Building a 800whp Time Attack NA Miata in Sweden
 

Hey 👋

I've been in the forum for a little while now, but I don't post too much. I used to live in California, and for the most part my Miata was the typical NA build: Xidas + VVT swap + 9Lives aero + 225 200tw tires.

However, I went more on the full race car direction with a few mods: full TC Design cage, completely gutted interior, motorsport harness on the entire car (engine and chassis) with an AiM PDM, PE Racing pedal box, etc and cut out everything I could to remove weight: front core support, hood and trunk reinforcements, trunk floor, etc.

At this point the car weighed ~1960lbs without driver, and had ~135whp. Not fast, but pretty fun. I'm not the fastest driver either, so it was a good match:
https://cimg4.ibsrv.net/gimg/www.mia...62aeba62ac.png


In the end of 2021 I moved to Sweden, and obviously I brought the car with me (that was very questionable decision, but a story for another day). It took me a while to get things sorted and make it out to the track (driving license, tow vehicle, trailer, etc), but I finally it made it to my first day with the Time Attack organization I planned to run with (TimeAttackNU) in August this year.

After tracking in California for 2 years and never catching a single drop of rain, this was my first wet track day, and it was raining quite a bit. After a long time without driving the car, lots of changes, new track, first time on the wet, old tires… oh, and no windows to top it off. It was a lot, but it was fun. The car had zero grip, I was seconds off the leader in my class, but I had a ton of fun. Here is a short video of me sliding around:
On that same event I had also agreed to meet with the organizers to go over the car and see in which class I should actually be placed. I had obviously read through the rulebook, so I knew that'd be "interesting". Power-wise, the car fit in the lowest class, called "Club Go!", which has a power to weight limit of 5.7kg/hp (~12.5lbs). However, upon inspecting the car the organizers told me I should be in the "Pro" class, 4 classes above "Club Go" with a power to weight of 1.4kg/hp (~3lbs), and the possibility of going as low as 1.2kg/hp 🙃

I could try to ask for an exception, rebuild the car to fit the lower class, find another organization, buy another car… the possibilities were endless, and yet here we are…

The final power figure is gonna depend on the final weight of the car, but everything is being built to handle 1000hp, and I should be able to run somewhere between 700~850whp based on the rules. For the first year, I will be "only" running 450whp though:

Powertrain:
Honda K24 (stock engine for the first year, will build with sleeves, rods, pistons, etc for the second year)
Garret GBC35-700 (again, for the first year, will probably run a G30-900 or G35-1050 later)
ZF 8HP70 gearbox
Ford Super 8.8 diff
Custom axles with 930 CVs
Driveshaft to be figured out.

The car will run with an Emtron KV8 and CanTCU for the gearbox. The whole fuel system is also being redone, I'm keeping the stock tank for now with a DW300 but adding a surge tank with a DW400 (it can fit a second pump as well).

Of course, to be competitive it will also need HUGE aero (the front splitter is 8ft wide and over 2ft long…). I'm doing all the aero design myself, running the CFD tests and 3D printing parts that will be either used as plugs or wrapped in carbon fiber. There is still a lot of work to be done in the aero package, but these are the current renders:
https://cimg1.ibsrv.net/gimg/www.mia...96cb861157.png


The hardtop was the first project, it's mostly assembled but I still need to finish glueing it, then I'll smooth it out, make a carbon fiber skin and ditch the 3D printed part:
https://cimg6.ibsrv.net/gimg/www.mia...d3e9765f18.png

I'm trying to share some build updates fairly often on Instagram, so if that's your kinda thing you can find me here: https://www.instagram.com/tzagallo_racing/

The first test day is in early May, so it'll be a long winter... 😬

One thing is for sure:
I would 100% shit my pants, when I had to floor that thing the very first time at 800 wheel.

What wheel size and tires are you planning? Those aero mods look ultra cool. The whole car looks sick. Please share some progress from time to time, doesn't have to be weekly updates, maybe a few pics every 1-2 months :likecat:

Good luck!

Thanks! The car is supposed to be on track in 4 months, so we'll see how that goes. When I get to 800whp I'll 100% be relying on the Emtron traction control for most of the time lol. In 2024 I'll be running 15x10s with 245 Nankang CR-S. For the next year I'll likely go up to 18s, and then I could run 315s, but it'll all depend on how the first year goes.

