Well, since this ain't going further, if OP was to panel the bottom of the car at the rails for win, what material would you use and how to cope with exhaust temps should you 'box' it in?

Wrap the exhaust from turbo to tip, use aluminum or CF with a skeletal structure, trans+diff coolers would be 100% required, and you would need to figure out a way to duct cool air to the inner CV boots.

C'mon guys he mounted it exactly how the manufacturer wants it mounted on an Elise. What could possibly be different between an Elise and a Miata?

https://www.miataturbo.net/attachmen...ine=1336000074

Oh, right.

The OP isn't really that far off of where he should be with the diffuser though is he? I mean, his is only a couple inches lower than these cars:
https://www.miataturbo.net/attachmen...ine=1336003107
https://www.miataturbo.net/attachmen...ine=1336003107

It seemed like everyone was talking like he should be hacking the bumper until it looked like this:
http://www.awrracing.com/blog/wp-con...7/DSC04771.jpg

(just bought a used Exige diffuser so this discussion interests me ;))

Yeah, only 8-12 inches off where the 2nd cars is at. What other goodies are sitting under those two cars?

1. The diffuser isn't where the bumper is cut.
2. ~9 inches from the bottom of the bumper is where the crease is. No idea if that's the factory location on Matt's car but it looks close so I doubt his bumper is cut even 8".
I'm aware. That's a completely separate discussion though.

Well, the stopwatch don't lie. Looks like the diffuser is easy enough to remove from the brackets, and if you can get 60 laps in a day at your local track, then you should be able to get some back-to-back tests in. Take some times and post 'em up. "Butt dyno" readings don't count either. :)

The bottom line is even the high-dollar F1 teams have a hard time correlating theoretical and CFD results with on-track performance, so this is all just armchair quarterbacking until you get some hard data.

I dont think you will convince anyone here that it has value with some numbers. in the rear defusers ive seen they dont mount flat they slat up at a significant angle and that leading edge is higher then the lowest point so the car is channeled and control. but Im sure you know this.

also when you do unconventional mods and post pics you gotta be prepared for criticisms. I go all kinds of ---- from people for spraying windshield fluid into my motor 10 years ago. didnt mater what i said right or wrong. now everyone is doing it and you can buy like 10 different kits all the new hotness. I should made a kit and proved it worked but whatever. so if you want to prove us wrong do it. casual talk is not going to do much. just sayin, I dont really care because doing something like that is way off in the distant future. I made a sick tray and diffuser for my RC car and it looks bad ass, no idea if it does anything....anyone want to buy a kyosho GT2 ;)

It is not a separate discussion. Diffusers don't work well without a flat undertray in the first place. Aero pieces should be thought of as a package, because they adding pieces to the front will affect the rear, and vice versa.

Guess even "real" racers don't go everything at once....:dunno:

My turn at armchair aero…


If you're adding a flat bottom later, as you say you are, then I see nothing wrong with the position of that diffuser, assuming the flat bottom will join to the front of the diffuser. Your ground clearance isn't helped much, but if it's a track car then that doesn't matter, and if it's a road car and you're prepared to live with it, then fair play.
I do think you'd still need to cut the bumper out a little more above the diffuser with a flat, sealed bottom, to help suck some air out from the space between the flat bottom and the underside of the car, just to help keep things cool. Assuming, that is, that air can be drawn in to that space from somewhere.

exactly.

https://www.miataturbo.net/attachmen...1&d=1336153649

I was only discussing the height of the diffuser at the time, which is why I said it's a "separate discussion"

Of course aero stuff only works well as a package but I was ignoring that in that reply because a lot of people were criticizing something that wasn't even that far off. The Miata doesn't have that much rear overhang so a 15 degree line from the rear differential area doesn't end up that high on the rear bumper.
Interesting find. Didn't realize Matt didn't have a flat bottom on that car. I assume that "diffuser" was designed differently than one would be for a proper setup then because Andrew Brilliant did the design IIRC.

if the bottom of the bumper was cut do air could travel over the top and the diffuser was left as is how well do you think this would work? would the air doing over the diffuser also help create downforce whilst not creating drag??

like this elise s1 diffuser

https://www.miataturbo.net/attachmen...ine=1336516276

The purpose of the diffuser is to smooth out the remaining airflow, this "remaining" airflow is what's left after a FULL F*CKING FLAT BOTTOM.....like the lotus pictured above, or any supercar photo....

if you have turbulent air on the front 80% of the car, the diffuser is basically nothing else but an aero drag. As now you have introduced another element In which the air flowing underneath the car has two different paths to take.

Yes, cutting holes in the parachute area will help, but think of all the videos of the failed skydivers with their cut/tangled lines. The tangled / cut parachute still slows them down, but not as well as a fully working one.

I.e. moral of the f*ching story here...... Retarded add on of a diffuser on an otherwise stock car will not net any usable..(read worth the effort) difference without supporting mods.


Or another way of thinkin. Would any of you, aside from fae, crank up the boost without adding fuel, or addressing timing? No, because you wouldn't do one without doing the rest.

There is no free lunch. You very rarely create downforce without creating drag (unless you're starting with a very poor design).

That being said, I'd do it. Even after you build a flat bottom I don't see that hurting as it's dead space.

I know that picture wasn't your car, but it's hilarious to see someone put in all that work to put a diffuser on the car and then leave mudflaps on the car. That is the first thing I removed on my car. :rofl:

How has aero suddenly become freakin black and white to some overly angry people on here?

Of course, ideally, a flat bottom would be of benefit to the whole package but some attempt at smoothing the the airflow and air transition at the back of the car CAN help in some small way...

You guys rave on about a package, well a package has to start somewhere....who is to say to you "experts" that a flat tray is the sum total of the package. To an aerodynamicist saying a flat bottom and a diffuser is "the package" is probably as ridiculous to them as this is to you, so where does a package start and stop?

Once again I say good on the OP for the effort and good luck with building the car as it comes along, ignore the haters and keep the rest of us informed.

Hopefully you haven't been scared off by the very angry, opinionated few....

I dont think anyone was angry, something gets lost in translation on the web sometimes. I would like to see some data, perhaps it works perhaps it doesn't. I'm interested and hope it works for its intended purpose.

my definition of a package is this: splitter, undertray, diffuser, wing. One affects the other. Adding only one thing may have adverse affects (i.e. adding a splitter may add rear lift).

Nooo, nothing angry here....

must be the web translation .... :eek5: