Hi,
Looks like I found my niche here. I have long been interested in fuel economy, however few people were as obsessed or actually knew as much about it as I did, and now I found a forum where people not only know more but have implemented what they know! Very impressive!
And what a torturous path to get here...googling undertray, to
these articles on autospeed about how to DIY a very partial undertray, to phil knox, to gassavers.
I am an engineer (EE) and as nearly all engineers do, I love efficiency. And as such, I can't stand most of the automotive world. We are in a stupid arms race for height and weight, with no one better off in the end. But fortunately rising oil prices are waking people up in a big way. It is very possible to get Cds of 0.20-0.25 (or lower!) and we are stuck with 0.35.
Only a few more years before we get cheap commuting cars for the masses. We aren't there yet, but at least those who are in the know can insulate themselves from fuel dependence.
CAR
On to my car. have a 1993 Daihatsu
Mira that I purchased recently. I spent quite a bit of time looking and researching before I purchased it. My goal was to minimize both the expense of the car and the fuel costs, with an eye to make a daily driver that was as fuel efficient as possible.
I bought it mainly for the engine. It has a 660cc, EFI engine. I figure it would beat a 1 litre carburetted daihatsu charade (which was the main alternative at the same price point). The 660cc combined with the EFI should set me up with the best base possible.
Cursory tests reveal that I get about 6.5l/100km in city with normal driving (no engine off or anything). Not that bad.
I would prefer a more bubble shape, something that would lower the height and width at the top (e.g. lower seats, less van-like looking), however, this was the only thing on the market at the price range, especially with the EFI engine.
It also has a 5 speed gearbox, better than the 4 speed van version you can also buy (although heavier).
Surprisingly enough the manual says that it should weigh 1000kg, which I am very skeptical of. But maybe so. I might remove the back seats since I have no need for them (or their weight).
MODS
The very first thing I need to do is have some way of estimating instantaneous fuel economy. This sucks because I am in Australia, my car came out before OBD-II. That means I will either need to measure fuel consumption directly (not sure how), or I will have to figure out how to measure injector pulse width, etc etc.
I'm more a programmer than an electronics guy, so it will be interesting to get my hands dirty with this. I do have a rough idea what to do, based on a newsgroup search:
Quote:
Computing mileage on an EFI engine is as simple as totalizing the
injector ON time, totalizing distance traveled, multiply in a
conversion factor and display. Hardware needed is a Parallax BASIC
Stamp (about $50) and an LCD display board (about $90.) We use the
PWM input across an injector to grab the pulse widths. We use a bit
line to read the vehicle's VSS to get distance. We write a little
BASIC code to wrap it all together and viola! Mileage/trip meter.
There are several methods of calibrating the fuel injector flow.
The most accurate is to build my fuel injector flow bench and
actually calibrate the injectors.
(http://www.diy-efi.org/diy_efi/projects/inj_flow/inj_flow.html)
The next best way to do this is to hook up a pulse generator (or
even better a PC using my FIT software at the above URL) to the
injector, fire off the fuel pump, discharge 20,000 pulses or so and
catch the fuel in a graduated cylinder. The pulse width should be in
the 2 ms range. This must be done instead of just yanking the
injector open to measure the flow to account for the opening and
closing delays in the injector.
The crudest but still satisfactory method is to hook the Stamp up
with some code that will display the raw injector and VSS totals,
put an accurate amount of gas in the tank, drive until it's used up
(or fill the tank, drive, fill it again and record the amount), then
compute the volume per injector pulse by dividing the fuel used by
the total number of injector firings.
John
--
John De Armond
|
So unfortunately that seems to be what I have to do first, and since there is no one here who seems to have gone this route, looks like it's up to me. (correct me if anyone has, I'd love to see a DIY of this).
After I have a base I can compare to and a means to compare with, I can then set about actually doing the various mods that actually improve the fuel economy.
So, I am starting with this:
Roughly 6.5l/100km city. Kerb weight 1000kg? At least 750kg, for sure. Cd 0.35?
Goal (UFE-III):
The
UFE-III gets 1.3l/100km, has a Cd of 0.19, kerb weight of 440kg, engine size 660cc. Notice especially the design of the undertray right in front of the front tires - this should be relatively easy to copy.
I will proceed to make modifications on the order of price/increase FE %.
In the pipeline are:
-corflute undertray (you call this "coroplast")
-corflute deflectors in front of front wheel and rear wheel (side skirts)
-reversal camera and removal of external mirrors
-rear wheel skirts
-smooth wheel covers
-blocked grille
-either raised bonnet or some sort of deflector over the wiper blades.
-LRR tires (+40psi)
-possibly larger tires
-aftermarket cruise control
Possible
-antenna removal
-front wheel bubble faring
-caulked gaps
-shaved door handles (no clue how to do this)
I hadn't planned on doing all this stuff when I got it, especially the stuff that won't be reversable. However, seeing as the car was cheap and chances are that the mods will improve the value, I suppose I shouldn't worry. It's just that I would have liked to have bought a beater since then it wouldn't matter what it looked like and I could have done a half assed job on the asthetics.
Please give feedback and any suggestions etc. certainly wouldn't go astray.
Again, welcome.
Linear Mode
