On the rolling road Aldon Engineering
Alan Rennie has always been
impressed by the performance of his MGBGTV8, but just recently had felt things
were not quite what they once had been. He had carried out all the usual checks,
but that old sparkle was simply lacking. Was it the timing? - well with a 123
fully electronic distributor fitted, very unlikely. What about the leads, or maybe
the plugs, even perhaps the carbs? All checked out, so what was denying the car
its legendary performance? (30.1.09)
of chums suggested I should consider having the car set up on a rolling road,
since that was probably the ultimate way of seeing just what was going on, and
whilst not entirely sure, having never had a car set up in this way previously,
I decided to go ahead and see if such a session might show up something I had
missed. Aware that Aldon Engineering had an enviable reputation in this arena,
I booked the car in. When I arrived Alan Goodwin, the proprietor, explained what
they would be doing and asked me to sign in. Signing in is a slightly worrying
experience as you are signing a document which says in essence, that should the
engine explode while being run on their equipment, it's not their problem! "It
has been known" was the the answer to my searching question of "was
it a regular occurrence?" The cheery response was "not regular, and
mostly with racing engines - you should be fine!" If this was meant to make
me feel happier it didn't, so with that nagging little comment in the back of
my mind, the serious business of the day was quickly embarked upon.
car was chocked into place, exhaust extraction connected, fans placed at the front
and the timing checked. Timing is crucial to how the engine performs, and before
any full power runs can be considered the timing must be correct, as detonation
could result otherwise. Since the car is fitted with the aforementioned 123 Electronic
distributor, the timing was of interest. These distributors have 16 settings from
which to choose, the setting having to be selected prior to fitment. Of interest
the 123 dizzy showed 15 degrees at 1,000rpm, the standard factory setting being
10 degrees, but from 1,500rpm it matched the factory settings through the range
until reaching maximum advance, whereupon the 123 reads 30 degrees, whilst the
factory recommendations are 33/36 degrees. Happy with the timing the runs began.
Standing beside a car traveling at a high rate of knots, at this point about 80mph,
is a peculiar experience, and a noisy one too. Once the commotion had died down
John Thacker, my master technician for the day, asked a few questions, the first
being "was it short of power?"
Now this was most interesting
as I had not said anything about how the car was performing. However he had immediately
detected poor throttle response between 2,000 to 3,000rpm, which was spot on.
I felt the car had increasingly, despite its massive torque, struggled to release
all of its power, especially when going uphill. He also asked if I had experienced
any misfiring, particularly in warm weather? This was uncanny, it was almost as
if he had been driving the car himself for the past year or so, for this was exactly
"Hmm" he mumbled and then drove the car up to 3,000rpm
again for a few moments, and then switched off. He then showed me that the unburned
at tickover were exceptionally high, and that the mixture was very weak throughout
the range. The hydrocarbons were reset quite easily, but the weak mixture was
a different matter.|
With the sports type air cleaners fitted to the car
plus tubular manifolds, the standard needles had been changed for a richer type,
however John explained that with modern fuels having a far lower flashpoint, a
richer needle than that would be required. Finding one however was not as easy
as might be expected, as all the needle profiles in the correct range offering
a richer mixture, tailed off to a rather lean specification at the higher end,
not exactly desirable at full power. Various needles were tried and discarded
until eventually, with some expert attention, a set of needles which offered a
better high end were machined very precisely to the profile required elsewhere
in the range. The mixture still becomes a little weak at 4,250rpm and above, but
how often is a road going V8 required to run at these revolutions for prolonged
periods? Not mine that's for sure.
I expect I showed concern when the
car was being run up to a high speed, and John admitted that it does all seem
a bit brutal initially, engines being run to high revs can sound worrying if you
have not experienced it before, and I had not. However I doubt whether the fueling
problems which were discovered would have been identified without the rolling
road equipment. John was sure that with extra time he could have produced a needle
which would have given the correct mixture at maximum revs, however with the manifolds
just showing a hint of orange I felt we had done enough. As I explained, I rarely
drive the car at more than 4,000rpm, and if I do it's only for very brief spells.
Of interest, as these things always are, the car was giving 130bhp at the wheels
at 4,000rpm. The factory figure is 138bhp at 5,000rpm, so not bad after all these
years, and over 130,000 miles!
sum up then, was it worth it? Well I think so, as I have mentioned although the
timing was correct and the mixture seemed fine at tick-over, the carburetors were
running really quite lean between 2,000 and 3,000rpm. Clearly I had not picked
this up, and I doubt I would have done so by simply trying different settings.
It seemed for all the world as though the timing was out, although I doubted it
could be. John said that this is a problem he comes across more and more with
our older cars due, he firmly believes, to the fuel problems already mentioned.
As for my car, well it runs beautifully now, and although with richer needles
it has shown a slight improvement in fuel consumption too, so I am very happy.
Sequel: Alan Rennie confirmed the original needles were BAC and the replacements
are BDL with the modifications mentioned above.
Alan Rennie (30.1.09
Breener Industrial Estate
Station Drive, Brierley Hill
West Midlands DY5 3JZ
Tel: 01384 572553
road tuning. More