Does reducing backflow decrease gas mileage?
Thread Starter
Drifting
Joined: Apr 2007
Posts: 1,619
Likes: 4
From: Houston TX
Does reducing backflow decrease gas mileage?
I have a C6 Corvette and have recently upgraded my exhaust to the Dual Mode Cat Back Z06 modded exhaust (and keep it on open mode all of the time)and have noted a slight decrease in my instant/average fuel economy...
Is this because the gurgling it does on deceleration cause the car to spit out unburned fuel?
Or is it because back pressure is required to pick the car up on lower gears? (Low end torque)
I have no idea... Wondering if anyone else has this issue...
I hope this does not hit the wallet hard... I was anticipating having improved gas mileage...
Is this because the gurgling it does on deceleration cause the car to spit out unburned fuel?
Or is it because back pressure is required to pick the car up on lower gears? (Low end torque)
I have no idea... Wondering if anyone else has this issue...
I hope this does not hit the wallet hard... I was anticipating having improved gas mileage...
Le Mans Master
Joined: Oct 2001
Posts: 6,798
Likes: 25
From: Pine Bluff Arkansas
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16-'17-'18-‘19-'20-'21
There's a certain tuner that says, the Z06 runs better without the M/W opened at low speeds. Of course, he has all the data to back it up, although it all looks like 'greek' to me. In my paticular instance I did not loose any MPG, but I didn't gain any either, which I figured I would with less back pressure. The new cars are just not that simple, I guess.
I read where guys have gotten better MPG, but it didn't happen with me....just a lot drone.
Larry
I read where guys have gotten better MPG, but it didn't happen with me....just a lot drone.
Larry
Drifting
Joined: Oct 2007
Posts: 1,565
Likes: 2
From: The Great Pacific Northwest...........I carry a gun cause a cops too heavy.
I have the same setup and haven't noticed any difference in milage As far as back pressure is concerned your cats maintain sufficient pressure.
Le Mans Master
Joined: Sep 2008
Posts: 8,022
Likes: 8
From: Stafford VA, home of our wolf den. No house break ins to date.
There's a certain tuner that says, the Z06 runs better without the M/W opened at low speeds. Of course, he has all the data to back it up, although it all looks like 'greek' to me. In my paticular instance I did not loose any MPG, but I didn't gain any either, which I figured I would with less back pressure. The new cars are just not that simple, I guess.
I read where guys have gotten better MPG, but it didn't happen with me....just a lot drone.
Larry
I read where guys have gotten better MPG, but it didn't happen with me....just a lot drone.
Larry
Le Mans Master
Joined: Oct 2001
Posts: 6,798
Likes: 25
From: Pine Bluff Arkansas
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16-'17-'18-‘19-'20-'21
Yeah....I do not know if the tuner used the word Z06 or not. I put that in there maybe by mistake. Just what came to my mind. The tuner was talking about the opening the flaps on the exhaust, I just assumed it was a Z06. Might be different numbers with the 436 hp, tho.
Edit: I checked....he was using a Z06.
Larry
Edit: I checked....he was using a Z06.
Larry
Last edited by lebvette; May 20, 2010 at 08:37 PM.
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Burning Brakes
Joined: Mar 2010
Posts: 1,019
Likes: 2
From: Woodland Hills Utah
To answer your question, yes you do need back pressure in your exhaust system to obtain optimum performance, both horsepower and gas mileage. That's why an "X" pipe is so important to have in the system. The back pressure helps scavenge the exhaust gases out of the heads and exhaust manifold. I don't know enough about your system to know if this is the issue with your case. Did you change the "X" pipe also or just the mufflers? Is the exhaust pipe diameter bigger with the Z06 system than the C6? Several issues could be at play and as Robsl6 stated; "You're probably just in the throttle more cause it sounds so good!"
CF Senior Member
Joined: Feb 2006
Posts: 23,313
Likes: 25
From: Tucson Arizona
I don't have a definite answer but I can't imagine the difference in fuel economy would be much, if any. Perhaps being left open 24/7 (with less restriction) you're running with slightly increased power and using a bit more fuel in the process. I'm not making light of your concern but you're driving a Corvette...fuel economy should be the least of your worries. 
I'm just spit-ballin' here but I don't quite understand buying a mechanically complex dual mode exhaust, adding a special switch controller and then only using it in a single mode. Aren't you missing the benefit of having a dual mode exhaust? If you just wanted a freer-flowing, better sounding exhaust wouldn't a conventional (single mode), after market exhaust served your purposes better?
I'm just spit-ballin' here but I don't quite understand buying a mechanically complex dual mode exhaust, adding a special switch controller and then only using it in a single mode. Aren't you missing the benefit of having a dual mode exhaust? If you just wanted a freer-flowing, better sounding exhaust wouldn't a conventional (single mode), after market exhaust served your purposes better?
Thread Starter
Drifting
Joined: Apr 2007
Posts: 1,619
Likes: 4
From: Houston TX
I'm runnign it in single mode for now, Waiting on Benjamin Stanley to send me his "exhaust Commander", but I will tell you, after posting the topic I went outside and removed my battery cable... waited about 3 min. and put it back on...All of a sudden my Instant Fuel Economy readings are the same as when I had my stock exhaust. No more rich burning engine.
My assumption is that the O2 sensors needed to be "reset"
This is ONLY a catback system. Everything else is stock including cats and H pipe.
My assumption is that the O2 sensors needed to be "reset"
This is ONLY a catback system. Everything else is stock including cats and H pipe.
Burning Brakes
Joined: Feb 2010
Posts: 1,051
Likes: 8
From: Clearwater Florida
Normally the more free flowing the exhaust the better the efficiency and fuel mileage. I probably use more gas because I love to listen to the music from the exhaust. I really like the subtle popping as the engine backs-off.
The big pipe syndrome can be overdone. An overly large diameter exhaust does a poor job of scavenging the exhaust compared to an appropriately sized pipe. Secret is finding the correct size.
The big pipe syndrome can be overdone. An overly large diameter exhaust does a poor job of scavenging the exhaust compared to an appropriately sized pipe. Secret is finding the correct size.
