Sorry about the lateness of this post, but Iim subscribed to
the digest list (and live over the other side of the world).
I have a petrol injected TR6 here in Adelaide, Aust. and have
often had the (very annoying) vapour lock problem. I've tried
going with the coiling coil wrapped around the pump's motor
body with the fuel return running through it with some success.
I can now happily drive around in 30 deg. C plus weather with
no problems (with the stock Lucas pump), however on the recent
42 deg. C (108F) I still had the vapour lock problem after
around 15 mins of driving. I now intend to improve the fuel
pump cooling system by doing the following:
1. Keep a cooling coil on the motor body, but improve the surface
area of the mating surfaces. Currently I just have some (scrap)
copper tubing wrapped by hand around the motor body (with the
return line hooked up to it). This results in poor surface contact
- only a small fraction of the (round) tubing contacts the motor
body. What I'll do is cut a lengthways slit some 4 inch diameter
copper tubing and bend it so it's a snug fit to the body. Then
I'll braze some coils of copper tubing to this, and reconnect the
fuel return to the coils. Hopefully this will improve the contact
surface area sufficiently. I'll also apply some heat conducting
paste to the pump body when slipping this assembly on it to improve
conductivity (this stuff is available from many electrical/electronic
supply shops - they use it to improve conductivity between power
transistors and their heat sinks).
2. I also want to get an aluminium finned heat sink (like those
used in electronics) and cut it so that it will mate on the flat
surfaces of the pump itself (NOT the motor - the bit with petrol
flowing through it). Not quite sure how I'm going to attach these,
but I'll find a way - again I'll use some of the heat conducting
paste when attaching the heat sink.
3. (and finally) I intend to change the mounting of the pump so
that it's in an open ended aluminium box (open at both ends), and
fit a 12V brushless cooling fan to one end of the box (the sort
used in some computer power supplies). This will be wired to be
running at all times the fuel pump is running, and should provide
enough airflow to help with the cooling.
Hopefully this will cool the pump sufficently to enable the TR6
to run in all weather extremes, for a total cost to me of around
AUS$10 (or less) depending on the cost of the heat sinks and
heat conducting paste (I have all the other bits). If it doesn't
I guess I'll not drive it in bloody hot weather (which is not
really all that comfortable anyway).
By the way this is my second fuel pump in the '6 - the original
was too worn, and only provided around 80psi pressure (with the
pressure valve cranked right up), and the engine ran terribly.
You definitely need a high pressure pump (at least 110psi).
I'll post results of this little experiment to the list at some
time in the near future.
One other possibility (in addition to the cooling stuff above)
that my father mentioned I could try is using an electronic
pressure regulation system, in addition to the mechanical valve
currently used. Essentially what you'd do (or in my case what
my father would do) is fit an electronic flow meter (sending unit)
to the fuel return pipe, which is the input to a voltage regulator
which supplies the fuel pump with power. So when there is fuel
flowing through the return (lots of it) you can slow the pump
motor down as it's trying to supply too much pressure. Doing
this should help cool the motor on the pump a bit more as it
wouldn't be going flat out all the time....
The fuel metering unit regulates the amount of fuel going to the
injectors by using the engine vacuum to change the amount of
movement that a "shuttle" (not really sure what it's correctly
called) is allowed inside the unit. The amount of movement allowed
effectively prescribes the "dose" of petrol to each injector. Low
vacuum => open throttle => more petrol, and conversely, high
vacuum => closed throttle => less petrol. If, like my '6, your
engine has lower than normal vacuum your engine will run rich and
you'll periodically have to clean the plugs - although there are
apparently other reasons why you might get fouled plugs. I
think in my case the valve guides are worn, as I have high cylinder
compressions, and can't locate a vacuum leak anywhere. Bear in mind
that you may have to adjust the fuel curve for the US spec cams
and compression ratios - you'll probably need less fuel than UK
spec cars for a given throttle opening/engine speed.
One final comment I would like to make is that if anyone is going
to try to put cooling fins/coils/whatever on their PI fuel pump
using the heat conducting paste, be extremely careful with the paste
as I understand it's quite toxic (ie don't eat it or you'll get sick).
Frank Biedermann
'69 TR6
work e-mail: frank@ssabsa.sa.gov.au
home e-mail: frankb@camtech.net.au
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