[Ducati Scotty]

You can put a twin spark in a UCE.  One of the ISM models has it.  Easy mod, just drill and tap the hole and get a Harley dual spark coil.  I've seen it done but there weren't any major performance gains.  It might help get more thorough combustion in remote areas where'd the quality of the gas is marginal.

Scott

[Arizoni]

Twin spark plugs reminds me of the Auxiliary Power Unit we designed for the Boeing 777.

We decided that because of the high altitude starting requirements to meet the aircraft's  ETOPS requirement we would design it with two igniters in the combustor.

During the Critical Design Review one of the Boeing reliability engineers popped up and pointing at the dual igniters said, "You've decreased the reliability of the ignition system by 50%.
With two igniters, the probability of a failure is twice as high."

One of our engineers countered with the obvious by pointing out that if one igniter failed there would still be one left to start the engine thus the likelihood of the APU starting was twice as high.

The units final design has two igniters.

For those curious, ETOPS is a FAA requirement for commercial aircraft with only two engines which will fly long distances over the ocean.
If one of the main engines fails the APU must be able to start and extremely high altitudes to take over the planes electrical requirements and to provide bleed air to restart the non-running engine.
With the APU providing the electricity, the remaining main engines generator can be shut down allowing it to be dedicated to just providing propulsion.

Officially, ETOPS stands for, "Extended-range Twin-engine Operational Performance Standards"  but we jokingly said it meant, "Engines Turning Or Prepare to Swim".

Getting back to the twin spark on a Royal Enfield, I agree that there is not much to be gained by using two spark plugs.
Twin plugs have a better chance of igniting crappy fuel or a fuel mixture that is badly out of adjustment but assuming there is not a misfire the other spark plug is basically just going along for the ride.

[raderj]

I feel if you have the proper piston and head shape for the "quench zone", that all the fuel will burn properly with one spark plug.  Not many internal combustion engines use twin spark plugs because the engineers design proper areas for the fuel/air mixture to burn.

If your chamber is all misshapen then not all the fuel will burn before the piston reaches BDC.  The 535 piston had a flat top, so this shouldn't be a problem.  It happens more with domed pistons that are "too high".  Like this:

[digstuffup]

I've been making plans along similar lines, higher compression piston + adding twin spark.
I was told that two ignition sources can also help compleat combustion in the cylinder to occur more rapidly.

[raderj]

I'm not sure if it will help or not.  It makes me wonder when high performance manufacturers and tuners don't utilize the two spark plug technique though...

[digstuffup]

alfa romeo use it.

[barenekd]

Airplane engine use twin sparks as a safety measure, in case one ignition system fails the other will keep running. There is a definite advantage to have both of them operating together, though. There will be a definite rpm and power drop if one of them is shut down.
Bare

[Desi Bike]

I had a 1982 Datsun/Nissan 200sx that was a twin spark. The manufacturer only really used it to help with emmissions. The second spark would burn up what was left unburnt.

Instead of carving up a head to add another spark plug, why not give an MSD 4217 ignition a try.  (Multiple Spark Discharge.. its like having many higher than stock sparks instead of just one at firing time.) Summit Racing lists them for $302, I know its a bit pricy, but atleast you wont have to replace the head if your plan doesnt work. The MSD could be resold if you dont acheieve what you are after and still have an intact head.

Read more here....
http://www.mpsracing.com/instructions/MSD/4217.pdf

[tooseevee]

I had a 1982 Datsun/Nissan 200sx that was a twin spark. The manufacturer only really used it to help with emmissions. The second spark would burn up what was left unburnt.

                     If that's true then the two sparks would have to happen at two different times with the 2nd spark retarded a certain number of microseconds. Whether there is one plug or two, unless they fire at different times, once the fuel/air mixture is burning, it's burning.

[raderj]

That MSD is pretty cool. You can program it and everything.  Know of anyone running it?

[Desi Bike]

I ran a MSD 6AL in a big V8 that I had in a monster truck in my redneck days. I was quite impressed with it, but I have no experience with the 4217.

[GlennF]

alfa romeo use it.

Mercedes Benz as well.

Two common applications of twin spark plugs are:
- high boost supercharged engines
- engines with oval pistons (for example the Honda NR750 with 8 valves and two spark plugs per cylinder).

[ace.cafe]

There is quite a lot to bite-off and chew with this subject.

After 5 years and 20 engines, I'm still probing the upper limits of the Iron Barrel compression potential for street use.
My recommendation is if you are thinking about trying something, keep it into the 9:1 range, or thereabouts. The existing fuel for the street really isn't that great.
If you can use alcohol or race gas, then go for whatever you want.

[barenekd]

There is a definite advantage to have both of them operating together, though. There will be a definite rpm and power drop if one of them is shut down.

Understand, though, most airplane engines have something in the neighborhood of 5" bores, so their flame front takes longer getting from one side to the other. The two plugs cut at flame front distance in half, ergo, the power gain using twin ignition. Using the standard mags, it's highly unlikely that the two plugs actually fire simultaneously as the timing method isn't that accurate. Close, but no cigar.
Bare

[raderj]

After 5 years and 20 engines, I'm still probing the upper limits of the Iron Barrel compression potential for street use.
My recommendation is if you are thinking about trying something, keep it into the 9:1 range, or thereabouts. The existing fuel for the street really isn't that great.
If you can use alcohol or race gas, then go for whatever you want.

The UCE isn't an iron barrel, is it?