WAI vs CAI test results

[MetroMPG]

Originally Posted by rh77

Filter efficiency is the amount of air resistance required to force a volume of air through the filter.

you're right in that that's the "normal" use of the word in reference to filters. but "efficiency" can refer to how well any specific effect is achieved. (in the case of the graph above, it's dirt trapping ability.)

It takes less force to get air through a K&N, but that doesn't mean that it won't pick up dust and dirt particles in its oil-laden sponge.

you're right again, but it's logical that the more open space you have in the filter media, the more particles will get through. it's not an enormous difference, but that's what the test above showed. that said, i don't know whether their test was representative of normal urban driving (particulates entering the air intake). the test may have simulated the equivalent of a desert dust storm.

the engine takes less engergy on the intake stroke to draw air in (using the principle that the engine is basically a big air pump)

this is true mainly at wide open throttle. at lesser throttle openings, the primary restriction is at the throttle plate, and it far outweighs any normal filter restriction. so i don't think we'll really see mpg or performance gains from a high-flow filter under normal driving conditions (diesel engines possibly excepted) - unless "normal" for you is foot to the floor a lot.

theoretically, a high-flow filter and a hot air intake are a good efficiency combination, because the throttle will be open wider to ingest more of the less dense air. (unfortunately, the theory didn't play out on my car.)

i agree with you that the effects would probably be more noticeable the bigger the engine.

i'm glad you liked yours. i've used them in my past 3 cars. but i proved myself wrong in expecting they would help my mpg though.

[MetroMPG]

Originally Posted by Matt Timion

guy on insightcentral that built the coolest WAI I've ever seen

i saw that thread. pretty inventive, those insight folks.

i take it your car doesn't already have one, right matt? my 89 accord had a factory installed vacuum driven variable WAI/CAI. but it was also carburated (can never remember how to spell that).

i think carbs are much more finicky when cold than fuel injection, so they benefitted from the wai more - it was a driveability issue more than a fuel efficiency issue.

ever experienced carb icing? i did a few times in the honda as the wai "collector" shield over the exh. manifold rusted away. by the time i sold the car this summer, the collector was gone. just the hose remained.

my brother in law said his late 70's mitsubishi colt (also carb'd) had a variable wai/cai too.

[Matt Timion]

Originally Posted by MetroMPG

having said that, k&n would probably not be very happy if this report was widely distributed.



"Filter efficiency is a measure of the filters overall ability to capture dirt."

much more in that link.

The deceiving thing about this report, as can be seen in the above image, is that the marginal difference between the best and worst air filter is 3.13%, which probably not only falls within a margin of error (or at least approaches it) but probably has no real world difference.

In the graphic K&N appears to be a total flop... but the difference between the filters is so minimal I want to conclude that most of those filters (if not all) are exactly the same.

[MetroMPG]

can't argue with you on the way it is presented to exaggerate the results.

let's all say it together: there are lies, damn lies, and statistics.

[Matt Timion]

Originally Posted by MetroMPG

can't argue with you on the way it is presented to exaggerate the results.

let's all say it together: there are lies, damn lies, and statistics.

Reminds me of an old Cold War Era joke.

The US and USSR were going to compete in some sort of race. Like all other competitions USA vs. USSR was just a way to find out which country was better. Rocky 4 anyone?

So the race happened and the USA won.

The newspapers in America read "USA wins the race!"

The newspapers in the USSR read "USSR gets second place in race. US finishes second to last."

[MetroMPG]

Originally Posted by Matt Timion

Now here is something I've been thinking about. We just saw that the WAI didn't help too much. Let's assume that something else you install doesn't help too much either (wheel skirts, etc.) statistically speaking do you think it might be possible for the two items combined to provide a significant improvement? My gut tells me no, but part of me thinks it might be possible.

just re-reading this thread and now i understand what you were asking there.

my opinion: definitely possible.

e.g. - some of the aero mods i intend to try are unquestionably going to reduce drag, but will probably be too small individually (e.g. wheel discs, deflectors ahead of the tires) to show up above the statistical "noise" (margin of error).

so come warm weather, i intend to test some of them as a "set". e.g. compare no aero aids to this "set": wheel discs, front wheel arch gap fillers & ride height lowering. i don't think anyone would disagree that these items would only improve aerodynamics (and therefore mileage), but each item's individual contribution may be small enough to potentially get lost in the margin of error if tested on its own.

let's say the margin of error on this hypothetical test is the same as i got for the WAI runs - .38 km/gal

and i measure - individually - improvements of .25, .25 and .35 km/gal respectively for wheel discs, gap fillers and lowering.

from a purely statistical point of view, i would be forced to dismiss the individual results as statistically insignificant.

but if i measured the 3 aero mods as a set and saw a total gain of .85 km/gal, we could deem the set of improvements to be statistically valid.

is that what you meant?

