Rep Power: 276

has it ever been proven on the d17 powerplant that it can/will achieve better mpg by having an "aftermarket" exhaust setup (header all the way to muffler)?

i have an test pipe with an apexi exhaust (and short ram intake), but i feel like i have been only reducing my mpg after reading the "post your mpg" thread whereas everyone is getting up to 400miles on a tank on highway when im only getting 320

few buddies said an intake can/will reduce overall mpg

 
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i've proven it. i had my greddy evo exhaust on my car for a long trip down to cali from WA state. i usually fill up twice.. each time around alil less the 1/2 tank...but when i switched to my stock exhaust on the way back i had to fill up four times..each time at around 1/4 tank.

 
Rep Power: 287

well actually to tell you the truth, the more performance(if you cann bolt ons performance on our d17's)you get from a motor, the less gas mileage it gets. period. how else do you think your motors making that power? the battery?

 
Rep Power: 276

i understand that concept makes sense for the air intake (IE: taking an oversized straw and sucking air through the bigger pipe = more "energy" needed/used).

but does it apply to the exhaust? does the motor/car require any "power" source to exhale the nitrogen/oxygen/etc?

 
Rep Power: 362

you can get better mpg from reducing the weight of your car ... making it more aerodynamic ... and reducing the rim/tire weight as well as reducing rim size

 
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i always thought getting an exhaust takes away more gas.

 
Rep Power: 811

well the thing is all the other stock piping is alot bigger. so getting an aftermarket catback makes the pipes match up better. who knows. usually the stock exhaust restricts power after 5k rpms, but below that it doesn't matter.

 
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Umm. i dunno. Making it easier for the car to get fresh air into the motor and exhaust out, should improve your MPG. think about it. You have to much back pressure on your motor, and only 70% of the exhaust is actually pushed out of the motor. This means on the next power cycle you only have 70% of the chamber filled with burnable air. meaning that 30% of the fuel you pump into the cylinder doesn't burn and gets pushed out of the cylinder during exhuast stroke. This means you have to press the gas down harder sending more air and fuel into the motor for the same amount of power, compared to an aftermarket intake and exhaust. now 75% of the exhaust makes it out. this means that only 25 percent of the air in the next power stroke is unburnable. Then add to it that your getting 10% more air then you use too with the stock airbox. also increasing the total amount of fuel you burn in the stroke.
although numbers are way off, the idea remains the same. AS long as you don't increase the amount of fuel your Injectors are pumping out, then your MPG should increase.
Now your computer can sence the increased airflow and in return increase fuel, but i don't this would be a problem unless your really jumping on the gas all the time.

This is just my thoughts on the subject.

I could be crazy

 
Rep Power: 370

You're forgetting air/fuel ratio. The more air coming in... the more fuel has to be added inorder to produce the proper mixture.