Turbo project – the start

Even during the throttle bodies build I’ve had a side project going with a well known fabricator of turbo manifolds/downpipes for MX5s, and it’s now starting to come to fruition.

Now, I’m not the first person to turbocharge a Mazda SDV Westfield. There’s at least two others, one in the states using a Mazdaspeed manifold, and one in the continent using (I think) an aftermarket interpretation of the Mazdaspeed manifold. The problem with the Mazdaspeed manifold is it sits the turbo down low, requiring modifications to the passenger side engine mount. Whilst this is out of my skillset, finding someone to do it would be pretty easy. Unfortunately, the manifolds themselves proved impossible to track down.

So I turned to someone on the MX5 forums who was well known for making custom turbo manifolds. I asked him if he could help me out and we started looking into the options. I gave him measurements of the engine bay and he suggested a top mount turbo would probably fit best. I then chose the turbo so that he could start mocking stuff up. I wanted a turbo that would spool quickly whilst also being readily available and cheap. This meant it was either a T25 from a 180sx or a TD04 from a Subaru. I went for the TD04 as it’s slightly bigger than the T25 but should still be making positive pressure from 2-2.5k. As long as I’m sensible, it shouldn’t run out of puff at higher revs.

Within an impressively short amount of time he’d made a mockup on a spare engine he had…

The downpipe curves back on itself to clear the triangulation at the rear of the engine bay.

With the guy being 1,200 miles away, a test fit was impractical so I adopted 21st century bodgery and photoshopped it.

Looked close, but also looked like it would fit.

We put a kit together…

And I went ahead and sourced a turbo. A TD04L-13T from an Impreza.



Fast forward to today and a parcel arrives… it contains…

Exhaust manifold

Exhaust manifold





Coolant lines - these essentially replace the thermostat bypass hose

Coolant lines – these essentially replace the thermostat bypass hose

Old drain

Old drain

Oil feed - this tees off from the pressure sender

Oil feed – this tees off from the pressure sender

Extra downpipe bits for mocking up the piping needed to link to the silencer

Extra downpipe bits for mocking up the piping needed to link to the silencer

This meant I could get started this weekend and see if it would actually fit! The first thing I did was bolt the turbo to the manifold and see if the oil drain would be in the right place:

Thankfully, it was. Of course, it was always going to be given it’s the same orientation as when it was in a Subaru, but I hadn’t considered that

I then double checked it all bolted together ok.

Looks like I’ll need to rotate the inlet housing, not a difficult job.

Downpipe also bolts on nicely:

Lastly for today, enthusiasm got the better of me once again and I went straight for a test fit. Here’s where it all needs to live:

So two things in the way at the moment. The coolant pipe and the oil breather pipe. Neither are exactly rocket surgery to reroute. I drained the coolant and removed the offending pipe, followed by the exhaust.

Then bolted the manifold on. Some of the nuts are now a lot harder to get to and torqueing them up will be fun, but that’s some pain I can save until later.

The turbo was next:

I was surprised that even with the inlet housing at the wrong angle it still fits with room to spare. Obviously I could never get a hose onto that, but it did look like the bonnet would close at least.

The downpipe dropped in relatively easily:

I’ll just have to move that relay box but it’s otherwise better for space than I thought it would be!

The downpipe also currently stops in a pretty good place! Not bad when the fabricator only has a set of measurements to rely on… and I’d taken those measurements.

In fact, the only bit of modification required is I need to file down the actuator mounting bracket slightly:

As expected, the actuator means the oil breather pipe needs rerouting.

In all, there’s plenty of space, more than I thought they would be so I’m quite chuffed about that:

Will hopefully get it all together by July. Not sure yet if I’ll take it off, refit the old manifold and actually use the car whilst I’m sourcing the bits.

Cooling-wise, I think I’ll opt for a RadTec radiator/intercooler combo. Expensive, but a pretty neat solution. Hopefully even with the intercooler in front of it the radiator should have the capacity to deal with all this heat.

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2 Responses to Turbo project – the start

  1. Interesting stuff. Any ideas what it’ll do to the power/torque curve?

  2. Dom says:

    I’m not sure. Hopefully not ruin it! It’s a lovely straight line at the moment, I imagine it’s going to get bumpier.

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