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There have been a couple dual plug head companies over the years. There was one in Melbourne FL I tried to get an interview with in the 90's.
 

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Dual plug setups were pretty common.

The trick setup was 4 valve heads.

 

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Nope, not stock from MoCo.

2nd set of plugs can be machined into stock heads (Shovel and Evo) though.
 

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Flat Land Redneck
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I had my last shovel heads dual plugged, ported, polished and flowed. My intake was knurled and matched to the heads.I tried dyna tech's single fire electronic ign., which was kinda cutting edge back in the early 80's, but it never worked quite like I wanted. I love a shovel. Before I bought my RK, I thought about finding and buying back my old shovel. It's still being ridden.
 

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A lot of that dual-plugging went on back in the day with not only Shovels but Iron XL's as well.
Looked cool, and was bragged about while in the taverns, but that was about where the fable ended.
Never saw any additional power on the dyno with a street engine from that work being performed/money spent.
For a fact, the Moco did not offer any dual-plugged Shovel engines.
Scott
 

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A lot of that dual-plugging went on back in the day with not only Shovels but Iron XL's as well.
Looked cool, and was bragged about while in the taverns, but that was about where the fable ended.
Never saw any additional power on the dyno with a street engine from that work being performed/money spent.
For a fact, the Moco did not offer any dual-plugged Shovel engines.
Scott
The trick with dual plugged heads is that the second plug needs to fire about 5 degrees later than the first one to get the scavenger effect on the un-burned fuel, and that is no simple trick.

Mazda did it in their rotary engine (I had one). It had two distributors and 3 sets of points. Second distributor controlled the other plug.

Bitch-in-a-buzz-saw to set the dwell...
 

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Used to use a degree wheel to configure the (locked on full advance) Dyna S ignition on our 4-plug STD head equipped AHDRA Mod bike.:)
Scott
 

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One thing you need to keep in mind with 4v heads vs 2v heads is that you trade off some low end torque for upper rpm HP.
 

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Wayward Son
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No intention of running them. T~S is way to mild, and staying that way. Could not take full advantage of the set up.
At that price, could really pump up a 2 valve Evo or TC.
 

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Not

My first Harley was a brand new '82 FXRS right off showroom floor..little over $5,000.00 out the door....put on 87k miles...never came with 4 plug...did not need 'em 2 up loaded down And it ran great...
 

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One thing you need to keep in mind with 4v heads vs 2v heads is that you trade off some low end torque for upper rpm HP.
I'd take that on my bike. It feels like it could uproot trees at low rpm's, but falls on it's face at about 4000 rpm.
 

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Yup, that's HD's trump card... the low end torque.
 
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