This article was provided by Wil H.
Wil Has built a sucessfull 998 Turbo drag and hillclimb Mini & in this article he will explain how he converted his everyday naturally aspirated 998 to Turbo.

There seem to be a few people interested or doing this conversion, so I thought that I would offer some advice from my own experience of building numerous 998 turbos.

This is my latest conversion, as you can see you need no engine mods and it all holds together. I've done over 1000 miles now, with no problems.

This conversion used the T2 Turbo from a R5 GT turbo. This a great all round turbo for the 998. Though won't boost efficiently over about 12psi, and will make a maximum of around 140bhp.

Other turbos I have used include the T3 of a metro and a GT17. The GT17 will make bags of power (160 or more I suspect) I have 155bhp and 1/4 mile times to prove it !. The T3 is a pile of junk, old technology, high inertia and enormous. The T3 will work and make 140 bhp easy, if not more but at the expense of driveability, you will not get boost below 4k, ok for track use, but little else.

Firstly I should point out that the 20 hours is the actual installation time, I had
spent a few months gathering all the bit that I needed, as follows:

Turbo Garrett T2 (Renault 5)
Mirage Motorsport manifolds
12G295 {998 Cooper} head (standard 28cc chambers)
Metro turbo Carb and manifold
Metro Turbo fuel pump
Metro turbo fuel pressure regulator
Oil return parts
Oil feed pipe
Actuator
Intercooler and pipes

First you need a normally aspirated 998 Mini. This is mine, a 70,000 mile
1989 Mayfair. It’s not the best, it has a few oil leaks and rust round the edges.
The engine had 60bhp using an MG Metro Cam 12G295 head and stage one
like goodies. It also has Megasquirt ignition , so sorting the timing for a turbo
installation would be easy.

So, you need to bin (or remove and hoard) the following:
Head, manifolds and exhaust system, fuel pump, carburettor.
Then the car will look a bit like this (it had got dark by the time I removed the bits!):

Next you need to install a fuel return pipe and fuel pump (metro turbo). The
standard fuel feed pipe is easily big enough to supply enough fuel and my
return ‘T’s back into the low pressure side of the fuel pump.

Then after a bit of trial fitment I managed to modify the breather on the back
plate and make an actuator bracket.

Then it’s a case of bolting everything together. Here is a picture of the turbo
and carb prior to fitment.

In the next picture you can see the head is on and the fuel pressure regulator
is fitted.

It really is a case of just bolting it all together now. It looks a bit like this now:

Now I know it’s all bodged together, but it was done in less than 24 hours and
has certainly made an improvement.
As a final flourish I added a boost gauge and a lambda gauge and sensor
(narrow band).

Checkout Wills website here - www.twin-turbo.co.uk