Would Buying An Aftermarket Exhaust Decrease My Gas Mileage?

[boogiesuperstar]

On my IS350, would an aftermarket exhaust lower my gas mileage or help to increase it. If so, is it better to go with stainless steal or aluminum mandrel bend piping?

[djspawn00]

most likely won't improve anything except for sound... and thats including most top manufacturers...

[BaddBoi70]

You "may" see a slight gain in hp, but nothing very significant. Not sure of the MPG or the metal alloy choice. You may want to contact "Smooth1" for some advice. He is a wealth of knowledge and can probably provide you with some valuable insight.

[IS250_rookie]

well considering that an exhaust is just a pipe for a waste product, it wouldn't matter what kind you have.

[smooth1]

On my IS350, would an aftermarket exhaust lower my gas mileage or help to increase it. If so, is it better to go with stainless steal or aluminum mandrel bend piping?

No, an aftermarket system won't change your fuel mileage. Axle back or cat back systems really only change the sound, and maybe move the torque curve a bit higher in the rev band. The 3-5 hp your going to get equates to about a 1-1.8% hp gain. If you go with a full header system, swap to a true dual exhaust and drop the cats, you can get a much more significant gain there. But for it to effect the fuel mileage by more than 1 mpg you would need to retune the ECU, and on the IS X50 that hasn't been done yet. I know someone who has successfully (so far) been running a piggyback ECU to modify the a/f ratios, but he's still deep in the R&D area to be able to really say yet.

And your going to want stainless steel. Specifically T304 which is the most popular type of stainless to use. It's inexpensive, high heat resistance, and high resistance to corrosion. Aluminized steel is an alternative, but the coating is compromised where the welds and flanges are, so they don't last as long.

I do want to mention though, that a cat back or axle back exhaust system can have a third party effect on fuel mileage in that, I know because I like to hear that exhaust rumble hard when I accelerate, that I tend to drive the car differently, and that has effected my fuel mileage......