Dual plugging EVO heads. A waste of money?

[gryphon]

I'm having some headwork done and will be bumping my comression up to approx. 10.5:1. The shop doing the work is very well known nationaly and has a good reputation. He recommended that I also dual plug the heads because of the compression increase. I asked him if that was really necessary since I'm running flat top pistons and he assured me it was. Now then, we used to do this on our Shovels because of the domed pistons and hemi heads. I'm not an authority on the subject but it has always been my understanding that with the EVO heads and flat top pistons nothing was to be gained by dual plugging. I can kind of understand the chicken soup theory of, "it couldn't hurt" but I'm not interested in a $150 bowl of chicken soup. Would anything really be accomplished by dualing the heads (other than lining someone elses pockets). Would it really help to prevent pinging?

[PC_Hater]

At 10.5:1 perhaps it is worth it?

I have a 1200S Sportster Sport. It has twin plug heads from the factory. There are a lot of similarities with an EVO top end, some part nos are the same as on the EVO big twins.

Not a direct answer, but Harley wouldn't have spent the money on the extra bits and pieces if they didn't have to.
Would they?

[CraigArizona85248]

If your pinging is a result of too much ignition advance then dual plugging will help.  By having two flame fronts you will get a much faster burn.  A faster burn allows you to dial back your ignition advance a few degrees which should reduce the pinging while still maintaining very good performance.  I doubt you will see as pronounced a difference as you do on a panhead or shovelhead, but it will be of some benefit.

If your pinging is a result of true pre-ignition (the mixture lighting off because of high compression and a hot spark plug tip for example) before the spark fires, I don't see that dual plugging would help you much.

-Craig

[fergy1940]

gryphon

F.w,i.w my old 97'' had dual plugs and you could the difference same compression as yours never had a ping.

Fergy

[wfolarry]

Dual plugging isn't really necessary on the Evo's because of the chamber design. the more open the chamber -or in the Shovel's case to get some fuel burning on the other side of the world- you would see a difference.

[Hillside Motorcycle]

Only Evo's we even dual-plugged were upon customer request, and our AHDRA Modified racer.

[Paniolo]

I put dual plugged heads on my '91 built EVO Heritage. It sure looked neat and was a good conversation starter but all in all I think it added very little if anything to the build. I would NOT do it again.

[Phu Cat]

I'm certainly no authority, but I thought the purpose of dual plugging a head with domed pistons was to get equal burn on both sides of the dome.  Isn't that why flat top pistons don't require dual plugs?

PC

[L-]

If you are running stock H-D cases I would consider less compression. 9.5 but not over 10.0.  Dual plugging with flat tops and a mechanic saying it has to be done is something I would ponder about.  Just my opinion. 

L-

[gryphon]

I hate to completely re-assemble the top end just to later decide that I should have dual plugged it. But personaly, I just find it hard to beleive that it would accomplish much. I currently have an HQ-29 cam with a 36 degree closing but will probably re-install my VT-3030 which will give me a 44 degree intake closing. This should help. I can also dial back my Dyna ignition to a later advance with a shallower curve.  I'm also installing the S&S electric compression releases for easier starting. The motor is a 97 inch S&S 4" bore motor. With 9.5:1 I'm pumping about 215lbs of compression with a 36 degreee intake closing.

[TheSwede]

Hi Gryphon,,Dualplugging,,is one time job,,if you planning
to keep the bike,,do it,,if the heads are of,,
the only way to really know is to try with or without
one or two sparkplugs,,myself have less pinging with dual plug
and be careful to increase later intakeclosing,,
if you can rule out pinging with 36 degree cam
you have so much more bottomend power.
Remember always,, late intake,,less volume gas
to compress  less power at low RPM
increase compression compensate less gas volume
but the Torguecurve move up,,maybe 800 RPM
Read what Miking expert Joe Minton have to say
about  camtiming

Best Regards
TheSwede

[attachment removed after 60 days by system]

[TheSwede]

Sorry wrong file
this should work

[attachment removed after 60 days by system]

[gryphon]

Yeah, I've seen charts similar to that before. However, there are lots of things that come into play. The truth is that I initialy swapped out my 3030 cam to the HQ-29 with the idea in mind that the much earlier intake closing and higher lift (.585 as opposed to .530 for the VT cam) would give me a noicable boost. I spent a good deal of time changing carb settings etc getting the new cam dialed in and honestly, the only major difference I noticed between the two cams was a very noticable increase in noise with the HQ cam. My thinking is that if I can get the same "on the road" performance and a much quieter engine using a less aggresive cam then that's the way I want to go. I may go ahead and dual plug the heads anyway though since they're gonna be off and stripped down anyway. Wouldn't be the first time I ever spent $150 with nothing to really show for it. Shoot, I used to drink that between friday and saturday.

