I would like to throw in my 2pence worth to the discussions on
Lucas PI. I think there is a lot of misguided info floating about Lucas
PI systems. I'll try to correct what i can in simple terms.
Firstly, the original lucas gear pumps always struggled in hot
climates. The Pommy designers had no perception of a hot day at all. Its
origin as a wiper motor didnt help. The "cooling coil" option is
basically a disaster as it causes fuel temperature in the tank to
gradually rise further exacerbating the problems. It worked "sort-of" in
cold places like UK , provided you kept a full tank of petrol, but
forget it as the cure-all for worn-out pumps, lousy electrics
and Californian summers. Some pump motors heated up and others did not.
Most of this was traced to lously electrics creating low pump voltages
but no amount of technical study ever sorted out the "randomness" in
pumps that had OK voltages. Careful rebuilding including rewinding the
armature, plus rewiring with a relay to give MIN 12V at ALL times,
solves 90% of the motor problems. A proper alternator with a
constant 13.5-14V output worked wonders
Apart from electric motor problems, many Lucas pumps have stuffed
sintered carbon bushes in the pump gears. This creates bypass and
reduces their flow and/or pressure to useless levels. Its not easy to
fix these sintered bushes , but it is possible. Anyone purchasing a
"rebuilt" unit would be wise to ask the suppliers exactly what they have
done in this department plus demand a pressure/flow test chart.
Next, replacing the Lucas main high pressure pump is not as simple as it
first appears. the high pressure is needed to open the injectors and to
ensure the shuttle metering systems works correctly. Unlike modern
systems that mainly alter fuel flow by altering injector open time, the
Lucas system relies on a fixed pressure and altering the volume of fuel
delivered to the injector via the metering unit.
Next, very few modern roller cell pumps will outperform the lucas unit
in terms of volume at the required pressure. Convertors need to look for
porsche 911 or Saaab turbo pumps to even come close to what a full bore
TR6 (+ 150bhp) needs. Low specification cars (less than about 120hp)
will get by with less capacity pumps and I can provide flow values if
anyone really wants them
Assuming you find such a pump. the original lucas pressure regulating
valve strongly objects to the pulsing created by modern roller cell
pumps. But,on the other hand, unless you are really working the engine
hard , the flow from these modern pumps is more than a TR can use, so
the excess goes over the relief valve. In doing so it heats up!!!!> The
circle continues!!
Alternative relief valves are available but none are as elegant as the
Lucas unit. Thankfully, the Lucas units are almost indestructible.
The most common solution to vapour locking in a Lucas system is to use a
low pressure primer pump like a Facet to feed the Lucas unit. All this
needs to so is keep the hot fuel moving around and it stops vapour locks
almost entirely. This is not so easy with non Lucas pumps as the roller
cell pumps used on modern injection systems will not tolerate any
suction line blockages. In fact, high performace cars like my Cosworth
Sierra use a special primer pump with 3/4" bore piping to stop problems.
Audi quattros never got this really sorted and used to cut out at most
embarrasing times.
Roller cell pumps will not tolerate ANY dirt ingress, however
microscopic. Lucas pumps will handle gravel (comparatively)
Original triumph petrol tanks & plumbing systems were notorious for
surge problems. the slightest sniff of air in a hot system spells
disasterous vapour locks.
There are solutions to all this and on our race car we run 2 Lucas
relief valves in parallel plus a Porsche pump which is fed by a 1/2 bore
hose. Both valves have the bleed ports "bored out". We also use an
inline fuel cooler which is a modified heater radiator fitted with mini
electric fans. This also acts as a great surge tank. We dont use a
primer pump. We race in 40C air temperatures.
Dont let me put anyone off. its a great system when sorted!!
Any advice gladly offered or knowledgable comments received
Terry O'Beirne
2500 PI racer
TR5
2.5PI sedan
etc etc
--
***** English Spare Parts *****
You neeed ESP!
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