I got the K24 + 8HP70 on Dec 31, just in time to start the year with the engine in place. It fit pretty nicely, plenty of space around the gearbox, but it sits just a bit under the frame rails. I'm using the Kpower oil pan and engine mounts and DomiWorks K24-8HP adapter. I had to trim the transmission adapter plate to clear the oil drain plug, will also have to trim bellhouse at the same place the next time the engine comes out.

https://cimg4.ibsrv.net/gimg/www.mia...2d02bd264.jpeg
https://cimg6.ibsrv.net/gimg/www.mia...b9d869b08.jpeg
https://cimg5.ibsrv.net/gimg/www.mia...c4b8f877d.jpeg
https://cimg8.ibsrv.net/gimg/www.mia...0ddebc94f.jpeg


I'm now working on the transmission and differential mounts, driveshaft after that.

Awesome car! Very much looking forward to the rest of this build.

How is the fitment of the 8HP in the trans tunnel? Any clearance issues? Is the trans pan sitting below the frame rails?

Edit: I'm an idiot that cant read. Are you going to leave the trans pan below the frame rails, or try to raise it a bit so it's more protected?

I don't think it's viable to raise the transmission, as the engine already doesn't clear the hood. The car will have a flat floor, so I'm hoping that will be enough protection.

Makes sense. Def following to see the progress on this and will be taking notes for myself in the future.

I noticed the significant change in handling with only 350whp going from a Spec Miata style 6pt cage to a near FIA style 10pt cage. It's a tub designed to be just barely enough for 125whp. I assume you have plans to add significant bracing in the interior and engine bay. If not, I'd recommend it. I presume you will be either heavily reinforcing the control arms and subframes or replacing them entirely. 150whp autcrossers tear subframes apart. Looking forward to the in car videos!

The cage was already the "Time Attack spec" from TC Design, so it has a few extra places it's tied down, like the middle of the door, the A-pillar, anti-intrusion bars, etc. What it doesn't have, and I plan to add, are the bars that go to the front shock towers. I'm adding significant reinforcement to the rear subframe when I add the diff, and also extra bars to tie down the rear air jack. I haven't planned out the front subframe and control arms though, I know the front subframe needs the gusset on the control arm pickup points, would you suggest doing more than that? At 350hp did you have issues with the control arms? I was hoping they'd survive at least the first year at 450whp.

https://cimg9.ibsrv.net/gimg/www.mia...c432dbf4d.jpeg
https://cimg7.ibsrv.net/gimg/www.mia...75455f24d.jpeg

We never tore or broke anything. But lots of others have at much lower power levels. Autocrossers tearing rear control arm tabs out of subframe. Spec Miata tearing fronts out. Wheel hop from rear control arms being noodles at 400lbs tq. Flex in the chassis was noticeable through the controls in my builds. The sway bars and spring rates needed some additionally tuning when we swapped to the beefier cage. TC built ours too. Fully seam welded, dash bar was curved attached to firewall. Look for our Vegas and OGK threads for those cages. Extensions to shock towers. We built a brace to tie the front frame rails together after we chopped the radiator support section out.

This is OGK set up for OEM booster. Vegas had a similar set up but with straighter extensions and Tilton pedals, no booster.
https://cimg2.ibsrv.net/gimg/www.mia...70e01f9bac.jpg

looking forward to following this one as I am planning to run an 8HP45 or 8HP50 on a turbo K24. Any details you can give on how the CANTCU works for you I'd be very curious about!

This is unhinged. I'm scared already. Having said that, can't wait to see the rest!

I'll keep that in mind when working on the subframe and add some reinforcements. I'll probably just hope for the best with the control arms for now. I'll look into adding the shock tower bars, my only concern is the clearance for the 18" wheels in the future, so it'll likely need a decent bend too. That brace is interesting, I'll see how the radiator and aero mounting goes and consider it. Thanks for the tips!

Yeah, of course. I should be receiving both the Emtron and the CanTCU soon, but it'll be a minute before I can get started on the wiring. The shop that is sponsoring me is helping plan everything, but they asked for a ton of sensors, so it'll be a much more complicated harness than the previous one I built. The car was fairly analogue aside from the PDM/datalogging sensors, and between the new sensors, paddle shifters, gearbox, ABS, EPS.... yeah, it'll be a lot of work 😅

I tore the rear subframe mounts for the lower control arms off at 350whp on drag radials. I ran the car about as hard as anyone could though at the drag strip, got some vids on my channel cutting 1.5x 60' times with a stick.

It's a weak link in my build now that I haven't addressed, but I know I have to do something about it soon. Not sure what I'm going to do yet as I like the stock subframe, sort of. I think I'm going to buy a spare and cut it up a bit, and then reinforce it. IMO, some of the tubular options are wayyyy less stiff than the stock one, and of course stiffness and strength both matter a lot.

