[stang500]

i recently added dual exhaust to my 05 4.0 mustang with magnaflow mufflers and an h-pipe and my gas milage has gone to crap and i have lost a ton of power can anyone tell me why ?

[stlwagon]

Do you still have the catalytic converters on there?

[my07clone]

I put the cat back on and gained fuel economy of 1 to 2 MPG

I have a 5 speed with no other mods. - my mixed MPG is 25.5 t0 26 and 29-30 on hi-way speeds under 80MPH

[BullMeister]

Originally Posted by stang500

i recently added dual exhaust to my 05 4.0 mustang with magnaflow mufflers and an h-pipe and my gas milage has gone to crap and i have lost a ton of power can anyone tell me why ?

We need more info from you to be able to help. Your question is way too generic with no details.

Are they long or short tube headers?
Are the cats still there?
Are there any other mods (tune, CAI, etc) and were they done at the same time?
Did you do the dual install yourself or did a shop do it?
Are the O2 sensors there and installed correctly after the change to duals?
If you read the OBDII codes is there anything listed?
What was your gas mileage before and what is it now?

[mrjimmy]

maybe they sound so cool you are just expressing yourself everywhere you drive...

[pmr2000]

Perhaps an exhaust leak somewhere, I would check the welds and clamps, need a certain amount of backpressure in the system.

Try going up a hill, give it some gas, and listen for strange sounds, hissing, etc..