Just installed (made) a 2 1/4" cat back system and so far so good. I used a Hedman pack which definitely increases the noise level (wife says it reminds her of her old Cobra) but it is not unbearable.
So far I have noticed an increase in mpg's even though I am running at higher speeds. I use to run 62-68ish mph and struggled maintain 49-52mpg now at 70-75ish mph and not paying any attention to the real time guage I have no trouble keeping 52-55mpg. If I can just pay attention to my speed I can compile some useful data for folks interested, this afternoon I am going to try and control myself .

Clif

 

Clif,I'm not taking a shot at you;I'm a big fan of modifying vehicles.Heck,I pulled the backseat out of my Titan so my dogs would have more room,and I'm leaving it out to increase the mpg(it weighs-80-100 lbs).
My question-Why would improving the exhaust improve part throttle mpg?
It should-might improve peak hp-but shouldn't have any effect on mpg-unless it is lighter.There just isn't much "backpressure" at part throttle,so it really doesn't take much force to evacuate a cyl.I always figured that it could only increase mpg a tiny amount,and the improvement would be lost by the aftermarket exhausts loss of OEM tuning effect at low RPMS?The OEM setup might even push the spent charge into a relative vacuum-and the aftermarket into pos pressure?Your numbers show a 6% improvement with increased speed?
Not taking a shot at you,but I have never had any luck improving my MPG with performance mods.Weigh loss,wheel weight loss ,seal loss(ha,ha)have given me small improvements,but never exhaust or intake mods.Drivings mods,of course,give bigger improvements.Let me know why it works?Thanks.Charlie

 

Well those are some deep questions and I am by no means the answer man, what I can tell you is I have less than 200 miles (just at) and so far I have seen an improvement.

My research started with air, I live in 'hill country" so the car seems to be moving backward more than forward in addition to that the road designers here put stop lights at the bottom of every up hill climb. Long story short I would lose 7mph climbing one particular hill everyday on the way home. I made/modified my air box and the same hill only hit me for 2mpg worst case day never above. Then I started reading about how to improve MPG (onthis site) by driving a lot tamer and sure enough I went from mid 40's to over 50 for the past few tanks. Unfortunately my inability to never leave things alone caused me to research exhaust and for the civic hybrid I could find nothing. I did however find a guy name jackmpg on the insight board who is a lot like me, he first did exhaust and got a 5-8mpg increase then built a turbo. I have no plans ( at least not soon ) on making a turbo but had to try the exhaust so after several e-mail back and forth I tried it.
I cannot explain the exact whys but so far so good.
Clif

 

Thanks.Keep us posted,I'm always curious about add ons that increase mpg.Thanks.Charlie

 

I live in Austin. I'd be glad to meet you for a beer (or two on me) and find out how to modify my HCH to attain a few more mileage points.

 

Will do. BTW this morning mpg's increased from the norm (50ish norm 56 today) same as yesterday evening (52ish norm 59 yesterday). I realize there are a lot of factors that play in but I am letting you know what I am seeing so far.
Clif

doppler
That would be cool, I drove with one other HCH 5spd out to Lago Vista and **** near ran him down on all the uphills. I'd be curious to run another or get the opinion of another driver who's car is stock. How many miles do you have and what is your avg mpg?
Clif

 

Duc,

Is there an exhaust setup you're aware of that may increase FE but not the noise? I have this thing about loud exhausts, or even modest ones. I won't go into the rant here, but would be curious if there were systems that would increase performance but not noise.

 

OK, I have no idea what this mod consists of, but am interested because it sounds cool. Would anyone care to explain what this is and what is involved to a layman? Thanks

 

I would think you could look into a quite one for a V8 and use it on our car, thing is you don't want to restrict it. I could only suggest experimenting but that cost money if you don't know/have the equipment. I didn't want the additional noise either but it was the only thing I owned that was quite so dealing with it is not a bid deal for me. I wouldn't call it loud but I will def say it is louder.
Clif

 

The short of it is the civic has between a 1 - 1 1/4" id stock exhaust with a muffler and a resonator, the thought is it restricts the exhaust flow. There are tons of articles good/bad toward this discussion and I have tried/made various exhaust for motorcycles to prove these good/bad theory's. Removing the restrictions and allowing the gases to escape easier in effect increases FE by allowing to car to breath better same as giving it more air. It is a cheap mod if you have tools/no someone and easily reversible if you do it right, I luckily found someone who had tried lots before he decided on the one that worked best and used his setup.
OK the actual short answer is you remove you exhaust (cat back) and replace it with bigger pipe and a glass pack.
Clif