Originally Posted By: FFeng7
Originally Posted By: Jim Allen
A well designed aftermarket intake system designed for fuel economy MIGHT add a skosh of economy (depending on how good or bad the OE system is... most OE stuff is biased towards economy) but a filter alone will not. That has been my experience and the study linked below pretty much proves it. INtake restriction has little effect of fuel economy just tooling around because the EFI is constantly trimming the fuel. It will have a big effect on power, as you will read in the study, but not MPG.
On top of that, it's just about impossible to measure fractions of MPGs. The usual margin for error ins about 1 mpg no matter which way you measure so you'll never really know whether you gained anything or not for the money you spent.
But for the sake of argument, lets say that $120 Spectre filter delivers a 1/4 mpg increase. Since you are talking about a 360 you are probably getting 15 mpg on a good day. Let's say you drive 10,000 miles per year and gas is stable at $3.50/gal. You are using 666.7 gallons of gas per year that costs $2333 annually. If you get 15.25 mpg 655.7 gallons per year for $2295 for a $38 savings per year. To recoup your $120 expense, it's going to take more than three years... if indeed you got the 1/4 mpg gain that you really can't measure.
The other thing about the oiled cotton gauze filters is low efficiency. That translates into more wear in the long run and shorter OCIs. How much that effect you long term depends on the area where you live. If it's dirty air where you live, especially with lots of fines in the air (the desert or the big city are the worst places for fines) the more junk the OCG is letting in.
The two things that have helped me with mpg are a programmer with a good fuel economy program and low rolling resistance tires. To that, add synthetic gear oil and you can see a difference above the margin for error. I saw a 2.4 mpg difference in tires between an All Terrain tire and an All Season on my F150 over a measured course, carefully tested Look
Tires & Fuel Economy for a test I did on this.
The biggest changes come from how and where you drive. That's the place where most people fall short because they don't want to expend the mental energy to do it or make any changes to their routine but if you concentrate on the driving, you can save 2-3 mpg on just about everything with an engine. Best part of that...it's free.
Intake restriction and Fuel Economy
This 2009 report tests the effect of dirty air filter on fuel economy using standard EPA dyno routines. They used later model EFI cars (2003-2007)and one 1975 carbureted car. The conclusion what that the fuel injection could compensate for the restriction up to the point where the car's performance had deteriorated to barely running and fuel economy decreased only by a percent or so. Performance degraded, of course. The carbureted car was more effected but fuel economy wasn't lowered by nearly as much as "common knowledge" dictates... only 2.5 percent.
In every case lower end performance was unaffected until the restriction reached the level at which insufficient air was being inhaled. Performance dropped mightily but the EFI could trim fuel to keep the mixture about right. They found that in "normal" driving situation, the car was almost unaffected by a clogged filter because the airflow needs were so low. In a few cases, the filters were so clogged that the engine sucked them into the intake tube.
I really enjoyed reading this response but I have a question. It states the the city and desert are the worst place for fine particulates in the air. In the desert obviously its sand and silt but what makes the city air so bad? Is it particulates from exhaust or just dirt in general?
This comes from the various SAE papers I've read and in interviewing air filter professionals. Big City air contains a lot of soot (exhaust particulates as you suggest) and fine dust particles. The thought, frankly, makes me cringe a bit and be glad I live a rural lifestyle ( : < )
