Topic: Regap plugs with 3 ohm coils?

[camelman]

Do 3 ohm coils require regapping the plugs?  This is for a 350f.

[HondaMan]

Yes. Use .040" to 0.050" with those high-output coils. The size of gap can affect the idle performance: let that be your guide. 

[Deltarider]

That's way too much IMO.

[Gordon]

Yes. Use .040" to 0.050" with those high-output coils. The size of gap can affect the idle performance: let that be your guide. 

I had never thought about the increased gap affecting the idle, but it makes sense.  On my K1 with Dyna 5ohm coils and Dyna-S I have the gaps set to 0.032".  Do you think that's negatively affecting the idle? 

[Silverback]

Using 3 ohm coils is essentially the same as using an ignition amplifier. What Hondaman is saying is to increase the gap until you see a drop in performance, then decrease the gap a little bit. What this does is give you a  spark with more surface area to ignite the fuel. This will take full advantage of the higher output coils.

[camelman]

Thanks guys, that makes a lot of sense. 

[HondaMan]

Yes. Use .040" to 0.050" with those high-output coils. The size of gap can affect the idle performance: let that be your guide. 

I had never thought about the increased gap affecting the idle, but it makes sense.  On my K1 with Dyna 5ohm coils and Dyna-S I have the gaps set to 0.032".  Do you think that's negatively affecting the idle? 

Those 5-ohm Dyna coils make a little more voltage than the Honda coils, but at shorter duration. So, use the same stock 0.028" gap on that setup.

It's the 3-ohm coils where the big difference comes in. They can make up to 35kV at 14vDC supply and with larger plug gaps (stock coils are about 7.5kV). But, they discharge about 30% shorter duration than the Honda coils, so the surface area that gets exposed to the fuel-air mix needs to be a little bigger if possible. Larger gaps are one way to improve things here. Adding higher plug cap resistance to the 3-ohm coils (10k ohms instead of the more usual 5k ohms) will also slow the discharge time down about 10-15%, making it spark "longer", effectively. This is a good thing...there's plenty of extra spark voltage available in these 3-ohm coils, largely wasted. The SOHC4 engines only really need about 5kV to run to about 8500 RPM, so long as the spark duration stays above 1.0mS (stock coils are about 1.5mS duration with 7.5K ohm plug caps, Dyna 3-ohm coils are about 0.9mS without any resistance in the plug caps).

[Doggie]

I just bought a set of GL1000 coils to put in my CB550F.
How many ohms are they and what gap should I set my plugs to?
                                  Thanks, Doug

[Deltarider]

What I meant is: by increasing the gap that much chances are sparks will be flying everywhere but between the electrodes (HT leads/plugcaps to engineblock for instance).
IMO our engines - unless highly tuned (higher compression) - will not benefit from higher sparkvoltages. Sparkduration on the other hand is another thing...

[Terry in Australia]

Yep, I took Hondaman's advice years ago, and have gapped my plugs at 1mm on both Dyna 3 ohm coil equipped bikes, with good results. Both bikes run 8mm silicon leads and molded caps, and I've had no issues with them shorting against the frame, head, etc. Cheers, Terry.