At the moment the bottom of my car under the rear tub/diff is open at the bottom. As I understand the parachute effect in this area can be quite significant so I would like to fill the area in and the obvious solution is to use a 'diffuser' type cover. I know this won't be anything like a properly designed diffuser but any aerodynamic benefit that I can get would be worth it.

So the first question is any tips on diffuser layouts / setup.

The second part is when in full droop, my wishbones at the outer edge of the floor are below the floor level. Hence to fi a rear floor/diffuser I either need to 'notch' out the flat floor, or cut a hole and then make a pocket/cover that sticks down below floor level to accommodate the wishbones. Any thoughts on which is best?

I am making one for my Megabusa. I have a GRP one from a friend that I am using as a model for the one I am making in alloy sheet with reinforcing channels pressed in. The alloy sheet is about 1m^2 with a curve at the back and will be removable. I have no pictures yet, still in production. Cost so far £30.

I just nailed a sheet of ali across it with pop rivits, not sure diffusers do much on our cars except lose ramp angle.

Started off with cardboard template, jig saw to cut ali with plenty of wd40 sprayed on the edge, has got a bend across it to kick up after the diff

[Edited on 26/1/15 by mark chandler]