on V8 distributors
Gordon Hesketh-Jones (Harvest Gold 1904) from Cornwall has clocked
up more than 400,000 miles in his MGBGTV8 so has had a higher maintenance
workload than many fellow V8 enthusiasts. He also uses his V8 for
touring in Europe so reliability is a key concern for him and one
area is the reliability of his ignition system. As an update on his
earlier V8NOTES on this topic, Gordon reports his experience with
fitting a Pertronix electronic ignition system. (Jun
I first wrote about the distributors for the MGBGTV8 in V8NOTE282
in March 2003 followed by V8NOTE317 in
December 2004 and then in V8NOTE365 (February
2007) reviewed the history and the various options for converting
to electronic ignition thus doing away with the increasingly unreliable
contact breakers. In the latter note I mentioned how dreadful the
trace of both of my Holden-rebuilt distributors with conventional
contact breakers looked on a Krypton analysis machine, but did not
have the opportunity to compare the traces of the conventional distributor
with the Pertronix replacement I had fitted to my V8 until the mini-disasters
on our trip around France in January 2008.
I returned from France with a conventional distributor unit in situ
then went up to see Tim Kelly - the MG specialist near Truro - for
the Pertronix unit to be re-fitted.
I made a point of taking my camera with me so I could record the traces
on his Krypton screen. Incidentally, the normal MoT station will no
longer have a Krypton-type ignition analyser as all modern cars have
had electronic ignition as standard since 1993, so the Mot stations
now focus simply on analysing the exhaust gas.
produced a 10% improvement in mpg and was much smoother
The first photo of the Krypton screen shows the trace from a distributor
fitted with the standard points in place.
Plug No 1 is at the top of the screen, then the rest coming down the
screen in firing order. On the horizontal scale it can be seen that
there is a variation from
2.92 to 3.55 of the actual firing point. Note: this scale does not
relate to 4° before top dead centre, it is a machine scale! The
centre-line of the two extremes would
be at 3.235, so the two worst cases represent
to Contents listing
Ignitor system is a compact and neat installation fitting
entirely within the distributor. No external box of electronics
is required, but you do have to bring a 12v ignition feed
wire ( by-passing the ballast resistor) to the unit. The high
voltage coils also require a full 12v supply.
in firing of a horrifying plus or minus 9.7%.
The electronic unit takes away the variations caused by wear on
pinion and cam of the distributor shaft and we no longer have to
worry about contact wear or contact bounce. The engine visibly and
audibly immediately runs far more smoothly when the electronic unit
is working, with the further benefit that on our 721 mile round
trip to Silverstone (550 miles of dual-carriageway and the rest
in country lanes or stop-start motoring) we averaged 32.2 mpg -
an absolute boon in these days of expensive petrol, and an improvement
of around 3mpg or 10% on the figures achieved in our various
long continental trips in recent years.
Incidentally we had a shock-horror situation when we first reinstalled
the Pertronix kit - the engine turned over but would not start!!!
It turned out that the brass contact strip had come off the rotor
arm. Thank goodness it happened at Tim Kelly's place and not halfway
down an Alp in France - even though I obviously carry spares.
It can be seen from the Krypton traces that our standard coils give
out approximately 8,000 volts but these Pertronix units produce
a big fat 40,000 spark leading to greatly improved combustion, more
power and better running.