why do LT headers kill gas mileage?

[xAustin]

i honestly have always wanted to know this.. just cant put it together on why exhaust mods, including headers, kill your mileage so much.

after the heavy foot, i still lost about 2mpg when i put the LT headers on

[mabutler]

I really didn't see a change either way with mine, but I know I had to add fuel at different spots on the map so that would have an affect.

[Matt2105]

Typically long tubes increase gas mileage...

[91chevZ71]

well, the better your engine can ged rid of exhaust the more air/fuel charge can ingest (to a point, of course)

[Tbi-MAX]

actually Long Tubes, LEAN out the engine... a more free flowing exhaust will cause the engine to LEAN out using less fuel, as it wants more fuel... most people richen up the mixture, and end up adding more gas into the tune... to have a better AFR..

i have no clue why your LTs would be using more gas, that is strange as hell... it should be doing the opposite.. unless you tune it, and richen it up to make the AFR be close as possible...

[91chevZ71]

running lean makes it squirt more gas, added through tuning or running high on BLM.

LT headers require a retune, IMO.

hell, I'm so addicted I re-tune whenever I drive (most of the time)

-I should say running lean on a truck with functioning O2's makes it squirt more fuel to get back to 14.7 AFR

[Tbi-MAX]

well you learn everyday, i didnt think running lean would make it squirt more gas... i guess that would explain him drinking for fuel.. cause its lean...

i agree with you, any major exhaust mods including LT headers, should get a RE-tune of the pcm/ecm...

i know tunning is addictive, i plan to leave my Ostrich permanently installed when i do get it.. and a laptop mounted to the center console permanently... i would also like wireless broadband for the road too.. :biggrin: what better than tuning while you drive, and posting a question on FSC on the road.. lol

[GM Muscle]

Yes if the Long Term Fuel Trims are in the positive, then the motor is running rich. If the PCM sees that you are say 5% lean, the computer will really dump 10% more fuel. Fairly common issue with Long tubes. Get a tune and your gas mileage should go up. :)

[91chevZ71]

i would also like wireless broadband for the road too.. :biggrin: what better than tuning while you drive, and posting a question on FSC on the road.. lol

now THAT is an idea!

[chadcmb]

ok. your milage went down because.... you romp on your exhaust. im asuming it sounds good right? well then you think ok. lets floor it or give it more gass to make it louder. atleast thats what i did..... i dont know. just my 2 cents

[Atomic]

If you got rid of your cats and didnt get them taken care of in the pcm, then the computer is going to run it rich to try and play it safe.

[xAustin]

isnt from romping on it... i've taken it quite easy since i've gotten the headers on..

i actually got the LTs on, and got my w4m tune at basically the same time.. so it is tuned for the headers. so jesse says.

still have cats so that couldnt be it.

i also did change my spark plugs same day, so could that be it? got ngk's and hell, i had to gap them to .06 /shrug

[Atomic]

hmmh, only other thing i can think of is your true dual 2.5" exhaust is too big. 2.25" would be more appropriate. Did you have it redone at the same time you but on the headers?

[xAustin]

no, ive had the exhaust on there for about a year.

emailed jesse @ w4m and he said its because of the headers. said LT headers helps with highend but it does kill mileage pretty good.

[Fast305]

no, ive had the exhaust on there for about a year.

emailed jesse @ w4m and he said its because of the headers. said LT headers helps with highend but it does kill mileage pretty good.

My experience is that my mileage ALWAYS has increased when I put long tubes headers on. The added torque allows you to drive with a lighter foot and keep the engine at a lower rpm for acceleration, reducing hp robbed due to friction in the engine and trans, increasing overall efficiency, and fuel mileage.

[GM Muscle]

no, ive had the exhaust on there for about a year.

emailed jesse @ w4m and he said its because of the headers. said LT headers helps with highend but it does kill mileage pretty good.

I wouldn't completly buy into that.

I bet if found a good local tuner to redo the tune. Your gas mileage would go up. Kinda hard to tune part thorttle through the mail.

Anyway, did you delete your EGR? That can effect mileage. Also, are you running high flow cats? I'm wondering if the COT (cat over temp) is kicking in and dumping fuel. It shouldn't at part throttle but you never know. Did jesse send you another PCM and did you have a crank relearn done?

[xAustin]

yes i did get the tune on an extra pcm and the crank relearn was indeed "done" at least my exhaust guy said he did do it.

dont know what ERG is, but the cats are stock.

thinking im going to throw in my stock tuned pcm and see what happens with that.

thanks for the help guys