Bonneville America Forums Forums Technical Forums Performance Mods Side Gapping Plugs

I didn't think that side gapping the plugs would make a noticeable difference until I changed my plugs about a month ago and figured what the heck, I would go ahead and side gap the plugs. Since I have done so, there is definately a noticeable difference in the way my bike runs. A worthwhile extra step when changing plugs.

Then the other night I was out riding and there are some gas stations in the area that sell Turbo-Blue Racing Fuel (115 Octane) and figured I would try a little in my bike (about 3 gallons worth). Now I am running Big Bore, modified air cleaner, Thruxton needles, 45 pilots,I believe 150 mains and DBA mufflers from Hermy's, and all I can say is WOW!!! Big difference, and I still want to try the Mikuni's and Freak yet. I don't know how much of a differnce the freak will make as I believe my carbs are getting plenty of air. She is actually still running a touch on the lean side. By sounds of it the Mikuni's should be yet another improvement and I will probably go with a set of the Nology coils and wires as well.

But any one out there that doesn't believe that side gapping the plugs will make a difference, I fully endorse the extra time it takes to side gap a new set of plugs.

I would also like to stick with about a 60/40 mix of Turbo Blue and Sunoco 93 Octane but at $5.79 a gallon it might get a little on the expensive side to keep up with it as I only get about 25 mpg as well.

Sorry for rambling on but the old girl is really running strong and I am happy as H*#L !!!

Where is Dazco when you need him ? Yeah I know he is on the Ratnet trying to post a million posts. Good on ya mate for trying something new and sharing the info.

O.K. ....so I've heard of side gapping but what exactly is it?

You cut the plug's electrode "arm" off even with the edge of the "emitter" electrode to increase the exposed spark area. It's the same principle used by Denso and others in their electrode-less plug designs. It should provide a better burn and racers have done this as well indexing their plugs for decades.

The higher octane fuel also makes sense if you've gone to a 10.5:1 compression ratio as it slows the burn to prevent the pre-detonation that is common in higher compressison engines. It also goes hand-in-hand that you'd need more spark for a "slower" burning fuel...

Here's a link to how to do it.
http://www.performanceunlimited.com/documents/plugsidegapping.html

Never heard of it before but it makes total sense, gonna do it tomorrow, after all a hotter slower burn is a cleaner burn, and more grunt
Hoffo

It looks like, from the article, that it should be cut off even with the leading edge of the center electrode. Is this correct?

Then you index them.

Oooh, do we get to hijack this toward indexing? Now we ARE heading toward a high performance discussion

tried the side gap, had better results with the iridium plugs.

FWIW, higher octane fuel won't do squat unless you need it. If you want to throw money away, I can give you my paypal address.

My SUV calls for dual electrode plugs but all the hype about Irridium plugs and Denso had a listing for my vehicle so I figured I would try them. I was not impressed in fact I went back to dual electrode with better results, much what side gapping would produce with my ride. As for high octane I can without a doubt tell a differnce when I added some 115 octane racing fuel. Just my seat of the pants opininion and with running 10.5 to 1 compression, I can use it!

with 10.5:1 you don't need any more than regular premium,92 , 93 octane. You probably wouldn't need 115 until you get up around 12:1

10.5-1 isn't all that high of compression. Like The Dog33 said, 92 octane is fine and you can probably use 89 as well. BTW, yes, I have a 904 kit in my bike too and I have the same compression you do. Like I said before, if you want to throw your money away feel free to do so.

Also, higher octane fuels will not burn as completely if your compression isn't high enough to need them (which it isn't) and they will leave carbon deposits on your pistons, valves, and combustion chambers. Not good.

My (professional) opinion is that the main benefit of side gapping is for the place that sells you the plugs, since they will wear out much quicker.

A correct, properly gapped spark plug will ignite your air/fuel mixture just fine.

If you want to pretend to be doing some cheap high performance mods, you'll do better to index your plugs.
Though the benefits to a stock or slightly modified engine are most likely psychological (just like side gapping)


And the fuel thing Dog and Sweat covered it quite well

Hmm... Wonder why NGK, Bosch and the others never figured this out? Snake oil?

Back a few years ago (about 91) I used to run these Torque Master .
Back then the guy used to hand make them out of modified Bosch plugs. I swear they made a difference and they lasted for as long as I kept the car (sold it in 2000 - about 8 years).

Show me a dyno run.

Ed, far as I know, you index to the intake valves and I would index them to point between the two.

And you know correctly . Except for the valves. Usually the mixture is oriented to the exhaust valves from the flow of combustion. So that's the direction to index toward.

But again, on stock engines I doubt that you'll have any noticeable improvement.

Other than that which comes from a new set of plugs.

You know, I might just have to side gap and index my old plugs and find out if my "seat-of-the-pants" dyno feels any improvement. Worst case scenario it will force me to buy a fresh set of plugs and that's always an improvement (when properly gapped). I kinda doubt a major improvement since I don't have a high compression squish area but I love to tinker...

anyone have experience with side-gapping and loss in fuel economy? I'm just asking because during my last service interval about 5 tanks ago, I side-gapped for the first time. Since then, I have gone from ~42 MPG down to 36 MPG, consistenty. I haven't altered my riding style or routes, and have filled up using the same octane from several different filling stations. I've been filling the tank in the same manner (e.g. w/ bike on side stand vs. upright) as before.

The only other thing, setup-wise, I changed during this last service interval was to remove the shims on my stock needles. If anything I would think that that would improve my milage. I have the mixture screws set at or below the old settings (3.25 turns) and I balanced the carbs as the last step of the recent service.

Also of note is that I did replace 7 out of 8 valve shims, but I can't imagine how getting those back into spec would have anything to do with fuel economy.

To further diagnose (after I have confirmed the 36 MPG one more time at the end of this tank) I plan to do the following:

1. Replace plugs with same (non-side-gapped), run a couple of tanks.
2. Put my needle shims back in, balance carbs, run a couple of tanks.

Mainly I'm just looking for other sources of my problem, and trying to determine whether the side-gapping could be the culprit.

TIA,
Joe

Hmm, I went on and on about this topic, many moons ago

Hi, goodtech here I tried the side gaping on the ngk's(dpr8ea-9)I found that my bike starts somewhat easier,but I did not found that the performance increced any, if any is in the upper rpm's but it seem's that five'o is lercking around the corner everytime I get on it.The gas mileage is the same as I ride acoringly,(40 mpg)the bigest thing I notest the bike is smother at idel and at stedy speeds

The exact thing happened to me when I side gapped my plugs, decrease in fuel mileage. And just to be sure that it was not caused by me I tried 3 different sets of plugs with different amounts trimmed off on each set. Went back to a new set of stock plugs and the fuel mileage was back to normal so I thru the iridiums back in which I had been running for the past 2 years and mileage remained normal. All these tests were done using brand new Nology coils and wires.

I have been using side gapped plugs on every vehicle I have owned for the last 5 years. I wouldn't run a vehicle without side gapping the plugs. I believe any power gain is negligible, but I notice on every vehicle smoother running and easier start up, that's enough for me.