MSD 6631 6 HVC-L Professional Race Ignition Box with Fast Rev Limiter

The MSD 6631 6 HVC-L is a professional-grade capacitive discharge ignition control engineered for circle track and road racing applications that demand sustained high-RPM performance. Capable of firing up to 15,000 RPM at 14.4 volts, this ignition box delivers 150 millijoules of spark energy and 550 volts of primary voltage output to the coil at every firing — ensuring consistent, powerful ignition even under the most demanding race conditions.

The 6631 features a built-in Fast Rev Limiter, which is significantly quicker and more precise than a Soft Touch rev limiter, protecting your engine from overrev damage caused by spins, missed shifts, or driver error — with no need for an external rev control module. The RPM limit is adjustable via plug-in modules for easy tuning between events.

Advanced internal components include hand-wound transformers, Field Effect transistors, and an Integrated Gate Bi-Polar transistor for improved coil saturation. The entire assembly is mounted in a clear epoxy potting compound for maximum vibration protection, and a transparent base plate allows for straightforward tech inspection. A built-in reverse polarity protection circuit safeguards the electronics from wiring errors.

Key Features:

• Capacitive discharge ignition — 150 millijoules per spark up to 15,000 RPM
• 550V primary voltage output to coil; 45,000V secondary voltage
• 15,000 RPM capability at 14.4 volts
• Operating voltage: 12–18 volts, negative ground
• Multiple sparks for 20° of crankshaft rotation
• Built-in Fast Rev Limiter — adjustable via plug-in RPM modules
• Built-in reverse polarity protection circuit
• Mandatory 6-pin Weathertight (Deutsch-style) connector — meets NASCAR ignition wiring rules
• Clear epoxy potting compound for vibration protection
• Transparent base plate for easy tech inspection
• Must be used with MSD HVC Coil (PN 8250)
• No CARB Exemption Order Number — race/competition use only

The MSD 6631 is sold individually and is intended for racing use only on vehicles not registered for street use. It is not legal for installation on emissions-controlled vehicles.