Author Topic: Best Sparkplug and gap for Shovelhead?  (Read 13125 times)

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Offline DJ Baar

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Best Sparkplug and gap for Shovelhead?
« on: Monday, December 05, 2011. 09:16:58 AM. »
 :emoGroan:

I know this may be opening a real can of worms, but I would really like to know what you Guys think is the BEST sparkplug for different Shovelheads, and what they should be gapped at (for electronic, points, or magneto ignitions)?

I have been running Champion RN12YC Sparkplugs and want to find a hotter recommended plug for my 96" Stroker (dual-plugged single fire Dyna-Tec Ignition with two coils).  I know I need to re-jet the Super B Carb (and/or go with a later Super E), but just got this old '74 Custom Superglide back together and it would be cool to start with the right plugs before I start tweaking the carb.  (This was a thought to be TLC that turned into an total engine rebuild, re-wire, etc....  Just down to the fine tuning now.)

Appreciate your feedback.

DJ Baar
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Offline 76shuvlinoff

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #1 on: Monday, December 05, 2011. 03:36:43 PM. »
I run an Dyna 2000i ignition, single fire, >dual plugged< set at a tight .025. It's been that way so long I don't even remember how I came up with that gapping  :embarrassed:

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Offline easyricer

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #2 on: Monday, December 05, 2011. 08:41:04 PM. »
In stock configuration, our Shovels have very low voltage ignitions. If I remember right it was like only 12000volts a the plugs. Modern ignitions put out upwards of 80000 volts.
 If you are still running points, I recommend the factory spec. of .025-.030. If you are running after market electronic ignition (and by that I mean a modern solid state unit), it will generally put out at least 40000volts. In that case I recommend .038-.042.
 The wider the gap is, the better chance of igniting the air/fuel mixture at the correct time. The sparkplug gap has more to do with keeping the coil cool and dependable. If you are using the old points and low voltage coils like I do, then you will be more in tuned to WHY the gap and the solid core wires are important.
 Modern electronics are not as prone to the coil heating up as the old ones. It's all controlled by the modules, now.
 As far as brands, every engine runs different. Some like the stock Champions, some demand Bosch Platinum. I've tried many different ones and have come to the conclusion that mine likes the Delco +4 platinum plugs the most. I've had the NGK Iridium plugs, the Bosch, Champion, and even Splitfire. Ol Betsie just don't want them.
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Offline 76shuvlinoff

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #3 on: Tuesday, December 06, 2011. 02:57:21 AM. »
 Easy,
Does that wider gap apply when running dual plugs? It seem in my foggy memory that's why it was recommended to me to stay tight, because there was "twice" the gap.  :scratch:  I do run it as retarded as I can turn the Dyna module or I will get some ping when hot.

As far as my coils I have two Dyna green uglies and all four plugs are Autolite 4265s (long)
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Offline DJ Baar

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #4 on: Tuesday, December 06, 2011. 04:20:05 AM. »
76shuvlinoff, 

I run the same Dyna 2000i single-fire, dual-plugged ignition system with the two Dyna green coils.  Another Friend told me he runs smaller gap on an electronic iginition on his race car too --- it has been my experience the higher voltage output electronic systems went with the wider (.038-.042) gap (as recommended in most every Tech Manual I have come accross - Hot Rod or Harley).  I also emailed Dyna Tech Support for thier recommendation on a sparkplug and will share when I get a response.  The plugs come pre-gapped to the smaller gap & I have to open them up -- I don't remember these problems with last Dyna electronic ignition I used on a Stroker Ironhead I built a few years ago --- Oh well, just trying to get it right so I can just enjoy the ride!  :nix:

Guess this wasn't such a dumb question about what sparkplug & gap since little reference to the "right" answer?   :scratch:
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Offline DJ Baar

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #5 on: Tuesday, December 06, 2011. 04:55:23 AM. »
 :idea: Found this website for AUTOLITE: http://www.autolitecatalog.com/Application.aspx?b=A

It lists the XTREME Sport XS65 or Standard 4265 and gapped at .040 for Harley Shovelhead (1200 or 1340).

Dont know if this helps or adds to confusion.  :doh:
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Offline easyricer

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #6 on: Tuesday, December 06, 2011. 06:41:56 AM. »
Mark, I wouldn't think that the smaller gap is going to hurt anything. The entire idea behind dual plugging is to expose the air/fuel charge to an ignition source at both sides of the high dome piston. It starts the burn process much faster, thus allowing us to retard the timing with the much shorter lag time. (lag time is the amount of time it takes the flame to completely fill the chamber)  In our hemispherical cylinders it is almost impossible to burn the entire charge before the exhaust stroke.
 If it were me, I'd try the larger gap and see what happens. I don't think you'll have any issues with it. Double the plugs does not mean double the gap, you also have double the coils. I've been considering dual plugging mine also, after the new year. I still have not torn mine down for the re-bore. What will likely happen, I'll tear it down and maybe send my heads off to get it done. I can always just plug the holes if it don't work out.
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Offline DJ Baar

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #7 on: Tuesday, December 06, 2011. 10:58:08 AM. »
 :idea:

Just heard back from Dyntek and told, "...with the 2000i and dual plugged heads, you should do the following. The total timing should be reduced about 4 degrees. Also, the plug gaps should be reduced to between .026 to .028."  So 76shuvlinoff there's a reason for your choice of small gap.  And for AUTOLITE both the XTREME SPORT XS65 or Standard 4265 should work.

