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.
Some parts for the supercharger project have arrived and they look great!
I got them from TR Lane a fabricator in the UK who specialises in this kind of conversion from the donor (2005 BMW Mini) to the patient (my MX5). They include (from left to right) an engine mount for the charger, the charger outlet adapter (where the compressed air comes out), a charger inlet adapter (with 2nd throttle body mount), and last but not least is the bypass actuator (that lets compressed air escape when throttle is closed).
It also came with a special belt tensioner bracket that mounts onto an existing power steering mount bracket (of which I didn’t have, but was able pick one up 2nd hand for around $50). This all bolts onto the existing engine mount point for power steering and keeps the belt tight for both AC and the charger. Note that the idlers are brand new MX5 cam-belt idlers which apparently work fine.
I had to grab quite a few bolts & fasteners from the local supply shop – a quick 15 min chat had me all the correct lengths, sizes and types. I love the little black hex head threaded screws – looks really pro!
I had to grab a 2nd accelerator cable that runs from the 1st existing throttle-body and heads over to the 2nd throttle-body mounted to the back of the charger. By keeping two throttle-bodies you ensure 1) that the throttle volume of the intake to the engine is small (easier idle and throttle response) and 2) keeps the charger in a vacuum when not needed (off throttle) and so keeps the engine load minimised (the charger doesn’t work so hard when turning blades in a vacuum!).
Someone was selling a brand new set of Remotec A 15×7 inch rims with Bridgestone RE002 – apparently they weren’t hard-core enough for him and was happy to let them go for a steal!
They really fill out the guards, and handling has improved yet again by having such wider tyres on the car… very happy.
MX5′s have always been seen as great handling car, with beautiful balanced weight distribution, rear-wheel drive and precise steering and feel. A real drivers car who’s owners like twisty roads and open-top fun!
Unfortunately, performance has never been one of the Mx5′s strong points, and the early NA6 with its 1.6 engine lacked that oomph that really made you feel this was a performance vehicle. Nothing worse than being beaten off the line by Mum in the family’s Holden Commodore.
So, being someone who is always willing to take on a challenge, I bought a 2nd hand supercharger originally out of a BMW MINI Cooper S (an Eaton M45) and will start the process of collecting the needed bits to bolt this on.
With this update I finally complete the installation of the MegaSquirt ECU into the car. This mainly involves wiring up a throttle sensor, rebuilding the intake pipes for an air temp sensor, and installing a Wideband O² sensor.
When finished, the engine bay looked remarkably similar as before, with the notable exception being the shiny customised intake pipes that replaced the air-flow-meter. With the flappy MAF meter removed I’m now 100% reliant on manifold vacuum to regulate fuel injection volume, along with air temperature and throttle position.
A manifold vacuum hose was taken from the existing fuel regulator tap, and using a Y splitter, a new line was brought into the cabin area and plugged into the ECU. The MegaSquirt contains a MAP sensor that measures air pressure and is used to regulate fuel delivery.
It is recommended if possible to use a Throttle Position Sensor (TPS) when using a MegaSquirt ECU – these tend to improve throttle response with acceleration enrichment, but my model MX5 only came with a Throttle Switch (simply closed/open and no measurement in between). Fortunately, the 3spd Automatic MX5′s did come standard with a TPS and as they are a simple bolt on, I acquired a 2nd hand throttle body and soldered some wires to the connector. To connect into the stock harness (and to avoid cutting it) I fashioned a plug using some plastic and stiff wire – the result is something that can be disconnected and yet be firmly secured to the existing stock plug.
The Air Intake Temperature (AIT) sensor needs to be mounted in the stream of incoming air and the first logical place seemed to be where the intake pipe would need to bolt onto the air-filter box. Unfortunately this required mounting the sensor right behind the radiator, and this resulted in unacceptable heat-soak (a condition where the sensor itself if heated to beyond the ambiant air temperature resulting in incorrect readings). I then had to move the sensor to inside the filter box, and this provided more regular air tempatures without heat-soak problems.
The final task was the installation and wiring of the Wideband O² sensor and this required installing a controller module within the engine bay (seen next to the washer reservoir). To enable the sensor, you need to supply 12V for heating of the sensor along with wires back to the ECU. The Innovate LC1 sensor (the type used here) provides a simple harness that I adapted to a DB15 connector that plugs into the DB15 port on the DIYPNP case. This provided a fairly simple place to mount the LC1 calibration switch and diagnostic LED – both of which are now mounted as part of my DIYPNP ECU case.
So, the final step is to connect the ECU to the stock harness, removing the original computer and neatly rest the new ECU into the protected cubby hole. After uploading a tune file (obtained from a fellow MX5 owner with a similar MegaSquirt ECU) I fired over the engine and it kicked into life – running a little roughly and spluttering to a stall when any throttle was provided, but it would start and idle reasonably OK. After a little tuning of the fuel maps, adjusting for acceleration enrichment, the car seemed to be running fairly well. Last step was to provide a method to easily connect to the DB9 communications port on the back of the ECU – so I added a ribbon DB9 extended assembled from $6 worth of parts from Jaycar.
Tuning the ECU is a subject I’m not going to cover here, but suffice to say I’m still doing it several weeks later and feel I’ve got a bit more to do to get it to behave 100% like stock… so you can have respect for the OEMs and the complexity that goes into modern computer engine management systems.
You can download my tune file for my car that would be a reasonable starting position for any similar NA6 owner who is keen to start at known good position with a recent firmware from MS2/Extra – at this time its based on the 3.2.0 release.
All-righty, I’m up to the stage where you hope it works and will allow you to load some firmware. There are no status lights or electronic display to tell if you if anything is right or wrong, so you rely totally on getting a connection to a standard computer verify the unit is working.
First step is to download the needed tools – which comprise of the latest firmware from the forum section of the MSExtra website and the tuning software TunerStudio from EFI Analytics. You can use the free version but for ~$50 you can get a pro version that includes auto-tune and a great log visualiser.
Next you plug the device into a USB-Serial cable and get Windows to discover and enable the Com port – remember this number (mine was Com4).
I downloaded from MSExtra the released version of MS2 being 3.1.0 and the zip file contains two .s19 files that are the binary firmware images (one for Megasquirt, and one for the DIYPNP with the Microsquirt module). Inside the zip is a windows batch file to download the firmware. You run this and it asks questions, you follow and it will upload the boot code and then you repeat and it then loads the firmware.
Once complete you can fire up TunerStudio and it will detect and connect to the device. Next you load a base tune (which I used from the DIYAutotune website for my model MX5. This base map sets the common settings for Cam wheel sensors, fuel injection sizes, spark and crank settings etc. It helps start the car and getting it to run, but you then need to fine-tune to ensure it runs correctly.
A good video of the setup and tune process…
Now the fun begins as I install the ECU into the car, and add a Variable Throttle Position Sensor to the existing throttle body, wire it up and start the tuning.
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 
ground round, I sprayed them in heat proof flat black enamel paint. They just look so good I could just eat em…. perhaps not!
