WAI vs CAI test results

[MetroMPG]

i'll post the details later, but the summary is:

CAI (performed 5 bi-directional runs)
54.3 F avg air intake temp
79.12 km/gal (US) avg consumption

WAI (performed 4 bi-directional runs)
106.7 F avg air intake temp
79.31 km/gal (US) avg consumption

it's always disappointing to put this much work into something and not see any significant results.

in case you're wondering, that's a .2% (point two percent) difference of WAI over CAI. i haven't calculated margin of error yet, but i suspect it's within it, which would make the difference statistically insignificant.

details and methodology to come later on...

[Matt Timion]

That is disappointing. If you ever need help with calculating your margin of error, etc just send me the numbers and I'll run them for you really fast.

[DaX]

I honestly believe this is the ECU correcting for the warm air. This makes me want to hurry up and throw my Hondata in. One thing at a time though...

[SVOboy]

I honestly believe this is the ECU correcting for the warm air.

Honda ECUs do not do this, they lean the mixture based on hot air, though I'm not knowing much about obd2 gm stuff.

[MetroMPG]

but the ECU may also be controlling the timing advance based on intake air temp. in which case the gains in air temp are erased by less advance.

i can only view "instant" timing advance on the scangauge, though, so i can't really make any comment on what it was doing on average.

btw, for the CAI data:

0.18 = standard error (using the formula: (STDEV(F13:F21))/(SQRT(COUNT(F13:F21))) where F13:F21 are the cells containing the individual data for each run)

correct me if i'm wrong, matt, but standard deviation (a.k.a margin of error) is 2x standard error, or .36% in this case. which confirms my prediction that the .2% difference seen is statistically insignificant.

[Matt Timion]

You're better off just posting the results from all four runs if you have it. Post the miles and the MPG. We'll run a t-test or even a two way anova to determine if it was statistically significant. I can post all of the relevant information as well.

[SVOboy]

On the ECU topic, does obd2 correct timing for it? That would be seriously sucky!

[MetroMPG]

* figures are average of bi-directional runs (cancels effect of wind/grade)

* "test" road: is a nearly level, 6.6km stretch (13.2km round trip)

* speed was set at 89 km/h - cruise control was set once, cancelled with the brake pedal between runs; "resume" feature used for subsequent runs (cruise control consistency verfied by "avg speed" feature on scangauge)

* car was up to steady speed on cruise control when passing a fixed "start" or "stop" marker; scangauge "avg" logging was either reset (at "start") or recorded (at "stop" marker)

CAI (units: km/gal)

78.5
79.05
79.4
79.4
79.25

WAI:

78.9
80.2
78.35
79.8

[MetroMPG]

Originally Posted by SVOboy

On the ECU topic, does obd2 correct timing for it?

yes, the level of timing advance is changing constantly, but i don't know what sensors it's using for input for the control.

it's a good point... when you get down to this kind of tinkering, you really need to know the precise details of how the ecu is going to respond.

it makse sense that temperature would factor in as one of the timing controls (but whether it's using coolant or air intake temp, or both, i don't know). it's certainly using throttle position in the formula.

throttle position also changes based on air temp. the hotter the intake air, the wider the throttle has to open to continue producing the same amount of power (thus reducing throttling or pumping losses - one of the several theoretical reasons WAI is more efficient). but the TPS is also a factor the ECU uses to determine a/f mixture and timing advance - a wider throttle would normally change both a/f and timing for the worse, mpg-wise.

it's entirely possible that there's a "sweet spot" intake temp which balances out the pros and cons of all these variables, and i just didn't find it today.

the only way to find it would be spending hours and hours on the road (this took me 3 hrs) testing across range of different IA temps... or simply having the proper info about how the ECU will respond to sensor input.

[Matt Timion]

