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      08-08-2006, 12:07 PM   #44
ksfrogman
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Drives: E90 330i 6MT
Join Date: Nov 2005
Location: Torrance, CA


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the price of power

Just to give an update...

Questions have popped up on intake threads regarding gas mileage. I noticed that on average, my city gas consumption decreased from around 19 to 18 mpg (computer figure). Spirited driving decreased my mpg to around 17 (note: I had never seen my gas mileage dip below 19 prior to this), and after a friend of mine test drove the car aggressively,my car displayed 13.2 mpg on the comp. By the way, I did reset the gas mileage computer before testing.

A synopsis of the dyno showed a max wheel HP increase of 5.5 HP at around 6660 rpm. Torque at that rpm increased 6.64 ft-lbs, but was even greater at around 2850 rpm (approx 8 ft-lbs)--the rpm the engine noise seems to be much more noticeably loud. Both HP and torque after the mod increased throughout the rpm band, and regardless of what anyone cares to say about butt dynos, I trust my seat-of-the-pants impression that this car is more responsive.

Over the past week or so, I have been monitoring my gas consumption relative to driving habits. I consistently achieved 20.1 mpg city in South Bay stop-in-go traffic by driving very conservatively, and not exceeding 2500 rpm before shifting. I would cruise in neutral while stopping, mild-to-moderately accelerate to cruising speed, and avoid temptation to aggressively pass anyone unless my speed from momentum allowed this.

In short, this intake is "sucking in" more air and gas, but proportional to the OEM intake (see dyno), which translates into more power and torque at the expense of gas mileage. If you drive aggressively, you'll pay in the form of poor gas mileage. From what I can see, if you drive conservatively, you can achieve practically stock-like gas mileage figures.

The physics behind the gas consumption is similar to modding a normally aspirated engine with a 2-barrel carb with a 4-barrel one.
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