Rear Diffuser help

[5uprahboy]

Hey guys

I'm starting to really get into track racing - even though I've only been once haha.
Anyway - I'm wanting to make my GA70 a fun, fast, and decent track car.

I have no spoiler at all on the back. I have lowered the car and it sits on a slight rack from front to back. The front is pretty low - chassis is about 85mm from ground and the back is about 15mm higher.
I'm wanting to make a rear diffuser to stop all the air getting trapped in the rear bumper and trying to rip it off.....

Does anyone have any suggestions or advice for this? I've noticed, most are made from fibreglass or carbon fibre. This will be too hard and expensive for me so I'm wanting to make it from aluminium. What thickness should I use? Any tips/tricks?

Also - Should I bother making a little boot lip? I'm thinking something like the pic below - maybe a little bigger and with a more aggressive angle?:

 

[supraguru05]

that little lip wont do much for downforce. if you want to add significant downforce with minimal drag you need to get the spoiler up in the clean air off the car. also there are alot of site on constructing a diffuser, heres one

http://www-htgl.stanford.edu/bradshaw/tunnel/wadiffuser.html

 

[5uprahboy]

that little lip wont do much for downforce. if you want to add significant downforce with minimal drag you need to get the spoiler up in the clean air off the car. also there are alot of site on constructing a diffuser, heres one

http://www-htgl.stanford.edu/bradshaw/tunnel/wadiffuser.html

Yeah - the boot lip probably wouldn't really help much. I'm really focusing on a diffuser now to help air escape the rear cleanly, rather than getting caught up in the bumper which will (I hope) in turn create a low/negative pressure zone, sucking the car to the road.....

I'm still unsure how to make the diffuser. I'm thinking of getting some really thing aluminum to get the shape, and then using that to make a fiber glass mold. The finished product I also want to be made from fiberglass......

 

[pocketkiriyama]

I'll probably get a rear diffuser too but also will get a front diffuser. I'll being doing this much later and it will be made of aluminum. With aluminum I can be sure that it won't break or shatter especially the kinds of road I drive.

 

[Wiisass]

If you don't do a full smooth underbody, you're only getting part of the effects of a rear diffuser.

And if you want to make a mold for it and make it out of fiberglass, you're probably better off doing it out of foam first. And then making a mold from that.

But if you're just trying to block air from getting trapped in the rear bumper, then just do that. Just make a blockoff plate that won't let it get in there and get trapped.

 

[Canuckrz]

From the look of the under body of the enzo it seems that most of the focus seems to be on the air entering from the sides behind the front wheels. Not sure if that helps at all buy hey I'm kind of interested in functional aero pieces for the supra as well. So I figure I might as well start investigating the various concepts.