What does a diffuser do??
 

I know it looks cool to have a rear diffuser on your Z but can someone please tell me what a rear diffuser does. Thanks

A rear diffuser is supposed to add downforce, and on a race car, it does. However, I doubt the add on diffuser for the Z does anything to the aerodynamics. I suspect it for looks only.

Les

None of the diffusers for our cars are tested through data(wind tunnel etc....). Im not sure if it helps our cars are not

im sure the top secret one for example protects rocks from hitting your exhaust lol

read the top 100?s.

diffuser on any car when placed correctly will improve under car airflow. based on the theory of venturi, where a constant volume of air when moving will move faster through a smaller opening than a larger one. so when added to the bottom of the car and using the grnd as the other side of a channel, if u angle a diffuser near the rear axel, air flows faster at the axel creating a lower pressure zone, which will suck the rear end of the car down (granted again, placement and angle of this diffuser as to maintain air flow attachment to the surfaces...)

ive used the ts diffuser at the track i think it allows air to be prevented from being trapped in the rear bumper due to the design of dual
canister designs.

a good book is racecar aerodynamics. look it up on amazon.com

joseph katz i think is author...

Cheston is on the money... not the best explanation but I'm sure he never took aerodynamics.

The venturi effect... is newtons third law of motion. The increase in the velocity of a fluid (yes air is a fluid) is directly proportionate to a decrese in the fluids pressure. If you increase the air's velocity under the car by the use of diffusers you are decreasing the air pressure. You are not necessarilly creating a pressure lower than atmospheric, but one that is lower than the pressure on the upper surface of the car (the body) creating downforce. The Z has no working diffusers available for it.

adds more rasp and hp.

(This is from what I remember watching a special on the GTR and the Z... I forgot what show maybe BM)

The Z was designed to have very little downforce near the rear (or was it zero lift in the front.. i forgot). For what reason, I don't know. But the show compared (the downforce) of the Z and the GTR in a high speed ring... I'll try to find the video...

i remember seeing the same thing

A diffuser will create downforce if applied correctly, but as turismo pointed out, if the diffuser is not wind tunnel tested, like the majority of diffusers out there, it's most likely purely for looks.

Even if the design of the diffuser good, the downforce that it creates needs to work in harmony with the rest of the aero pieces on the car. Again, without wind tunnel testing, it's nothing but looks.

Expensive looks

i agree with the looks on a street car since you really do not need downforce when commuting to work

Just because it wasn't put threw "wind tunnel testing" doesn't mean it won't create downforce.

True dat, but just because someone comes up with an asthetically pleasing design doesn't mean it will produce the correct balance of downforce if any at all. That's why objective wind tunnel evaluation is essential for any practical use.

Plus - Those gawdy defusers kinda fall into the catagory of "Saladbar Wings, Rice, etc" since it attempts to make the car "look" faster than it really is. If it had some actual functional purpose on the street, I'd be all for it.

no aero pieces are going to produce any kind functional effects for street driving

The literature states that the Nismo Z creates functional downforce as low as 70mph.

But yes, for typical street driving, it does not make a difference.

Not true... I go 120mph on my street every night... and my front splitter and rear wing adds LOTS of downfarce.

a diffuser will also lighten the weight of your pocket

LOTZ huh? How many pounds of downforce does LOTZ equate too again? I don't think that one ever got covered in Physics class. Lol~

I'm pretty sure this is what your feeling, Mr. "120 every nite" Speed Racer. Lol.

Heheheh... that's why I said downfarce... ayee..

old thread, I know but I've been looking into obtaining the rear spoiler of the grand touring Z model and then noticed it has a front chin spoiler and rear under body defusers and I was interested in knowing if these too, were not wind tunnel proven to work?

not everything needs to be, or can be wind tunnel tested (mainly due to cost)

if the fundamentals behind the design are sound, the form follows the desired function, and if the execution is correct as in solid/secure installation, bolted to the correct places, etc, it'll work.

granted the measurement of 'effectiveness' will be hard to quantify unless you're comparing lap times or something...

your best diffuser is your OEM rear exhaust.

I think i'll just make a flat underbody out of carbon fiber for the car, and have it "diffuse" out the back following the profile of the fujitsubo exhaust. I'm sure Nissan did there homework when doing the aerodynamics of the car. (i hope)

http://www.my350z.info/download/file...1278&mode=view


a member of the german 350z community is doing trackracing for Nissan. He said their Z is doing 20 Km/h more topspeed thru the "Schwedenkreuz" on the "Nordschleife" with their made underbody and diffusor.

