Ignition system

Mongo43 · #1 05-02-2008, 12:38 PM

I have a 1998 Fat boy with a engine upgrade (S&S Hot 89 Kit) what is the best ignition system for my bike? and what is the Difference between the dual fire and single fire?

Dr.Hess · #2 05-02-2008, 01:08 PM

Single fire is coil-on-plug. Each plug has its own spark coil and driver. I understand some of the single fire systems have the ability to retard one cylinder and not the other, that is, you can set diferent timing for different cylinders. A local top fuel drag racer I was talking to said that retarding the rear cylinder was good. You can also run higher RPM on a single fire system, but on a HD, I doubt your motor is going to have to worry about spark at 12K RPM (more than once). Single fire also adds complexity and expense. You now have two coils (even it it looks like one) and a more complex control circuit and trigger.

Dual fire is also known as Waste Spark. In it, both plugs get the spark at the same time, every time. One cylinder is ready to fire on the compression strokeand the other is in the exhaust stroke somewhere. The ready to fire cylinder goes boom. The spark in the exhaust cylinder doesn't do anything (all the gas/air should be used up already). Also, the exhaust cylinder will have a lower resistance at the plug, so it can be thought of as having the plug shorted to ground there electrically and the spark voltage goes to the high pressure ready to fire cylinder. Waste spark (and coil on/per plug) also eliminate the need for a distributor.

There's really nothing wrong with dual fire/waste spark. I run it on my 20 valve motor, which is a very high tech beast at about 160HP from 1.6L (97 cu in) and 8K RPMstock. Waste spark is also stock on a whole lot of other motors from DSMs to Camrys, Corollas, small block Chebys, Lotus Esprits, etc. Virtually every "coil pack" is a waste spark system.

So, what's best for your motor? You could spend the money and maybe see a difference with the dual fire, and maybe not. If you play with retarding the rear cylinder, you might see something, you might not. If you don't mess with retarding the rear, I really don't see much advantage.

Anyone have any real dyno sheets done properly, that is, in time, new wires, new plugs, run dyno. Replace with dual fire system. Run dyno. Compare results? Usually these dyno tests go: Take old worn out system, run dyno. Put new whatever system on, run dyno. Woa, a HP boost.

Personally, I think that the best bang for your buck is to use high quality ignition wires such as Magnecor and a good coil.I used to likeAccel, but I've had some bad experience with their products lately and so have others.

miacycles · #3 05-02-2008, 04:01 PM

Crane Hi-4 is the easiest to set up and is quite adjustable, plus their support is terrific.

rivercityslim · #4 05-03-2008, 08:42 AM

I have a Spyke dual fire ignition and coil. It gave a noticble performance improvement - the bike ran much smoother afterwards, and even felt as if it had a little more power. Although I'm guessing it wasn't a real power gain, just the impression of it happening due to the smoothness.