Ok, on my 2003 Silverado with the 5.3L engine, its all stock except for 07 efans and a dynomax ultraflow muffler in place of the stock one, rest of the exhaust is stock.

I have a set of the pacesetter LT's and ORY here already and waiting to go on, i also bought some universal 3in high flow cats to put in the y-pipe tp make it legal, but now my truck is registered in a county that doesnt do any emmisions testing, only safety, so im thinking of just putting on the ORY as is.

My question is if everything else stays the same, and i drive the same as i do now, will the headers and ORY actually increase MPG or not really affect it? I know if i bury my foot in it its going to get worse, but with gas prices creeping up i dont want to do anything that will really take a hit in the MPG, Im going to hold off on the LS6 cam swap for now because of this.

I want to do the headers and y-pipe and a cold air intake, either the volant with the scoop or the tri power from vararam. and will probably get a tune cause i know i will see better MPG with that.

 

I'm interested in hearing this also.

 

i did headers/ORY and ran it untuned with the rear 02 codes on for almost a year and got 17mpg.

I installed my cam, asp pulley kit, tuned it and im now getting 22mpg still on the clutch fan. I'm lazy and havent made brackets for my efans yet lol.

 

a more efficient pump is going to be more efficient but only if you keep your foot out of it good luck with that!

 

I'm already getting over 20mpg on the highway. I've had a best of 25mpg drafting behind a beertruck going 65-70mph. But I'm only getting mid teens in town.

I'm actually looking at putting on a set of F-body Mac midlength headers with ORY. Supposedly my rear O2s have been deleted already.

 

When I put an audio system in my truck(2006 silverado 5.3-sold two months ago) It gave me the best MPG I ever got because I would mess with the stereo so much and it was so freaking loud that I would keep my foot "OUT OF IT"!!! Always in cruise mode HAHAHA I was pushing 17.5-18mpg in the city and the freeway 21-23mpg Good luck with your mods.....

 

well even with a cam in mine I am slowly getting back to the same MPG I was getting before if and when I can stay out of it. But my best to date has been about 18 HWY driving.

 

Header and tune come will net you some mpg gain...

 

well i don't exactly have town, err city driving...takes me like 3 minutes to go across town if that tells you anything, lol.

 

With a good tune you'll gain 2 to 3 mpg. I did.