<p align="center"><strong>Group Statistics</strong></p>
<table width="100%" border="1">
<tr>
<td>GROUP</td>
<td>N</td>
<td>Mean</td>
<td>Std. Deviation</td>
<td>Std. Error Mean</td>
</tr>
<tr>
<td>WAI</td>
<td>4</td>
<td>79.3125</td>
<td>.84101</td>
<td bgcolor="#FFFF00">.42050</td>
</tr>
<tr>
<td>CAI</td>
<td>5</td>
<td>79.1200</td>
<td>.37517</td>
<td bgcolor="#FFFF00">.16778</td>
</tr>
</table>
<p align="center"> <strong>Independent Samples Test</strong></p>
<table width="100%" border="1">
<tr>
<td rowspan="3">&nbsp;</td>
<td colspan="2"><div align="center">Levene's Test for Equality of Variances</div></td>
<td colspan="7"><div align="center">t-test for Equality of Means </div></td>
</tr>
<tr>
<td rowspan="2">F</td>
<td rowspan="2">Sig.</td>
<td rowspan="2">t</td>
<td rowspan="2">df </td>
<td rowspan="2"><div align="center">Sig. (2-tailed)</div></td>
<td rowspan="2"><div align="center">Mean Difference</div></td>
<td rowspan="2"><div align="center">Std. Error Difference</div></td>
<td colspan="2"><div align="center">95% Confidence Interval of the Difference </div></td>
</tr>
<tr>
<td><div align="center">Lower</div></td>
<td><div align="center">Upper</div></td>
</tr>
<tr>
<td>Equal variances assumed</td>
<td>6.372</td>
<td>.040</td>
<td>-.463</td>
<td>7 </td>
<td>.657</td>
<td bgcolor="#FFFF00">-.1925</td>
<td>.41545</td>
<td>-1.17488</td>
<td>.78988</td>
</tr>
<tr>
<td>Equal variances not assumed</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>-.425</td>
<td>3.956</td>
<td bgcolor="#FFFF00">.693</td>
<td>-.1925</td>
<td>.45274</td>
<td>-1.45504</td>
<td>1.07004 </td>
</tr>
</table>
<p><br>
<br>
<br>
Explanation:</p>
<p>In order for something to be statistically significant at the .05 level (that's what psychology uses, medical is often .01) the Mean Difference must be greater than 2 standard deviations of the error. In other words, error is always introduced into an experiment. The two numbers in yellow in the first table are the error. In order for two groups to be statistically different the difference of the means has to be more than TWO SEMs (std. error of the mean). In both cases the mean difference (.1925) was no where near 2 SEMs for either group.</p>
<p>The conclusion is that on MetroMPG's Firefly, there is only a 30.7% chance that the increase of gas mileage was due to the warm air intake and not something else.</p>
<p><br>
<br>
<br>
<br>
</p>

[SVOboy]

Hmm, all I can say as a starting point is that the older honda ecus do not do that, I will poke around for you though.

[MetroMPG]

more notes on methodology & test conditions:

* an A-B-A-B test method was used: 3 CAI runs; then 3 WAI runs; then 2 more CAI; then one final WAI

* when switching between A and B, the car was driven for 10 minutes to allow the intake tract to either cool down or warm up to a steady temperature before returning to the "test course"

* i used about 6.9L of fuel during the test, so the car got lighter by that amount from run 1 through run 9 (plus the cool down/warm up drives_.

* the ambient conditions were as follows, based on info from an online weather station located several km from the "test road" location.

time....wind-dir...wind...gust...temp-F

12pm......ssw.......10.....10......39
01pm......ssw........8......8......38.1
02pm......ssw........7......7......39.6

(wind data in knots; the test went from approx noon to 2pm.)

* the car was warmed up prior to the test: block heater 1.5 hrs & 30 minutes of mixed city/hwy driving

[MetroMPG]

Originally Posted by SVOboy

Hmm, all I can say as a starting point is that the older honda ecus do not do that

sorry, don't do what, specifically?

matt: cool analysis. where do i get me some of that program?? i was just using the STDEV function in excel and a formula I found on a stats web site. it's close enough to the figure your program gave you for std error and std deviation for the CAI group.

[SVOboy]

Adjust timing based on anything besides knock, and then they don't even do that unless they are japanese.

[MetroMPG]

not even vacuum advance? surely timing is controlled by something dynamically.

my car doesn't have a knock sensor. and i'm running enough base timing advance that i have to be careful not to mat it at low rpm or it will ping.

[rh77]

With the WAI -- do you have a way to get the actual temperature of the air? I'd venture a guess that cold air is slipping into the mix somehow.

To answer the OBD2 question, my '98 Honda (Acura) ECU leans-out the mixture with the detection of warmer air, as shown from a datalogger. With the CAI on there, I was getting an average of -2 to -3 long-term fuel trim, whereas the WAI ranges in the -4 to -6 range. Economy was instantly noted to increase from around 26 to 31. Timing advance is all over the place, so I can't really report any changes in that department. There is a definite decrease in horsepower, especially at higher RPMs, as shown in 0-60 times. Merging onto the highway, if I have to floor it, seems like it's choked-off struggling to get to redline. Have you noticed a decrease in power?

