I'm seeing more and more of the quicker/higher DF Time Attack cars running what appear to be either raked splitters, or wing-profiled splitters with a distinctly higher height at the trailing edge. I'm wondering which is which.

I would suggest that without appropriate levels of track time and redefining diffuser splitters would be a waste.
It is only one element of the entire package so developing it would require at a minimum tuning of wings and such if not full redesigns of floors, diffuser(s) and wings.

I had only about 120 hp, and much aero. Makes a massive difference, despite lots of people saying that if I took it off I would have gone quicker. (maybe they were right...)

Picture below is an example of the aero I was running with the stock engine making no more than 120hp atw.

https://cimg3.ibsrv.net/gimg/www.mia...c1935eba61.jpg

However now I run a much smaller splitter that only protrudes about 75mm following the contour around. Reason I made it that size is because a book said they tried 25, 50, 75, 100mm on a Porsche and 75mm was the most efficient.

Smaller splitter as per pic below.

https://cimg8.ibsrv.net/gimg/www.mia...9d55c9004f.jpg

Do you have any close up pics please

Got any more pics of that front fender? Preferably without wheel to see how you pinned the flap.

Tim - would you mind sharing what core material/thickness you used for your V1 (larger) splitter? Thanks

Another question
 

That that is an excellent question. Please start a new thread for it.

Materials used:
Carbon fibre with 3mm corecell
Size/thickness of materials:
Top and bottom layer 2x2 Twill, two 411 dual bias carbon, 3mm core cell between

This is taken from page 67 which is actually referring to the new splitter, but I used the exact same material thickness and types as I knew they would work for me.

In relation to the fender, think the poorest man solution ever.

The top of the flap is fixed with bolt with about a 10mm washer on the external side through a hole in the engine bay.

The guard is fixed out with the smallest aluminium tube the hardware store sells, squished down and bent with bolts through it.

Pretty sure I have nothing at the bottom.

And there are closer pictures of the fenders on page 66 however the fixings still don't show, and it isn't as simple as going outside and taking a photo. (garage poor)

May as well do an update on some DIY aero tested over the last couple of months.

Obviously conditions over a year cannot be expected to be the same, but this is how I have to gauge things as I don't have the luxury (like most of us) to go back to back testing. So I will preface the below findings with the knowledge that the engine was rebuilt over the off season last year. The only internal difference was a new set of rods, only slightly lighter and a new set of replacement valve springs. The car was dyno'd at 178hp, down from 182hp pre rebuild. Oh and 20kg lighter (titanium exhaust and 1kg lithium battery).

The Aero modification was for the bumper, which was planned to be a diffuser.

I used 3mm ply wood to make two strakes, and cut the bumper to accommodate. These were fixed to an aluminium angle which was in turn fitted to the rails. I then used some of the black plastic from the crusher style front to make flat surfaces where I had cut after the rear wheels.

Times again dropped from a 57.8 to a 56.88 (remember the above point), so I figured that it was doing something, most likely just reducing drag? I then made some CF versions to replace the wood, one layer each side of 2x2 Twill and a 3mm Core seemed plenty.

Also looking at data from the previous year, pb v pb with the new setup I was going faster at 6,000rpm by about 2-3km/h consistently - Thinking possibly due to less drag.

Rear tyre temps were also a little higher, so possibly a little more DF...?
https://cimg0.ibsrv.net/gimg/www.mia...3791168b8c.jpgStrake


As previously stated I really want a diffuser, so I made one to sit up between these strakes. The angle is about 12 degrees over about 830mm (roughly what my 2b rules allow). I didn't add enough strength to the leading edge, and it was dragging on the ground. This has been cut and strengthened but I still haven't tested it again.

https://cimg5.ibsrv.net/gimg/www.mia...5f2b44413f.jpg
https://cimg6.ibsrv.net/gimg/www.mia...f92874c520.jpg


Next modification tested were endplates on the splitter. I'd previously tried with and without on all splitters I had tested, but I finally decided to put some on my newer design since I had already taken a few gouges out of it over the last 12 months. I think the endplates are around 6 layers of CF 2x2 - the shape is just emulating a F488 GT3 or something like that, which is why they are also angled in.

At the same time I also put wheel spats back on to block the air hitting the front wheels head on. Testing was not going well, and it felt like speed was affected, so I kicked the wheel spates off, and instantly the speed returned. I was supprised that such a small increase in frontal area had such a big impact.

