what about this rear diffuser idea

[J__]

im looking to make a rear diffuser, either outta fiberglass or cf. what do u guys think of this idea

 

 

 

it would be done in pieces, the curved piece + 4 fins.

just bend a piece of metal to the correct curvature, lay glass/cf over it, peel off and cut/sand to shape. then make the fins (lay on flat surface, peel, cut to shape), and then rivet the fins onto the curved piece. wat do u guys think. also do the fins have to be at a certain angle, or r they straight, i knw very minimal in terms of splitter effects.

[naviathan]

Nice shop job, and it would probably be effective. Give it a go and lets see how it turns out.

[proxlamus©]

the aerodynamics testing Hybridz did a few months ago determined that a rear splitter/diffuser would be close to useless..

 

it would look cool.. but thats it

[Savage42]

I would agree. Unless you can build a full flat bottom tray to smooth out all the air going under the car and they diffuser/vortex generators would need to go farther forward under the car to do anything. As was said, it would look cool.

[DHale_510]

Without a flat or tunnelled bottom leading to these slats all you have are rudders.......

[johnc]

Funny, both myself and Chet Whittle (of ITS ARRC fame) made diffusers using custom fuel cells and few other tricks and we both saw positive improvements in rear grip. The underside of a 240Z is basically flat, you just need to get the car low enough to the ground to make the diffuser work. You won't see any huge gains but you will be able to give the car a little more throttle in the turns.

[tube80z]

Funny, both myself and Chet Whittle (of ITS ARRC fame) made diffusers using custom fuel cells and few other tricks and we both saw positive improvements in rear grip. The underside of a 240Z is basically flat, you just need to get the car low enough to the ground to make the diffuser work. You won't see any huge gains but you will be able to give the car a little more throttle in the turns.

 

I won't argue with your results but I wonder if it's really the diffuser that's helping or the fact that you don't have a parachute in the back of the car creating a high pressure zone?

 

Cary

[johnc]

I won't argue with your results but I wonder if it's really the diffuser that's helping or the fact that you don't have a parachute in the back of the car creating a high pressure zone?

 

Could be that, could be that we stayed at a Holiday Inn Express the night before the race... . Its anecdotal information so its not something you can take to the bank.

 

Now, if you want my experiences with a front splitter that DIDN'T work...

 

[Datsun350Z]

Looks good... Go for it.

 

I don't see any reason why the fins would be anything other than straight.

[rags]

Could be that, could be that we stayed at a Holiday Inn Express the night before the race... .

 

That's great! ^

 

I say if your thinking about it why not try it? What's the worst thing that can happen, you do see any improvement in aerodynamics but the rear of the car looks better? I don't think it's gonna hurt anything. Give it a shot!

 

Joe

[Mayolives]

QUOTE FROM ABOVE "the aerodynamics testing Hybridz did a few months ago determined that a rear splitter/diffuser would be close to useless.."

 

Perhaps you should study the aero test findings more carefully, before you "spout" misinformation to those who are interested in diffusers.

[J__]

i do plan on making a full, flat belly plate and front diffuser to go with this rear one, as without them, the rear's pretty much just for looks...

 

for the angle of the fins, some rear diffusers ive seen have the fin start out narrow and close together and eventually opening up funneling outwards, maybe creating a low pressure zone? like the ford gt's rear difuser

[blueovalz]

That makes sense. A purposefully designed diffuser is to SMOOTHLY increase the channel(s) cross-section area. That could be horizontally or vertically. To rapid of an increase in area will result in turbulence, and reduced effectiveness. And has been noted, all surroundings must be taken into consideration as well. Outside of all of this I think it would look cool. Last year I contemplated the same for the rear of the BlueOvalZ, put I hate putting anything on it that is non-functional, and as yet I can't determine if it would, or would not, be functional.

