I'm looking into purchasing a set of these as well. I have some questions about 'what else'....

Such as, after they're installed, can the rear O2 sensors be reinstalled and function properly? Or should I have someone 'delete' that circuit from the OBDII functions?

My truck already has a 'custom tune' with no other physical/mechanical mods other than a generic cat-back (single in/dual out) Flowmaster muffler. After the LT install, would I need to have the truck retuned to compensate the extra exhaust flow?

Is it recommended to do the 'free mod' to the stock intake air filter box to provide a better fuel/air charge?

I'm towing a boat and not racing, so I'm wondering exactly what kind of improvements I could expect from these headers/y-pipe vs the stock manifolds?

 

I cannot say definitively about the rear O2's, but these headers do come with those little resonators, which do indeed have somewhat of a baffle inside...similar to a mini glasspack muffler. Since the rear O2's only measure the slight difference between the fronts, I'd have to think that rear O2's would, or should, work OK without a re-tune,

but...

the fueling requirements DEFINITELY change with the addition of headers and a free flowing Y pipe, and you'd DEFINITELY benefit (at least a little) from a tune to take advantage of the much better flowing exhaust. Lots of people say "you don't NEED a re-tune", but for YOUR truck to run it's best, it really should be re-tuned for YOUR mods.

p.s. I found that my 2 chamber Flowmaster 1 into 2 muffler was way too loud after the longtubes. Your results may vary.

The "free mod" to the stock airbox definitely works and I proved that on quite a few datalogs. I think I had a thread on here somewhere?

Obviously, every truck is different, so the results will be as well. With tuning for the headers (and modded airbox) I gained 3mpg consistently, truck revs much smoother/faster, and just all around "feels" better. My son has a 5.3 powered 2005 Avalanche (Southern Comfort model) and one day he drove my truck and said he couldn't believe how responsive my truck was, compared to his. His is DBW throttle body I think, so that surely makes a difference in "feel", but his is bone stock aside from exhaust and mine will eat his alive, lol...

For $300, I can't think of another mod as cost effective. My truck is a daily driven, often abused, work truck that regularly tows, hauls, and is tuned for 87 octane gas. It will DEFINITELY be LOUDER! lol

 

whats this airbox mod for "free"? I didn't see anything in your threads about it

 

I can't find the thread (I thought for sure I had one), but I found one I replied to with pics of my airbox...basically cut the bottom out of it, as well as the steel part underneath it. Works great and cost me 1/2 hour of time with a cutoff wheel.

https://www.performancetrucks.net/fo...1&postcount=58

 

Anyone done these on a 2003 1500HD 2WD CrewCab?

 

Installed a set from Ebay (DNA) were $290 shipped only took 4 days to arrive.

This thread helped out a TON with gathering everything needed for the install!

All in all i had everything all laid out and ready to go ....put the truck up on the lift and from start to finish took about 3 hours and 20 mins give or take....helps having a nice shop on Post with a lift and air tools at my disposal and my dad to help out.

Very happy with my purchase....now just waiting for my retune from nelson and i will be set for LSFEST in Bowling Green.

 

Glad it helped you out.

and THANK YOU for your service!

 

I just got a set for my 02 avalanche Z I took the OEM exhaust off today everything came off good... except one manifold to y pipe bolt which I rounded off so i got nasty and cut the y pipe right close to the manifold... I have two oem header bolts which the heads off the bolts came off but they came off just driving... which was causing a slight tick at start up.... and since I had to take the OEM **** off to fix I decided to go with the headers.... anyways I have to get those bolts off I got about an inch sticking out of the head.. I'm going to go get some map gas and heat up a bit and try to get out in the morning and install I'll let you guys know about the fitment

 

okay after wrestling those two broken head bolts out... everything went pretty smooth header was rubbing on front drive shaft...... okay i beat it up some and got clearance but its still rubbing a bit so i have to beat it up some more... and order some bandclamps the u clamps just suck!!! I had some MSD wires from my vette when i switched to the GM performance parts wires... both have adjustable boots the MSD's are a little short but thats good they work good on the hump pipe and no need to zip tie them or anything... so I should be finished tomorrow gotta take drivers side off one more time to make it clear the Front drive shaft

 

Does anybody have the passenger side hanging lower than the driver's side? Mine sure do that... hangs below the frame on that side.