Ignition systems

Need to be versed in ignitions systems.What I have is 95 Heritage.when I bought it had the screamin eagle ignition installed. I want to put 120" El Bruto in will I need to change the ignitions out? I believe the Ultima has a single fire ignition, will it be compatable with the sceamin eagle? And explain the difference between Double fire and single fire.............Thanks........Rob.

Is the screamin eagle ignition a single or double fire?

Chuck is there away to check it the box under the seat would there be switches on it or something like that?never really looked at it that close.

Thanks......man............Rob.

That's backwards - with "dual-fire", the spark plug fires on both the compression & exhaust strokes - you get the "wasted spark" & that's the old style. It's easier & cheaper to make 'cause the coil just fires both plugs @ the same time, even when one cyl. doesn't need it.

With "single-fire", the plugs only fire on the compression stroke. You won't see any HP difference on the dyno, but a single-fire bike does tend to start easier & idle smoother. From what I've seen on the street bikes, by about 3000 rpm any noticeable difference is gone, but I do like the single-fire better, especially around town.

But with a more modified engine, you can have problems with dual-fire - with lots of "overlap" in the cam(s), you can get a pretty serious backfire if there's any unburned fuel in the pipes when the "wasted spark" fires.

Now here's a trick for engines with domed pistons & especially Ironhead Sportsters - dual-plug the heads, use 2 dual-fire coils but a single-fire ignition. Flame-travel can be an issue (especially in Ironheads) & having a plug on either side of the cylinder resolves that issue. It also allows you to slow the timing down somewhat & get rid of "pinging" problems since the fire doesn't have to go from one side of the cyl., over the piston dome to the other side.

Notice the best-running carbureted Harleys ever off the showroom floor were the 1200S Sportster models (discontinued after 2003) which came with dual-plugged SE heads & a single-fire ignition. Those heads really aren't all that great either (Thunderstorm & XB's are better), but it's interesting to note that the 1200S bikes get better gas mileage than an 883 & the dual plugs is why.

I set my race engine up in a similar fashion - a simple Crane HI-4 single-fire ignition with a dual-fire coil for each cylinder. The ignition sends the signal to each coil as to when it should fire (just once during each cycle) & both plugs in that cyl. fire @ the same time. Domed pistons but no flame-travel issues @ all.

You can get real fancy with programmable ignitions but I've never seen the need to do that. We do have a nitrous setup & if we get around to putting it on then I will have to change, as the timing must retard quite a bit when the silly gas comes on & the Crane doesn't have that feature. But for a "daily driver", a good single-fire adjusted right is all you need IMO.

Also note that the SE ignition modules just raise the rev limit - the advance curves are the same. They cost less than the stock module, so if you keep your eye on the tach you'll be fine, but putting a 7500 rpm module in your bike can let you blow the engine up if you don't.

dual spark plug heads

speaking of them im looking dfor a pair of dual spark plug heads for my 1983 1000 cc ironhead sportster if u have pls message me with price thx fubar

Art_NJr

Thank's I did get that figures out About the single fire, and double fire the Utima 120" I just installed came set and equiped with a single fire ignition set up from the factory .there for I had to purchase I single fire coil evrything is good .Thanks again.....strickt9rob

dual plug heads

Any good machine shop can dual plug heads you've got for around $140. Ironheads love it but you can do it to others too, although there's not as much of a benefit with flat-top pistons as there is with domed.

I'm pretty sure this motor is has flat top pistons and it's making pretty good power the way it is.It's like nite a day compred to the old 80" that was in there.it's making almost twice the HP it's a square motor 4 1/4bore X 4 1/4 I stroke love it so far still braeking it in.

I'd bet it does have flat-tops to keep the compression down so you can run pump gasoline. I got most of my race engine from Zippers & they sell one complete with flat-tops for street use. The domed pistons I've got make for 13:1 & needless to say that's way too high for pump gasoline.

It's a "square" engine too & that's the best combination of torque & HP you can get. Undersquare engines (like nearly all Harleys - stroke is longer than the bore is wide) make gobs of torque, while oversquare engines rev quicker, higher & make more top-end HP, but a lot less torque. And with a pushrod valvetrain there's only so far you can go rpm-wise before you start bending pushrods & other bad things happen, so it doesn't make sense to rev high & Harleys love the mid-range anyway.

You should be very pleased with that engine & it should last you a long time. For the street bikes, I'm a "If it ain't broke don't fix it" guy - but @ the track, "If it ain't broke, fix it 'till it is." ;-)} That gets REAL expensive, but you don't know where the limit is until you hit it.

I could have gotten by without dual plugging the heads, but when a 10th of a mph may mean the difference between getting a record & not getting one, you go for every little bit of advantage you can get.

One other thing I'll mention is a guy gave me a set of Denso Iridium spark-plugs to try & I really, really like those. They're expensive too - about $12 each. No difference on the dyno, but there was on the time-slips & the engine starts so quick you don't even hear the starter. And that's with a bone stock Sportster starter too.

Once it's broke in .I'm going to use AC platnium plus and index them always had good luck with those plugs they use a tungstin electrode is sharpened to a real point if I can cross-refference the heat range. Man just waitin for the weather to break around here.At least get in the 50's the winter just dosen't want want to let go...................later.......... strick9Rob.