MPGs run, Aspire SE

[FestYboy]

yeah, look at the volt, flat sharp edges to promote clean seperation from the body, same as the above picture. actually, if they wanted to improove that desogn, a 3/16-1/4" wall at the end of the black edges would keep swirl down above the boundary layer. you'll see that put to use on F1 car's rear wings at the trailing edge.

[Movin]

I get the sharp edge but the area of separation is so much larger..like a larger hydraulic piston with the same pressure will exert a lot more force. In this case a much larger area of separation with the same vacuum will pull on the car more?? The best areo shapes look like the lathe turned bullets for long range sniping only the point of the bullet is the rear of the car. Again, this schooling is dated so I may be missing some schooling lol !!

[FestYboy]

that "larger area" also becomes part of the body as far as the air is concerned. the air just above the boundary layer will continue on it's liesurely path just as if there was body work there. its all in how the air seperates from the body, not where.

[Movin]

Like the boat tail on a bullet that has the edge of separation added.

Dang it , this makes a lot more possibilities instead of a few simple answers!

[OL' MAN]

Could you tell me if that dam will fit my 91 festiva and where to get one !

[mikeyjd]

Could you tell me if that dam will fit my 91 festiva and where to get one !

Home Depot garden edging

[mikeyjd]

The Aspire's hatch has a 25* average with a maximum angle of 35*, with the glass starting at about 22*. A vortex generator is also a possibility if you wanted something cheaper and easier. Here is a video of a similar rear end to the festy showing increased attached flow with a VG.

[mikeyjd]

as opposed to without ^

[mikeyjd]

I was able to find an aspire template overlay for you



you can see how detached and erratic the stock airflow is in the video

[mikeyjd]

This is a tuft test after adding vortex generators

these were the ones used http://vortekz.com/generators.htm

[Movin]

The newest research on this subject Inhibiting boundary layer separation, miniaturization of devices, and devices achilles heel.

http://prl.aps.org/abstract/PRL/v109/i7/e074501

I cannot download or view the PDF perhaps someone in an univercity, military or ? can?
Even though I am driving the Humvee of festivas this is fascinating study material.

[TominMO]

Could you tell me if that dam will fit my 91 festiva and where to get one !

My front airdam is homemade, and can be made to fit any car. It is composed of aluminum gutter guard and duct tape, with stainless brackets and fasteners used to mount it. I used zip ties to connect sections of gutter guard. All parts available at any big-box hardware store. Paint the duct tape for durability. Total cost about $30.

Total build and installation time (excluding waiting for paint to dry) about an hour, or less.

[TominMO]

OK, did another test yesterday. I made a kammback similar to the one mikey provided in a pic above. Didn't do rear skirts like in the pic tho. Drove on the hwy for 176 miles and got 53.3 MPG with front air dam, kammback and new skinny Kumho Solus tires.

Aspire SE mileage testing synopsis
(All tests done at 60 MPH except the first one)
MPG.......Description
45.0.......stock; 185/70x13 tires; 55 MPH; approx 250 miles
55.0.......small front air dam, same tires; 100 miles
52.7.......larger air dam, side/rear wheel skirting, 165/80x15 front tires on steelies; 155/80x13 snows on rear; 100 miles
59.7.......larger air dam, side/rear wheel skirting, 185/70x13s on front, 155/80x13 snows on rear; 100 miles
51.3.......larger air dam, side/rear wheel skirting, 155/80x13 snows all around; 100 miles
54.0.......as above but with new 155/80x13 Kumhos @44PSI, removed wipers and mirrors; 243 miles
53.3.......Kumho tires, reinstalled wipers/mirrors, removed all side skirting and added kammback; 176 miles

My conclusion from all this is that the Aspire is pretty well designed aero-wise, and that it's hard to improve on without drastic measures like extending the nose and tail. A lot. The only improvement I have seen so far is with the front air dam. Nothing else seems to matter. I would consider my 59.7 result an anomaly, either due to a tailwind or fill error, or both. All other results fall between 51.3 and 55.0, so I think we are dealing here with trying to maintain a constant speed without the benefit of cruise control; and of course environmental issues. Fill errors seem to be small or nonexistent for this group.

Notes: not easy to see in the pic is that there is a small lip at the end to direct the airflow slightly upward; and that there is an 18" x 24" acrylic window in the kammback, courtesy of Lowe's ($15). The kammback is sitting on the SE spoiler.

This concludeth my aero testing for now, except I might do a test @ 50 or 55 MPH. But with the aero this good, I doubt there will be any major gains (altho lower RPM might help here). Next I will focus on balanced injectors and Matt's header, then add his MPG cam.

[bhazard]

Perhaps a 4 door aspire would work better?

[TominMO]

Perhaps a 4 door aspire would work better?

Don't see why it would matter. Pretty much the same body. I expected to see all sorts of interesting changes based on my mods, and was surprised how little changed after the front air dam.

Edit: oh BTW I just ordered Matt's MPG roller cam, header, and injector balancing. Gonna be a while before testing tho, since the header takes longest to do and I want to test it before the cam.