1380 Race Mini - Fuel injected

This Mini was one of the first cars fitted with our ignition ECU when it was released - it's invaluable to know that a product can stand up to competition use. For background reading about the ignition system upgrade, click here.

In it's original guise (1380cc block, Piper 300 cam and 45 Weber DCOE carb, Canems ignition) the car has performed faultlessly in competition for the last 18 months, setting a few class records along the way.

It was time for a change however, and the work we've been doing with fuel injection meant this was the obvious choice. The aim was to increase mid range torque to give a better pull from corners (the car is used in hillclimbs and sprints). Two hurdles had to be overcome; the camshaft duration of 316 degrees is unfavourable for injection, and producing 135bhp (the previous output) requires large quantities of fuel in a short time period.

To solve these problems, four fuel injectors are used. Each inlet port is fueled by two injectors, with the upper pair acting on their own until 4000 rpm. After this point, the lower pair kick in, to provide the required fuel. This enables a reasonable idle quality - on a par with or slightly improved over the carburettor.

The throttle bodies used are from a Honda VTR1000 (Firestorm). These have twin injectors fitted as standard with a capacity of 335cc/minute each - just about right for our target 140bhp. The throttle diameters are extremely large at 51mm (although they do taper towards the head). Conventional wisdom would suggest these are vastly oversized, but thankfully we ignored that...

Both injectors on the Firestorm throttle bodies have their injectors at an equal distance from the cylinder head - this is good news for injection on a five port head, because the injection timing doesn't alter once the second pair activate. Remember that with the five port head, the fuel pulses are timed to prevent excessively rich mixtures on cylinders 2 and 3 and lean mixtures on 1 and 4.

An alloy inlet manifold was fabricated, and the throttle bodies themselves respaced and rotated (they originally sat in the vee of a V-Twin). The only other modifications were to add a late Mini fuel tank and return line and a coolant sensor to act as an automatic choke. The air flow characteristics of the new throttle bodies and manifold are far superior to conventional carburettor layouts, so we were hoping for good results.

After original mapping on the road with wideband lambda sensors, it seemed that throttle response was improved through the gears. Certainly, revving to beyond 8000rpm was all too easy. Perhaps most importantly, the fears regarding such large throttles failed to surface - the car pulled much better at low revs (from around 2000rpm). At this speed, the carburettor would simply kick back and refuse to pull. Remember that the carb had previously been set up by a rolling road specialist, so there was no problem in the setup.

To get reliable power readings, we really needed back-to-back tests. For this reason we headed back to the Fuel Injection Centre in Bolton, which was the same rolling road we used to set up the ignition system. The rolling road plot below explains all...


Click plot for an enlarged view

As you might have guessed, all of the higher readings were produced by the engine fitted with fuel injection. Most noticeable is the much flatter torque curve which should give the low down pulling power we wanted.

Although the gain in maximum power was 'only' 6bhp, the car has gained 15bhp and 15lb/ft torque at 5250 rpm - not bad for 'impossible' fuel injection on a five port head.

The final tests were to be in actual competition - the favourable impressions and rolling road results meaning little if results could not be improved. On the first competitive outing after the conversion, at Elvington airfield, the class record was lowered by 0.96 seconds. This same car had set the previous class record only four weeks ago - everything else was exactly the same, even the weather conditions.

Click here to see the class record being broken at Elvington - yet another success for Canems.


Click picture to view video


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