COP Conversion

RC51 Coil-on-Plug Conversion

RC51 Coil-on-Plug Conversion (Using CBR600RR Coils)

This modification replaces the RC51’s traditional ignition coils and plug wires with modern coil-on-plug (COP) units sourced from the Honda CBR600RR. It’s a popular upgrade for improved spark performance, reduced clutter, and better long-term reliability. If you have checked out our RC51 ECU Upgrade, you will see this conversion was performed using a Fueltech SparkPRO2 Ignition module, eliminating the OEM CDI unit.

Community Credit

This modification concept was inspired by discussions on RC51Forums, particularly contributions from members who explored the use of CBR600RR coils on the Honda RC51, especially TheGrabulator. This page builds and expands on that idea with original documentation and implementation notes.

Benefits

Eliminates bulky coil packs and plug wires
Improves spark efficiency and reliability
Reduces electrical noise

Parts Required

Most parts can be purchased online through retailers like Partzilla or eBay. Some parts need to be fabricated or sourced from the community. Below is the minimum required for this modification:

2x CBR600RR coil-on-plug units (typically 2003–2009 models)
Correct spark plugs (modification usually required)
Custom wiring harness or adapter leads with correct connectors

Honda CBR600RR Ignition Coils

The ignition coils are Coil-on-Plug (COP) style, unlike the RC51’s remote-mount coils. Honda began using these COP units on the CBR600RR in 2003, and they remain unchanged through the 2024 model year.

Component	Name	Manufacturer	Part Number	Compatibility Notes	Remarks
Coil	Coil-on-Plug Ignition Coil	Honda	30700-MEE-641	CBR600RR (2003–2024)	Direct fit into RC51 plug wells — sealing required

'Dumb' Ignition Coils

These coils are "dumb" because they lack internal dwell control circuitry and require an external driver or ignitor to trigger the spark. This applies to both the RC51’s OEM coils and the CBR600RR COP coils in a retrofit context.

While CBR coils are mounted directly on the spark plug, they are passive transformer-style coils that rely on an external ignition module for timing and dwell. In the RC51, the OEM CDI unit handles this.

Ignitor Modules and Dwell Control

An ignitor module (coil driver) switches the coil’s primary circuit, controlling:

Dwell time — how long the coil is energized before firing
Spark timing — when the spark occurs relative to crank position

The RC51’s OEM ignitor handles both functions based on ECU signals. For standalone ECUs (e.g., FuelTech, Haltech, Megasquirt), an external ignitor like the FuelTech SparkPRO is required.

Important: The SparkPRO cannot be used with the OEM ECU, as it requires precise dwell management from the ECU, which only standalone systems provide.

OEM vs. Aftermarket ECU Considerations

With the OEM ECU, the OEM ignitor is fully compatible with both RC51 and CBR COP coils, assuming proper sealing and mounting. For standalone ECU upgrades, refer to our ECU Upgrade documentation for ignition tuning guidance.

Honda RC51 Spark Plugs

Use standard Honda-specified spark plugs based on your bike’s version (SP1 or SP2). Unless using older spark plugs with removable twist-on caps, modify the plug tips to fit CBR600RR coils. Spark plug gaps should be set to 1.00–1.10 mm (0.039–0.043 in).

SP1 Honda RC51 Spark Plugs

Manufacturer	Part Number	Compatibility
NGK	FR9BI-11	Standard
DENSO	IK27C11	Standard
NGK	FR8BI-11	Cold Climate
DENSO	IK24C11	Cold Climate

SP2 Honda RC51 Spark Plugs

Manufacturer	Part Number	Compatibility
NGK	IFR9H11	Standard
DENSO	VK27PRZ11	Standard
NGK	IFR8H11	Cold Climate
DENSO	VK24PRZ11	Cold Climate

Modifying Spark Plugs for CBR600RR Coils

CBR600RR coils require an M4 threaded tip. Modify spark plugs using a grinder and threading die:

Grind the plug tip to 3.75–4.0 mm, keeping it concentric to avoid seating issues. Avoid damaging the porcelain insulator and grind slowly to prevent overheating.

Thread the tip using an M4 × 0.7 mm die, cutting threads as deep as possible. Deburr with Scotch-Brite, sand if needed, and clean thoroughly to remove metal debris.

Modified plugs should fit snugly into the CBR600RR coils and install into the cylinder heads. See the image below for reference.

Modified SP2 Spark Plugs

CBR600RR Coil Connectors

The connectors for CBR600RR ignition coils are listed below. You can also purchase the CBR sub-harness on eBay and splice it into your adapter harness. Listings often include both coils and sub-harness.

Manufacturer	Part Number	Compatibility
Furukawa	FW-C-2F-B	18 or 16 AWG Recommended

Adapter Harness

Section to be updated shortly.

Contribute Your Experience

If you’ve completed this mod and have wiring diagrams, photos, or fitment notes, please submit a contribution to help the community.