And they also didnt do any wind tunnel tests.
feed this!:icon21:

BTW: Strosek bodykits are windtunnel tested! they do alot more downforce then the normal body.


BTW2: I have aps 2,5" true dual and TS diffusor. Could I call this double diffusor :x?

The TS rear diffuser has been tested and is actually fuctional, Mastergrade has a new front diffuser that is functional as well.

Hey Germanguy, i don't suppose you have more pictures of that flat underpanel on the car?

I thought all Top Secret did was make a few high speed runs with their diffuser/lip/body kit, which showed that the car wasn't unstable with their product installed (and everything else they say is speculation). Correct me if I'm wrong, but I'd like to see evidence first though.

Smoky Nagata took his Top Secret widebody G to over 211mph on the Autobahn in 2005. Aside from the Top Secret wide body kit and the rear diffuser, I'm not aware of that car having any additional underbody aero mods. (If somebody knows otherwise, please don't hesitate to correct me.) The car didn't have a huge GT wing either.



They discussed all this stuff in this thread...

https://my350z.com/forum/forced-indu...-mach-1-a.html

It is an awesome read if you have the time... So far it seems very few rear diffusers have been tested and data logged. I have found more information on the testing other then just that thread ( on page 11 they start dicussing the TS) But I dont feel like trying to dig it all back up. If I ever come across proof and documentation I will be sure to post!!

Regardless of any diffuser or aero mod you have to be going a pretty decent speed before any of it is functional. Like someone else posted the NISMO has to be over 70 to get more downforce.

Many aero mods in research I have done dont get used to thier full effect untill you are in excess of 120MPH.

Diffusers were originally designed for F1 cars. The aerodynamics of the diffusers would evenly channel the air going under the car out the back in a none disruptive manner. The way the diffuser channeled will effect the down force on the car. That all being said diffusers don't work properly without the entire bottom of the car being flat/covered to properly channel the air under the car. So while the rear diffuser adds "some" down force if setup right most of the time it's for looks.

It also effects the speed of the air as it comes out from under the car to create the proper ratio to meet the speed coming off the top of the car for optimal downforce when set up properly.

And it has been determined and researched that the entire body of our cars does not need to be covered for the diffuser to work properly although for optimal performance this would be true...

How about the Voltex diffuser. I think they do wind tunnel tests for their aero parts. Definitely lightens the wallet.

A diffuser - Thats easy, a Diffuser well - Diffuses the situation. (i.e: FBI Negotiator!)

I hope I was helpful!

That's exactly what I was getting at. Just because he did a few high speed runs, it doesn't mean it was "tested" (not in the definition that we're discussing). Yes, it was "tested" to make sure it doesn't fall off and it doesn't destabilize the car, but it wasn't data tested to see what actual numbers it produces on the car vs the car without it.

And I've been following that thread since day 1. :)

unfortunately, not.

Also worth mentioning is that a diffuser has to be mounted to something that can actually support it's downforce and transfer those forces to the vehicle chassis in order to be effective.

The way most of these diffusers are mounted seem to be laughable at best.


Interesting read:
http://www.specialprojectsms.com/ind...?categoryID=30

also it makes your car look like a Hot wheels toy or a shopping kart...i saw a guy with a celica diffuser...i tip my hat off to him, nice clean and OEM looking...not ricey at alll. but dont take other people's opinions bro....its YOUR car....u do what you like, not what others like on YOUR car

:thumbup: Yea I cant wait to see documented results!!!:thumbup:

Lots of misinformation.

1. The diffuser isn't subject to the same forces as a wing, and need not be secured in the same fashion. Its function is to decrease high pressure under the body, not to increase high pressure above the body. It creates a larger net pressure difference from above the body and under the body, but doesn't generate any extra forces.

2. The entire bottom doesn't have to be covered. It helps, but its more important that it's sealed from the sides, meaning side skirts practically touching the floor. The function of the diffuser is to recover pressure of the air flowing under the car, by increasing the cross sectional area and slowing the air down. Slower air increases in pressure, while faster air decreases. Assuming the sides are sealed, we'll call this the ground effects channel. As the air speed decreases at the diffuser, the pressure increases, in order to increase it's pressure it has to pull in more air from in front of it, so it will in effect pull in air even faster at the inlet, in this case the front of the car. The diffuser is indiscriminate. It will pull in air from wherever it can. If the sides aren't sealed, it will just pull in air from there.

3. The most important part of design, is that the diffuser is capable of all this without generating a lot of drag. Meaning at the rear of the diffuser, where the air exits, its speed and pressure are similar to the speed and pressure of the air going over the car, thus shrinking the wake left behind the car.

TK