[strickt9Rob]

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.

[chucktx]

single fire= both cylinders fire at the same time....older style

dual fire= both cylinders fire at there own preset cycle....newer style

i think you would be better off with a new ign system,,,one that you can tune on the bike without all the dealer hassle.....my opinion.........

[strickt9Rob]

Is the screamin eagle ignition a single or double fire?

[chucktx]

i think they are available both ways.......

[strickt9Rob]

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.

[chucktx]

i would look in the service manual....i dont think there are any switches on it. it is a download from the dealer type of box.......

[strickt9Rob]

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

[Art_NJr]

single fire= both cylinders fire at the same time....older style

dual fire= both cylinders fire at there own preset cycle....newer style

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.

[fubar]

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

[strickt9Rob]

Originally Posted by Art_NJr

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.

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

[Art_NJr]

Originally Posted by fubar

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

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.

[strickt9Rob]

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.

[Art_NJr]

Originally Posted by strickt9Rob

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.

[strickt9Rob]

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.