[norbert24]

Sorry to dig up such an old post... but this seems to be the only place on the net where people seem to know what they are talking about!!

I sold my soul and decided to trade my 1989 325i for a 1998 honda civic hx. I am doing more commuting these days and I just needed better mpg. In my quest to get better gas mileage, I have decided to make a rear diffuser for the honda. Its a little besides the point, but if you have to know, its because the underside of the car is fairly consistent until after the rear control arms. There is an expanse under the trunk that allows the rear bumper to act as a parachute. So at the least I am going to seal that off, but also, since I am a nerd, I am going to add in diffuser fins to try and decrease the overall drag of the car.

So... yes. This is for a street car, and not a race car. Furthermore its for a very slow and underpowered street car. And yes, I understand that the benefits of a rear diffuser are probably not very substantial at free way speeds. But I am going to do it anyways.

Can anyone clarify which angles you are talking about here?

Are these angles of the "bottom" of the fins relative to the ground? Or are these angles of the fins relative to each other?

Thanks!