K9KUZ

I swapped the exhaust on my 2005 for the NPP dual-mode. I have noticed an apparent drop in mpg by about 2mpg since that time (highway). At highway speeds, the valves are closed .... any ideas?
(mileage is 25K now, was about 20K when exhaust changed)
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other info: A5 trans, convert - always with top up on the highway.

jdwk

Just guessing here, but your exhaust could have leaned out your O2 reading causing the car to add more fuel, but you would have needed to know your LTFT's beforehand to really be certain.

mneblett

When did you install the NPP? Middle of winter (when oxygenated gas wsa in the pumps)? That alone could explain the drop. Or your foot farther in the throttle to hear the new noise

Seriously, the open exhaust drops the backpressure, allowing a bit more HP on top, but otherwise I can't see how it could have no effect on mpg (I'm doubtful about the comment on leaning out -- unlike a huge increase in flow from long tubes, the increase with NPP is relatively insignificant).

1 C6 2NV

Go have the car tuned

Andy 53

I added NPP's on my 2005 and saw no difference in mpg. I did hit the gas a bit more to hear the exhaust every now and then but it wasn't enough to affect the mpg. I didn't think that adding NPP's was enough of a change to need a tune.

Andy

old motorhead

If your decrease is real, you have other issues. The NPP's are more restrictive than stock when closed and slightly less restrictive than stock when open. At crusise or lite throttle driving, you're not flowing enough exhaust gasses for any of that to come into play. I'd bet the stock tune (performance wise) is exactly the same for an NPP equipped car vs a stock muff equipped car.

el es tu

Freeing up sections of exhaust (especially that far down the line) will make the car more efficient.

There is some other factor affecting your mileage.

Walt White Coupe

Just because A follows B doesn't mean A caused B. Look elsewhere.

speedraider

mufflers aren't gonna make no difference, Its all in your heavy azz right foot.

Mike Campbell

I added aftermarket exhaust a year ago and my gas mileage has dropped too! However, I really believe it's more due to the added ethanol to premium gas than it is to the exhaust. In this same period, many of the stations where I gas up have added 10% to the high test.
Take notice next time you fill it up.

hondaamer

I guarantee that because the car sounds so much better with the NPPs you get on it more just to hear it. That alone will drop the mpg as it did on mine when I installed the M2W

K9KUZ

Many thanks for all the replies. It could be the ambient temp/humidity. I am comparing last summer (without the NPP) to this spring (with NPP). Perhaps by the end of this summer I will be able to report a similar situation. Thanks again. JIM.

sampaschal

Hell yes it cuts down on your gas mileage...the sound of those NPPs blasting away doesn't occur unless you stick your foot in the throttle...lets face it ...if we really are concerned with gas mileage...would be driving Corvettes and putting $2000 exhaust systems on our cars. Get real...We like the noise...We love the cars....if we wanted to get more MPGs...we'd have bought a 1.8L 40 mpg Elantra....which, by the way....is my other car. Does this mean I am bi-polar?

sampaschal

The louder the noise....the less mpg...direct corrollary...more noise...requires....what....more gas.