May have posted this in wrong forum, but here it is again:

Looking at buying an 07 GMC crew cab, short box, 6L. Not wanting to change anything looks wise, but what can I do as far as exhaust and tuners? I was thinking maybe just cut the cat and muffler, and put in a better flowing muffler and leave the cat out. Try to make it look as stock as possible. Don't want it loud either, just some better flow. What size is the stock exhaust? Are the stock headers descent? Would cutting cat and muffler be good enough to get some better flow? As far as tuners, don't need anything extreme, just something to get me some better fuel mileage and more towing power. Any suggestions?

Bump for suggestions.

Talking to a guy today and said the computer will throw codes if I cut the muffler and cat and throw in a better flowing muffler. Anyone comment on this? Do you need a tuner to do anything to the exhaust?

which 07 NBS or OBS....

SLP, MagnaFlow, FlowMaster all make kits CAT back and have high flow CATS for header back systems, box tuners are HyperTech and Diablo, Jet is pretty good and better priced

any intake or exhaust changes SHOULD have a tuner installed to go along with them to maximize the performance abilities of the part. some ECM will "self tune" to the new parts but al that is is just enough to get back to within what it whats to "see" for in puts from the sensors in factory settings....some parts without a tune you can actualy LOSE power because of this

which 07 NBS or OBS....

SLP, MagnaFlow, FlowMaster all make kits CAT back and have high flow CATS for header back systems, box tuners are HyperTech and Diablo, Jet is pretty good and better priced

any intake or exhaust changes SHOULD have a tuner installed to go along with them to maximize the performance abilities of the part. some ECM will "self tune" to the new parts but al that is is just enough to get back to within what it whats to "see" for in puts from the sensors in factory settings....some parts without a tune you can actualy LOSE power because of this

It's the older style 07. I'd prefer to just get rid of the cats altogether. On my fathers truck we simple cut the cats, and welded in a piece of 3" pipe and welded the sensors right into that. Then the sensors in the cats didn't throw codes. Not sure if this would work on this truck as well. I was looking at Predator and it's pretty pricey. I'll have to look at Jet and see what the price is like. Not looking for serious power increase, more or less better fuel economy. Heard bad things about fuel economy with the 6L's, so I wanna do what I can to get better fuel mileage out of it. Would cutting the cats and muffler, replacing the muffler with a better flowing one and welding the sensors back in not work? Taking them right out will cause codes, but having them welded back in shouldn't, as long as they read properly.

AFE or K&N FULL intake filter and tube change out, long tube headers and Y pipe from DYNATECH will relocate the CATs and give you high flow CATs add a 3" or 3-1/2" "CAT back system" will give the best in/out flow numbers ( Gibson makes a good CAT back system ) and now just need to figure out your tuner....most of the tuners come with 3 or 4 tune levels, just pick which level load it and unplug the wire from the dash and good to go...

look over the SLP site http://www.slponline.com/car.asp?C=GM%20Truck%20and%20SUV and give them a shout; pretty good customer service

AFE or K&N FULL intake filter and tube change out, long tube headers and Y pipe from DYNATECH will relocate the CATs and give you high flow CATs add a 3" or 3-1/2" "CAT back system" will give the best in/out flow numbers ( Gibson makes a good CAT back system ) and now just need to figure out your tuner....most of the tuners come with 3 or 4 tune levels, just pick which level load it and unplug the wire from the dash and good to go...

look over the SLP site http://www.slponline.com/car.asp?C=GM%20Truck%20and%20SUV and give them a shout; pretty good customer service


Is the stock intake really that bad? I've found out most stock intake are actually half descent. Heard a lot of bad things with K&N to. They give you better airflow, but don't block much of the dirt going into the intake. This truck will see a fair amount of gravel, so I need a good filter as well. What size is the stock exhaust size? Look's like 2-7/8", or something close to. Would a tuner like predator disable the sensors in the exhaust so I could take the cats and muffler right out and throw in a nice muffler?

Stick exhaust if I am not mistaken is 3 inches, with 3.5 at the tailpipe, but I could be wrong. As far as tuning, one I have read good about is blackbear performance.

I went with a full CAI with ram air setup from Volant. Very happy with it and it increased my MPG. I have a pic under the volant thread a few months back.

Stick exhaust if I am not mistaken is 3 inches, with 3.5 at the tailpipe, but I could be wrong..


I'm thinking that is the 8.1L sizing....either way any factory bends are crimp bends not mandrel bends and the stock mufflers dont flow very well. mandrel bends and a decent flowing muffler will make a difference in any enigne

I'm thinking that is the 8.1L sizing....either way any factory bends are crimp bends not mandrel bends and the stock mufflers dont flow very well. mandrel bends and a decent flowing muffler will make a difference in any enigne


Flo-Pro direct fit 2500hd big oval mufflers are at 3in inlet, 3 in outlet. Same goes for flowmasters 530513, except it goes 3.5 outlet. So ithat would make it 3in to a 3.5 at the tail. Both of those products fit either the big block or 6.0.