RH77

[SVOboy]

Ah, well I took vac advance for granted. Timing is on a big table with the variables being load levels and rpms.

[Matt Timion]

Originally Posted by MetroMPG

sorry, don't do what, specifically?

matt: cool analysis. where do i get me some of that program?? i was just using the STDEV function in excel and a formula I found on a stats web site. it's close enough to the figure your program gave you for std error and std deviation for the CAI group.

I used SPSS to get my results. I was trained on SPSS and some other old powerful command line program that everyone still uses (can't remember the name now).

I might be able to swing you a copy of SPSS. I think I have one around here somewhere. I think it is generally used for behavioral research but any statistics can be run using it.

I was originally planning on programming all of this into the website and letting users simply input data and then have teh website spew out the results. I'm sure I could still do that, although it would take a while to do.

[Compaq888]

Originally Posted by rh77

With the WAI -- do you have a way to get the actual temperature of the air? I'd venture a guess that cold air is slipping into the mix somehow.

To answer the OBD2 question, my '98 Honda (Acura) ECU leans-out the mixture with the detection of warmer air, as shown from a datalogger. With the CAI on there, I was getting an average of -2 to -3 long-term fuel trim, whereas the WAI ranges in the -4 to -6 range. Economy was instantly noted to increase from around 26 to 31. Timing advance is all over the place, so I can't really report any changes in that department. There is a definite decrease in horsepower, especially at higher RPMs, as shown in 0-60 times. Merging onto the highway, if I have to floor it, seems like it's choked-off struggling to get to redline. Have you noticed a decrease in power?

RH77

I have to quote on this. i used to have a WAI and I will tell you I lost a lot of low end with it. I didn't gain any mpg either. All that happened was I gained a lot of top end. I had an Injen WAI. My mpg stayed the same. The best mpg I'm getting is with the stock intake system. As for the top end I lost .4 in the 1/4 mile thanks to the Injen WAI. that is not .04, but .4, which is almost half a second.

[MetroMPG]

Originally Posted by rh77

With the WAI -- do you have a way to get the actual temperature of the air?

yup, from the air intake temp sensor (inside the throttle body i think) - via scangauge.

To answer the OBD2 question, my '98 Honda (Acura) ECU leans-out the mixture with the detection of warmer air, as shown from a datalogger.

yeah, i'm starting to realize that to go really hardcore, a scangauge doesn't cut it. i need something to hook to the laptop to gather data for experiments, and the scangauge for normal driving. SG doesn't report fuel trim, so i can't report on those figures.

Have you noticed a decrease in power?

my car feels gutless at the best of times

i haven't stuck my foot in it to see if i notice any difference. this car doesn't encourage (or reward) that kind of driving. though i may have felt it bog down a little the other day when the AIT showed that it was really warm.

[MetroMPG]

Originally Posted by Matt Timion

I used SPSS to get my results.

i remember using that prog in a stats course i took.

don't worry about sending me a copy. you've confirmed that the key is to be able to figure out the standard deviation and standard error and from there you can figure the margin of error (2x standard error). if the difference between the 2 sets of data is smaller than the margin of error, it's not statistically significant.

i double checked excel, and it does give the same calculation as SPSS did for you (i made a typo when i reported the standard error was .18 further up this thread. i meant to round to .17 but accidentally made hit '8'. excel wasn't the problem, it was me.)

so this is good. it's nice to be using proper stats analysis on these tests. i'll go back to my aero tests and my k&n filter test and update them with proper margin of error info (i had it partly correct for the aero test, but not completely)

[Matt Timion]

Originally Posted by MetroMPG

so this is good. it's nice to be using proper stats analysis on these tests. i'll go back to my aero tests and my k&n filter test and update them with proper margin of error info (i had it partly correct for the aero test, but not completely)

Feel free to post results for anything you've done here. I would love to install wheel covers if it helps, as well as the K&N filter.

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.

okay, done rambling now.

[MetroMPG]

Originally Posted by Matt Timion

Let's assume that something else you install doesn't help too much either (wheel skirts, etc.)

i'm sure i've mentioned this already, but wheel skirts work. i've tested them on my car and they improved mileage by 2.8%. under controlled conditions, like today.



the k&n made no difference to steady speed fuel economy. i was so disappointed (because i blew 80 bucks on it), i actually ran a second test just to make sure (once at 80 km/h, once at 95). nada. not statistically significant. if only i knew then what i know now..

[SVOboy]

the k&n made no difference to steady speed fuel economy. i was so disappointed (because i blew 80 bucks on it), i actually ran a second test just to make sure (once at 80 km/h, once at 95). nada. not statistically significant. if only i knew then what i know now..

