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      02-25-2012, 10:00 AM   #49

Drives: 2006 325i Sport
Join Date: Jun 2006
Location: Virginia

iTrader: (0)

Originally Posted by mlifxs View Post
fyi yes hwy mileage. Prior to install I took the time to measure mpg on a specific roadway, cruise control on, air conditioner off. Reset the computer at at a marker on the roadway and noted average mpg at the end point. Did this several times.
Did the same shortly after install. Same conditions. Ambient air temp was very close before and after as was wind speed and direction.

I did the same for my AA tune, measuring before and after.

I don't know if your assertion about the manufacturer is necessarily true. Perhaps it's true in this case (I really don't know, I'm simply passing on my personal experience about a product), but manufacturers do not always optimize performance; sometimes they compromise to meet the preferences of many people in different markets.
Well although you tried to keep the test conditions the same, your increase in MPG is not a result of a true scientific test. You cannot exactly duplicate the engine load and % throttle position on every test run. I’m not saying you are being dishonest about it, I’m just saying you don’t have enough data to absolutely state the filter improves gas mileage.

It's been my experience after keeping strict MPG records for all my cars for the past 20 years or so, that the average MPG per tank varies by more than 1.5 MPG. When I fill my E90 up at the same gas station and same fuel pump (every two days) and then drive unobstructed on a rural 55 MPH highway (not an interstate), my MPG reading from the BC (after resetting it to zero upon fill up before I restart the engine) starts out low, then slowly climbs to over 34 MPG then backs down to around 28 (using numbers just for example). So resetting the BC to get a MPG reading is not an accurate measurement to ascertain the precision of 1.5 MPG.

Using my data of average MPG per tank over hundreds of fill ups before and after installation of a K&N filter on three of the five vehicles I installed a K&N filter (for my wife’s cars I don’t keep gas fill up data), I never saw a discernable upward trend in average per-tank MPG. The vehicles were a 1989 E30, 1999 F-150, and a 1999 Honda Valkyrie Interstate.