Diffusers, functional? (copy)
 

This thread is a copy of the one in the 3rd gen forum. I thought the racers of any generation might be able to provide a more complete and accurate answer to my questions.

Yes, i know what a diffuser is and what it allegedly does. Which ones work the way they're supposed to, and how fast do you have to be going for it to have any effect?

Also, did you notice any other differences after installing it?

Well, look at it this way. Even really well designed wings placed on a car provide about a 1.4 downforce/drag ratio. A well designed diffuser provides about a 7.0 downforce/drag ratio. This would suggest that even a relatively poorly designed but functional diffuser should give better performance than any wing - and especially better than the idiotic ricer wings that most people put on their cars in an effort to get attention.

On the other hand, any underbody aerodynamic device is VERY dependant on ride height and attitude, so they are hard to make work as well as they should on a road car. Suspension movement should be minimized to get good stable downforce numbers, but that makes the car an absolute torture device to drive anywhere but on the track. You also need to manage the airflow all the way from the nose of the car, not just the cosmetic area behind the rear axle that most fake diffusers cover. At the height of ground-effects performance in Formula 1 back in the 80's, cars actually had sliding side skirts to keep the low pressure area from spilling out from under the car to maximize downforce. As with most aerodymanics the effects start becoming measurable over 30-40 mph, but both downforce and drag increase exponentially with speed so it is much more pronounced at higher speeds.

What I would ask is what is the highest return for your effort/cost and least involved to get a benefit from regarding Aero?

I would assume that would mean a chin meant to work at virtually any angle the car can reach without the wheels leaving the ground (so it maintains at least a neutral AoA at full lean back from acceleration) and some kind of a wing that also can work that way via the angle it is at if not some sort of negative lift.

... right? This is just my somewhat educated guess :p

And, of course, with anything you do, eventually you hit diminishing returns... and bear in mind that if you have to ask on RX-7club you can't really maximize it. This ain't a GT500 car, its a street car that has to have the suspension travel and spring rates to not bounce off potholes.

Diffusers are very functional, if they are well thought out, designed correctly and installed properly. You cannot just bolt on a rear diffuser and magically have your car glued to the ground- you will have to smooth out the entire length of the bottom of the car and use the venturi tunnels created at the rear of the car (by the diffuser) to keep the rear of your car glued to the track at high speeds

check the race section threads as there should have been a recent discussion covering much of this