1972 Mini (throttle bodies)

A common question is whether the Canems ECU can run a Mini with motorcycle throttle bodies. The answer is yes. To prove the point, the test car (originally fitted with an MPI injection setup) was converted with throttle bodies from a Kawasaki GPZ1100 and a custom-made inlet manifold.

Motorcycle throttle bodies give the opportunity for a significant power increase for minimum outlay, due to the abundance of second-hand motorcylce spares. From the factory, the GPZ1100 was fitted with four throttle bodies (one per cylinder). Naturally, the Mini engine only requires two, as pictured below. These castings were actually 34mm in diameter which provides adequate airflow for a 998 engine whilst maintaining a crisp throttle response.

As a first step, the throttle bodies were respaced to suit an A-series cylinder head. With an extended throttle linkage this can easily be achieved (particularly with separate throttle castings, such as these Mikunis).

When fitting a Weber carburettor, it's widely known that a longer inlet manifold gives better results. Typically, this requires a bulkhead box to enable physical fitment of the carburettor itself. One of the advantages of the Canems injection system is that the ECU maintains balanced air/fuel ratios between all four cylinders, rather than relying on the 'wet-manifold' principle of a long and convoluted casting. Thus, the throttle bodies can be mounted almost straight onto the cylinder head itself. This makes fitting easier and maximises air flow through the manifold itself.

For this car, a manifold was fabricated from mild steel. A simple jig (pictured above) was employed to ensure accuracy. Fabricated from scrap metal, the cost of these two inlet manifold stubs was minimal. Rubber mounting boots help to insulate the throttle bodies from the heat of the engine itself .

Fitted on the car itself, there is more space available than there is with a single SU carburettor. Naturally, performance is also vastly improved over such a setup. The car remains entirely tractable around town, providing good fuel economy. When required, there is the power (and distinctive Weber-style bark) available however.

For the time being, foam filter socks are used - placed onto the original motorcycle ram pipes. Naturally, a plenum with cold air feed could be installed as there is plenty of room.

The complete specification of the injection system is as follows:

Kawasaki GPZ1100 throttle bodies (34mm diameter)
MPI Mini fuel-rail and 3 Bar pressure regulator
BMW Cooper S injectors (330cc/min)

For the time being the car has been tuned on-the-road only, with data from two lambda sensors. Despite this, there is already a vast improvement in performance over the previous setup (ie. factory-fitted MPI injection). The engine is much more willing to reach higher RPMs, and it seems all of the low speed torque of the factory setup is maintained.

Greater airflow through the twin throttles means more fuel is required (at the top-end of the rev range, under load). The injection timing has also been retarded, due to a greater distance from injector to cylinder.

It goes without saying that the car will be back on the rolling road soon and you'll be kept informed of results. From the feel of the car, we're expecting good results.


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