NA6 Brake upgrade

The NA6 was not exactly blessed with large brakes from the factory. On my track car this had been previously dealt with by using integrated brake ducting which I installed by welding 3″ exhaust pipe onto the backing plate as a mounting flange, and then feeding some SCAT tube into the bumper opening. This worked well enough for the pace I was managing to achieve out of an NA6 with a stock motor.

Brake ducting seen here

The brake ducting worked well enough and for my purposes was significantly cheaper than a brake upgrade however after a while the NA6 stock calipers started leaking, the caliper pistons showed significant scoring so a rebuild wasn’t worth the effort.

The decision was made to move to the NB8B brakes, in Australia all NB8Bs came with the big brakes from factory, in North America these are referred to as “Sport suspension brakes” the calipers were sourced from rock auto. Second hand these brakes cost around $600 aud locally, or I could buy reman calipers from rock auto for approx $400 aud delivered. A no brainer, the stock master cylinder was retained during the upgrade.

This brake upgrade is a very significant size upgrade for NA6 owners, with the brake disk sizes below

NB (1999-2005)
Front disc Sport brakes = 270 mm
Rear disc Sport brakes = 276 mm

Front disc Non Sport brakes = 255 mm
Rear disc Non Sport brakes = 251 mm

NA 1.8 (1994-1997)
Front disc brakes = 255 mm
Rear disc brakes = 251 mm

NA 1.6 (1990-1993)
Front disc brakes = 235 mm
Rear disc brakes = 231 mm

The upgrade process is reasonably trivial, a little bit of trimming of the backing plate and they’re done. The only caveat is you need to make sure you source the caliper bracket with the caliper.

I am using Enkei RFP1 15×7 +30 wheels and they did foul on the caliper ever so slightly. Some people suggest that running 5mm spacers will fix this however I’m not a fan of spacers in general and I found that the outer casting marks on the caliper were only hitting ever so slightly on the inner barrel of the wheel, the wheel would mount and fit however you could hear the caliper dragging on the wheel. I was able to take an angle grinder to the casting dags and make enough clearance, for the wheel to spin freely, no more than 1mm of material was removed

You can see here where the rust is forming, this is where the caliper had to be shaved down

Fitment on these enkei wheels is very tight, however they have an unusual step in the barrel you wouldn’t get with most wheels .

The brake bias has moved somewhat to the front, not an issue for street driving but it is noticeable on the track. A bias valve would be recommended but not strictly necessary.

Prototyping, racecars and lockdowns

So the Covid-19 in Australia has been in full swing for the past 5+ weeks, while in my day job I’ve been working from home since early Feb. Normally spare time is something I’m in very short supply of and I would revel in the extra time at home to work on the cars, prototype some new parts. But the landscape has bought in challenges.

I cannot get supply of filament, most filament is sourced via China and as a result it has been on back order since February. All remaining stock will have to be earmarked for customer orders.

I also cannot source electronic components needed for parts like the MX-5 Center console delete , as these were sourced out of China and the final design of this part was only completed just before the lockdown.

So on to the cars, the MR2 needs a lot of work, however it’s all major labor and getting parts is a challenge again. The laundry list includes.

  • Engine removal
    Timing belt, clutch, waterpump
  • Oil system removal
    Laminova core removal, turbo feeds, remote oil filter
  • Fuel tank removal
    New fittings and walbro 460
  • Radium Fuel pulsation dampener install
  • Relocate FPR800 fuel pressure regulator
  • Install E85 sensor in the return line
  • Trim 222D hatch to fit better

A lot of the work is major, and with supplies thin on the ground I don’t feel like dismantling major systems which I wasn’t prepared to do. As I’ve gotten further along in my car career I prefer to have all my parts sitting down ready to go, with fresh seals, gaskets and other spares in the event of issues.

The MX-5 is in a good space with very minor work needed, the largest of these jobs is to colour code the hardtop and refit the front splitter/undertray. Perhaps I’ll update the build thread of that car with more information and details later.

