4 July, 2021 by Simon Descoteau
Project Synthia: 1991 Eunos Roadster – The Story So Far (Part 3)
When we last left her, Synthia was once again at Wheels in Motion to fix a knocking noise that had come about since we had installed the new exhaust system. Bigger brakes and breathing modifications had otherwise transformed the experience of driving the car. You can refresh your memory on part 2 here.
The knocking noise turned out to be a hilarious oversight on our part when we had installed the new exhaust system. In our tired state, while we were re-assembling the exhaust system, we had installed the de-cat the wrong way around. This meant that it was striking against the transmission tunnel. There was no need for the uprated engine mounts, but as they were already ordered and the ones on the car were almost 30 years old I decided to install them anyway. An oversight that was quickly resolved while the car was up on the ramps. Joe and the team at Wheels in Motion swiftly (relatively) installed the rest of the chassis modifications which I had acquired to stiffen up the car.
The result was a significantly stiffer car, which was much more responsive to the steering inputs, and subsequently easier to drive, and more predictable when pushed around my usual country lanes. The door bushes gave the door a more heavy close and greatly reduced the vibrations in the door. The close fit between the doors and the chassis of the car also improves the overall rigidity of the car which aids the predictability, and the ability of the car to cope with bumps in the road. Roadsters are notorious for “scuttle shake”, which is where the whole car tends to shake when one corner of the car goes over a pothole. This shake reduces the ability of the suspension to correctly do its job so reducing it improves the handling of the car to no end. The engine mounts had a similar effect on the front end of the car, and as the engine was able to turn less in the mounts more of the power of the engine went to the rear wheels which again increased the throttle response and predictability of the car.
When I had sourced the sports brakes, I had also found a lead on a 6-speed gearbox, but it had taken a little while longer to get that delivered to Arrow5, my preferred MX-5 specialist in the South. The gearbox is responsible for transmitting the power from the engine to the road (via a differential in rear-wheel and four-wheel drive cars) and the ratios of the gearbox multiply the power of the engine on route to the wheels. The mark 1 MX-5 comes with a 5-speed gearbox, and the early ones are mated to a 4.3 ratio differential. The mark 2.5 sport comes with a 6-speed gearbox which has a closer gear ratio, with the 1st and 5th gear being approximately equivalent to the 1st to 4th gear in the 5-speed. The 6th gear is actually marginally shorter than the 5th gear in the early gearbox which means that this gearbox is much better suited to acceleration rather than top speed. However, the mark 2.5 sport mates this shorter ratio gearbox to a 3.9 or 3.6 ratio differential, the combination leading to a longer overall drive ratio. I decided to mate this gearbox to my 4.3 based on my previous experience of this same combination in Nina. The shorter differential ratio and the short ratios of the gearbox mean that while I lose a marginal amount of top speed, Synthia would accelerate much faster in between gears which suits the roads I drive her on much better.
As I was having the gearbox removed anyway, it only made sense to replace some service items while they were easily accessible. From BOFI racing, I acquired a Competition stage 2 clutch kit, and an ultra lightweight Competition flywheel, both for the 1.8l engine so that they’re able to handle more torque once I increase Synthia’s power. The lightened flywheel had the benefit of allowing the engine to rev more freely, which greatly suited the natural characteristics of the 1.6l engine.
As with the other modifications to Synthia, the close-ratio gearbox improved the enjoyment of driving her through my favourite country lanes and I was excited to pick the car up from Arrow5 with the work complete. The long drive home on the motorway though did remind me that the in-car entertainment (I.C.E.) needed to be brought into the 21st century. When I had first purchased the car I had installed a cheap Bluetooth head unit in the car so that I would be able to listen to music from my phone but the quality of this was questionable in keeping with the cost of the unit. I decided to upgrade this to the Pioneer SPH-10BT which is a single din unit that uses a very intelligent combination of a phone app and Bluetooth to use the screen of the phone as the display for the head unit. It also provides a great place to mount the phone while you’re driving which keeps the phone secure and in your line of sight for satellite navigation. By using the phone as the display, the head unit was also very affordable. This was installed with the help of Nxt Gen Autos who were also responsible for bringing to life my brilliant solution for the rear foglight.
Japanese cars do not require a foglight in the rear, but UK cars do. This means that when these cars come to the UK they are often retrofitted with ugly square boxes attached to the rear tie-down hooks. My Eunos also has a third brake light in the boot at a central, high level. I had the idea to install a dual filament bulb to the third brake light, much like the brake/rear light used in the rear light cluster, but with the dimmer of the 2 filaments used for the brake light, and the brighter of the 2 used for the foglight. This means Synthia would have a stealthy foglight while still being legal for road use. I would also not lose the functionality of the brake light and even the dimmer filament is still brighter than the smaller bulb it replaces. Nxt Gen Autos very kindly did the modifications to the brake light housing, as well as the necessary wiring for this modification. They also installed the flash-to-pass diode for me which allows you to pull back on the headlight stalk to simultaneously bring up the pop-up headlights, and flash the high beams so that you can signal to other road users to thank them for letting you past, or to just say hi as you pass other MX-5 owners.
With all of the performance modifications done to the car for the time being, and coming up to the 12 month mark of owning Synthia, it was now time to upgrade the aesthetics of the car and do some minor rust repairs which had become required in order to pass the next MOT. I like a more subtle OEM+ look to my cars, and so I ordered OEM front and rear splitters for the car to aid with downforce and stability at speed, as well as a ducktail style subtle rear spoiler. I also used this opportunity to have the front bumper numberplate removed and the holes filled, so that I could run an offset numberplate. The final finishing touches were replacing the tie down hooks with more substantial front and rear tow hooks which gave Synthia the race car look and feel while also being beneficial for towing the car should the need ever arise. The icing on the cake was a vented nearside headlamp cover, turn signal intakes, and a Track Dog Racing front splitter add-on which really finished off the racing car look while also aiding with providing cold air to the air intake filter and engine bay.
The final piece of the external puzzle was to upgrade the roof which was in rough condition to a custom made mohair roof from Jack R. Smith Motor Trimmers in Swansea, so with the bodywork all done and with a fresh MOT on the car, I took a drive across England into Wales and spent the day at Jack Smith’s workshop where he installed a fresh tan mohair roof, new seals and cables to Synthia so that she was once again water tight and ready for the winter ahead.
The car was now ready to be driven and enjoyed over the summer period, and that is exactly what I did. The modifications made to the car over the past 12 months had totally transformed the stock Eunos which I had purchased into the perfect back roads and weekend toy.
This brings us up to date with the story so far with Synthia as of the beginning of my second summer of owning her. Thank you so much for following along for the journey so far. From this point onward I will go into the next stage of modifications for Synthia which will transform her from the mildly modified weekend toy into a more serious and exotic performance machine. I hope you will continue to enjoy the journey Synthia and I are taking together.
With that, I will sign off on this article. When next we meet, I’ll go through the first part of the next stage of her transformation, and what the future holds. I hope my experiences will help you along your own journey with your Eunos or MX-5, wherever it might take you. Please do leave a comment or question below, I’d love to hear from you.