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Old 12-12-2012, 07:10 PM   #11 (permalink)
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I found a stock exhaust and put it on. Then I heard the exhaust leak I had missed. So on monday as I drove around the car actually felt really weak. It struggles to get up hills and no improvement on mpg's, maybe a little less if anything. I'm guessing it because of the leak. On tuesday I put the 2.25" exhaust back on and the car is back to running normal. I did notice that if I use 89 octane instead of 87 the fuel economy goes up from 31mpg to 33mpg. I know the EX motors have a slight increase in compression. So has anybody else experienced this or any ideas on whats going on

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Old 12-12-2012, 08:52 PM   #12 (permalink)
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The second oxygen sensor has nothing to do with your mileage. It just checks to see if the first one is doing it's job properly. Big wheels, lower final drive ratio, larger exhaust will all cost you mileage. So will your driving habits and your driving environment.

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Old 12-12-2012, 11:30 PM   #13 (permalink)
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Black and Green - '98 Honda Civic DX Coupe
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Quote:
Originally Posted by chito View Post
I found a stock exhaust and put it on. Then I heard the exhaust leak I had missed. So on monday as I drove around the car actually felt really weak. It struggles to get up hills and no improvement on mpg's, maybe a little less if anything. I'm guessing it because of the leak. On tuesday I put the 2.25" exhaust back on and the car is back to running normal. I did notice that if I use 89 octane instead of 87 the fuel economy goes up from 31mpg to 33mpg. I know the EX motors have a slight increase in compression. So has anybody else experienced this or any ideas on whats going on
Not sure I agree with Old Mech about taller tires necessarily costing in FE, since Sentra-SER seemed to find somewhat different in this pretty thorough test: Tall tire test (taller gearing advantage offset by wider, heavier wheels/tires?)

As for the differences in mileage you describe driving around, I think you have to consider something else Old Mech said: that driving style (and conditions) will affect FE significantly. I would keep the stock exhaust on the car... that's "normal." The EX is only rated for like 127 HP, so it's not surprising it feels slower than what you might be used to. My DX in 106 HP, and it does scale hills a little slowly. But it does all it needs to do and then some.
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See my MODDING THREAD for ongoing projects. Black and Green's garage entry has more details. I plan to DIY rebuild this car over decades as parts die--replacing or modding small and major parts until it becomes a different car of roughly the same shape. My fuel economy goal is 60+ mpg while averaging posted speed limits.
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Old 12-12-2012, 11:48 PM   #14 (permalink)
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The large primaries on the dc header are hurting your low end torque. Couple that with a small exhaust and you have a recipe for abysmal economy. The stock manifold is where the economy is to be had. The exhaust after the cat converter isn't of any importance as far as economy is concerned.

I've also found that mid grade fuel and 1 to 2 degrees of advanced timing can help torque under 3k rpms, where it's most beneficial when trying to hypermile.

With narrow tires at sidewall max, proper shifting, and optimum engine tuning it should be easy to crest the 38mpg mixed driving mark.

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