Go with the flow – how a NACA duct works

The NACA duct get’s its name from the organisation that initially developed it, the National Advisory Committee for Aeronautics (NACA), an American organisation that predated NASA, and was eventually incorporated into NASA in 1958

The duct was designed with aerospace applications in mind, any amount of drag in these applications increases fuel consuption and limits top speed significantly, this makes minimizing drag critical. The NACA duct brings air into a vehicle with a very minimal increase in drag, this is one of the most common types of low-drag intake design, and when properly implemented, it allows air to be drawn into an internal duct, with minimal disturbance to the flow. The design was originally called a “submerged inlet,” since it consists of a shallow ramp with curved walls recessed into the exposed surface of a streamlined body, such as an aircraft. It is especially popular in racing car design.

The function of a NACA duct is to increase the flow rate of air through it while not disturbing the boundary layer. When the cross-sectional flow area of the duct is increased, you decrease the static pressure and make the duct into a negative pressure zone, but without the drag effects of a protuding scoop. The reason why the duct is narrow, then suddenly widens in a graceful arc is to increase the cross-sectional area slowly so that airflow does not separate and generate turbulance.

NACA ducts are useful in applications where air needs to be directed into an area which isn’t exposed to the direct air flow the scoop has access to. Quite often you will see NACA ducts along the sides of a car or engine bonnet. The NACA duct takes advantage of the boundary layer, a layer of slow moving air that “clings” to the bodywork of the car, especially where the bodywork flattens, or does not accelerate or decelerate the air flow. Areas like the roof and side body panels are good examples.

H-Fab NA6 MX-5 Track build

The story so far goes… I have an AW11, it’s in my opinion becoming worth a bit too much and becoming a bit too hard to repair in Australia to be a viable track car.

Entire the NA6, why the NA6? My criteria was;

  • Mechanically simple
  • Eligible, or close to eligible for historic registration in NSW (30 years)
  • Well supported and easy to source replacement parts for
  • Rear wheel drive
  • Manual
  • Ideally lightweight

From this criteria the only real two standouts were the MX5 and the E36, but with two door E36 not being released here for some time they were far off Historic rego, and the 6 cylinders not being all that affordable – so it ended up being an NA6.

A 1990 NA6 came up in Newcastle, some 150kms away at the right price and with 140k kms, so it was worth the drive. I bought it on the night and began determining what this car needed to be reliable enough to get through it’s first trackday. The car was in fantastic condition and was truly better than I required.

The first issues wer the suspension was entirely flogged out and the 16″ wheels – not a concern ultimately as it was an expected cost when buying this car – I decided to go with the BC Coilover range as a starting point. I’ve found these to be a reasonably reputable unit when setup correctly.

For the wheels the tried and true RPF1s were chosen in 15×7+35

The car also seemed down on power and had issues idling – this was found to be an ECU issue after the ECU had been have submerged in water due to the previous owner not installing the cover over the cabin fan – fortunately this wasn’t a problem as at the time of purchase I had a spare adaptronic 440 Select on the shelf with the plan to put this in the car.

The ECU install was painless, a few alterations to the existing loom to remove the AFM, a new vacuum hose and the 440 plugged in as it shares a very similar pinout to the stock NA6 loom.

A 3d printed adapter was also used to remove the throttle switch and replace it with a fully functioning throttle position sensor. This gave far more accurate control of tuning transient throttle states than what is afforded by the throttle switch.

After this, a sparco sprint and roll cage was fitted, along with some V70A tyres. The day before the trackday the radiator split, an emergency changeover and we were good to do. Hawk HP pads were in, new RDA rotors were on

The car survived it’s first outing and and a few points were observed. The RDA rotors disintegrated after 4 sessions – I have historically never been impressed with RDA rotors, however for the purposes of this car I figured they could handle it’s meager requirements. I also learned the value of the stock undertray which my car was missing, after extended periods on the track the car would begin to overheat. We also had a leaky front right tyre which couldn’t be patched on the day.

All in all a successful outing but more work to be done before the 2020 super sprint series starts.