I finally got around to swapping out the Mini stock nose pulley for a KAVS 15% reduction pulley. The idea of the smaller pulley is that it spins the charger faster, earlier – and this means you get a bigger amount of boost earlier!
Removing the old pulley wasn’t easy, and is press fitted onto the end of the charger nose shaft. This press fit requires a specially pulley and I’ve seen folks destroy standard pulley pullers trying to pull it off.
So I didn’t bother trying and attacked the pulley with a ginder. After much grinding, sparks and metal filings, the grinder won the battle and the poor pulley finally came off!
Installing the KAVS pulley was easy as it simply slides on the nose shaft using an internal split boss that is clamped down by a concave outer pulley housing. The housing is clamped on the boss using 4 threaded hex bolts. The final result was the charger now producing just under 12psi of boost and the scream from the charger coming on much sooner than before. It is now very much an animal when on full throttle. So much so that the clutch isn’t up to the job and now slips in high gear when you plant the go pedal… looks like I’m pulling the gearbox out!
Installing the intercooler certainly keeps the incoming air from the supercharger much lower than it would have been without it. Before the intercooler I was seeing air temps near 100°C and this was just too hot to reliably run the car without risking pre-detonation, or having the timing so retarded, that the engine lacked torque. Having completed the brackets needed to hold everything, it was now simply a mater of assembly.
I had to find space for the water pump, and decided to locate it just behind the radiator and in front of the air-conditioning pump. Unfortunately there isn’t a lot of space, so I ditched the stock cooling fan, and installed a slim-line unit that was half the space. I also took the opportunity to permanently wire the AC and cooling fans into the same circuit, so now when the engine water needs cooling, the AC fans also comes on to assist (a little bit noisier, but extra cooling is always better).
The final step was installing the heat exchanger (mini-radiator) and this was installed in front, forward of the two existing radiators (the engine cooling, and the other air conditioning). The small exchanger also included a push-fan to keep air flowing and was wired into a “always-on” power source along with the water pump. Effectively the intercooler system is always running keeping the water cool and hopefully the incoming air charge even cooler.
I now see the air charge around 15°C above ambient and only climbs slightly under a heavy workout when the water becomes heat soaked and the effectiveness of the system is reduced due to the small front heat exchanger.
I’m already thinking it could benefit from a larger heat exchanger unit, as the 10″ square radiator probably isn’t big enough to cope.
I just love the way this photo looks – close up of one of the several brackets I’ve made for the inter-cooler.
I decided I wanted a very professional installation so I took the time to make it as good as I could with my non-professional skills
First stop was too the metal supplier, and for only $5 I snapped up 3 meters of 20mm flat bar strips (3mm thick). The bar is really stiff but just bendable in a vice (and appropriate encouragement with a hammer etc). Once in the right shape, drilled and then ground round, I sprayed them in heat proof flat black enamel paint. They just look so good I could just eat em…. perhaps not!
The charger install is finished and everything works well. There is only one problem – air intake temps are too hot! With boost pressure peaking at 7 ½psi I’m seeing the incoming air temperature approaching 100°C
That’s just too hot and dangerous – an easy recipe for pre-detonation. The solution is to install an inter-cooler that can quickly absorb the incoming heat out of the air before it hits the engine (after the super charger). There are two methods; Air-to-Air and Air-to-Water. To be different and due to the flexible mounting options, I decided on an Air-to-Water system.
The process of installation begins be removing the entire front end of the car. Removing the front bumper, radiator and wheels just means the entire install goes easy and with plenty of room. As side benefit, I get to inspect the car and clean out the guards and ensure all is in good order.
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!
Decided it was about time to put all the parts for the charger together to determine if any parts can’t socialise with the other bits… I like to weed out the trouble makers early!
Nothing too problematic – I did need to use the grinder, file and hacksaw on some stubborn points on the charger to ensure the fabricated parts got along without issues. Took the opportunity to remove the BMW Mini power-take-off housing (used on the Mini to drive the water pump) – see the two rabbit ears at the end of the charger? Yup, that whole assembly is now removed. Removing this means I have one less thing to maintain (as it uses oil to lubricate an internal drive gear) and means the super charger is more efficient (due to less moving parts) – Yay!
I also connected the charger to my electric power drill – and gave her a spin… and she spun up and whirled… music to my ears.
My custom engine management system is going well… I’ve really gotten into tuning it and have started creating my own firmware code for the computer. I’ve posted my work on the Megasquirt MSEXTRA / MS3EFI forums.
I’m also building a new injector harness so that I can switch to sequential injection (stock is batch meaning all injectors fire at once – not good for fuel economy, plus sequential allows for smooth idle control). The new harness will plug directly into the ECU and bypass the stock wiring – that way I don’t have to cut or damage the existing harness should I ever decide to return to standard.
I finally got around to swapping out the Mini stock nose pulley for a KAVS 15% reduction pulley. The idea of the smaller pulley is that it spins the charger faster, earlier – and this means you get a bigger amount of boost earlier!
destroy standard pulley pullers trying to pull it off.
