(can you quote yourself?)

These things are right in the path of only the slow moving air in the boundary layer around a moving car. A quick search for "boundary layer car aerodynamics" will leave your head spinning but from the Wikipedia entry on 'hood scoops':
"To be effective, a functional scoop must be located at a high-pressure area...The scoop will be most effective if it is either mounted high enough to clear the boundary layer (the slow-moving air that clings to the surface of a moving object)"
I can only imagine that the same rules apply to these things--they won't be effective unless they are in a high pressure area (nose, base of the windshield and ?).

The Evo crowd has something like this:



And Chargespeed makes this for the WRX



but I dunno what they're supposed to do.

 

DEFINATELY placebo....to get 5MPH differences in a 1/4 mile run, you'd need to swap the body with an Insight...
Aeirodynamics just won't make any difference for a 1/4 mile run... if the Xb were the same weight and power... it would run the same time, even though it's a box.

 

If you really want to make a big difference in the Fit's aerodynamics, have a tailcone (like the one NASA used to use when they had the shuttle piggy-backed on the 747). That blunt rear end is the biggest problem.
That could really make a huge difference for a road trip.
Before the Fit, I had a VW GTI. My mom has a Passat with the same engine and transmission. The Passat got 4MPG better at highway speeds, due entirely to the sloping rear window...

 

Air inside the boundary layer is still moving pretty fast, once you're a few millimetres from the surface. That Wikipedia page says "The thickness of the velocity boundary layer is normally defined as the distance from the solid body at which the flow velocity is 99% of the freestream velocity". Stick your hand flat on the side of the car, you'll still feel the wind there...

So I think I know what fooled me into thinking it accelerates much faster (at less than 90mph; over that I think it probably would). It takes much less pressure on the pedal to make it go at normal speed, and that makes it feel like a more powerful engine. At full throttle, which I rarely use, the difference is going to be way less, maybe not enough to notice. Oh well, I guess it's just a fuel-saving thing after all. Road trip this weekend, I'll get some miles on it. Over 40mpg so far.

 

I was just reading everyone's mileage reports and I just had to add mine in since it seems insanely good.

Fit Sport A/T, everything is completely stock and my odometer is dead on by mapquest and yahoo maps standards. My best mileage is on a 350 mile trip from Virginia to Pennsylvania and I have gotten as high as 47 MPG.

My favorite MPG trick is truck drafting. I get as close as possible while staying far back enough to be able to see around the truck. I'm thinking of swapping the air filter for the K&N and installing a Fitch Fuel Catalyst. If I hear good results back on those airtabs things then I might stick a few of them on as well. Maybe I can get 50 MPG if I drive nice.

 

TrickyPantz,

Be sure to read the two warning threads on the K&N Typhoon!! The Fitch Catalyst is very interesting, but sounds like the chances are 50/50 that it works as advertised. If you try it, PLEASE post your experiences. This is the perfect place to expose both the good and the bad products. I was the first to try the K&N intake system with enough savvy to know and show how badly designed and made it was. I was also the first to buy and post a DIY on the Progress rear sway bar. You win some, you lose some, when you gamble on high-tech modifications. My K&N experience has made me much more resistant to gambling. If you tell us that the fuel catalyst system works as advertised, I will buy it and I'll bet that a hundred or so other fitfreaks would do the same.

 

You should be very careful about doing this. 50 MPG or not, it's dangerous for you and the truck driver.

 

I did read up on the K&N Typhoon thread earlier, I'm just talking about getting the filter alone, not the intake. Besides, with the intake I've heard that there is a drastic mileage decrease over 3500 rpms.

Also about the truck drafting thing... I am aware of the dangers of following too closely. I make it a point to never follow so closely that I wouldn't be able to stop in case of an emergency. Obviously optimum draft off of a truck at 75 miles per hour is going to be around 30 or 40 feet back, but I'd rather sacrifice a mpg or 2 for safety's sake and hang around 80 to 150 feet back depending on weather and traffic conditions <-- its a BAD idea to get close to anything when the other lane isn't clear.

 

Hmm, I dunno about that. There's such a long history of people making ridiculous claims about fuel catalysts that giving them a 50% chance seems awfully generous. I'm not touching that one until they describe exactly how it's supposed to work in a way that actually makes sense.

 

Your intake system mileage decrease rumor is groundless. My best mpg. to date was 38 with mountain driving at 80-85 mph. My K&N system is junk, but it does not decrease mpg.

 

Thanks for the correction on the intake system. I know you said its junk, but does it do anything at all, or is it just a total waste of money?

 

I believe that an aftermarket drop-in filter is worthwhile because it is with most brands, including K&N, cleanable and reusable. I also believe that the K&N filters have less flow restriction than stock filters. I also feel more power with the K&N intake system. The "junk" issue is due to the poor fitment design. All of the competing brands of SRIs or CAIs actually fit in such a way that there is no problem in removing the filter for cleaning or replacement. There is a large problem with this in the K&N system, and ONLY the K&N system.

 

I know this is a VERY old post.. but losing 1lb. of rotating weight (unsprung) is equal to losing 7 lbs of sprung weight. So losing 5lbs x 4 wheels = 20 lbs x 7 = losing 140lbs off the body. BIG difference.
-bix

 

I know that it helps, but is it really that much? Got a ref for that one? (Seriously, I'm super curious about some light-weight wheels!)

 

has anyone gotten any information back on those airtabs things?

 

So I'm back from Toronto, where I drove in about the least efficient way I could imagine, bringing my average so far back down below 40mpg. Here's some more about the airtabs.

 

Aerodynamics appears to be difficult, so they'd probably say something like "dunno... stick it in a wind tunnel".

If you can find a long, steep, paved, deserted hill, and a calm day, you could mark a starting point at the top and see how far you roll. Do at least half a dozen runs, alternating with and without airtabs, or better yet, have a second person install or remove them without the driver's knowledge.

From reading other sites, it seems that there is no clear answer on airtabs, or perhaps, on where to place them to do good rather than harm. Mods that seem to have consistently shown some aerodynamic benefit include belly pans, side skirts, side mirror removal, grille blocks, wheel covers, and splitters or air dams (most of these involve trade-offs, so research first and read the disclaimer at the bottom of the page here...).

 

The better method is to time how long it takes to coast down to a particular speed. If you measure distance to stop instead, you end up with much of the time below the speed where aerodynamic effects make any difference, thus adding a lot of noise to the results. As I think my account of it shows, it's more work than it sounds like. Starting on the steep part of a hill that leads to a flat stretch sounds good though, it'd make the start easier.

...of course, you'd want a big enough hill that you'd get up to 60mph or so, might be hard to find.

 

RE: going to south to Seattle and back, staying roughly between 55~70mph and then mixed it up with 70kms worth of city/hiway driving (that makes it 85%hiway/15%city), I get 5.7L/100kms or roughly 42.19mpg, with 15% of the time A/C on.

This is off of a tank of Texico 87 gas fueled up @ Everett.

 

Sooo... the next tests will start with coasting at 115 mph?