ahahahaa.... so I guess this is where I admit that on the weekend I bolted some sheet metal to the bottom of my car. I just do not like the thought of that little pocket of high-pressure turbulent air in the small cavity below the spare tire being squeezed under the rear bumper cover. So I covered it up with some thin aluminum.

It's a work in progress, but seems like it might help a bit. I took care of the top half of that bluff rear end last year with vortex generators, now for the underside. A brief coast-down test, two runs before and after, indicates some improvement. So far I've gone 120km and the fuel guage is still on the 'full' mark. I recall from last year when I was keeping track of such things that 122km was the furthest I ever noticed it going before there was space between the needle and the full mark on the guage, so looks like I'll break that record today. Summer gasoline probably hasn't worked its way into the local gas station's tanks yet, so maybe that's not a fair comparison.

Anyway, it's very crude and doesn't fit quite right. Good thing that unlike aerocivic, at least you can't see it unless you look under the car. Maybe I'll finish it next weekend.

 

Sfenders, Great effort. Can you post some pics? Do you happen to have a SG so you can get results fast?

If you prove this works I'm sure many DIY will want to follow your lead.

 

Well, it's really quite ugly, just a quick experiment you know. Results look promising, so I'll probably do a better job of it some day soon. ScanGuage isn't calibrated to my car at the moment as I'd lent it to someone else. I stopped to fill up the gas tank after 210km though... um, best wait for more data but it looks surprisingly good on the fuel efficiency so far. I didn't really expect an easily-measurable change, but maybe I was wrong.

 

Thanks for the pic. Smart to use metal tape. Was wondering if you drilled for the test version.

Just a suggestion. When you feel your test is conclusive and have the data you feel is fair. Take it off for a tank or so and see if it's goes back. Then you can claim the results are from a A-B-A test.

 

Can you explain what you did to create "vortex generators" and do you have any pictures?

 

sfenders, very interesting mod. Keep us posted on your mileage with the underbody mod. I am definitely interested in this one.

Theres link to a picture in post #43. The word "ugly".

 

Description and pictures, from last year, are here:http://s89686473.onlinehome.us/airtabs-test.html

It occurs to me that maybe they influenced the wake vortex system somewhat, and the change from the underbody aluminum interacts with them to push it into some totally different mode. Aerodynamics can be unpredictable that way. So, maybe some large part of the huge increase in fuel economy on my first fill-up is for real.

By popular demand, I'll do a proper A-B-A test on the weekend.

 

I noticed an extra 4 mpg when I went to the 11 lb Heliums.

 

+ 1 rep for you.
Being an engineer, I can appreciate fully you taking the time to try and do a decent job of posting results based on math and science ie physics.

I get so tired of reading the BS claims with POOR data driving the recommendation.

 

I plan on adding a grappling hook to the front of my fit. On the highway I'll shoot the grappling hook onto the back of a car, van or truck in front of me and then use the other vehicle to tow my fit. I'm working on a way to disengage the hook and reel it in so that I won't need a new hook every trip I take. I figure this mod should get me up towards the 50 mpg range. Wish me luck

 

Running less and/or an oil with a higher lubricity helps a lot.

Obviously you want to run enough oil so the engine has proper lubrication, but running a little shy of the factory recommended amount will cut down on windage and reduce parasitic loss.

Running an oil with a higher lubricity will also help reduce windage.

That is why I run Royal Purple Fully Synthetic Race Oil of the same weight as factory. Royal Purple's extreme lubricity and tendency to reduce foam, greatly reduce parasitic loss caused by crank windage.

I have dyno proof of the gains realized from my 2005 Nissan Altima 3.5 SE V6. I gained 11whp and 15wtrq when I moved from Mobil 1 fully synthetic to Royal Purple. This is tremendous! I swear by the stuff.

 

correct me if i am wrong here. BUT, how can you get an actual increase in mpg with a CAI or any intake for that matter? By bringing in more air, you burn more fuel....no?

I learned to not be in such a hurry and just leave 5 minutes earlier. I used to get 32-33mpg 1/2 city 1/2 hwy just going to work and back. Since i have learned cruise control at 70mph and let the rmps build, i now get an average (3 tanks worth) at 37/38mpg.

 

Exactly. The only thing I can see a new CAI doing (if it's actually drawing in cold air) would be the reduction in air inlet temperature, thus allowing the ECU to add more timing and thus reducing fuel use. This would, of course, only offset the increased fuel that is being used by the ingestion of cooler, denser air. Seems like it would all even out in the end to me. Also, most CAI that I've seen for the Fit so far do not pull cold air into the air inlet as well as the stock Honda intake, so that would negate any benefit right there. In fact, I don't see how any of the short-ram intakes help with getting cooler air into the engine since they're sitting right behind the radiator.

Maybe a small benefit in fuel economy might be had because the intake track is usually smoothed out, or ''tuned", by a new intake system. This would make it easier for the engine to pull in a given amount of air. But, again, at the throttle angles and RPMs that most of us are running to achieve good fuel mileage, I don't know if the fuel economy gain would be evident. It would be interesting to see from someone with a ScanGauge to look at MAP readings perform an A-B-A test to see if an aftermarket intake lowers the MAP reading at a steady cruise speed.

This is the best advice you can give anyone trying to increase their mileage. Just be patient and go with the flow. After getting my ScanGauge I have become much more conscious of my driving surroundings and how I'm driving and have subsequently increased my MPG to over 40 now. I keep trying to challenge myself to get better and better.

 

Why not just install a "tractor beam" instead?!? LOL RLElliott
'07 VBP Sport 5MT w/ minor appearance & comfort mods!

 

Because everyone knows that tractor beams take up a lot of power to run and would therefore lower the mpg. With the grappling hook I can just hook on to the car or truck in front and turn off my Fit altogether and get infinite mpg for the time I'm in tow.

 

But I thought you would use "dilithiium crystals" to power the tractor beam?!? RLELLIOTT
'07 VBP Sport 5MT w/ minor appearance & comfort mods!

 

DUDE! Have you seen how much dithiium crystals cost these days? Well over $4.00 per gallon!

 

You sure about that? In the 2 years I owned my 2.5 liter Subaru Sti I averaged 14 mpg

 

Apples and Oranges.

I've thought about turbo charging to increase MPGs for a while. The theory is you're going to use the smallest turbo possible. You want the turbo to move air (not necessarily positive pressure, but near or at 0 vacuum) on light engine loads to free the engine from pumping losses. I'm not sure what this would do to the top end of the powerband, but that's not what it's for. This is all theory and I have no proof backing this.

I like the undertray and diffuser ideas. Not too into the vortex generators.

 

Turbocharging with a good water injection system FTW

With the proper safeguards a 50/50 water/meth injection system is a great way to get the same amount of power with less gas from the tank. Atomize it into inlet air just before the TB, at a flowrate that is a function of the MAP. It keeps your top-end clean, your exhaust tip clean, and allows you to maintain the AFRs you wish. Another level of tuning required of course.