[gryphon]

Well, I called two other performance shops and told them what I was doing and asked how much to have them dual plug my heads. Both said the same thing, "We'll do it if you want but you're wasting your money". Pretty much sums up my initial thought on the subject.

[TheSwede]

Well Gryphon,,We Harley freaks do allot of things
just because it feels good,,one thing is dualplugging
One very common thing is Hypercharger,,Forcewinder
that have nothing to do with power either,,,

This is just,, that is all about,,feel good..
many feel that with dualplugs..
regardless of tech motivation or not.

Best Regards
TheSwede

[Paniolo]

many feel that with dualplugs..
regardless of tech motivation or not.

The Swede is correct in my case. I saw another guy with dual plugged heads and wanted them on my bike too. Part of me justified it by telling myself "If one plug fails you have a back up already in the head and firing". But the only person I was kidding was myself. The looked high tech and all but that was it. If you really WANT them, get them.

Mark

[gryphon]

That's why I have a hydraulic clutch.

[Pilgrim]

If your pinging is a result of too much ignition advance then dual plugging will help.  By having two flame fronts you will get a much faster burn.  A faster burn allows you to dial back your ignition advance a few degrees which should reduce the pinging while still maintaining very good performance.  I doubt you will see as pronounced a difference as you do on a panhead or shovelhead, but it will be of some benefit.

If your pinging is a result of true pre-ignition (the mixture lighting off because of high compression and a hot spark plug tip for example) before the spark fires, I don't see that dual plugging would help you much.

-Craig

Craig, did you ever run into detonation that was induced by dual plugs?

I did, on a 103" Axtell (well, Axtell/STD/Delkron) motor I rebuilt after it had been trashed.  I couldn't hear it, but I found it on the heads and pistons when I tore the motor down for another reason.  I went looking for an answer and found a few paragraphs somewhere (D. William Denish, maybe) that said the sudden increase in chamber pressure caused by two flame fronts can push a ping into full-fledged detonation in small areas prone to it anyway.

Sure as hell, I was getting it in an area of the quench band that I had relieved to much; clearance was around .040 near the exhaust valve instead of the .025 I'd used other times.  It was just sloppy hand work on my part and I didn't catch it.  But the Gods of Combustion did, and showed me where with a very rough, sandblasted-looking surface.

Pilgrim

[CraigArizona85248]

Interesting info Pilgrim.  I haven't run into this personally, but it's good to know.

-Craig

[76shuvlinoff]

 If your afraid of having to take it all apart again I suppose you could machine em for dual plugs and block em off or save the holes for compression releases.  Not sure that you'd need compression releases at 10.5:1 though.


  $150 chicken soup, that's a good un.

[lasmittys1]

I'm having some headwork done and will be bumping my comression up to approx. 10.5:1. The shop doing the work is very well known nationaly and has a good reputation. He recommended that I also dual plug the heads because of the compression increase. I asked him if that was really necessary since I'm running flat top pistons and he assured me it was. Now then, we used to do this on our Shovels because of the domed pistons and hemi heads. I'm not an authority on the subject but it has always been my understanding that with the EVO heads and flat top pistons nothing was to be gained by dual plugging. I can kind of understand the chicken soup theory of, "it couldn't hurt" but I'm not interested in a $150 bowl of chicken soup. Would anything really be accomplished by dualing the heads (other than lining someone elses pockets). Would it really help to prevent pinging?

  Everything that has been written is good advice, and here's one more thing to think about, if you don't have a ignition system, coils, spark plug wires, spark plugs, than you have to get them, and sometimes getting to the plugs between the pushrod tubes is a pain. To me waste of money and time if any benefit.