Ok i just installed this headers on my Mustang Gt and and my mpg drom big time from 19 city to 16 city does this sound right plus i have off road x pipe borla cats jlt intake sct x3 tunner now do i need to change the setting on the car with tune please let me know also i feel like i lost power should had gone better with 1 5/8 LT instead?

 

Hmm...I think I did drop down a few mpg after installing my headers. Did you weld the connections, or are they just bolted up? May want to weld if you haven't. It took me a while go get adjusted to the headers, as at first I thought I lost power. Turns out, I gained it throughout different ranges, and once I figured out where they were at, I can fill a huge difference. You can always get it dyno'd to make sure everythings ok.

 

i bet its just your right foot that got heavier.
with each mod i've done, no matter if in theory its supposed to get better mpgs, my right foot got heavier and heavier loving the new found power, and my mpgs as a result got worse, but the smile on my face got bigger.

 

lol! nice but really i been driving my car normal no speeding i been driving like a old man lol! and my mpg went up to 16.8 but do u have to tune the car with my sct x3 tunner some told to change the setting on the fuel ration is that right?

 

Did u also went with mac headers 1 3/4 whats ur mpg and also told to buy a trottle body spacer that would help out

 

You need to have those LT headers tuned. Is there a dyno shop near you? If not, call whoever programmed your SCT and tell them what you've got going on. I still wouldn't expect a massive gain, on a dyno or seat of the pants, from the LTs.

 

My next plan is up grading my gears to 3.73 every tells me i should feel difference and also its my daily driver car so 4.10 would be to much and hurt my mpg more than i did lol! but ok i will call evolution performance that's where i bought my kitt

 

Unless your getting a CEL, there should really be no reason to retune. I'm running Boost Brother headers. I was getting CEL all the time until I had Doug at Bama write me a new tune as the revised brenspeed tunes never got rid of the CEL. Your tune you have now should already have the rear O2's off. Again, if your not getting a CEL, no need to retune. Unless you like throwing money away, don't get a throttle body spacer. If you do, it would work better as a paper weight vs a performance part.

 

You shoudn't have to tune for headers except if you get the O2 heater DTC (P0155) which is just because the front O2 sensors are further back and dont heat as fast.
Never waste money on a throttle body spacer it does NOTHING at all.
Also you cant change your tune with a handheld. You can only minor tweak spark and fuel ratio. When I installed my 1 3/4" Kooks my air-fuel was the same before and after the install. I doubt yours changed. Remember you mass air sensor adjusts the fuel ratio as needed so if their was a slight change it will adjust.

 

You can do much more than that with a handheld. I made huge gains from a a custom tune using an SCT X3.