And from J&P, "Early Shovelheads use the early short reach sparkplugs (3/8 reach) like where used in the Panheads. The late Shovelhead spark plugs are long reach (3/4 reach) like used through the end of the Evolution engines. To know what is best for your application, you will need to measure the spark plug hole thread depth. Personally I don't recommend Accel Spark Plugs for any application. I have used Champion Plugs for many years with excellent results."

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Offline DJ Baar

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #8 on: Tuesday, December 06, 2011. 11:16:51 AM. »
I've been considering dual plugging mine also, after the new year. I still have not torn mine down for the re-bore. What will likely happen, I'll tear it down and maybe send my heads off to get it done. I can always just plug the holes if it don't work out.
EASY

This is second old scoot I have had with dual plugs and totally like it! You are right about the Hemi-heads and burn.  (I don't recommend for an Evo tho as it dosen't have that problem with the flat pistons and more efficient burn area.)   :gob:

DJ
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Offline DJ Baar

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Re: Best Sparkplug and gap for Dual-plugged Shovelhead?
« Reply #9 on: Tuesday, December 06, 2011. 11:22:10 AM. »
Just got something more from Dyntek, "... You need to "retard" the total timing (4 degrees).  When dual plugging the Harley motor, especially the Shovel motor with large piston domes, you increase the efficiency of the combustion chamber and the result is a faster flame front, or, a faster burn time. If you do not retard the timing, the motor will have a greater chance of detonating or pinging.  With a lean air/fuel ratio, you need the larger plug gap to expose more of the spark to the fewer fuel molecules in an effort to start the burn process. This is why in the late 1970's plug gaps, especially in card, went as high as .080: Given this is not an emissions controlled application and will be run richer, the gaps can be closed (.025 - .028")."

I also use single-fire but that is a WHOLE 'nother discussion....   :potstir:
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Offline Trouble

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #10 on: Tuesday, December 06, 2011. 06:13:06 PM. »
This will sound a bit different but I run Beru Silverstone non-resistor plugs and solid core wires. Believe the gap on all four plugs kept at around .035". Dyna single fire, black Dyna coils. Runs good.
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Offline DJ Baar

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #11 on: Wednesday, December 07, 2011. 06:22:00 AM. »
I saw those Beru sparkplugs and thought about getting them, just a bit concerned my friends with the ECUs (Electronic or Engine Control Units) may not like the "static" of me riding along side?   :bike:
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Offline shovelbill

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #12 on: Friday, December 09, 2011. 04:16:05 PM. »
if you round off the ground strap you'll be less likley to experience detonation, no sharp edges to heat up.......and i run the coldest plug i can get away with. index your plugs as well, don't shroud the spark with the groundstrap.

like this.



« Last Edit: Friday, December 09, 2011. 04:19:46 PM. by shovelbill »

Offline Hillsidecyclecom

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #13 on: Monday, December 12, 2011. 11:58:49 AM. »
Easy,
Does that wider gap apply when running dual plugs? It seem in my foggy memory that's why it was recommended to me to stay tight, because there was "twice" the gap.  :scratch:  I do run it as retarded as I can turn the Dyna module or I will get some ping when hot.

As far as my coils I have two Dyna green uglies and all four plugs are Autolite 4265s (long)

Yes, as the coils are dumping power to both plugs, and the closer gap is needed.
If you ever push ccp waaaaay up,(usually not needed for the street) then .020" would be wanted. :up:
Scott
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Offline 76shuvlinoff

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #14 on: Monday, December 12, 2011. 03:22:52 PM. »

I am running a tight gap but can't get my head around it.

With my dual plugged mill running single fire... would not that be the same as a single coil firing a single plug in each cyl  simultaneously? Since there is only compression on one cyl at a time does that make the difference?

 Thinking out loud and probably mistaken but doesn't compression attempt to extinguish a weak spark? Is that the point of the tight gap?  If I'm running a more or less modern electronic ignition shouldn't I be able to run a bigger gap .... and why would I want to if I could?

 Crrraaap, I can see I'm going to fix something till it's broke again.....   :banghead:

 The last I checked I had 200 + psi per cyl on a autozone compression tester.
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Offline hotrodshovel

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #15 on: Monday, December 12, 2011. 04:56:58 PM. »
Wow  so whats the verdict here? dual plugged heads, the green uglies (what the hell were they thinking) Dyna S.  I'm at 32 with Champions (RJ12YC/RN12YC) and no issues.
John

Offline Hillsidecyclecom

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Re: Best Sparkplug and gap for Shovelhead?
« Reply #16 on: Monday, December 12, 2011. 05:03:07 PM. »
The wider the gap, the weaker the spark, although the spark kernel may be larger,
The tighter the gap, to a point, the more intense the actual spark event becomes.
At 200 psi, I'd try .022", just for the hell of it, and see what you experience.
The higher the ccp the more it trys to blow out the spark. :smile:
Scott
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