Also thinking about taking apart and modifying the stock lower A-arms to stiffen/strengthen them but not sure yet. Would love to do some sweet 3d metal work but it sounds like a big project to do it right.

This is correct, as someone with direct experience with popular aftermarket tubular arms and subframes.

I found a local fabricator that will help me out with the rear subframe project, should be a good chance to improve my skills (which is much needed) and make a proper stronger piece. Unfortunately I can't remove the front subframe right now, as I need it in place for measuring everything else (driveshaft, turbo manifold, etc), but I'll get to that later.

I got a sponsorship from Nuke Performance and will be running their surge tank, FPR, rails, fuel filter. air jacks, etc. I will probably try to keep as much as I can of the fuel system in the trunk (minus the regulator, of course), then will be running AN-8 feed and return lines to the front. The idea is to make an aluminum bulkhead closing against the cage.

https://cimg8.ibsrv.net/gimg/www.mia...2b8c688af.jpeg

I'll be running a 3 air jack setup, and the idea is to place the front two near the front jacking point and the rear one in the subframe as mentioned. The fitment near the pedal box is tight, but it'll be a lot better once the clutch pedal is gone.

https://cimg3.ibsrv.net/gimg/www.mia...b2e2894b80.jpg

These past two weeks I’ve been working on fabricating the transmission, diff and rear air jack mounts. This is something I have very little experience with, so progress hasn’t been as quick as I’d like, but that was expected.

The transmission mount I built on my own, it’s super simple, and it’ll still add some reinforcements later. The first side took me a ridiculous amount of time, but the second side was 10x faster, so at least I’m learning. The welds range from passable to embarrassing, but they have good penetration.

https://cimg2.ibsrv.net/gimg/www.mia...c14271a10.jpeg

Last week I met with a local fabricator (@nordic_restoration on instagram) to learn from someone who actually knows what they are doing. We worked on the rear subframe together all day, and while we couldn’t quite finish it, we made good progress. The first photo is how far we got: we got the rear diff mounts in place and the air jack mount tacked. I'm now working on the front diff mounts in the second picture.

https://cimg1.ibsrv.net/gimg/www.mia...250aa6907.jpeg

https://cimg3.ibsrv.net/gimg/www.mia...ba143b14a.jpeg

Over the last weekend I also got some time to mess with the 3D model a bit. The rough ideas are pretty close to what I want, but I need more rear downforce and I’m still fiddling with things to try and increase efficiency. One of the big things was just the dirty air from the front tires interfering with both the rear wing and the floor. I added fender vents, barge boards, turning vanes and air curtains to try and work together to control the front tire wake. I also added some fences to the side skirts to try and seal the floor a bit better. Finally I added some extensions to the rear diffuser strakes to create a vortex on the outer edge and try to protect the diffuser from the rear tire wake. I ran the simulation with all these changes combined, as I’ve been running more accurate simulations and these take a couple of days to run. The whole package seems to work, and had a pretty big bump in efficiency, about 20% better L/D.

https://cimg5.ibsrv.net/gimg/www.mia...dcfc83c4c5.png
https://cimg6.ibsrv.net/gimg/www.mia...b61065ad7e.png
https://cimg4.ibsrv.net/gimg/www.mia...8249c84d16.png

I ran some lap time simulations in OptimumLap, and I’d like to target a Cd of 0.8 and Cl of -3, without any major increases to the frontal area. The challenge is that I’m already pretty close to that Cd, but need a lot more rear downforce… about 30% more. I still have a little bit of time to play with this while I finish some other things, but I don’t want to go too far, so we’ll see what I can come up with in the next few weeks. Looking at the front projection and the drag bubble I think there's a lot of room to reduce the drag. The first that sticks out (literally) is the rear wing. That is tricky because of the added height of the fastback, so even at that maximum allowed height for the wing the low pressure under it is already interfering with the fastback. I'll design a new wing and give it a try, current thinking is a triple element with smaller flaps/higher aspect ratio. The other area is the front fender, the rear part sticks out quite a bit, and although I like how it looks, I suspect it might not be very efficient, specially considering that the current struggle is adding rear downforce.

https://cimg7.ibsrv.net/gimg/www.mia...344913bdaf.png
https://cimg8.ibsrv.net/gimg/www.mia...a458d382ec.png

This is getting serious

what are you using to run these simulations?

I use OpenFOAM to run the simulations and ParaView for the visualization.