The advice i got from some SCCA guys was 3-4" and the splitter near vertical. For track, I'm following Emilio's advice of airdam/undertry only and haven't built an autocross version for my car yet, so YMMV.

I had a 4" splitter on 245 RS4, Xidas, etc and could NOT get the car aero balanced while running the BFW spoiler regardless how many adjustments I tried. I had exit oversteer. This year I switched to the NLR wing and all those problems are gone.

While this is not really "aero" directly, I wanted to post this here because it is aero impacted and I have come to really respect the ideas/options in this thread.

I have a need to place an auxiliary coolant heat exchanger in my system due to the rear mount turbo. Last track day saw temps hitting 260 when pushing it hard in the heat of the TX sun.

I have 2 options I am looking at for placement and I'd like to get some input.

1. In the duck bill lid like a Porche
https://cimg4.ibsrv.net/gimg/www.mia...68666e6556.jpg

2. Where the license plate is at.
https://cimg7.ibsrv.net/gimg/www.mia...fb3e0e1dec.jpg


I plan to run a GT-250 wing so unsure how that would impact option 1 and not a huge fan of cutting into my fastback but I think it would look good.

Fans will be wired in reverse for both options so the fans are inside the trunk and will force air out of the lid or plate area.

Thanks to this thread, I am also currently building a front air dam and splitter to hopefully balance out the rear wing. (Will trim the splitter to match the final shape of the air dam)
https://cimg7.ibsrv.net/gimg/www.mia...7a39d7a9e3.jpg

Interested to hear how the undertray Naca brake duct worked out?

Vegas has the best setup I've seen for a rear mounted heat exchanger. Take the high pressure wheel well air and duct it into the low pressure license plate area. Should provide a small lift reduction with minimal drag penalty.

https://www.miataturbo.net/build-thr...s-89595/page8/

Ha... what do ya know! 2 birds with one stone and I can mount it so the fans draw air the way they were designed to rather than push. I recall seeing a post where a guy ran ducts to the backup light holes he broke out. Good idea but the license plate spot just looked "right" to me. Glad to see someone else thought the same. Thanks for the link!

The top of the decklid would be a high pressure area, especially with the duck tail, so an exit vent wouldn't work there.

Many higher HP race cars use the license plate area. Its a naturally low pressure area.

Thanks to all those that replied! Now back to work on the air dam....

https://cimg6.ibsrv.net/gimg/www.mia...39888b17ca.jpg
https://cimg6.ibsrv.net/gimg/www.mia...6757530628.jpg

Not definitive yet, and unfortunately I didn't measure *before* temps. (I monitor caliper temp now though.)
The brakes worked ok at the last event, but still suffer from heat after about 4 hard laps. I want to add a form of backing/duct to feed the air better at the hub, but that'll take some engineering.
Either my driving style / power level / grip levels are too much for the brakes now, or Wilwoods just aren't good enough.

For our 1/2 hour races we switched to Superlite and made a huge difference to heat capability AND pad life.....over the Dynalite style.

Are you on Superlite or a Dynalite type?

Big weight/mass difference though. For Superlap we might move back to the dynalites.

But keen to hear how the undertray ducts work out.

New CSP trim!
 

https://cimg7.ibsrv.net/gimg/www.mia...06bbe461cd.jpg

Interested in your continued testing of this. Did you have ducted brakes before? Is there a reason you chose the splitter bottom over the front fascia? You should be able to get much higher pressure from the fascia.

Neither actually. I have the Dynapro kit from Trackspeed. Sadly the Superlite option didn't exist when I purchased them.

No ducts previously (in this iteration of the cars setup). I wanted to try something different, and try keep an efficient and low drag front... and I don't like holes in the front bumper of the car. I can just iteratively test different things until I get something I like.

What brake pads?

Ahh, getting a little off topic now, but Hawk DTC-60

One of my off season project is to add a bit of front / rear aero to my car. Figure I would post here as I got a lot of inspirations from this thread.

This is a rough start of the 'street / track / have fun' version with 3" of protrusion from the tip of the hood. The 'autox' version will be mostly the same though wider to incorporate some fenders to flow air over the wheels. Maybe protrude up to 6" ( class limit ).

For now, I kind of like how it looks with the "big mouth" large front opening but .. am debating if I should try to reduce the height of the front opening a bit ( and blend it back to the bumper ) to help reduce drags since I don't currently have any cooling issues.

Also feel free to throw out suggestions for improvements.

https://cimg3.ibsrv.net/gimg/www.mia...1c1fdd3d99.jpg

Awesome fun cars these.

Smarter people than me will correct this but I think the rough rule of thumb (with proper ducting) is the opening can be 1/3 the frontal area of the heat exchanger (rad/intercooler etc) size. Possibly even less?

You will have HUGE drag (and likely lift) issues at medium and up speeds like that currently.....

My friend builds and tunes these mx5 derivative type cars and he tops out speed wise very easy with drag (nose, uncovered wheels and so on) even with the proper nose...

but man did that 13B sound good

You're right about that the drag. These cars are kind really bricks over 80mph. The best thing to do aero wise would probably be putting the Miata body back on. Luckily my main game is autox so most of the time I'm under 100. That said I have an idea for a revision that will reduce the frontal area more and will start work on that.

Could you point out where you're thinking the lift could be created ?