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IGNITION RESERVE CROSS FIRE”
The most important (and least understood) factor con Cross fire or induction leakage will occur whenever igni
cerning good ignition performance in racing is IGNITION tion cables are grouped closely together and run in parallel
RESERVE. There’s really no reason for any confusion about for some distance. This causes engine roughness and can
this “reserve”... it's simple. result in damaging preignition or detonation.
Cross fire is not caused by defective cable insulation.
Rather, it is traceable to the magnetic field which surrounds
any high tension conductor. Thus, the lead which is carry
Simply stated, igni
tion reserve is the dif ing high voltage at any given instant tends to induce volt
ference in kilovolts (one age into an adjacent lead. Troublesome cross fire is most
likely to occur between consecutive firing cylinders when
KV equals 1000 volts) these cylinders are located closely together in the engine
between how much block. Do not tape spark plug cables together. Do not run
voltage the ignition sys spark plug wires through metal looms.
tem can develop (volt
age available) and how COIL POLARITY
much voltage it takes
for the coil or magneto Polarity should always be negative at the spark plug
to discharge to ground terminal as this considerably decreases voltage required for
(across the plug gap). POOR SYSTEM ignition. This effect is due to the higher operating tem
perature of the center electrode ... electrons will leave the
hotter surface at lower voltage.
Polarity can be checked in a number of ways. IF POLARITY
IS»WRONG, REVERSE THE TWO PRIMARY LEADS AT THE
IGNITION COIL.
a) Oscilloscope or Plug-Scope ... trace pattern will be up
Actually, when you side down if polarity is incorrect.
tune an engine, you’re b) High reading voltmeter... ground positive lead, then
really building ignition touch negative lead momentarily to spark plug terminal.
reserve. First by replac Needle will move up-scale if polarity is correct.
ing components (points, Most magnetos, of course, reverse their polarity.
condenser, etc.) and Ignition coils should not be installed in high heat areas.
making adjustments Mount coils away from exhaust headers, etc. Coil leads
that help increase volt should be as short as possible from the coil to distributor
age available. And sec- cap. Overheated coils and long hi-tension leads lower avail
ond, by selecting able voltage. Primary coil-distributor leads should be firmly
components (plugs, dis anchored and able to tolerate vibration and flexing.
tributor cap, rotor, etc.) Low battery voltage (on race engines without magnetos,
to help decrease volt alternators, or generators) is a major cause of misfiring or
age required. ignition failure. A battery should be at full charge at race
start. Loose battery terminal leads are frequent causes of
hi-speed misfiring.
It’s a bit like your bank account... when you make a
deposit you increase your financial reserve. The minute you BOOSTER-GAPS in RACING (U-PREFIX)
start writing checks, you begin reducing the reserve. Write Booster-gaps, although proven ideally suited for traffic
a check for more than your balance and your banker will let and turnpike usage, are not always advantageous in “flat-
you know about it. So will your’race car if you “short change” out” racing applications. Sustained wide-open-throttle and
the ignition reserve. maximum engine RPM stress ignition system output (in
crease voltage required) to the limit.
The use of a booster-gap spark plug raises the spark plug
voltage requirement. Under racing conditions, many ignition
systems do not have adequate ignition reserve, consequently,
Decrease Voltage Available Increase Voltage Required it is recommended that “U”-prefix plugs (plugs containing
booster-gaps) be “pinned.” Merely insert a straightened
worn breaker points breaks in high tension leads paper clip in the booster gap vent hole and clip it off even
with the top of the plug terminal.
defective coil wide plug gaps It is not necessary to “pin” the vent hole in HO-8A, HO-3,
TUNE-UP FACTORS cracked distributor cap reversed coil polarity UJ-7G, UJ-11G, UJ-64P, or UJ-60P plugs.
The Booster Gap type spark plug offers added anti-fouling
retarded timing
defective ballast resistor
defective condensor corrosion in distributor towers protection in many engines operated in heavy traffic areas.
The voltage requirements of this plug, however, are slightly
poor electrical connections wide rotor gap
higher than conventional types. For this reason, Booster Gap
plugs are not recommended for competition where high
engine speeds may limit the voltage available from the
OPERATING FACTORS cold starting cold starting pletely comparable results:
ignition system.
high engine speed*
sudden acceleration
The following substitutes can usually be made with com
extra electrical accessories
heavy loads
J-1OY
J-13Y UJ-10Y
UJ-12Y
J-6 UJ-6
'Transistorized ignition systems, however, are relatively
insensitive to high engine rpm. N-11Y UN-12Y
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