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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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