[godot]

Ten folks will give 10 different opinions as to why Single Fire coils are better than Dual Fire ones. And if 10 others are asked, they may say the total opposite, at least in my experience.

Can anyone shed some light on this argument?

Thx...

LR

[hotroadking]

Sure

simple single fire only fires on the compression stroke where the plug should fire, this reduces stress and vibration on the motor.

Reduced will increase performance.The older dual fire will fire the plugs when they don't need to be fired more vibration etc.

[shovel66]

godot,
IMHO taking off a perfectally good peoperly tuned dual fire system and replacing it for a single fire system is just a way to spend money. You will NOT see, feel or hear any difference at all. Even a dyno would not pick up any increase in performance (if there was). About the only benefit this change would bring is the spark plugs would last a little longer. Personally I change my plugs every year anyway just because they are so cheap.
If the dual fire system is improperly tuned and has a lot of unburned fuel in the chamber during the exhaust stroke, yes the "wasted spark" could ignite that fuel and cause very minor vibration.
The only people who actually say that it makes a difference are the people who want to justify spending the $260 or so it takes to make the mod.
This is just my opinion based on years of riding and wrenching on Harleys.
shovel66

[CD]

Shovel66,

I agree a stock engine with electronic ignition in good working order will benefit far less than a high performance engine. However, once you begin to modify an engine and increase the capacity of the engine pump more and more air and increasing compression, you soon get to a point where the spark kernel can be washed out and produce a much weaker flame front and can totally be blown out and a misfire will occur.

The intensity of the spark is as critical in performance gains as is the choice of cam, compression, etc. The ability to alter the advance curve can add more HP, aid in eliminating or reducing pinging or detonation if needed.

There have been many tests over the years demonstrating the HP gains possible with high performance ignitions. The most significant gains are in the advance curves but, spark intensity is a factor. On a stock dual fire system, a lot of the spark energy is wasted on the non firing plug since electricity follows the path of least resistance and a plug under compression has more resistance than the other. Single vs. dual fire was always a hotly debated subject where H-D continously claimed there was not an advantage to single fire systems. Odd how we now have all bikes using single fire isn't it?

Older models with point type ignitions benefit greatly by converting to an electronic ignition. No more wasted points, thrown weights or sacked out springs or timing every time you turn around. It is not a permanent mod and can be totally transparent.

[godot]

I did go with a single-fire coil and noticed a difference, both in power and in less vibration.

[Ole Blue]

Ole Blue here, a stroker shovelhead rider, 52 years old (still a kid) that has had both dual (factory points) and single fire ignitions.

Over the last 35 yerars or so, I have always had dual fire basically stock ignition systems with the addition of high output coils to strengthern the spark delivery and offset some of the energy loss to the non-firing cylinder.

I've had some great running sleds over the years and never had much problems with these set ups.

This year, I put together a highly modified 93 incher using an S + S unassembled longblock so I could toss in about 50 other, better improvements. Along the way, I added a single-fire, dual-plugged, twin 85,000 volt coil programmable ignition system.

I agree that this type of ignition system really shows it stuff (improvements) when you start adding compression (high-dome pistons are not the best encouragement to flame travel) and cubic inches (more air-fuel mix to ignite). I added my first ever electric starter and find that even when kick starting, it fires off very easy.

I can't really say the ignition system has made signficant performance improvements as I added gears, motor, ignition, & a DiVinci carb at the same time and have to belive part of what I am feeling is related to motor & trans & belt & clutch.

But... from the performance books I've bought & read (numerous @ $$$$$) there is a benefit to these ignition systems although I'd agree that the improvements must be accompanied by other, more important changes.

I do know it starts easy, runs like a banshee, and is about all I could ever expect in an engine that is on the smaller end of the strokers available today. I do think, that everthing you do needs to be implemented in concert with other changes in order to enjoy maximum return on your $$$.

I personally think it has certainly added to the performance capability of my motor. I like the built in rev limiter and adjustable timing curve. As the motor broke in and got some miles on it, we just changed the performance curves a little, and allowed it some additional RPM's and.... Ole Blue smiles like a mule with a mouth full of briars.

Good luck... Blue

[godot]

But... from the performance books I've bought & read (numerous @ $$$$$) there is a benefit to these ignition systems although I'd agree that the improvements must be accompanied by other, more important changes.

I fully agree. This upgrade, in my opinion, should be viewed as the icing on the cake.