And matt and I were gonna go out and buy them though...But I'm still doing WAI because I know the crx adjusts fuel based on IAT and not timing, so I figure I won't run into ecu errors.

[Matt Timion]

Originally Posted by MetroMPG

the k&n made no difference to steady speed fuel economy. i was so disappointed (because i blew 80 bucks on it), i actually ran a second test just to make sure (once at 80 km/h, once at 95). nada. not statistically significant. if only i knew then what i know now..

Let's talk about cost then. How many regular air filters will you have to buy in order to break even on the K&N? Since they are good for life that has to account for SOMETHING, doesn't it?

Oh, and I think the K&N air filters are only like $40-50 for my car, so that's a plus.

[MetroMPG]

despite the test today, i think it's still reasonable to state that the WAI probably improves fuel economy on my car. just maybe not at constant speeds, as tested on a warmed vehicle.

but as matt pointed out elsewhere, WAI will cause the engine to warm up faster. warmed up engines get better mileage than cold ones. fact.

unfortunately, (1) i have no way to reliably measure this, and (2) it's probably just a tiny improvement anyway, hard to measure.

i went back into the insight forums tonight, and the primary reason they do it is because the car won't go into lean burn until the IAT sees a certain temp. everyone there claims WAI makes a measurable difference (though I never saw any talk of controlled tests - maybe the improvement is so obvious on an insight that they're not needed).

as for k&n, already figured it out: it will take 125,000 km for mine to pay for itself.

i actually considered selling it on the teamswift site, but kept it partly because it's reusable, and partly because my test was only for mpg at a constant speed (throttle opening). the filter may still offer performance and/or mpg benefits under variable throttle conditions (i.e. wider), which of course i can't test reliably.

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.

[rh77]

Originally Posted by Matt Timion

Let's talk about cost then. How many regular air filters will you have to buy in order to break even on the K&N? Since they are good for life that has to account for SOMETHING, doesn't it?

Oh, and I think the K&N air filters are only like $40-50 for my car, so that's a plus.

If it's any consolation, I just washed and re-oiled mine with 50,000 miles on it, and it can go a LOT longer. Air flow is increased, and top end has to be improved, although, more air can mean more fuel consumption, unless your're at cruise, then a small percentage in economy can be realized. But the kicker is that fuel IN-efficient vehicles are tested for the results and benefit the most. Pleated filters can be restrictive at high air flow rates (larger displacement engines benefit as more air is moved).

RH77

RH77

[MetroMPG]

here's another thing...

in reading some more at insightcentral.net, i discovered the claim that using a WAI in warm conditions doesn't increase mpg above "normal"; it only helps raise winter mpg up closer to the summer values.

the temps yesterday were pretty mild - the coldest CAI measurement was 53.5F and ambient was 39F.

i think i should do a second test when it's much colder to see if it reveals a larger difference between WAI and CAI.

the problem with cold weather testing is it takes the car so long to get to normal operating temp. when it's really cold, long after the engine temp has stabilized, i can watch the mpg continue to climb steadily for half an hour or more until the transaxle, cv joints, tires, bearings, etc, all reach stable temps.

makes it more difficult to do a controlled test.

[Matt Timion]

MetroMPG,

There is a guy on insightcentral that built the coolest WAI I've ever seen. I think I posted a link to it once, but I'll do it again.

http://www.insightcentral.net/forum/viewtopic.php?t=1769

Basically it's a variable temperature intake. If the temperature drops below, say, 60 degrees a butterfly opens and lets the warm air into the intake. If it's a normal summer/spring day the butterfly remains closed and only lets the cold air in.

This would be an AWESOME "how to" if you could get it working.

[rh77]

Originally Posted by MetroMPG

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

I'm not sure about that. Filter efficiency is the amount of air resistance required to force a volume of air through the filter. 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.

I have used K&Ns for many years, and it has its pluses and minuses. It's very efficient -- I like like that -- 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).

After 50,000 miles, I ran a q-tip and paper towel around the inside of the intake, after the filter. It's surgically clean, so it has to be doing its job. Now I don't come across fine, sandy particles, nor have I over-oiled the filter at the last cleaning (to ruin the MAF sensor, etc.) I have a conventional pleated filter in the TL, since I don't plan on keeping it very much longer, and it's also clean.

I think if you're moving a lot of air (like in a big-block Chevy), you'll probably see big differences in power or economy with a change to a low-resistance filter.

RH77