Spark plugs

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Surprised no one has brought up plug indexing here...that's an old school method of "improving" performance by positioning (via rotating) the sparkplug such that the gap is facing the center of combustion chamber rather than away from it.
 
Tornado said:
Surprised no one has brought up plug indexing here...that's an old school method of "improving" performance by positioning (via rotating) the sparkplug such that the gap is facing the center of combustion chamber rather than away from it.
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MexicoMike brought it up, two hours ago.
 
Lineslinger said:
So does anyone have any insight as to which plug is the most resistant when considering quenching...or do the plugs referred to previously offer a charge/spark hot enough to take it out of consideration.
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Well, a plug with sharp electrodes and/or tight gaps are going to resist quenching, not that tight gaps is best for power.

But quenching is not normally a problem unless your running a supercharger or cylinder pressures higher than you would see in a Norton.
 
Quenching enters when dynamic running conditions present such high cylinder pressures that the flame kernel is suppressed or can’t propagate. It also occurs with colder fuels. Or, when you have both cold fuel and high pressures.

These conditions are very rare for our street bikes but a racing Norton could certainly see good fuel and/or high dynamic pressures where the power lost to quench is only perceptible by way of temp sensors and a dynamometer or loss of top speed.

I’ve had turbo engines lose power when given “better” fuel. I’ve also fixed high boost ignition miss by swapping in iridium plugs (or reducing plug gap). In both examples the problem can be called “quench.”
 
comnoz said:
They may be good for some applications but I bought a Mercedes 190 a few years ago really cheap because nobody could fix the intermittent warm start problem. It always started cold but when it was anything but cold -you couldn't count on it. After a lot of time and a bunch spent on parts I finally took out the nice clean e3 plugs that were in it and put in a set of Bosch's. Problem solved.

Never tried them again after that.
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Any curiosity is gone now and will stick with the purchased Denso's.
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Best price for those I could find in Australia was here...fwiw.
http://www.brettstruck.com.au/

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A while back I ask a guy well known in the USA about what spark plugs he recommended having owned and works on (his day job) this particular bike brand for decades.
I was surprised to get back, plain old base line plugs, BP6ES in this case.

That made me curious enough to google the subject and a good deal suggested exotic tipped spark plugs were mostly aimed at longevity in cars more than performance.
I ask the dude at a large parts store (He could have tried to talk me out of ES's) and in our chat mentioned unless he was mistaken, top fuel dragsters were using copper plugs last time he was at the strip.
 
I suspect that there are moments, measurable in milliseconds, where engine speed/cam position/throttlle, even with our street Nortons, where we do have imperceptible quench which can be resolved with electronic ignitions and fine wire plugs.

What an awful sentence. Too hard to fix on this phone
 
Time Warp said:
Any curiosity is gone now and will stick with the purchased Denso's.
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Best price for those I could find in Australia was here...fwiw.
http://www.brettstruck.com.au/

#
A while back I ask a guy well known in the USA about what spark plugs he recommended having owned and works on (his day job) this particular bike brand for decades.
I was surprised to get back, plain old base line plugs, BP6ES in this case.

That made me curious enough to google the subject and a good deal suggested exotic tipped spark plugs were mostly aimed at longevity in cars more than performance.
I ask the dude at a large parts store (He could have tried to talk me out of ES's) and in our chat mentioned unless he was mistaken, top fuel dragsters were using copper plugs last time he was at the strip.
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He's right. Exotic metal electrodes are all about keeping a sharp edge on the negative electrode so the plug fires more easily.
A fresh copper electrode plug and a fresh iridium electrode plug are going to perform the same.

But 100,000 miles later the iridium electrode is still going to be working while the copper electrode is going to be gone...
 
Fast Eddie said:
100,000 road miles or 20 fast race laps...
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I can guarantee that the riding I do around here is a whole lot tougher on a motor than any road race course.

As Kevin Cameron says "air cooled roadrace engines have it easy, there is always a corner coming up to give the pistons and head a chance to cool".

Out where I live there are sections of road where you can run 100+ mph and not roll the throttle for 100 miles. And 5% or more grades, without curves, run at interstate speeds that may go on for 20+ miles.

That is tough on an air cooled motor. And I have a whole pile of scrap forged pistons as a result.
 
Well, I’m not speaking from any spark plug knowledge Jim, just personal experience. I used to suffer ign problems and eventually realise it was plugs. An old boy on the paddock basically said it was no wonder as I was using ‘normal road plugs’ and I should use race plugs. Even 20 plus years ago these were around £15-20 each! But they were worth it. Road plugs wouldn’t last a two day meeting, race plugs would last a season.

I later discovered that iridium plugs seemed to last just as long, but were much cheaper.
 
I used race plugs too, but just because there were no street plugs available in a cold enough heat range to survive with the engine tune. I normally ran an NKG11 -with a copper center electrode. Then I went to a Champion C53 which was a better plug all around. [but no longer available]
 
Having some misfire issues I stuck in a couple of ancient rusty KLG FE 75's , as their look matches the rest of the bike they may stay.
 
so , just to clarify in my foggy state , iridium plugs offer, not more performance but longer service life... thanks ! also would that rule apply to liquid cooled engines as well , I ask as I have seen claims elsewhere, that you could expect better performance with the iridium plugs ....
 
On my nitrous Busa I always used stock NGK plugs as the first point of failure was when the earth electrodes eroded - but even then the motor would still run dieselling along until the inlet valves also eroded, all in a matter of milli-seconds it seemed. Expensive game, playing with NO2
 
I run BP8ES gapped at .028 in a moderately tuned motor: 9.5:1, 312a cam, flow ported head with big valves, Brooking 850 exhaust, TS ignition.

Motor runs strong, and revs freely. Love it. And I do get on the stick on twisty 100k roads, quite often on hot days.

My question is what is optimal gapping, and how can you evaluate?

Spark plugs
 
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gortnipper said:
My question is what is optimal gapping, and how can you evaluate?
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In very general terms, bigger is better when it comes to plug gap. A bigger spark exposes more of the gasses in the combustion chamber to the flame front and contributes to more complete combustion. Widening the gap was one of the first things automakers did in the 70's to help meet EPA emissions and mileage regs.

However, how big you can go is a direct function of how much voltage is available to the plug. We can't run a GM HEI ignition that needs 12 amps and makes 50,000 volts, with a .060 gap. For practical purposes, a coil ignition drawing 3 amps peak is limited to about .025 if you want reliable performance. Your .028 should be OK. Misfire at high rpm would be the symptom of too wide a gap.
 
My VERY LIMITED understanding is that the super thin electrodes of the exotic plugs create the same effect as a bigger gaps on a normal plug, but without the necessary increase in voltage.

Is this correct?
 
Anyone tried BRISK plugs ? I've read good things about them. (They recommend L14YC for the Commando)
 
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