I installed my headers 2 weeks ago and have gone from 13 to 10mpg. I have Pacesetter LT's with 3" ORY. I dont have any exhaust leaks and did'nt notice any power gain. I contacted Justin to see if it needed a retune and he suggested that the headers could be too big for my truck. I sent him a data log and am waiting for him to get back with me. So is the 3" y too big for my truck or is there some think else going on? The truck is in my sig.

 

Re-tune, it will make all the difference in the world.

 

Adding performance mods will drop mpg, just part of the game.

 

now my truck is on 35 inch tires. I swapped to 4.56 gears,HT1 cam, had it tuned and it picked up 2mpg went from 15 to 17. I added SDPS cnc heads 1.8 roller rockers. pacestter LT's and y pipe and it dropped to 14. I thought I was headed the right way for mpg when this adventure started for mpg's.

 

my truck gets about the same mpg as it did stock, IF i keep my foot out of it. it mostly has to do with a well combined setup and spot on tune.

 

I am getting about 16.8 MPG with my truck and I have OBX knockoff longtubes. Now mine is a 5 speed manual so I am sure that helps, but I also have 295/70/17's with a 230K mile old 4.8.

 

My truck got the same MPG before and after my headers. On a mostly stock 5.3 you wont notice much of a gain. Maybe 10-15hp. add a cam, and a better intake manifold like the tbss intake it will be more noticeable.

 

What size did you go with and has it been retuned yet?

Since when? Any mild setup thats not a strip queen will yeild stock or higher mpgs with good tunes,its been shown many times on here..
A stock truck with just headers isnt going to loose mpgs

 

They are pacesetter 1 3/4" primaries and 3" y no cats. Engine is an lm7 and is mostly a stock setup besides exhaust and tune. I plan on doing a cam and stall converter by fall I'm just starting to look for parts to slowly peice together everything I need.

I emailed Justin with BlackBear and asked him if I needed a retune for the headers early last week. I also asked him to check out a data log b/c my commanded afr would command odd ratios. He told me the odd commanded afr issue probably needs the cat test disabled. Haven't heated back from him again but I will see.
I drove it to San Antonio today and I picked up some hwy mileage! I went from 18 to almost 19 running @ 80 and 89 octane! My city mileage is at 10.8 from 13 running 93 octane. I will post up my mileage running around in San Antonio and post what Justin has to say when he gets back with me. Thanks

 

Headers need a retune to gain there worth so i dont know why he's leading you to think its something else or something is wrong