I left the endplates on, and I think they are doing something, but honestly not sure what. (explained at the bottom)

https://cimg7.ibsrv.net/gimg/www.mia...5e90c10b9f.jpg
https://cimg9.ibsrv.net/gimg/www.mia...9ddab62b24.jpg

Final aero mod so far is the fender wheel vents. After stuffing around with trying to make a mould to make CF vents, I thought I would just try some poor man vents and see what happened. I tested them on a spare cut up guard, then gave it a shot on the car.

A small gurney was added to the front vent, yes not the best design, but something I've wanted to do for a while, and an easy way to test.
https://cimg4.ibsrv.net/gimg/www.mia...97548d2728.jpg
https://cimg5.ibsrv.net/gimg/www.mia...7c7bd9142a.jpg
As mentioned above I can't really tell you anything specifically from a seat of the pants feel for the last two especially, however the last outing I went to my usual track, fresh from not having been there since the start of the year, and on Mighty Mouse (WTAC CRX) A050 15" made in 2015 hand me downs that have been used and abused, and dropped 0.6 off my previous best time with them in one session, on the only hot lap I did. This makes me think that one of the three things above, or two, or all of them are making a difference.

Sorry I don't have a better answer, or better layout for how these were done, but they were all pretty ghetto, and done with scraps I had laying around.

Great to see you trying new things on your car Tim and getting results. I will need to catch up at some stage and have a look at the car in person, as I'm just starting to think about aero on my SE time attack car. When are you guys running again? I'll be out at Lakeside for the next Time Attack event on the 27th of October.

Nice work and interesting findings Tim. I'm surprised at the size of those elements that you were able to discern a difference from the driver's seat. I suspect that you would have found the same or perhaps even a bit more improvement in drag if you had removed the endplate and left the tire spat. Perhaps with how things were attached the spat was the item that was easier to remove trackside so that's why you went that route. The spat and endplate together create that corner pocket on top of the splitter that adds drag (and downforce). Improvements to the drag when running the two together could be had by shifting the endplate further forward or altering the design so it tapered down as it went rearward so there was an area that allowed the pressure to evacuate out to the side ahead of the tire spat.

Aiming for the Mx5 & 86 race meeting at QR on 3/4 of November, and then Lakeside for the last round of the year 18/19 November.

Ryan I would have thought the same, but I tried the tire spats only at the end of last year on the same track, and I had a similar result in it not hitting the same top speed. This is why I decided to try removing them first. The picture below is from last year with just the spats. https://cimg1.ibsrv.net/gimg/www.mia...3c24761068.jpg

I by no means believe that the tyres should not be covered, I'm just going to try to design a better version that maybe isn't so perpendicular to frontal flow. Maybe I just don't have the hp for that track to make the slightly larger frontal area push through, or maybe I was just not driving well enough that day also.

I would like to be able to increase the front downforce, obviously canards are an option, but perhaps perfecting the spats/endplates would be a better solution first. The endplates are quite easy to cut down, and easy to replace as they are literally glued on (part of the test was to see if they would hold) so I will give them a taper as suggested and see how it goes.

I'm running the wing quite flat, so it would be interesting to dial some more wing and front DF in if I could.

You probably don't want to hear this since you've already made it, but a larger splitter is going to be the best way to get more downforce with very little increase in drag. You have a lot of pressure in front of that nose at speed and the relatively small splitter extension beyond the airdam can only make so much use of it. Same pressure, more surface area.

Agree with Ryan. L/D ratio best at somewhere between 4-6" on most body shapes. However, downforce gains till increase fairly linearly a few inches further out before the curve drops precipitously.
So at low power on full size tracks, L/D ratio is the target. A well setup Miata can actually have a lower cd and almost zero lift compared to a full stock body. That was the goal with the "Crusher" style aero of flat air dam, 4" splitter, high mount GT250. If you have a bit more power and can afford a slight lower L/D ratio, adding splitter length is the low hanging fruit. We haven't tested really huge splitters with the GT250 foil but my guess you would start to over power the foil at somewhere around 7-9" splitter length. Meaning to to balance the car would mean running the foil at a relatively high AOA where the it's efficiency is dropping off.

Didn't notice if you have a gurney flap on , but they work very well on the GT250 and similar foils. Pretty much everyone in S1 runs the gurney everywhere except ACS where we have a long sustained straight-oval section above 145mph.

What about incorporating something like this Tim to smooth the airflow over the spat?

https://cimg9.ibsrv.net/gimg/www.mia...ba915c44b9.jpg