Airdam - suprise result! - Fuel Economy, Hypermiling, EcoModding News and Forum

kingsway · 03-03-2012, 08:58 PM

My little 3 spd automatic Daihatsu clone (Perodua Kelisa) badly needs some help in reducing FC.

I've already fitted new Michelin Energy E3B tyres - one size up and inflated to 40psi.
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I have a grill block - which certainly speeds warm-up (3 minutes!)

But I suspect that it is about as aerodynamic as a brick. I've mentioned elsewhere that on a cost-down test it would slow from 50mph to 40mph in 14 seconds - compared to 34 seconds in the case of my (much heavier) VW Golf Wagon...

Today I tried a simple air-dam using 5inch lawn-edging. It isn't ideal, as it is slightly too low (being below the lowest items under the car) and is also more flexible than I'd like. It is only 1mm thick plastic, and I am pretty sure it must tend to fold back under air pressure at speed. So I wasn't very hopeful as far as results are concerned.

But to my great suprise, when I did the cost-down test again, from 50 to 40 mph, instead of slowing in 14 seconds, it took nearly 20 seconds!!! (I repeated the test several times)

Now, it was just a quick and dirty test - with no account of wind (although the air did seem fairly still) but it does look like a very encouraging result.

mcrews · 03-03-2012, 09:09 PM

Holy Crap Batman!!!!!
tha't great!
THe only thing better would be it it was just layin around the garage and didnt cost any money!!
Actually looks good.
Of course, sight uphill drive ways will take on a new 'look'!!!

kach22i · 03-03-2012, 10:29 PM

Will the authorities allow you to do some of the crazy stuff (body modifications) we get away with here in the USA?

Something over that rear window would help out the old bread box.

kingsway · 03-04-2012, 01:02 PM

I see plenty of youngsters who ruin their cars with bizarre body-kits, so I'm guessing my few mods will be acceptable!

I did find a source of body-kit parts in Malaysia, but the cost of shipping etc means it probably would not be worth the expense.

I'm now thinking of finding some better material to make a permanent air-dam, and am looking for some guttering that might be suitable for sode skirts.

I am very keen to try a Kammback of some sort - but making something that doesn't look like a load of ahem... 'manure' is the difficulty.

gone-ot · 03-04-2012, 01:09 PM

...curious, but how much "ground clearance" do you have? Can't really tell from your head-on picture. If it's much greater than 5-6 inches, then your airdam results are probably 100% justified.

drmiller100 · 03-04-2012, 01:48 PM

air under a car is BAD for drag.

Congrats!

MetroMPG · 03-05-2012, 01:55 PM

Quote:

Originally Posted by kingsway

But to my great suprise, when I did the cost-down test again, from 50 to 40 mph, instead of slowing in 14 seconds, it took nearly 20 seconds!!! (I repeated the test several times)

Now, it was just a quick and dirty test - with no account of wind (although the air did seem fairly still)

Wow. That seems really encouraging!

If I were you, I would want to do the test under identical conditions (excuse me if my reading of your test is wrong - I got the impression you did your coast downs on different days). I'd want to be sure the effect is from the mod, and not something like a tailwind or the wake from vehicles ahead of you, or ???, etc.

Why? Whenever I do a mod, I always say to myself: "there is a remote possibility this mod could in fact be making things worse." The only way to know for sure is to do the best test possible and be careful I don't accidentally deceive myself into leaving a bad mod on the car!

Grant-53 · 03-06-2012, 02:42 AM

If the lawn edging is too thin, try some strips of rubber cut from those large mud flaps on trucks.

kingsway · 03-06-2012, 11:13 AM

I still need to try some proper tests. But the results do seem to be fairly consistent.

This encouraged me to try a similar airdam on my VW Wagon. I tried some before and after testing this morning, with quite different results. I could find no measurable difference with or without the airdam!!! The VW already has quite a low ride height - maybe of the order of 5 or 6 inches - so the dam kept scraping everytime I cornered, or went over a bump...

The little car, in contast, still has 3 or 4 inches clearance below the airdam. The airdam itself is 5 inches deep - so is about 4 inches below the bottom edge of the front bumper/fender.

The biggest variable I have found, in my limited amount of testing of the VW, is transmission temperature! If I do a coast down test when the engine is just at running temp, the time to slow from 50 - 40 might be 21 seconds. After running the car for an hour and getting everything properly warm, the time is then 34 seconds!

I am seriously considering refilling the VW with fully synthetic MTF... The cost might well be worth-while.

(I may do the same for the little automatic, too)

kingsway · 03-06-2012, 11:49 AM

Similar car - no airdam...

The main question remaining is - will the airdam on the little automatic make a noticeable difference to my fuel consumption?