 

On a side note, I've found it extremely interesting lately about how the theory of lift on wings appears to be getting "edited" so to speak. It seems that the theory now includes air displacement rather than solely in a difference in pressure as a primary force. Interesting to note that the new thoughts on this match exactly what the F1 wing does in the rain, which is that it creates a huge rooster tail as water (air) is forced upward quite dramatically behind the wing.

[MoNkEyT88]

The air flowing through the diffuser exits through the rear of the car. Figure 2 depicts a close-up of a diffuser exit, from the perspective below and behind a Ferrari. Although wings and diffusers work similarly, they are based under different concepts. A diffuser serves to eject air out from the underside of the car. This pulling action increases the velocity of the air below the car, so that the more slowly moving air above the car will push the car into the ground. Diffusers, when working properly, can be extraordinarily important to the aerodynamics of a car. When F1 cars travel around the track, the diffusers produce 40 % of the total downforce. When not working properly, these devices can befuddle even the most experienced drivers."

 

Fig-2

 

 

Here are the beginnings of my diffuser project. I really don't have anything to work with now, as I have no car to fit it to, but I started making flat pieces of carbon fiber. The fins will be carbon, with a 90* bend at the top to rivet to the diffuser panel.

 

This is a bit wet cuz i wiped it down.

 

 

You can see here a simple diffuser. Some say simple is better.

[tube80z]

Just putting a ramp in the back of the car isn't really building a diffuser. Sure it's a crude one at best. But a real diffuser has a throat section that leads to the ramp and often a aero plug as well. If you look at how these work they are really to accelerate air under the flat section ahead of the diffuser and that's what creates your low pressure zone.

 

If you don't have a copy of Mcbeath's new book (he writes aerobytes in RCE) then you will want to get it.

 

Cary

[proxlamus©]

Mayo..

 

I will go back and re-read the data..

 

I just recall a thread that determined it was not very effective..

 

thank you

 

 

I found this mentioned from good ol Jon

The wind tunnel operator thought the rear diffuser was a waste of time, not Mike Kelly. It was stated that bigger gains could be had working on the top of the car than the bottom.

 

and this from Mike Kelly

And yes, Bob Smith said rear difusers are a waste of time. Here's why I personally agree with him:

 

On both my C5 Corvette, AND on my 996TT, the bottom of both cars is flat as a sheet of plywood. We don't have that with out Zcars. Further, cleaning up the underside of the car might impact a number of areas negatively. Impacting that is the simple fact that our Zcars have a lot of sharp and abrupt edges. Unless you completely redid the whole underside of the car, and then worked dogedly to do a widebody kit (Like Bob_H's) and covered all the other issues, doing a rear difuser would be a complete waste of time. We're dealing with 35 year old cars, and we're also trying to get the biggest bang for the buck in testing for ALL of our members.

[johnc]

which is that it creates a huge rooster tail as water (air) is forced upward quite dramatically behind the wing.

 

You're seeing the combined effect of the wing and the diffuser. In F1, CART, IRL, ALMS, etc. the rear wing and diffuser are designed to work together, multiplying their effectiveness. That's why you see some incredible downforce numbers for diffusers/underbody aero. The rear wing helps the diffuser extract air from under the car.

 

Also, a Gurney lip on the bodywork above the diffuser (where the high pressure moves off the back of the car) increase diffuser effectiveness. Audi used one on theri R10.

 

http://www.mulsannescorner.com/audir10-2.html

[johnc]

We're dealing with 35 year old cars, and we're also trying to get the biggest bang for the buck in testing for ALL of our members.

 

Best bang for the buck is a big wing on the back. Period. Given other parameters (rules not allowing wings/spoilers, style concerns) a diffuser can give some downforce gains, although no where near as much as a wing.

[MoNkEyT88]

whos car is this?

k.. found it.. http://forums.hybridz.org/showthread.php?t=114152&highlight=stunning

[proxlamus©]

Thats Toms car.. (mayolive) if i recall