getting some JBA headers and maybe some Hi-flow cats. Is this a good combination to go with or is there another direction I should go? Anyways thanks for the help!

[chakis24]

your truck already has high flow cats, 2 actually (assuming its the same as mine- which it should be).

i really liked the dynomax kit- long tube headers and new cats that just bolt right up and match up with the existing y-pipe

you just want it louder? cut it right after the exhaust and just dump it under the bed- thats my plan. or just install the cutouts that let you bypass the cats.

[nailhead425]

Originally Posted by jkool725

Hello fellow truck nuts,

I am new to the forums and have a few questions about my exhuast on my truck, so please bear with me!

Ok, I have a 2006 GMC Sierra 5.3L V8, and I want to do the exhuast on it. I already have a Flowmaster super 44 on it but I'm looking to make it louder. I was thinking about getting some JBA headers and maybe some Hi-flow cats. Is this a good combination to go with or is there another direction I should go? Anyways thanks for the help!

I see that you call CA home. So tell me, is Fresno a non-attainment area? Meaning that they have smog testing? If so, leave the exhaust alone ahead of the cats, or else only use parts that are CARB approved. After the cats there is alot less hassle and you can make it plenty loud, if that's what you are after.

[fish factory]

A simular question.

Has anyone removed stock muffler and run cats only? Patch back pipe and run out behind truck bumper? Seems cats are restrictive enough to act as a muffler.

Z-28's used to have a chambered exhaust exit at bumper w/o mufflers or cats. As I remember, wasn't too loud.

[smokyn454]

Originally Posted by fish factory

A simular question.

Has anyone removed stock muffler and run cats only? Patch back pipe and run out behind truck bumper? Seems cats are restrictive enough to act as a muffler.

Z-28's used to have a chambered exhaust exit at bumper w/o mufflers or cats. As I remember, wasn't too loud.

Yes, people do it all the time. It gets pretty loud, especially with the 6.0 liter.

I don't know how much louder this guy wants it, a flowmaster 44 is pretty much as loud as you can go without straight piping it.

[fish factory]

Originally Posted by smokyn454

Yes, people do it all the time. It gets pretty loud, especially with the 6.0 liter.

I don't know how much louder this guy wants it, a flowmaster 44 is pretty much as loud as you can go without straight piping it.

IYO, would a no muffler w/cats installed on a 5.3 to the back bumper be louder than single FlowMaster set-up?

[smokyn454]

Originally Posted by fish factory

IYO, would a no muffler w/cats installed on a 5.3 to the back bumper be louder than single FlowMaster set-up?

Yeah, it would be louder. Its a different kind of loud though.

A single flowmaster would have a somewhat tuned sound. Kind of a bass and rumble. Quieter at idle and cruising but loud when you get on it. At high rpm's it would crackle. Sounds like it is echoing or commonly described as inside a trash can.

While a single set up without a muffler, would have a deep bass sound but always has a crackle. It is loud at idle, cruise, whenever. A straight pipe sounds really good on a 4.8. On a 5.3, it tendsto get a little loud but not too bad. With a single pipe, they don't pop too bad either.

With dual straights, it is a lot higher pitched tone with a lot more crackle. It also pops a lot. An X-pipe will cancel some of this out but it will still pop.

A 12" glasspack is about all that is louder than a flow 44. Maybe a 10 series flowmaster or some other type of racing muffler but I don't like how they sound on normal vehicles.

[jkool725]

Thanks guys for the replies. I think what I am going to do is cut out the cats and go dual flowmaster 10 series.

[nailhead425]

Originally Posted by jkool725

Thanks guys for the replies. I think what I am going to do is cut out the cats and go dual flowmaster 10 series.

Do it at your own risk.

First it is illegal.
Second you'll need 2nd O2 simulators or the OBD-II will register a fault code.
Third, in 3 years you'll have to smog test.

Since at any point in time your vehicle can be inspected and impounded for faulty/removed emissions equipment, don't do it.

My $0.02, it is your truck, wallet, life.

[jkool725]

[quote=nailhead425;1589900]Do it at your own risk.


Second you'll need 2nd O2 simulators or the OBD-II will register a fault code.
Third, in 3 years you'll have to smog test.

QUOTE]

This I was not aware of. Thank you for bringing it to my attention, it seems I will have to rethink my plan.

[fish factory]

Originally Posted by nailhead425

Do it at your own risk.

First it is illegal.
Second you'll need 2nd O2 simulators or the OBD-II will register a fault code.
Third, in 3 years you'll have to smog test.

Since at any point in time your vehicle can be inspected and impounded for faulty/removed emissions equipment, don't do it.

My $0.02, it is your truck, wallet, life.

WOAH!

Back up that Flowmaster equipted Denali!

My 5.3HO Silverado has 2 converters, and 2 ox sensors, 2 exhaust pipes that converge just in front of stock muffler. Are you saying there's a problem with me cuttin off stock muffler and runnin duals?

[smokyn454]

Originally Posted by fish factory

WOAH!

Back up that Flowmaster equipted Denali!

My 5.3HO Silverado has 2 converters, and 2 ox sensors, 2 exhaust pipes that converge just in front of stock muffler. Are you saying there's a problem with me cuttin off stock muffler and runnin duals?

Nope, you can do anything you want after the emissions. So after the rear O2's, anything is game.

Most exhaust shops will not touch anything else but the muffler back.

[nailhead425]

Originally Posted by fish factory

WOAH!

Back up that Flowmaster equipted Denali!

My 5.3HO Silverado has 2 converters, and 2 ox sensors, 2 exhaust pipes that converge just in front of stock muffler. Are you saying there's a problem with me cuttin off stock muffler and runnin duals?

Nope, you're fine. As previously stated, after the 2nd O2 sensors (which are post cats) mods are generally accepted as legal. As always check local laws first. In your case, running dual mufflers instead of the 2 into 1 system, is a good idea and probably helped with mid-range and upper rpm power. Plus, the sound is really sweet.

jkool was going to cut out the cats. That's the problem.

I don't want anyone, kids, uninformed, or the Feds, thinking that GMI supports, suggests, or endorses the removal of any emissions control device.

Besides, there is so little power to gain from removing the cats it wouldn't be worth it.

[chakis24]

Originally Posted by nailhead425

Nope, you're fine. As previously stated, after the 2nd O2 sensors (which are post cats) mods are generally accepted as legal. As always check local laws first. In your case, running dual mufflers instead of the 2 into 1 system, is a good idea and probably helped with mid-range and upper rpm power. Plus, the sound is really sweet.

jkool was going to cut out the cats. That's the problem.

I don't want anyone, kids, uninformed, or the Feds, thinking that GMI supports, suggests, or endorses the removal of any emissions control device.

Besides, there is so little power to gain from removing the cats it wouldn't be worth it.

just out of curiosity, what about the cat bypass cutouts? you basically remove some of the pipe before each cat, put in pipe with kind of a trap door in its place, and off you go. how would that affect it? would a code or something trip everytime you opened them up? does that kind of thing reset itself? just wondering.

[nailhead425]

Originally Posted by chakis24

just out of curiosity, what about the cat bypass cutouts? you basically remove some of the pipe before each cat, put in pipe with kind of a trap door in its place, and off you go. how would that affect it? would a code or something trip everytime you opened them up? does that kind of thing reset itself? just wondering.

Also illegal and it will likely throw a code. The second O2 sensor has a band in which it has to operate, or it throws a code. No cats, or no flow (cut-outs) will trigger it.