When we were approached by the guys at Tegiwa Imports with a picture of an NSX and the words ‘race car build’ being shouted through a huge grin, we immediately dropped tools, ran over and listened…

We are huge fans of retro and classic cars here at Motion and to have the opportunity to build such an iconic JDM supercar into a race car is something special, especially given that it was none other than Ayrton Senna who developed the NSX into a truly exceptional car out of the box.

NSX stands for ‘New Sportscar Unknown’ and is rear wheel drive, has a full aluminium body housing a 3.0 V6 mid-engine. The NSX was a massive project for Honda with the Formula One world Champion Ayrton Senna tasked to develop the chassis and set up of the car prior to production. Prototypes were tested extensively on the famous Suzuka Circuit and the Nürburgring with Senna’s feedback and chassis development carried through to the car that went on sale. The NSX hit the market in 1990 and was a staple of Honda’s range undergoing various revisions, a facelift and even a Targa model until production ended in 2004. It was the first production car to feature an all-aluminium body, having a total gross weight of 1370 KG which under cut its competitors; the Ferrari 348 by 130KG and the Porsche 911 964 by 100KG. The NSX was a true JDM supercar.

Arrival

The NSX arrived at the workshop as a rolling shell, looking quite sorry for itself on a set of tiny steel wheels, but that didn’t take away from our excitement to get stuck in. The car already had a roll cage installed by the previous owner which meant that the car was already mostly stripped, saving us some work, but also giving us some problems in that we were uncertain where various loose parts and pieces that were supplied actually went. Think of it like un-boxing an Ikea flatpack set with no instructions.

We were given a deadline to build the car in time for Spa Francorchamps round of Club Enduro. Luke from Tegiwa started to organise the components and parts needed whilst we got to work on the car.

The Build

The car arrived as a bare rolling shell which meant there was a decision to be made first and foremost with the engine. As the stock V6 wasn’t present in the car and with used units being hard to find and even harder to get any real power from, the obvious answer was to use a K series engine and gearbox. The wealth of tuning options, reliability and ease of finding another should there be a failure, means that it is a no brainer whilst also helping save some weight – lovely!

The plan to use the NSX in Club Enduro means that we need to think about: additional fuel capacity, the engine conversion which calls for additional cooling support, we also need bigger brakes and ultimately need to make the car reliable. The list of parts was coming together nicely, with Luke pulling out all the stops to get some manufacturers involved that Tegiwa work closely with, making us super excited to watch the build evolve.

Engine and Gearbox

As we mentioned before, the engine of choice is a K Series. The K series is an in-line 4-cylinder Honda engine available in 2.0 and 2.4L variants. It’s found in pretty much every Honda from a Civic to an Odyssey. The variant we are using is a K24/K20 hybrid (‘Frank Motor’ in the Honda scene) which consists of a K24 bottom end and a K20 cylinder head. The engine will be mated to a 6-speed gearbox from an EP3 Civic type R with different gear ratios which we will go into more below…

Skunk2 were quick to put their hands up and help with supplying an engine once Luke had made the call and they didn’t mess about with the build spec! They upped the capacity even further to 2.45 with their Ultra conrods and Wiseco pistons, Skunk2 Ultra cams with VTEC delete, major head porting work and supporting valvetrain which means we should see 300hp plus on the Dyno. That’s a chunk up on the stock V6 along with uber K series reliability and much better options for gearing. Exciting! The engine arrived with a steel sump after being run-in on Skunk2’s engine dyno prior to being shipped to us. The first job was to change the steel oil sump pan and replace it with a cast aluminium K20 sump with the proven Clockwise drop in sump baffle to stop any oil starvation. We then fitted the K-tuned electronic water pump setup, the alternator and belt. As with any build, there are things that evolve as problems arise and this water pump and alternator setup was to be removed in favour of the stock items at a later date but, I digress.

The gearbox started out as a stock K20 6 speed EP3 type R unit which the guys at Tegiwa sourced. We did some calculations based on RPM and wheel size to work out which ratios we would need and Luke pulled them all from the Tegiwa shelves along with a set of bearings and synchro’s. We decided on a short ratio 3/4/5/6 gearset, shorter final drive and plated differential, all from M-factory. We’ve used M-factory gears and diffs on hundreds of road, track and race cars, the quality, fit and performance are superb!

The gearbox had a full strip down, clean and inspection prior to installing the new bearings and seals, gearsets, differential and all relevant synchro’s and sliders. We then mated it to the engine via the Competition Clutch stage 4 clutch, dressed the assembly with the engine harness from K-tuned, engine mounts from Innovative and a freshly painted rocker cover from 4Designs before offering into place.

