First off, apologies for my lack of update in over a year. Early last year my daily threw a rod and I had to see about sorting it out, which ended up meaning between running Peak Autos and sorting a daily, I had less time to work on my MX. After a pretty stressful summer I was left bummed out and demotivated, so the coolest project I've ever undertaken was shelved for a little while. 

Towards Autumn, however, I got my s**t together and got back to the coal face after missing having smashed knuckles and no money.


One of the major problems that I was deliberating over was the PPF. Anyone doing this conversion seems to fight a battle between shortening the PPF or moving the steering rack forwards. I was not going to move the steering rack forwards under any circumstances.

There had been a few designs thrown around as to what this custom PPF should look like. I originally planned to use the 6 speed RX8 box, however there was a problem. Many problems to be honest. But mainly it hinged around the mounting of the gearbox. The MX5 gearbox has two large mounting holes and a smaller further back, sitting on the driver's side, with the PPF running along the same side to the differential. The PPF mounts to the diff on the drivers side too. The RX8 mounts the gearbox to a PPF on the passenger side. Drawings of crazy tubluar steel lattices were made, I began calculating what profile tubing I'd need, and it all seemed like a really complex way to overcome what seemed like a very complex way to do this.

Ideas floated around of something using twin (or even three) tubes with a triangle lattice going on but keeping it light was going to be impossible, and I was sure there was an easier way.

I had an RX7 FC gearbox that came with the old 13B engine I bought for use initially. Rather than creating an engineering nightmare I just took the RX7 and MX5 gearboxes and split them both at the tail shaft. Some of the parts from the RX7 FC and the MX5s are interchangeable, and luckily this was one of them. The MX5 tail shaft/selector unit slotted straight into the gearbox of the RX7 FC to create a hybrid which would make creating a PPF much easier. I then got busy with a tape measure, ruler, and various other high precision tools to cut the PPF at the only point I figured would allow me to get it joined back together and maintain straightness.

I then went to a friendly local TIG welders called JNC. As well as being experienced and talented guys (they showed me a range of surgical steel instruments with minute TIG welds holding them together), they were friendly and reasonably priced, leaving me with a shortened modified PPF and a solution to a major pain in the arse with my build.

I would recommend these guys to anyone.

Exhaust Manifold

I wasn't away from JNC for long as I needed an exhaust manifold. The most cost effective way to do it was to MIG weld the manifold bends together myself and then take the pre assembled structure to the professionals. This meant absolutely hours of test fitting, grinding back, test fitting again, grinding et al et al. When constructing eg. a turbo manifold when you've comparatively) plenty of room, it's possible to make the entire thing from 90 bends or 45 bends and calmly weld up the whole lot in situ over a couple of beers. Not this one. The space between the custom subframe and the engine was so tight that none of the tubes followed regular 45/90 paths, I was inserting 3-5-10 deg wedges and crazy twists from the original RX8 manifold I'd bought until I had three tubes gathering into a fat collector ready for a straight through exhaust once I'd got the thing fired up. 


My original engine mount design used large uprights from the subframe which bookended a large tubular structure with PU bushes from a Subaru Legacy. 

In practice though, this design was overbuilt, uneccesarily bulky and actually quite wasteful of space. I scaled both sides back and used a generic Land Rover style mount - cheap, plentiful, tried and tested. I stuck to the use of 4mm steel blasted together with the welder on 12 so the welds were still fizzing and popping a couple of minutes after they were done. Finally I invested in some 12.9 hi-tensile bolts to hold the mounts to the engine - completely over the top but tell me that you'd save 50p and get 8.8s or 4.8s or whatever. Alloy steel with 1220 MPa tensile strength thanks very much. 

Above: Passenger side engine mount sitting on a Land Rover mount, oil cooler line out just next to it.

Radiator/ Oil Cooler

I invested in a Tegiwa alloy radiator from a lad on Facebook. Not wanting to make the job too easy, I made sure the radiator was from a Honda Integra Type R. These are slightly taller than the MX5 radiator and fraction wider (there is some more room horizontally that they don't teach you about). My original plan had been to build a V-mount setup with the oil cooler at the top and the radiator at the bottom. When I fitted the Duce front bumper though, the left and right ducts were asking to have an oil cooler sat behind them. 

Above: Tegiwa Integra Type R radiator mounted 

This way I could start with a smaller 19 row Setrab Proline. If this wasn't enough I'd could easily mount another one on the other side. Using a couple of threaded holes on the outside of the chassis rail, I made a halfway sturdy oil cooler mount which only just fitted into that space between the outer wing and chassis rail. This is a hugely underused part of the MX5, especially if you have a front bumper which facilitates airflow round this part of the car. Or a big holesaw.

Either way I now had a mounted oil cooler.

Other Oil System Bits

One of the main reasons I decided against using the standard RX8 oil coolers was that a) most of them are pretty battered by now and b) I'd heard a few stories about the thermostat in the OEM oil cooler being less than ideal. I decided to use Earl's inline oil thermostat which opens at 160-180F, allowing the oil to get up to a sensible temperature before being the oil was allowed to flow into the cooler(s).

Above: Earls remote oil filter mount

Above: Earls remote oil filter mount

Mazda mounted the RX8's filter in a frankly silly place, especially when viewed through the lens of trying to fit one into an MX5. The filter sits on a pedestal which extends it incredibly high, however this interferes with the bulkhead area straight away. This is a problem to be solved later. The upshot, however, is that the filter needed to be mounted elsewhere. The oil filter return also goes back into this pedestal, 

The new filter I decided to mount not too far from where the original filter was, just using a remote filter pedestal, also from Earls. Finally I got 4 of the 5 oil lines from a small(ish) hydraulics specialist in Doncaster. I'll post most details about these guys later because they're very helpful and stock basically everything you could possibly need to get oil, coolant, air, fuel, or pretty much any fluid or gas from point a to point b at any temperature or pressure without any drama. 

The next stage, however, would be about transferring electricity...