Catback and decreased MPG?

Anyone here have a catback exhaust installed? Have you noticed a decrease or even increase in MPG? I've normally gotten less on my Accord and S10 when I did it. My dad's Turbo Diesel Truck gets better MPG with the Turbo Back Exhaust, it's also 4" piping.

Wild Hare

2015 Golf R (TUNED)
I did on my Audi A4 1.8t not too long ago...

Never saw I decrease or increase in MPG. Stayed the same.

I did see a 2 MPG increase once I chipped it... the car idled better and was easier to drive (less hesitation).

alf said:
more air flow = more gas mileage, just dont get too happy with it.
I figured it was kinda the opposite. More air flow, less MPG because the A/F Ratio has to adjust and will increase the Fuel to compensate.


FIA World Rally Car Newbie
dallas, tx
i don't know what this whole "gas" thing is you guy's keep refering to? ive always filled my cars with love.


Houston, TX
2006 TR GTI
TeknoGroover said:
I figured it was kinda the opposite. More air flow, less MPG because the A/F Ratio has to adjust and will increase the Fuel to compensate.
iono, i always heard that it was better. urs sounds more feasable though.

i heard that the restrictiveness always messed with the engines ability to breathe correctly, smoothly. also butt=tests kinda came out to my favor when i replaced the intake and exhaust on previous cars.



Rally Car Champion
changing the exaust voids your warranty.

sometimes too much flow will acually decrease the horsepower. Usually open or unresricted is used at the dragstrip when the rpms is going to stay at redline. Alot of exaust companys claim gains that arent true.

not sure on this, but catback means replacing the system from the cat converter back. Its not a performance thing. Seen many motorcycles with so called performance exaust acually lose power over the stock system. The amount that you do gain is not worth the price they are charging for these systems. If you just want the noise , remove the resignator and replace with a nice custom bent tailpipe and put your stock tips back on the end of it. You will get the loud sound your looking for. for hundreds less. If your not modifiing the air intake system, turbo, and computer, your not going to gain anything much other than noise and less gas mileage. THIS DOES VOID YOUR WARRANTY ACCOURDING TO MY VW DEALER!!! (any mod)
tydale3 said:
changing the exaust voids your warranty.
I've changed the exhaust on all my cars, under warranty, and still got service under warranty. Dunno about VW though. They were telling me about chipping my car too, and supposedly voids your warranty too, but they still suggested it. Also, that's why you keep the OEM exhaust in case something does happen.
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FIA GT Champion
It can't void the warranty if you replace parts on your car. The Magnusen Moss act (?? spelling) prevents them from doing that. Your exhaust doesn't last forever. Plus if that was the case anytime you changed the wiper blades that would void the warranty. They are blowing smoke up your arse. They, not you, actually have to prove that whatever you put on your car voided the warranty. Just because you swap out your suspension doesn't explain why you just threw a rod with only 400 miles on the car. Or, because you put on new exhaust your sunroof no longer closes.....


Drag Race Newbie
Audi S5
it voids the warrenty on the exhaust if you put an aftermarket exhaust on your car. Also federal law protects you and the dealer will have to prove that any malfunction is related to the mod. so they can say they wont fix the A/C or power stearing because you put an intake or exhaust on. unless it some how did mess it up but that would be unlikely