xpimpitox

Flowmasters claim their catbacks and mufflers will make for better gas mileage? how much gas mileage gain do you get from hooking up thier stuff to your car? I wanna know since in a few short weeks my roc will have its American Thunder put on. Thanx

black89ws6

i don't have any hard data, but my guess would be something like .1 or .2 mpg highway. Don't let that discourage you from getting that exhaust tho. I hear the american thunder sound pretty bad (er...good...er, you know what I mean).

The catch with exhaust is, if your driving it for mileage, you're giving it 25% throttle or less, 90% of the time. While the stock exhaust may be too restrictive at WOT, at 25%OT, it's just not overloaded yet.

85TPI400

Most exhaust companys claim better mileage with cat back systems and/or headers. This is an interesting subject and I would also like to hear if anyone noticed any differences.
Tony

Mark A Shields

It makes sense, a better flowing exhaust puts less strain on an engine meaning it doesn't have to work as hard, thus better mpg. But I wouldn't bet on it helping a whole lot, unless you have a clogged system now.

xpimpitox

Thanx for the replies. I was just curious since I have a lil over 100 mile road trips frequently to visit my girl and well u know how gas is now

86BirdSE

My Dynomax 2.5 system cat-back has given me on average about 2 more miles/gallon. I also gave the car a good carb scrubbing and tune up and oil change since the cat-back, which added another 2-3 mpg. I've got a stack of pay-at-the-pump slips, and I've been putting all of the data into an Excel Spreadsheet to chart any kinds of obvious dips in the data.

If I don't get too crazy with it, it consistenly gets 20-22 MPG, and about 17-20 if I do more "spirited" driving. I'm considering removing the cat convertor and headders when I swap in a 350 this summer and 3.23 gears out back. The she'll be a totally different monster.

But I'm rambling. With the 2.73 rear and AOD, it's not bad as far as mileage goes, and I did see an improvement over the rusting stock-replacement system.

90v6rs

how do you know if your system is clogged?

would exhaust have anything to do with my car stalling?

black89ws6

Mostly, a noticeable loss of power, especially in the upper rpm range. I don't mean loss of power like a few tenths off the quarter mile, I mean like, getting half way down the quarter mile, and wondering if you'll even make it to the end.

you can measure your exhaust backpressure to see it it's plugged. you unscrew one of your AIR tubes, and put a pressure gauge on it. Then rev it good and hard a few times (all the way to redline). It should never go above a few psi with crappy stock exhaust. With decent aftermarket, probably never much over 2 psi.

90v6rs

would driving with bad piston rings cause the exaust to clog?