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Duel plug heads

Started by Panzer, August 15, 2020, 07:58:28 PM

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Panzer

What was the purpose of duel plug heads and what did it accomplish?
Need educating on this.
Everyone wants to change the world but, no one wants to change the toilet paper.

PC_Hater

I have a 2000 1200S.
The dual plug heads make removing the centre plug a real pain. You have to take the tank off. Happily the plugs last a long time.
As to WHY they did it? I suppose a cheap and easy way to run higher compression and different cams for more power yet still meet the emission regs.

Also I am fairly certain the 1200S was HDs first use of a MAP sensor on a carb'd bike.

If it had been a really really good idea 1200S heads would be sought after items for tuning. But they aren't.
1942 WLA45 chop, 1999 FLTR(not I), 2000 1200S

PC_Hater

I suppose I should add that on the Iron Head Sportsters and Shovelheads once you got into high compression ratios and radical cams the combustion chamber shape with those massive domes on the piston became so non-ideal that twin plugs was often the only way out. And then add methanol so you can use even higher compression ratios!

If you go back into the history of piston engines all of the 'best practice' was in aircraft engines.
EVERYBODY, HD, car manufacturers, bike manufacturers used their ideas because they were the best there was.
Then with car and bike racing the state of the art moved on but was often very secret.

That'll do as the simple intro.
1942 WLA45 chop, 1999 FLTR(not I), 2000 1200S

rigidthumper

Dual flame fronts travel faster than single, so ignition advance can be reduced to improve smoothness, fight detonation, improve lean burn, and allow for increased compression.
Ignorance is bliss, and accuracy expensive. How much of either can you afford?

Ohio HD


^^^^^^^^^^
What Rigid said


Also was used on Pan, Shovel and iron Sportsters because they had large combustion chambers, high domed pistons, the piston would be moving back down (reducing the compression) before the fuel mixture was completely burned. Lost power and detonation occurs. Lighting the fire on both sides of the dome helps insure that all of the mixture gets burned.

Also in most cases with dual plugs, you want to reduce your timing a little.

Hillside Motorcycle

And you will need to decrease the plug gaps also.
.020"-.025".
Otto Knowbetter sez, "Even a fish wouldn't get caught if he kept his mouth shut"

Racepres

Quote from: Ohio HD on August 16, 2020, 09:49:47 AM

^^^^^^^^^^
What Rigid said


Also was used on Pan, Shovel and iron Sportsters because they had large combustion chambers, high domed pistons, the piston would be moving back down (reducing the compression) before the fuel mixture was completely burned. Lost power and detonation occurs. Lighting the fire on both sides of the dome helps insure that all of the mixture gets burned.

Also in most cases with dual plugs, you want to reduce your timing a little.

Agree with all ...except the reducing of Timing... If you really are looking for Performance... leave the timing.. I can show a Marked difference [on an Ironhead] in the ET and MPH

jsachs1

I built quite a few Aerocharger equipped engines, Evo, Sportster, and Twin Cams, back in the day. I always used dual plug set ups on those engines. Easy to curb detonation, with great timing options vs. boost. :wink:
John

Panzer

Thanks gents, better understood by me now.   :up:
Everyone wants to change the world but, no one wants to change the toilet paper.

Hillside Motorcycle

By the time the machine time is paid, multiple coils/wires/plugs/mounting system, and a good ignition,($650-800.00 total?) for street application, the incremental gain in my opinion from witnessed dyno results, is not worth the dollar spent.
Maximum effort engine...yes.
Otto Knowbetter sez, "Even a fish wouldn't get caught if he kept his mouth shut"

Buglet

 If you want a clean burning efficient motor it might be worth it.

Racepres

Quote from: Hillside Motorcycle on August 19, 2020, 04:22:46 AM
By the time the machine time is paid, multiple coils/wires/plugs/mounting system, and a good ignition,($650-800.00 total?) for street application, the incremental gain in my opinion from witnessed dyno results, is not worth the dollar spent.
Maximum effort engine...yes.
Certainly Not on a Newer, more efficient combustion chamber... ie Evo and newer..
Unless trying to Squeeze the last ounce of Performance out of it... ie, Professional Racing

Hillside Motorcycle

Not on a hemispherical chamber either for street use.
We ran double plugs in our 108", and 114" Shovel race bikes, and also in our 108" Evo AHDRA Mod bike.
The Shovels were 15.0 cr and ran the Evo as high as 17.25 cr.
Otto Knowbetter sez, "Even a fish wouldn't get caught if he kept his mouth shut"

Ironheadmike

They ran dual plugs because of the shape of the pistons . They would almost make 2 separate chambers . So it was for a cleaner burn . Also because of the shape of the pistons , a single plug would actually push the piston to the side of the cylinder and cause premature/uneven wear . So the dual plugs would drive the piston straight down the cylinder .