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Ive heard of some engine and exhaust modifications that will decrease your mpg like for example, i read on the forums that a straight pipe axle back or muffler delete will decrease mpg due to lack of back pressure, but what are the engine mods that will increase mpg?
 

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i thought that tpms light will go off if the tire pressure is too far from recommended psi whether its too much air or too little. i drive in a lot of traffic and ive been getting 34 mpg average with a high of 36. is that normal
 

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i have a 6 speed manual btw, and the 34-36mpg included one night of no traffic where i cruised at 70mph in econ. but man everyday its traffic. before the hour long drive i was at like 33 mpg
 

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Basically engine loads and intake temps effect mpg. Gasoline types too effect mpg due to density and BTUs. More air in requires more fuel and needs a bigger exhaust but having a oversize exhaust pipe will hurt mpg and power. Back pressure is needed for the EGR system to work efficient but the EGR also reduces power due to leaner mixtures.
 

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I'd actually written a reply in a different thread roughly covering the same things, so I will paste it here rather than rewriting it.

I've got a K&N Typhoon and also a P2R downpipe (no aftermarket exhaust yet, but soon) and I've seen a pretty major change to be honest. The K&N gave me an extra couple of MPG's and pushed me up to 40MPG at average crusing speeds (Averaged 43.5 MPG on a run to Penn from NYC)

The P2R turned it into a monster, now during a normal run the MPG meter hovers between 45 and 55 mpg under highway conditions, car runs better and under heavy acceleration there is at least 1 more block of MPG present at all times (had 2 blocks in the bar when I had the Typhoon and the stock pipe, now it's between 3 and 4 blocks with the P2R).

Hope that helps a little bit
 

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ethanol, sure affects mpg.....
 

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The single most important thing that changes the Z's MPGs is the driver. I'm not trying to be coy either. With no modifications (or training), running stock tire pressure I've managed to pull 51mpg out of an entire tank. Others on this forum have done even better. The only single mod I know of that could create that kind of mileage gain is a horse and tackle attached to the front bumper.

Past that anything you can do to reduce drag or weight will have some benefit. But it will pale in comparison to what you can do simply by being careful.
 

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mpg verses hill and traffic

I'm getting an average of 42mpg and no matter how careful I am thats going to be it with an 18 mile comute to work with a lot of hills to contend with and nose to tail traffic on the journey home the best one way was 47 mpg but the return traffic was so bad this was back to 42 time I got home
 

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Something that I didn't realize until rather late on is that MPGs aren't a very good way to measure fuel economy. Gallons per mile makes for a better comparison.

With MPGs, you get the impression that an increase from 40 mpg to 50 mpg is just as good as from 30 mpg to 40 mpg, but this is not even close to true.

At higher MPGs, each additional mile per gallon is less significant. The difference between 48 and 40 mpg for a 25 mile drive is about $0.29. Between 28 and 20 is $1.25.

My point is that pinching for MPGs once you get into the 40s may not be worth too much effort.
 

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With MPGs, you get the impression that an increase from 40 mpg to 50 mpg is just as good as from 30 mpg to 40 mpg, but this is not even close to true.

At higher MPGs, each additional mile per gallon is less significant. The difference between 48 and 40 mpg for a 25 mile drive is about $0.29. Between 28 and 20 is $1.25.

My point is that pinching for MPGs once you get into the 40s may not be worth too much effort.
Calculating the difference in MPG for a 25 mile trip is rather pointless.

Also whenever you share calculations, include the price-per-gallon figure that you are using in your calculations.

Stretch the the 48/40mpg comparison out over 25,000 miles (at $4 a gallon), and the difference between 40mpg, and 48mpg, is about $500. Over the course of 100,000 miles, the 48mpg-er will save $2,000, over the 40mpg-er, driving the same exact mileage.

Or to put it another way, if both drivers spend the same exact amount on gas, the driver getting 48mpg can go an additional 5,040 miles, for the same cost as the driver getting 40mpg.

The comparison only gets better as the gas prices increase. The days of $2.50 a gallon will never ever return.
 

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Calculating the difference in MPG for a 25 mile trip is rather pointless.

Also whenever you share calculations, include the price-per-gallon figure that you are using in your calculations.

Stretch the the 48/40mpg comparison out over 25,000 miles (at $4 a gallon), and the difference between 40mpg, and 48mpg, is about $500. Over the course of 100,000 miles, the 48mpg-er will save $2,000, over the 40mpg-er, driving the same exact mileage.

Or to put it another way, if both drivers spend the same exact amount on gas, the driver getting 48mpg can go an additional 5,040 miles, for the same cost as the driver getting 40mpg.

The comparison only gets better as the gas prices increase. The days of $2.50 a gallon will never ever return.
Good point for the gas price. $3.50 was the figure I used, I believe, but it was only $3.25 to fill my car this morning. I also believe your gas savings calculation is probably mistaken. For 25,000 miles, you're talking about between $290 and $380 savings depending on gas price.

And that really isn't a lot of money in my opinion, for something spread over two years. And again, we're talking about a quarter per commute.

My real point, however, was that using mpgs to compare mileages is not as useful as using gpm. As i showed, the difference in mpgs in the two comparisons was the same (eight mpgs), but the difference in actual efficiency was five times greater for the comparison in the twenties! MPGs distorted the comparison by 500%! That was what I was getting at.

Also, keep in mind how much more expensive a Prius is to a CR-Z. Sure, you gain several mpgs, but due to the way mpgs scale out, it's not actually a substantial difference, especially given the price of a Prius.

Now, we all have to govern our wallets to our own best judgment, so fifty cents may be worth it to alter your driving habits enough to yield a few mpgs. For me, it isn't, but there are people who just enjoy hypermiling for its own sake. One thing that is cool about the CR-Z is that you can actually change the mode of the car to suit your attitude on that issue.

I am unsure if we'll have $2.50 gas again. It depends on too many factors. If one day they develop the technology to turn shale into gas efficiently instead of with tons of water, we'll probably see gasoline get much cheaper. But that's a complicated issue. I don't care about gas price very much anymore thanks to driving a pretty efficient car. Life's too short, ya know?
 

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Very valid points. Thanks for the info on the price you were going off of. And yeah, the difference between the two twenty-mpg comparisons is a lot more significant than the two forty-mpg comparisons, but in this economy every little bit helps. Having a car this efficient does take some worry about gas prices out of one's mind though, life is too short you said it.

And I agree completely about enjoying the vehicle, and driving it without as much care for the instantaneous-mpg every so often. :thumbup: It does have a sport-mode button after all.
 
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