Is there a chance a aero mod hurts your mpg

[HypermilerAX]

I think it is max. 12°.

[christofoo]

Mods can increase drag if they aren't right.

Here are my $0.02 on your mods:

• Rear wheel skirts look good except maybe the gaps. I have some skirts with even bigger gaps, my feeling is it's still a net positive, but not ideal.
• I'm not sure anyone knows, certainly I don't know, but I would bet that an air dam bending inward can increase drag. If the air is not stopped by the dam, but continues under the car, then the result is a larger number of messy interactions. A camel with one hump is better than a camel with two humps. A stiffer dam that is angled forwards if possible, is probably better aerodynamically. Not only does a dam need to stop the air, the air needs to end up going over the top or sides of the car - that's the whole point. I'm worried about your air dam, especially if it's not stiff enough.
• Others mentioned bending your Kammback down a bit, I would also say it would work better with some sides, but I'm still guessing.
• I would suggest (partial) grill blocks next.

Unfortunately, I think that you either have to copy tried-and-true designs, or else treat it as a research project:

1. Mockup in cardboard and tuft test, if possible. Differences in audible noise levels also provide clues. A-B-A coast-down or fuel consumption instrumentation tests are better but take more time. CFD would be ideal, but it's expensive and most of us don't have access.
2. Fabricate.
3. Setup a definitive test to verify efficacy, if A-B-A wasn't done in step 1. It's fine to group mods together, more especially if you have confidence you know what each one does. If the magnitude of the improvement is large enough then tank logs or a known road trip and weather monitoring may work. Statistics can help.
4. If the mod didn't work as expected, go back to step 1.

(EDIT: Actually, even if you pick a tried-and-true design, but if your car has a different starting shape that might affect the mod, it may still be a research project.)

[aerohead]

Originally Posted by SmellyCat

Ok here are the pics. The front skirt is bending under the car. Bad?
The rear wheel covers, Seem ok but a racer guy said it creates turbulance, The spoiler, x-cookie pan, looks like its ok, or is it? SC

*I think (as others) that skirts are okay.Taping/sealing the leading edges would optimize them.
*I recently pushed the nose of my truck forward,with a flexible lower urethane rubber airdam which lays back just a few degrees which forces the air to travel up and around,and shearing off the airstream at the bottom 6-inches with a hard edge.I'm recording the highest-ever mpg with this nose configuration.You'll see many manufacturers doing it today.
*A square-back body,as on your car does not produce lift.And the base pressure of the wake is fed from a perimeter separation line of near uniform pressure.Since your spoiler is 'open',the wake underneath is still receiving pressures telegraphed from the side edges ahead of the spoiler.
The only way to reduce the drag of the low base pressure is to move the whole back of the car further rearward with a boat tail elongation which will simultaneously reduce the wake size and increase the base pressure behind the new 'transom.'

[christofoo]

Originally Posted by aerohead

...
The only way to reduce the drag of the low base pressure is to move the whole back of the car further rearward with a boat tail elongation which will simultaneously reduce the wake size and increase the base pressure behind the new 'transom.'

I think a box cavity is also an option, with less effectiveness but less fabrication.

[SmellyCat]

Great info, Some wire can pull front air dam forward. When I screwed it on, it was more outward but the air force appears have bent it inward.

The rear skirts need some bending, the new rims are wider than the originals and high speed turns make the wheels grind the skirts and has pushed it out. The previous tires were Diff sizes. 195 on the left and 215 on the right, My rear differential thought I was always turning to the right.

It has a grill block also.

The rear spoiler has enough metal over lapped that I could bend some sides out, but that will ruin the cool round cookie pan edge... Deal breaker. I'll have to survey my junk pile for a suitable side for the spoiler.

I'll angle the rear spoiler and run the super volvo down my test
hill. , SC

Oh!, one more thing, There is a 15 watt solar panel on the roof, would it be better if it was near the front windshield or toward the back of the car?

[aerohead]

Originally Posted by christofoo

I think a box cavity is also an option, with less effectiveness but less fabrication.

Yes,a number of open box designs have been proved out in tunnels.There is a bit of loss in performance,but as foe ease of fabrication and weight-savings,you could do a lot worse!
It's just important that all 4-sides of the tail be enclosed by the box.

[aerohead]

Originally Posted by SmellyCat

Great info, Some wire can pull front air dam forward. When I screwed it on, it was more outward but the air force appears have bent it inward.

The rear skirts need some bending, the new rims are wider than the originals and high speed turns make the wheels grind the skirts and has pushed it out. The previous tires were Diff sizes. 195 on the left and 215 on the right, My rear differential thought I was always turning to the right.

It has a grill block also.

The rear spoiler has enough metal over lapped that I could bend some sides out, but that will ruin the cool round cookie pan edge... Deal breaker. I'll have to survey my junk pile for a suitable side for the spoiler.

I'll angle the rear spoiler and run the super volvo down my test
hill. , SC

Oh!, one more thing, There is a 15 watt solar panel on the roof, would it be better if it was near the front windshield or toward the back of the car?

Actually,if you lost the cookie pan,and integrated the PV panel into the top of the rear spoiler/box it would be best.If it would fit.

[SmellyCat]

I'm not clear on the box spoiler, is there a link? I was thinking that the front wheels could use some spoiler action. Would doing something to the front wheels like this picture do any good? SC

[Gealii]

Originally Posted by SmellyCat

I'm not clear on the box spoiler, is there a link? I was thinking that the front wheels could use some spoiler action. Would doing something to the front wheels like this picture do any good? SC

i wouldn't for as far as the front wheels there are other mods that would help more

- front wheel skirts
- smooth wheel covers
- front wheel arch gap filler
- tire spats

You want to try to keep frontal area down to a minimum so the very limited area to put block would be very small compared to performing the above mods located on our 65+ efficiency mods list with the corresponding links. The least effective out of those 4 would be the tire spats which would be as you are saying just below the fender blocking farther below the car directing air around the tires

[SmellyCat]

All right, bent the spoiler down and added sides, lets see what happens.sc