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