Advice for improving airflow with live rear (axle)

[crashnzuk]

I was going to ask what the hole in the bumper was for. Since it is now unnecessary, I'd close it back up.
Travis..

[Sporty Modder]

How about a splitter, and belly pans?

[RedDevil]

Some more ideas:
- Loose the mudflaps. Very short flaps may reduce air resistance, but yours are way too long.
- Set those gurneys ahead of the front wheels in your close up picture at a sideways slant, that will lower the pressure under the car. (they are like that under my car, as OEM)
- Add gurneys ahead of and behind the rear wheels to push the air out and back in.
(the 2012 Insight has gurneys - 'air splitters' - behind the rear wheels. See the link for details.
(EDIT) only registered users see the pictures, sorry. It is basically a rubber strip about a foot long and 2 inches wide, starts about behind the middle of the wheel almost straight aft and bends inwards to about 30 degrees toward the rear.

[euromodder]

Originally Posted by RedDevil

- Loose the mudflaps.

I was going to suggest that as well

Replacing the mudflaps with a teardrop shape aft of the wheels is the most effective

- Set those gurneys ahead of the front wheels in your close up picture at a sideways slant, that will lower the pressure under the car. (they are like that under my car, as OEM)

Positioning these is quite tricky.
Flow already tends to be at an angle (going outboard) there.
That's why they are often positioned slightly inboard of the tyre, some curving around the arched bottom opening of the wheel well (i.e. around the opening that allows the wheel to steer)

Angling the spads could reduce their effectiveness.

- Add gurneys ahead of and behind the rear wheels to push the air out and back in.

I've seen them added in front of the rear wheels - my car has them as well - but not behind it ?

When adding spads in front of the rear wheels, take into account that the air is flowing outboard there (10-15°) ... unless the rear end of the car has a diffuser, i.e when the aft pan angles upwards, creating lower pressure aft, which straightens out the flow underneath.

It's a sedan, so it'd benefit from a slight diffuser effect at the rear.


Adding a lengthwise plate on the inside of the wheel would help as well - doing on the inside what a wheel skirt does on the outside.
When mounted on the axle, it'd be in a fixed position relative to the wheel, and could take the shape of a semi-circle where it's alongside the rim.

the 2012 Insight has gurneys behind the rear wheels. See the link for details.

Insightcentral requires one to be registered over there and logged in to see the pics ...

[Sam Powell]

Originally Posted by UltArc

Can I come over and use your lift? lol

I will try to find my images of what I did (a kind of similar situation), and post them. I attached it under the rear axle, on the rear sway bar (attached to it at the sides and center).

You may come over and use the lift. Especially if you bring the car you have applied aero treatment to. I am in Maryland near DC.

Sam

[Sam Powell]

I know the mudflaps are a drag, but without them the wheels throw crap all over the back fenders. Maybe I could design more aero friendly ones. Without them the car ends up looking like an off roader. The plan is to add some to the front as well. The door and rocker panels get the junk there now. It was worse before I went to wheels with an increased offset. I previously had custom wheels which set the wheels out 3/4" further on each side. I went back to stock wheel this Summer, which not only look nicer to me now, but the car handles better. And now I read that setting the wheels in further improves the airflow. When I was into racing I regretted the semi wheel skirt design of these rear fenders as they limit the size tire you can put on the back. Now I admire them.

The gurneys actually do angle in slightly, and are curved at each end. I could angle them a bit more. Because of the cutout on the bottom of the belly pan for the wheel, you end up with limited material to mount it to. It would be simple though to angle it a bit more. The question is angle it in or out? Out runs the air into the wheel. "In" puts the air into the mess under the car. These were made from an old trash can. I could find one with a more curved side I suppose. I will keep my eyes open at the market. This can was just what was sitting in my garage.

One of the goals of the airdam was to NOT change the appearance of the car much. I feel like I accomplished this. No one has ever mentioned it at a car show. But in order to make it less noticeable I had to keep it inside the lower edge of the front fenders. This does limit its effectiveness. If you click on the photo you can then scroll through my car album on photobucket and see and older version which was smaller in every way. The old one used a Ford Ranger airdam as a starting point, the new one uses a full sized Chevy pick up air dam.

I have actually added the inner lining as suggested. I suppose I could make it deeper. There was nothing there before. Here is a photo of that fabrication. I used the inner wheel well from a Cadillac for that one.



Thanks much for the ideas. They are all going in the mind and churning around. I do not know much about diffusers and how they work or are designed. I also have a BMW 328, and there is a stock M series rear diffuser available for it, and was considering adding that to that car. Can you supply a link or explanation for what a diffuser is please? Thanks again. I am all ears and learning every day. I feel I can fabricate anything I can imagine as long is it is not too visually distracting.
Sam

[UltArc]

Originally Posted by Sam Powell

You may come over and use the lift. Especially if you bring the car you have applied aero treatment to. I am in Maryland near DC.

Sam

Ah, I was just kidding about coming over. I do go to Maryland every now and then, but rarely take the Mustang now.

I searched like crazy for the photos of what I did, but I cannot find them. That's one of the issues with having tens of thousands of photos- and never enough time to organize.

[Sam Powell]

The invitation is still open,and I love your Mustang. I would love to give it a long look.

Sam