[Matt Timion]

Originally Posted by MetroMPG

just re-reading this thread and now i understand what you were asking there.

my opinion: definitely possible.

e.g. - some of the aero mods i intend to try are unquestionably going to reduce drag, but will probably be too small individually (e.g. wheel discs, deflectors ahead of the tires) to show up above the statistical "noise" (margin of error).

so come warm weather, i intend to test some of them as a "set". e.g. compare no aero aids to this "set": wheel discs, front wheel arch gap fillers & ride height lowering. i don't think anyone would disagree that these items would only improve aerodynamics (and therefore mileage), but each item's individual contribution may be small enough to potentially get lost in the margin of error if tested on its own.

let's say the margin of error on this hypothetical test is the same as i got for the WAI runs - .38 km/gal

and i measure - individually - improvements of .25, .25 and .35 km/gal respectively for wheel discs, gap fillers and lowering.

from a purely statistical point of view, i would be forced to dismiss the individual results as statistically insignificant.

but if i measured the 3 aero mods as a set and saw a total gain of .85 km/gal, we could deem the set of improvements to be statistically valid.

is that what you meant?

This is what I meant, but there is another factor you have to consider. The margin of error is a direct function of the variability of the results.

In other words, the more varied the results are the greater the variabiilty and therefore the greater the margin of error. Unless your control and results have low variability I suspect that adding more items to the experiment will raise the margin of error on these experiments.

What I'm saying is that the margin of error might raise higher than .25 with the addition of more factors.

[MetroMPG]

i can't see how testing a set of items (vs an individual item) would increase the variability of the results (these aero mods specifically).

the variability comes not from the mods themselves (they're either going to work or they're not), but from outside factors: measurement errors (scangauge), variability in the cruise control, experimenter error (i don't know... maybe pressing the "resume" button too late so the car hasn't leveled off by the "start" marker...) wind gusts, changes in temp, etc.

---

this has nothing to do with the point made above, but just out of curiousity, i went back to look at margins of error on the other controlled runs i've done:

* .28 km/gal (N=4 bi-dir runs, mean = 68.85 km/gal) = 0.41%

* .39 km/gal (N=3, mean = 78.06) = 0.5%

* .35 km/gal (N=3, mean = 66.68) = 0.52%

that seems pretty damn good if i do say so myself - my range of error so far is around .5%, meaning i can statistically observe changes in mpg on my car at the level of .25 mpg (us) (hypothetical 50 mpg baseline) under controlled conditions.

[Matt Timion]

Originally Posted by MetroMPG

i can't see how testing a set of items (vs an individual item) would increase the variability of the results (these aero mods specifically).

the variability comes not from the mods themselves (they're either going to work or they're not), but from outside factors: measurement errors (scangauge), variability in the cruise control, experimenter error (i don't know... maybe pressing the "resume" button too late so the car hasn't leveled off by the "start" marker...) wind gusts, changes in temp, etc.

---

this has nothing to do with the point made above, but just out of curiousity, i went back to look at margins of error on the other controlled runs i've done:

* .28 km/gal (N=4 bi-dir runs, mean = 68.85 km/gal) = 0.41%

* .39 km/gal (N=3, mean = 78.06) = 0.5%

* .35 km/gal (N=3, mean = 66.68) = 0.52%

that seems pretty damn good if i do say so myself - my range of error so far is around .5%, meaning i can statistically observe changes in mpg on my car at the level of .25 mpg (us) (hypothetical 50 mpg baseline) under controlled conditions.

Agreed... you've managed to keep things very constant in your testing.

The only reason I say that testing a number of things will increase your variability is because the possibility exists for there to be more malfunctions. A screw can come loose and change an aero mod, etc. It's not likely, but the possibility exists.

[MetroMPG]

A screw can come loose and change an aero mod, etc. It's not likely, but the possibility exists.

a loose screw? no way - all my aero mods so far have been duct tape, duct tape, duct tape!

(i just hope the adhesive comes off the paint when i do up a proper grille block in the spring!)