Tachometer & Spark Plugs

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We offer a range of street and racing/performance spark plugs for all rotary engine applications.

Since a rotary engine fires each spark plug once per revolution of the eccentric shaft per cylinder, if you use a distributor to trigger an electric tach, a 2--rotor engine has the same firing pulses as a 4-cylinder reciprocating engine and a 3-rotor fires like a 6-cylinder. However, other combinations are possible. If you attempt to connect a tach to an 1986 and later leading coil, it will still function as explained above, but if you connect to one of the trailing coils, the tach will only see half as many pulses since each trailing coil only fires once per eccentric shaft revolution. Thus, in the case of the trailing coil used as a trigger, the engine fires like a 2-cylinder reciprocating engine for a 2-rotor, or a 3-cylinder reciprocating engine for a 3-rotor.

We have seen instances when the failure of a tachometer, when hooked to the leading ignition coil, has caused the leading ignition system to fail as well. For this reason, we suggest you consider wiring the tachometer to the trailing ignition; in the event of a tachometer failure you still have a functioning leading ignition.

Spark Plug Gap/Torque

Virtually all modern stock engines use relatively large plug gaps for good idle and emission purposes. However, as power and RPM increases, large plug gaps require more and more ignition energy to fire reliably. There is no exact relationship, but expect to reduce plug gap as power and RPM increase. In all high output race engines we use a gap of .015". If the gap erodes to .020" or more, power loss usually occurs.

When using our Racing Beat recommended spark plugs in street applications we find a gap of .020" to be a reasonable compromise. When using the following plugs for performance applications: BR7EIX, BR8EIX, BR9EIX, and BR10EIX - we recommend a gap of .015". We recommend that a drop of engine oil be applied to the threads, and using our Thin Wall Spark Plug Socket.

Each plug should be torqued to 15 ft/lbs.


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Factory Recommended Spark Plugs
100x75 1974-85 Rotary