How 2 Guides

Turbo Conversions

After designing & fitting 3x Mx5 turbo conversions and assisted with many more,

Ive acquired a wealth of knowledge through research and more importantly actual experience.

This section will document my experience of the conversion process from start to end.


The guides will be broken into multiple areas.

  • The quest for more power?
  • Turbo, Manifold and Downpipe
  • ECU + Fueling Solutions.
  • Oil + Water feeds
  • Clutch and Drivetrain.
  • Intercooling.
  • Radiators
  • Track day checks and setup

The quest for more power

Why do some people start the journey for more power ?????

What is enough power for an MX5 ?????

How much would you like ????

Let’s start at the beginning. The Mazda Mx5, Eunos roadster or Mazda Miata is essentially the same car for different worldwide markets. The UK got the Mazda Mx5. Japan got the Eunos Roadster and the USA got the Mazda Miata. The rest of the world got one of the above variants.

They were launched in 1989. Being a front engined, rear wheel drive sports car with excellent handling, they quickly gained an excellent following and were eventually crowned the best sports car in the world by many!

Literally millions of Mx5’s have been sold from the early Mk1 pop up headlight model, moving through to the facelift static headlight models Mk2 and 2.5 to the latter Mk3 variants. There have been many special editions, tuned and fancy models made over the years too.

For this guide I will be looking at Mk1, 2, 2.5 Models (Not mk3 / onwards). The Mx5 engines were very well developed for their time and power outputs ranged from the basic 90 bhp 1.6 models to the 140 bhp Mk2 1800 engines with quite few others in between.

The Mx5 chassis was also very well developed too and as a result, it was common to find people wanting more power to exploit the brilliant handling that the Mx5 gave. From experience the lesser powered models were great fun but not really that exciting. Even the Mk2 RS 1800 wasn’t ‘that’ great either. The 6speed box helped mid gears acceleration but I felt it always needed a little more.

What are the options for more power?

Roll back 12 years or so when I first turbo charged the Silver 1600 Eunos Roadster Japanese Import. There was very little info on turbo conversions. The internet was relatively young and the Mx5 communities were not as resourceful as they are today. The majority of info was lead by the USA Miata owners who seemed to have more forced induction knowledge that we had in the UK. This maybe due to more USA cars out there or they were more adventurous?

The knock on effect was that it took a long time to develop my own turbo kit from a range of different suppliers and parts. Without wanting to spend thousands on a ready made kit, I opted to do much of the research and development myself and gathered the parts over year long, steep learning curve.

EBay was used to order a 2nd hand turbo from the USA, along with a 2nd hand manifold from there too.

They arrived and I immediately got stung with an unexpected import tax bill. Almost the cost of the used parts. I hadn’t factored this into my budget.

LESSON 1- Importing items from outside countries – may attract import and handling fees. Do your homework first as an initially seeming ‘good deal’ may cost you much more than expected.

The turbo didn’t match the manifold and it cost me more money to fix. Using UK Renault 5 turbo housing and the USA Mitsubishi turbo I managed to mate the two together to fit the manifold.

The Intercooler was from a rover 200 turbo which was donated by the local college to the project.

The fuelling was ‘taken care’ (just) by a rising rate fuel pressure regulator with boost input to raise fuel pressure when the turbo came on song. It was crude, but simple.

Along with the turbo, intercooler, manifold I needed a downpipe. An off the shelf Renault 5 turbo elbow was bolted to a short custom downpipe which mated to the OEM exhaust centre section.

The back box was a home made stainless steel affair using a different centre section off another car with tail pipe welded on.

The turbo install was crude but worked – 5 psi – no timing management and a basic fuel setup.

The silver Eunos had been turned into a pretty mental little car and I also got the nickname ‘Turbo Dan’ from many people for doing this conversion in a day when people didn’t really do things like this!

The conversion had cost around £900 and had added around 50bhp onto the standard car.

It was fast, fun and reliable.

Was it enough power? It certainly was a large improvement over standard, but sadly it wasn’t enough.

The car was sold and a lotus Elise bought instead. Different animal – same cheap thrills.


As time progressed I found myself missing the Mx5. It wasn’t the most expensive or fastest car in the world, but I had a bond with it. It was offered back to me a few years later and I jumped at the chance.

Repeat the above process but this time with the Mx5 and a VX220 turbo and I was in the same position again.

I had now owned it 3 times- quite a few owners on the log book, but most of them me!

This time was to be different. The car was totally overhauled and refreshed. Fully respray, wide arches, new turbo, new engine management, more power, new wheels and the list went on. It had a magazine feature and produced 210 Bhp.

See the build thread here for the full story.



Turbo, Manifold and Downpipe

The main components of a turbo conversion consist of the above.

The turbo unit is the power house – it makes the boost to allow the engine to run under forced induction rather than relying on the atmospheric pressure for combustion. See the web for how a turbo works – lots of info on YouTube etc.

The Manifold is the part that connects the engine to the turbo – this is what replaces the OEM manifold to allow the turbo to be introduced to the system.

The Downpipe is the exhaust after the turbo and usually integrates into the OEM system or a new system to the back box.

There are many suppliers of the above 3 parts. Ranging from the cheap to the very fancy (and expensive Tig welded works of art Manifolds.

Turbo’s - There are two main players in the Mx5 turbo conversion game. Garrett and Mitsubishi.

I have always used Garrett. They come in many sizes ranging but for the Mx5 I will discuss only a few.

T2 Size – Often found on older cars such as Fiesta Turbots – these give excellent and fast spool up times but can be the limiting factor when trying to build a high powered car- I wouldn’t use this size.

