Corralling the Horses

Install a rev limiter to keep RPM under wraps

Story and photos by Leonard Emanuelson

Racers aren’t the only ones concerned with over-revving their cars. Parents of teenaged drivers who own classic sportscars undoubtedly wonder what kind of abuse their engines undergo when the kids borrow the keys on Friday nights.

Installing a rev limiter is cheap and easy insurance against engine overload. These units control engine rpm by cutting the spark to the cylinders when engine speed exceeds the specified level. One such unit is the Pertronix Flame-Thrower Digital Rev Limiter (222-635). According to the manufacturer, the system’s digitally controlled microprocessor is more accurate (+/-0.01 %) than analog configurations. The Flame-Thrower also reportedly reduces plug fouling by randomly “stealing” spark among cylinders when the rev limit is exceeded.

Another Flame-Thrower feature is internal filtering that prevents false triggering from coil voltage noise. Further, the tach output is compatible with modern electronic instruments, and the Flame-Thrower has reverse voltage protection that operates over a range of 6 to 18 volts.

This rev limiter will work on any 4-, 6-, or 8-cylinder engine having a non-capacitive-discharge ignition system. In other words, it’s compatible with breaker-points, electronic (HEI), and even aftermarket inductive-type ignition systems.

Installation is painless. The Flame-Thrower’s compact size allows it to fit in a variety of locations in the engine compartment. For non electronic ignition systems such as the one on the TR6 shown here, hook-up uses only three wires: black to ground, red to ignition ON, and yellow to the coil’s negative terminal. The harness’s white wire goes to the output on an electrical tachometer, and the orange wire is included for HEI installations.

The bottom line is that a rev limiter and about an hour of time will give the British sportscar owner who has average mechanical aptitude peace of mind.

The Pertronix Flame-Thrower Rev Limiter kit is a digital brain box and adapters for 4-wire mounting.

 Rotary switches on the side of the rev limiter are for number of engine cylinders and rpm cut-out level. The customer can easily set the rpm limit with 100 rpm accuracy by turning the switch dials. Setting all switches to 0 makes the unit non-operational.

Optimal mounting location for the rev limiter is a reasonably flat surface that’s away from direct heat, vibration, and moisture.

Non-HEI ignitions are wired with three or four wires (for mechanical and electric tachs, respectively), and HEI systems use an additional wire.