Suspension and Brakes

Yellow Speed stepped in here to help out with the suspension and braking setup used on the NSX. The dampers are a three-way unit which gives us a wide range of setup adjustment and the remote oil reservoir helps to keep the oil cool and ensure the damper works as intended over an endurance race distance. Three way means we have high and low speed compression adjusters along with a single adjuster for rebound per corner. There was some slight modification needed but installation was pretty straight forward. At this point, there are no easily available options of adjustable arms, rose joints etc and so we will be using new stock items before upgrading in future based on the feedback and data we collect in testing.

The brakes we’re using consist of 6 pot front calipers and 4 pot rears, both over a 330mm floating disc and bell. Although the calliper gives us a huge choice of pad compound options, we’re starting with Pagid RS29 which should see us through a 2-hour race with ease. The NSX has had the ABS removed and uses a single master cylinder so the addition of an in-line rear brake limiting valve in the cockpit gives the driver some level of control of the brake bias in the car, although we’re sure this will be another point of upgrade and evolution in the future, so watch this space!

Livery

The livery really makes or breaks a car. Think back to some of the most iconic race cars of the past and the one thing that really defines them as a wall poster is the way that it looks. Dave from Tegiwa came up with the design for the NSX and it looks incredible, really keeping the JDM character of the car alive. Chris and his team at CN Signs have been wrapping the cars for Tegiwa and ourselves for a couple of years now, Chris being a racer himself. After working his magic, Chris has absolutely fallen in love with the NSX and has signed up to drive it at Spa for its first race!

Fuel

The NSX starts life with a 70 LTR fuel tank and we know already that we need to increase this capacity so we can make our mandatory fuel stop window as big as possible during a race. Normally, budget permitting, we would use an ATL tank and re-design the fuelling system around that but as the stock tank is sat upright between the cockpit and engine bay, we can’t actually fit a ‘universal’ fuel cell in the space and would need a costly custom bag tank.

The decision was made to use a secondary tank in the boot space which will gravity feed into the stock tank. We can then use this as the point to fill the car, giving us a total capacity of 120L - perfect. Now, it’s a bit of a challenge getting big enough pipework to connect the 2 tanks together in the space we have. Then we have to ensure the tank breathers and vents work in harmony to allow fuel from the top tank to the bottom tank quickly with both tanks needing to breathe sufficiently as fuel is pumped via lift pumps and main pumps to the 300+hp K24.5 sat in between them.

As you can see, there is a lot on AN hose and fittings going on here but it’s an effective and cost saving solution to a problem!

Wiring

The NSX wiring loom was the stock Honda item but had been chopped and changed to add various things such as an AIM dash and electronic PAS which was fitted by the previous owners. It looked ugly, un-necessary, heavy and as we were running a different engine now meant that aside from the essentials of lights and wipers, we could remove a huge portion of it.

When it comes to race car wiring and K series engine swaps we always enlist the help of Paul from Racing Circuits. If you’ve seen his work, then you will know its outstanding. Not only is it neat but its simplified and that is crucial in a race car. Wiring and electrical problems are not something that want during a race!

We removed the entire wiring loom, leaving only the plugs connected to headlights, wiper motor, fuel pumps etc. Paul then completely re-wired the car utilising all of the components we asked for, allowing a few spare power sources in a fuse box for future installs and also includes an Upaclick steering wheel control panel. The control panel is a great way to get rid of the factory indicator and wiper stalks and have everything you need at thumb reach, leaving the rest of your hand on the wheel. The total install saved 58kg, not too shabby at all and as always, Paul’s work was faultless meaning we could get the car running and handed over to J.Cal for mapping.

Setup and Mapping

With the car built, we spent some time on the flat patch (the flat platform needed to accurately set the cars ride height, camber, caster and toe settings) to see how much of a setup window we had available with the various adjustability we had. It’s also a good time to check what settings affect one another. This is a really useful process to go through prior to getting the car on track as it allows us to understand the kinematics in the suspension - if we need to remove half a degree of camber quickly, how does that effect toe? If we lift or lower the car by 10mm, how does that affect the camber and toe?

After a day of playing around with various setup options, we had the car ready to roll onto the dyno. Jesse of J.Cal was charged with tuning the NSX, he’s somewhat of a Honda jedi and knows his way around Hondata better than anyone we know.

On Track

Now that the car was built, it was time to get on track for a shakedown. We first went to Oulton Park with Chris to give the car a run, carry out various system checks and ensure that the car worked and responded as we’d like. It wasn’t without issue and a few minor niggles were discovered which we needed to remedy in the workshop but fundamentally, it was clear that it was going to be a very fast car. Issues at Spa cost us a great first result but the next time out at Oulton Park, the car took a class win! It even beat numerous cars in the class above showing the true potential of this super cool JDM icon. Bring on 2020… 

The NSX build was a pleasure to be involved in, big thanks go to Tegiwa for getting the car and complete build into motion (see what I did there?) and allowing us to be a part of it.