Aerodynamic mod

[chumly]

Originally Posted by Krusty

I love that you had red and black duct tape on hand.

I got it from Wal Mart, they have several colors available, the red does match my car pretty good.

[deepblueQ]

Originally Posted by chumly

I did some testing today and here are the results.I used the scangage trip meter to test mpg over a 10 mile stretch of road (5 mile each way up and down some small hills).Using the cruise control to keep things equal, at 70 mph with the mod I got 39.7mpg, without was 39.0mpg. At 60 it was 46.9 with and 45.6 w/o.At 55 it was 50.6 with and 47.9 w/o.At 50 mph it was 52.4 with and 50.7 w/o.O.A.T. was 90. I.a.t. got up to 184 at one point but didn't set off any c.e.l.s.This was with a hot air intake.I then tested it without the mod and with the factory air box and my homemade pvc air pipe (c.a.i.) at 60 mph and mpg was 42.5, at 50 it was 45.2 mpg.The h.a.i. seems to make the biggest difference in mpg but the temps can get pretty high. The highest water temp got to 198 degrees, I did not notice the cooling fan come on at any time.This mod works but it is a good idea to monitor temps as they can get up there.I don't know if this would work in stop and go traffic or not, but so far so good! Chumly

Did you account for differing smaller variables, most importantly oil temperature?

A-B-A testing is good, if that was A-B then the error bars are quite a bit bigger than the recorded diff caused by the mod...

If you need to redo it A-B-A, no need to use so many different speeds. We're just trying to verify that it works, not how much it works. You can't show how much it works with a Scangauge... it calculates fuel usage as k/(RPM*MAP), no volumetric efficiency correction.

If it works, it'll show up regardless of the speed, though it'll probably show up more at higher speed since aero is more of a factor relative to rolling resistance that way. The SG will return a much smaller difference than reality, because of the nature of its inaccuracy.

In my experience oil temps have a very big effect on smart's MPG, so I'd be particularly careful about that in testing. I'd personally go for a good drive to get it up to temp first, then A-B-A-B-A-B with a set time allowed for the mod in between tests.

[chumly]

I did 1 warm up run first(10 miles) and it showed 38.1 but it was at various speeds.I did the runs with the mod 1st and then took it off for the unmodded runs.I don't expect the scangage to be perfect but it should be close.

[kennyrayandersen]

though it's true you can make it more efficient by tweeking the front (at risk of overheating), the real gains are at the back of the vehicle. Years ago NASA did some research on a rolling van and was able to show that the front of the vehicle is 'relatively' unimportant compared to the back. IF you are looking to REALLY make it more efficient, what you need is a big ole bob-tail on the back! Air will naturally pile up on the front of the vehicle, and kind of make it's own aerodynamic shape. However, at the rea of the vehicle, there is a huge amount of drag (speaking about it as a blunt body). The flat back is just about the worst shape possible. Putting a tail on it will make that transition smoother and reduce drag significantly. Do a little search on modding a car for high mpg and you'll see some really good ideas

Tail cone
wheel covers (flat disks)
wheel well covers (including the front, which much follow the wheel)
fairing for the wheels and
belly pans are all high on the list of things that have the biggest influence.

The big problems is:
1) getting the manufacturers to follow form fits function
2) getting the public to accept it

The physics isn't that hard, but overcoming peoples idea of beauty and aesthetics is! IF you put an aerodynamic body on the smart it would return 55-60 mpg on the highway. In fact if you look up Mercedes Benz bionic car you will see they have already done the research on this to come up with a vehicle that has a good interior volume, and still maintains an outstandingly low coefficient of drag. A car shaped like this with a good diesel engine (say turbo 800 cc? sound familiar?) would return well in excess of 70 mpg.

Image Search Results for mercedes benz bionic car

File:Mercedes-Benz bionic car.jpg - Wikipedia, the free encyclopedia

The Bionic Car project

for your reading pleasure you can see what others have done (I don't think anyone has pushed the fortwo to the limits talked about here -- you could be the first!)

65+ vehicle modifications for better MPG -- MetroMPG.com