After what seemed like many months of planning, part buying, reading and thinking – the Supercharged beast has come alive!
The entire assembly and build was conducted over a period of three to four days, and generally went fairly smoothly (though I did buy several belts trying to figure out what was the best fit – in all the Goldilocks too small, too large, trying to find one that was just right! I settled on a 4PK1335 which requires a bit of force to get on, but provides plenty of scope to tighten up).
As I had some time to focus on the car for several days, I took the opportunity to accomplish several things. As well as adding the supercharger, I also finalised the sequential injection harness, added Coil-Over-Plug, swapped the injectors for 425cc RX8 yellow tops, and painted the rocker cover wrinkle-red.
One of the many customisations needed was the addition of a 2nd throttle body. Lucky for me, I had a spare throttle body due to swapping out the OEM manual switched-TP for the automatic variable-TP throttle body. Using the spare throttle body mounted to the intake ensures the supercharger remains throttled minimising parasitic loss, and will also keep it quiet when off boost.
I had to wire up the pre-supercharger throttle body and make a bracket to mount a second accelerator cable. After scouting the isles of the hardware store, I found some nice steel brackets that were drilled and repurposed as mounts – looks good and is very sturdy.
The standard cable bracket from the primary throttle body wouldn’t support two cables, but I knew that some MX5′s had dual mount brackets for cruise-control. So I hunted around and was able to source a 2nd-hand bracket. I bought a brand new Mazda B2200 accelerator cable (cause it was very long) and used the existing wired T-connector at the primary end (as the throttle body had dual cable support on the spindles) and crafted a split-pin and cable screw-clamp at the other end. With the cable sorted, this concluded most of the custom assembly I needed to do and was the bulk of the cutting, sanding, drilling and filing work I did!
I needed to figure out how to mount the IAT (air temp sensor) into the post-supercharger intake path, and so I cut a small hole into the elbow of the red silicone hose and locked it into placed with a threaded bung. As the hole wasn’t a perfect fit, I applied gobs of clear silicone to set the sensor and plug any air leaks (unfortunately I’m not 100% convinced I’ve got it air tight yet!!).
Along the way I read somewhere that strong spark becomes a critical component of a healthy Forced Induction (FI) system – there is actually the possibility of the forced air blowing out the spark before it can ignite the fuel! As such, I took the opportunity to switch to COPs (coil over plug) which is essentially 4x Toyota coil-plugs and a custom-made wiring harness that plugs straight into the stock igniter harness. There is plenty of details on the web if you search for them – and here is one that I found amongst others.
As mentioned, I also took the opportunity to replace the stock 240cc injectors with RX8 ”yellow-top” 425cc injectors. I actually got the car running on the stock injectors, but noticed that under full boost, the duty cycles were at 80% which means the injectors were close to maximum flow. So I’m glad I made the choice to buy the RX8 injectors in advance, as after installing them, the duty cycle dropped to 48% which is much better and safer!
Finally I also took the original rocker cover off, and replaced it with another 2nd hand cover I bought for $40. Painted it in VHT Wrinkle Plus and I’m really impressed with the results – looks very professional and suits the red silicone hoses. It actually now looks as good as it sounds!
… and how does it sound? How about you be the judge!
