Most areo dynamic body kit
 

wich one is best for down force - there are tons!!!

varis arising 1&2 look good

Nismo is on the 370z race car

and then there is the chunky nismo S tune

plenty of others

so many but none speak of downforce and no one seems to talk about that or how the aerodynamic coefficient is changed

Because the only ones that have be wind tunnel tested from what I have seen is the nismos. All the rest are cosmetic, but can they create downforce, sure, to what extent, who knows. I remember reading somewhere the extra down force the 09-14 front provides, but can remember.

despite all the fancy talk, i think stock for stock, the base with sport package is still faster than the nismo's with all the decorations. that said, the aero dynamic coefficient is pretty useless on the streets... so why not make your car look good vs spec racer talk. if ur going to race, chances are you're going to need more down force anyway.

to me function follows form, Ive got a 09 370 touring (not sport) that is my project car while im in school. The end game for the car is to be the ultimate sport touring car - quick enough to have some fun at a time attack, and nice enough on the inside to not hate it everday

Amuse tested theirs.

if what you want is a great sports touring car (assuming you mean something that drives great but is comfortable to ride in on a daily basis or over long distances) you already own that. if you are looking to do some time attack. add a bigger oil cooler, grippier tires, better brake pads, thicker sway bars, and get on a track. you don't need a body kit to achieve either one.

now if you are going for a certain look and want to also be able to tell folks that it isn't just for looks, then the Nismo and Amuse kits claim improved downforce, and have been tested. Although, there is a thread floating around that at least from a theoretical standpoint claims that the Nismo kit doesn't much if any improvement at speeds. Note the use of the word claim in the last couple of sentences, very little substance there imho. If anything I'd be inclined to believe the fact that they in fact do jack diddly.

You can start by pulling the fuse

I think you meant form follows function. As in you're more concerned about performance attributes than aesthetics.

As others have posted, unless you are building a designated track car, the body kit aerodynamics are almost negligible. If you want to change the body and gain performance benefits purchase parts that aid in cooling. These cars run hot in stock form and get ridiculous when modded or tracked. Purchase a front bumper that allows more airflow, a vented hood for heat release, ect.

:iagree: they don't only design body kits for "looks" but mostly functionality, thus the high price for an original JDM part due to the real R&D involved

If your looking for downforce as a functional aero kit the Nismo (not s-tune) is the best option.

Here is how I plan my setup:
Nismo front bumper
--Center duct for Intake (installed)
--Brake Ducts (installed)
--Front Splitter (Still in development)
--Dive Planes "canards" (still in development)

Nismo sideskirts: They reduce lift as they protude and eliminate some air from flowing under the car.
--Side blades (In development)

Rear bumper:
--Cut and modified for custom exhaust and diffuser.

Rear Diffuser: I have a custom Difflow GTR diffuser modified to fit the nismo.

Rear Wing: The Nismo rear wing does a good job however I would put my faith in the APR GTC 500 with a gurney flap. This will be taller and get into more clean air allowing for more efficient down force... and its adjustable...

Lastly,

Under body panels: I am working on developing a nice set that will work with side skirts and be efficient. Pairing this with my rear diffuser will do alot to reduce lift and increase downforce...

http://i234.photobucket.com/albums/e...pso1bcmuxr.jpg
http://i234.photobucket.com/albums/e...psaxnyho9x.png
http://i234.photobucket.com/albums/e...psqqxouksq.jpg
http://i234.photobucket.com/albums/e...psu7bdyh55.jpg
http://i234.photobucket.com/albums/e...psu7bdyh55.jpg
http://i234.photobucket.com/albums/e...psu7bdyh55.jpg
http://i234.photobucket.com/albums/e...pshnpo1owr.jpg
http://i234.photobucket.com/albums/e...pspwqs5d36.jpg

Lol yes that what I meant - I'd like to build a street able race car...like very nice interior but other otherwise it's a track machine

Ah okay so it's really more a looks thing with these other companies wich makes sense some of the designs are just...blocky

That's exactly what I'm after - except I like the look of 2015 nismo rear - did you build the rear stuff I will absolutely buy a 2015 rear bumper with that diffuser - and I agree 100% for under body stuff only thing I've found so far is a Zspeed front only aluminum thing - are you going to be selling under body flats when you make them.

let's just say they are untested, so as not to come to an incorrect conclusion. but likely, yes, the majority are just for looks. i even have doubts regarding the nismo and amuse kits, unless you do some addons like bullitt posted. then again, i tend to be pretty cynical if i don't get to see the numbers.

also following that same train of though, i wonder if the nismo kit is adding much value, or if the sideblades and diffusers are doing all the work. i know the nismo front has a bit lower drag coefficient IIRC, but other than that are you gaining much? bullitt, thoughts?