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I get avg 31 city/hwy with the a/c on. 98 Civic coupe, auto. I have heard that a K&N air filter, platinum plugs, and 2" exhaust all the way out will help mileage. My car has a 2" through the cat and a round muffler, back to about the Right Rear wheel - where it has a bolted flange down to a 1 1/2" pipe and a second muffler. Why is this? Would I be better off to get rid of the 1 1/2" and the second muffler and go with 2" and a resonator tip? I don't want the thing loud at all but a low mellow sound would be ok if I got 4 or 5 more mpg... And if so - do they sell the pipe and resonator tip that would just bolt on to that flange?

 
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The mpg gains won't balance out with your purchase. In theory, you should see a gain, but come on. Are you seriously gonna drive less aggressively with those on there? Think about it.

 
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calls himself racing fan and asks about mileage and open exhaust... TROLL! definitely...

 
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Sorry I asked. Been a member of several forums for many years and never been called a troll for asking a simple question. I have a Nova that will smoke most of your Civics - and I know how to make it run. Not so much experience with 4 cylinders and foreign cars though. Guess I don't need to be a member of this forum anymore...

 
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Ah. Don't worry about sdai. . We get a few trolls now and then who ask along the same lines of questions. So he probably was going off of something we ran into in the past. Like I was saying, you won't see any noticeable gains from those add ons. My car had iridium plugs and I didn't see any gain. Same with my intake. If you want better gas mileage, keep your car tuned up, tires inflated properly. Most importantly, don't go all Paul Walker on the throttle .

Having accessories constantly running robs the car of available power, which can take away a little HP and could cause a little dip in MPG. A/C on the highway has proved to be better than driving with your windows down because you're causing too much drag with the windows open. You'll notice your fuel economy drop in the winter because of the blend of the gas. That's all I can really give you. I've tried many of those techniques and I can get 40mpg combined if I really try hard enough. I guess it comes down to discipline in the end.

 
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Thanks MelJ! I guess 31 combo city/hwy isn't that bad. I pretty much baby the car - don't know when or if the timing belt was ever changed and it has 175k miles on it. Don't have the $ to have it done right now. I try to keep it under 4000 rpms always. I do run 70-75 mph on the highway though - so I know I lose a little there... I always run with the a/c on. Can't stand windows open...

 
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best trick - when you are on a downhill, take the foot off the pedal, do not put in neutral. idling uses more fuel than coasting in hondas - they cut the fuel completely when close throttle/downhill.
Exhaust will not help, especially if city driving - it will rob precious low end torque. very low power engines after all - need to understand momentum car driving - "do not lose momentum - keep it moving" - i don't brake in most corners, no need for light/low power cars anyway.

Calling troll was beacuse of combination of "race" in username+asking about exhaust but wants better gas mileage when doing 31MPG (which is pretty darned good )

 
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I try to drive it pretty conservatively except for the highway speed. You aren't kidding about the power - shoot I can feel the car slow when the A/C compressor kicks on. I would like a little more "Git" from the stoplights - but since I probably keep it below the powerband anyway - that may be the issue with that. I have heard guys talk about getting close to 40 mpg with a 2" exhaust and K&N. That is why I was asking - sometimes the better you make something run (more power or "flowthrough") - the better the mpg is as a result. I have had this on other vehicles I've owned - but those were all V-8's. My Nova gets 5mpg. But it is a Big Block and supposed to go fast - not worried about MPG with it! 750 Holley Double Pumper will do that...

 
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Oh, yeah, but the vics have a pretty well "finished" design engine (the D17/D16, i mean, not the B or K types).
They are very hard to get more power with bolt-ons, pretty famous at that, actually.
and as said, the low power makes exhaust/intake changes loose power in the lower range (they higher rev designed - not screaming high, but high - mine EX type with the VTEC-E (economy) is at 3200 RPM at 70 MPH and still gets me at 27 city/HWY. Now testing the mileage with the new crower cam, though - seems to get pretty close to 30MPG so far?

 
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Mine is about 3000 at 70. Best mpg to date on a tank was 32.7. I drive about 50 miles a day - 2/3 freeway and 1/3 suburban roads. Avg mpg has been about 31. I have never had it out of town on a longer trip - so don't know what it gets on that...

 
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Lol. 70@ 3k. Sounds about right . Your mpg isn't too bad though. Anything below 30 I would start being a little concerned.