Do rear deffusers actually work? or are they purely a cosmetic thing?

 

If they do work, what could you expect to be improved from fitting one? e.g. better acceleration as you would have better grip, better handling? etc. etc.

 

Could this also mean i could remove more weight from the rear of the car as the deffuser will halp keeping the rear end stuck to the road.

Not sure mate but i'll let you know when i've finished making mine, its gonna be a copy of the Aston Martin DBS

They do work, many race cars have them from Vipers and corvettes all the way to F1.

 

But they would not work at low speeds, under 70mph for example, as there is just not enough air flowing for it to work properly.

 

Aerodynamic devices work better the higher speed you achieve.

They do work, i've got one coming from a company called Revere.

They will only work above certain speeds and that speed will largely be determined by the aerodynamics under the car. So, I suspect that just bunging one on the back will make less difference than if additional work is also done underneath.

They will only work above certain speeds and that speed will largely be determined by the aerodynamics under the car. So, I suspect that just bunging one on the back will make less difference than if additional work is also done underneath.

 

Correct. Rear diffusers work in conjunction with panels underneath the car. In its most basic terms, the underside of the car needs to be as smooth as possible with incorporated "channels" that feed the rear diffuser. It is all about aerodynamics. The purpose of the diffuser and underbody panels is to create a low pressure area underneath the car in the correct location. This causes a "suction" effect, thereby pushing the car harder onto the road.

 

As stated above, diffusers will only work over a certain speed and even then their use will be rather limited on a road going car as you'll pretty much never need the benefits that a diffuser offers, even at (legal) motorway speeds. Furthermore, the aerodynamics of our cars is such that by the time the air reaches the rear of the car the airflow is so turbulent that there wouldn't be a benefit anyway. What is often far more effective is a propperly designed rear spoiler. That will produce more downforce at the rear of the car than a diffuser would at normal speeds.

Doubtful you'll get any difference from an off the shelf job.

To expand on what Danny said, the actual job of the diffuser is to get the air from under the car back to the same speed and pressure that it was at before it went under there, and to do so with minimal drag.

It's the reduction in area under the car and associated increase in air speed/decrease in pressure that causes the downforce, the diffuser just acts on the end of it to reduce the drag caused by the transition back to the original speed / volume.

Without being attached to a proper undertray and being angled/sized/shaped correctly you'll just have something that looks OK and probably causes more drag.

Look at how most of this aftermarket stuff monts. Are you really supposed to believe that a spoiler / diffuser held on by a few M6 bolts is carrying any aerodynamic load? Would you expect it to hold 40kg if you hung it on there as weight?

This is what you need:

You can't get the underside of a zed as smooth as that for start.

 

So basically what's on a fast VX Astra and what's on an Enzo is the difference between show and go!

UAS 300zx Track car :

 

Hmm slick rears, semi-slick fronts!

 

 

:D

Thanks guys.

 

I would like to do the underside at some point. Mainly as the plastic undertrays are fiddly and a pain and always brake.

 

Might use some thin aluminium sheet. Also will protect everything in the engine bay from crap off the road.

UAS 300zx Track car :

 

 

That's a interesting pic, surely the rear undertray is a bad design? as the air can get under neath it where the edge is?

 

I would want a full under tray front to back over lapping them slightly to avoid the air getting in.

 

What would those hose pipes be feeding air to?

That's a interesting pic, surely the rear undertray is a bad design? as the air can get under neath it where the edge is?

 

I would want a full under tray front to back over lapping them slightly to avoid the air getting in.

 

What would those hose pipes be feeding air to?

 

The hose is for air feed ducting to the rear diff and rear brakes.

ooo.... i get ya.

 

I guess it wouldn't actually cost that much to do this. Would be a nice addition to do.

Beautiful piece of work - might as well have gone and put in the diffuser fins as well to channel and accelerate the airflow before it exits the back.

Beautiful piece of work - might as well have gone and put in the diffuser fins as well to channel and accelerate the airflow before it exits the back.

 

they have since those pictures were taken ;)

look at this

 

http://www.uniqueautosports.com/pricelists/pricelist_300zxstyling.htm