T25 / T28 – larger than the T2 and more suited to the Mx5 engines. These give good spool times to help stop turbo lag and should make more than enough power for the average Mx5 turbo conversion. These can be found on many Nissan turbo’d cars from the 1990s and can be found cheaply on eBay and online forums from free to a few hundred pounds. Check that there isn’t any excessive play in the bearings; ask the seller if they smoked before removing. A little shaft play is ok, smokey turbos may need a refurb – usually costing several hundred pounds.

T3 – Larger than the above – probably takes 500 rpm longer to spool and therefore really suited to the high powered builds.

Having said all that, don’t get too hung up on the size really. Any of the above on a good mx5 will still give a much needed power increase and large smile:)

Pick the size that meets your needs and goals [more on goals and setting them later].

I don’t have much experience with the Mitsubishi turbos, but generally a lot of people use the TD-05 size on the Mx5 with great results.

As well as a turbo you will need oil feed lines – go for stainless braided items (they last longer) and also oil return line and fittings similar to this.


ECU and Fuelling

In the past there were not many options for good aftermarket ECUs at an affordable price.

Many people used Greddy Emb (emange blue) – which was a compromised solution for being able to offer limited additional features (timing and fuelling) to the original ECU. It was a piggyback and as such the standard Ecu was left in situ and controlled most functions with the EMB doing some fuelling and other functions.

In the latter years the Megasquirt ECUs have dominated the Miata / Mx5 scene as they offer a full standalone solution and are available off the shelf as plug n play (Ms PNP) or build your own kits.

Budget around £500 for this new ECU. Ive personally used several over the years and are excellent to use / tune etc. There is a vast amount of info on the net on these and many very talented people who can help via the forums (mx5 Nutz) too.

The MS ecus can do much more than just fuelling and timing – they can also do logging / boost control (with additional hardware) / Launch control / dual maps / etc etc

Along with the ECU its necessary to be able to monitor the fuelling of the car to enable it to be tuned properly. I would advise using a wideband controller to monitor the fuel / air ratio which will also connect to the new ECU.

From my experience the best wideband controller is the AEM offering – we now stock these as they are ultra reliable and use a bosch O2 sensor which is fitted in the exhaust manifold where the standard 02 sensor would be fitted.


Manifolds + Downpipes

These need to match the turbo you are fitting. Garret style manifolds won’t fit the Mitsubishi turbos as their mounting footprint is different.

I would recommend getting a manifold and matched downpipe. The reason being that there are several styles of manifold (cast, log and tubular) and they all seem to mount the turbo in different positions.

Top, bottom, horizontal etc. The downpipe must match this or it may not fit the car.

Point to note :- Sounds obvious but 1600 turbo manifolds will only fit 1600 engine and the same for 1800. Don’t mix and match 1600 and 1800 manifolds.

There are a few different styles of downpipe from single to twin (exhaust + Wastegate feed) but don’t worry about which one to get unless you are planning on a mega bhp monster, the standard style (single) downpipe will be fine for the average Mx5’er!

Here is the setup which was run on the red Mk2 demo car.

Turbo (in a few pieces on left), Turbo core in centre, exhaust downpipe on right.

Oil return at the bottom of the picture.



Installation of turbo Manifold – Pictures speak a thousand words

Make sure the engine bay is clean before starting. This helps identify any oil leaks, and also makes working on the car much more pleasant in the future.


Standard (1800 engine)


Air box and filter removed to allow access to the exhaust manifold area.


Exhaust heat shield removed – this may not come off in one piece as the attaching bolts are usually rusted to death.


Old manifold removed. Quite a few bolts (some hidden) to remove. New turbo manifold installed.


Turbo installed to show mock-up of how it fits – downpipe isn’t fitted in that picture

Sump Drilling

The turbo is lubricated with oil. The oil is provided by the engine either from a source on the block (1600 engines are easier in this respect as there is a feed on the exhaust side of the engine near the back) or from the oil pressure switch fitting which needs a t-piece fitting inline to supply oil.

Once the oil has passed through the turbo and done its job, it then drains by gravity back to the sump.

The sump needs drilling and tapping to allow a fitting to be screwed into the alloy sump.

see pics below.

5 Psi pressure was applied to the engine to positively pressurise it. This means that when the drilling takes place, and loose swarf (metal bits) are blown out of the engine not in! It works really well.


Sump drilled for turbo oil drain – 3/8 18 NPT Tap used to make the threaded hole


Fitting with 3/8 taper one side and 3/4 threaded on the other to screw into new braided hose


JB Weld to secure and seal the fitting in the sump once the hole was cleaned.


4 litres of white spirit flushed through the engine to remove any swarf.
Drill bit and tap was heavily greased up to ensure any bits were trapped


Although this process may seem hard to do – its not. Take your time, have all the parts to hand do it methodically. EST time for this is around 1 hour.

This process is much easier than removing the sump which is a difficult and time consuming job.

Track day setup

Track days are becoming very popular. You can have use of a race track for a day, half day or number of laps. I would always suggest an ‘open pitlane’ session which allows you to come onto and leave the track at your leisure rather than in set groups of cars. This allows variance when on the track so you are not always out with the same cars all day.

There are a number of track day companies offering these days. Mazda on track is a great one for the Mx5 community- they also offer drift and other car control days too.

Main checks (from experience) before joining a track day session.

  • Your car must be roadworthy – check tyre depths, water coolant levels, brake fluid, suspension etc
  • Any faults your car may have will only be exaggerated on the track.
  • Tyres and brakes will be the main thing that gets worn on a track day so ensure they are in good condition taking into account that you need to drive home ‘legally’
  • Most tracks require driving licence, helmet and long sleeve shirt to be worn
  • Check exhaust noise levels – each track differs. Loud exhausts may fail scrutiny and need additional silencers


This document is work in progress and will be updated with more valuable info shortly.

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