MPGs run, Aspire SE

[TominMO]

Today I went out and did a MPGs run in my Aspire SE. In my previous Aspire SE (sold to Arty), I got 48.25 MPG @ 60 MPH over an 85-mile hwy course. In this one, I went to Indy, about 250 miles away, and got 45 MPG @ 55 MPH.

So today I was testing out my simple and cheap aero mods. I closed off the hole in the bumper, and installed a 5" air dam under the front bumper. Both pieces were made of that expanded-aluminum gutter-guard stuff, covered with duct tape, painted an appropriate color, and held in place with zip ties & duct tape (bumper hole cover), and stainless steel fasteners and L-brackets (air dam).

The car: totally stock, 5-speed; 40 PSI in the tires; tools etc. in the trunk; 185/70x13 tires. 5W30 dino oil in the motor, 20W50 Valvoline synthetic motorcycle oil in the tranny. Also bear in mind that the Aspire has a lower final drive, 4.10 vs. the Festy's 3.78. This means the Aspire motor spins about 8% faster at a given cruising speed. RPM @ 60 was 2700. Also, Aspires are about 300 lbs heavier.

I jumped on the hwy and drove for 99.1 miles, keeping it pretty consistently at 60 MPH. Wind was basically nonexistent, and the temp was about 72. I went back to the same pump to carefully fill it to the brim again. It took 1.8 gallons before overflowing a little. This gave me a figure of 55.0 MPG.

My best MPG run @ 60 with my Festy, when it had the 1.3, was 52.1 MPG, even tho it has the taller final drive and is lighter. So aerodynamics are making the difference, despite the Aspire's greater weight.

Total parts cost: ~$10.

Next tests will involve side skirts (another $10) and super-tall tires, 165/80x15, on the front, to effectively raise the final drive a bit. I'll put 155/80x13s on the rear. This should just get me to 60 MPG.

Edit: it's quieter in there too. Didn't have to turn the radio up as much as before.

[zoom zoom]

if your going for mpg's why don't you use 175's?

[TominMO]

if your going for mpg's why don't you use 175's?

165s are what are available. It's an old VW Beetle tire size.

[mikeyjd]

Thanks for doing the mpg run. It would be really awesome to see you hitting 60 in an aspire. It's very nice to see more people doing aero mods! I've been contemplating a front air damn, but thought that the increased frontal area might cancel itself out since I already have an under-panel. I will revisit this ^

[TominMO]

Thanks for doing the mpg run. It would be really awesome to see you hitting 60 in an aspire. It's very nice to see more people doing aero mods! I've been contemplating a front air damn, but thought that the increased frontal area might cancel itself out since I already have an under-panel. I will revisit this ^

Both are effective in different ways, an air dam or an underbelly pan. Less air or slipperier path.

Personally I think a front air dam with side skirts will give the best results. If you add that to your car, you would get even better results. What I think would happen, tho, is that the belly pan would be less effective due to less air going under the car with the dam/skirts; but still it would help by cleaning up the airflow still coming under the car. Best-of-both-worlds kinda thang.

Edit: after my next 60 MPH run with skirts and taller tires, I will do a run at 55 just for bragging rights. Fully modded with dam, skirts and tires @ 55 MPH , I would expect to see 65 MPG. Also I would like to experiment a bit with pulse-and-glide.

[FestYboy]

running both pan and dam will net you less frontal lift (a good thing for high speed stability) and if you reduce the amount of air needing to be processed by the pan, the rear disturbances will also deminish.

[mikeyjd]

Both are effective in different ways, an air dam or an underbelly pan. Less air or slipperier path.

Personally I think a front air dam with side skirts will give the best results. If you add that to your car, you would get even better results. What I think would happen, tho, is that the belly pan would be less effective due to less air going under the car with the dam/skirts; but still it would help by cleaning up the airflow still coming under the car. Best-of-both-worlds kinda thang.

Edit: after my next 60 MPH run with skirts and taller tires, I will do a run at 55 just for bragging rights. Fully modded with dam, skirts and tires @ 55 MPH , I would expect to see 65 MPG. Also I would like to experiment a bit with pulse-and-glide.

Pulse and glide ftw! you might be able to crank out 70+mpg with 65-45mph coast downs (or more with 60-40 lol) I am gonna do some more research about the air damn (since they're cheap and easy) and I have my rear wheel coroplast skirts already cut out, I just need to remake my brackets (i dont want to drill into the metal so i'm using some diy attachment brackets like this)

[TominMO]

Can't see the pics for some reason. I was thinking about what to do for side skirt attachment, and rear wheel skirts too.

[Movin]

Nice, I assume you are keeping techniques out of the equation to quantify mods only?
Your RPM's sure are high, the taller tires will help. How would you rate your engine condition?
How old and what brand is your O2? Sorry for the questions but when you are playing on the cutting edge of what is possible I hope you expect them! Awesome!

[TominMO]

1. Nice, I assume you are keeping techniques out of the equation to quantify mods only?
2. Your RPM's sure are high, the taller tires will help. How would you rate your engine condition?
3. How old and what brand is your O2? Sorry for the questions but when you are playing on the cutting edge of what is possible I hope you expect them! Awesome!

Thanx.

1. Correct, I am deliberately avoiding hypermiling techniques so as to not cloud the results.
2. Engine is in excellent condition. I will have Matt D. balance my injectors.
3. Nippondenso owe too sensor, about a year old.

[mikeyjd]

I looked into the air dam + belly pan, and apparently it's more of a one or the other thing on cars as low as ours. If you have a belly pan then the dam is just going to add to your frontal area without improving your coefficient drag. The dam by itself should be beneficial as well as a belly pan by itself. If it were on a truck then there would be some benefit to having both.

[TominMO]

I looked into the air dam + belly pan, and apparently it's more of a one or the other thing on cars as low as ours. If you have a belly pan then the dam is just going to add to your frontal area without improving your coefficient drag. The dam by itself should be beneficial as well as a belly pan by itself. If it were on a truck then there would be some benefit to having both.

Interesting. Earlier today I was wondering what racecars did. Driving on smooth tracks, they have very low air dams. Do they also have belly pans or is that even necessary? Because of their much higher speeds, I could imagine that there would be more advantage for them to have both, since higher speeds would mean higher pressure for what little air did get under the dam.

Today I built better dams for both the Aspire and my Festy. They wrap all the way around under the bumper. I will test the Festy one tmw probably. The Aspire one I will test next week, after I get side skirts on.

[FestYboy]

pix!!!

[TominMO]

pix!!!

Love to, but Photobucket isn't cooperating. Every time they change it, it gets harder to use. Can you suggest a better site to post pics to?

[drddan]

Tom, I switched to Imageshack, after Photobucket gave me problems. There was a period where I couldnt post pics for more than a week with PB, and this happened right in the middle of my swap/ build thread. I switched over to Imageshack so I could post pics!!!

I havent had a single issue with Imageshack, and is easier to use than PB.