Testing wheel skirts A-B-A
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Last weekend a student and I put wheel-well skirts (one coroplast and one cardboard) onto my Civic. You can see them as tested in the attached pic.
We tested them B-A-B around my usual 18 miles mostly flat freeway test route. From noon to 130pm, and after thoroughly warming up car and tires, in temperatures that were between 62 and 64 the whole time, with slowly falling humidity, gradually clearing skies, and wind at a steady 3mph from one direction with gusts up to 5mph, we made three complete runs around a circuit at a steady throttle position of 15.3. I'm disappointed in the results and I'm redesigning the skirts for another test but I would like constructive criticisms and input. The one run without the skirts reached 52.1 mpg and the average of two with the skirts was 51.3 mpg. The skirts seemed to HURT the FE. An execution and a design error seemed to have contributed to the result: 1 - Execution. I had the alternator enabled the whole time, but it seemed to cut on much more often during the runs with the skirts on (I have a dash-mounted volt meter). Since I had depleted my deep cycle battery fairly heavily on my way to the site with the alt disabled, I think this might have been a significant confound. 2 - Design. To keep them from rubbing the wheels and keep them easily removed, the sections were duct taped into place with a little bowing for tension. The bowing is what I wonder about. I wounder if it had a parachute effect. So the lesson: I redesign the skirts so they have the minimum clearance from the wheel and plan a shorter test route of 10 miles so that I can run the tests easily for three or four rounds with my alternator disabled. Did I miss anything? What else should I try to account for? |
I had the same result, but only a .3 mpg difference, less with skirts.
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Why not just leave the alternator on for all the runs? Current consumption should be the same if you don't use the radio.
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ConnClark -
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CarloSW2 |
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This is just me but why not cut your circle in half. The first half run it with the alternator off. the second half run it with it on. this way it will charge up on the back half.
then with the data you get with it off you can get a better idea of the side skirts. and at the same time you can get some data on the alternator stuff too. you are a few steps ahead of me on mods so i would love to see it. my trip to work is 30 miles of flat texas highway. so the aero mods and alternator delete really get to me |
Not to add to the confusion but if I have a say in this,I would vote for the alternator enabled for all runs and hope that the voltage regulator plays a fair game for all runs.
When the alternator is disabled and you start with a freshly charged battery,the fuel pump is running at a higher output,using more amps,producing higher fuel rail pressure and the car could run a tad richer than in later runs where the battery voltage is sagging and the fuel pump output is significantly less than with a fresh battery! ( think of how the headlights dim with sagging voltage). I realize your car has fuel pressure regulator and the ECU has control over fine tuning fuel ratio but it still has an effect. Story: Modern vehicles actually use this method as a desperate attempt when something goes wrong. I worked on a GMC Yukon recently (forgot year) that ran rough on a cold start. Long story short it thought that the fuel alcohol content was 87% so the PCM richened the mixture and then it was fun to watch the fuel pump control module dropping the pressure from a steady 55psi down to 45psi as an attempt to achieve the correct ratio. Reprogrammed it for 10% ethanol and problem was gone.(and fuel pressure back at 55psi). Just my opinion! Barna |
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with a 3+ mpg improvement. Could fuel rail pressure really rival that impact? If I did something to recharge the battery in between runs, that would deal with the problem entirely, correct? How much recharging to you think? What voltage level should I look to maintain? |
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Barna |
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that means a higher speed if the skirts working. this make the difference smaller. maybe i´m totaly wrong, but can imagine, higher revs and shorter driving time is the killer in this case. what about a coast downhill test? |
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