Sparks plugs.... What are the actual differences?

[Rockburner]

I've always wondered this, but never really found an answer:

What is the actual physical or material difference that makes one plug give a 'better' spark under fixed conditions than another?

another way of putting it:

What's the actual difference in manufacturing between (say) a BR5 and a BR9 ?

I know that some plugs have different materials for (say) the core, or the coating - but what is it that actually changes the heat-rating?

Is it more (or less) of a certain component part?

[porter_jamie]

heat range, some are hotter than others

https://www.denso.com/global/en/product ... 950%C2%B0C.

[Skub]

Remember the days when we used to use a hotter plug for running in a stroker,to sto it oiling up,then swap it for a cooler one for normal business.

[Mr. Dazzle]

The heat range is set by the insulator - the ceramic white bit. The plus gets feckin' hot (duh!) and it's primarily coolant route is conduction into the cylinder head. By changing the design of the white bit you can change how 'big' the conductive path is between the plug and the head.

EDIT: What porter said

[Rockburner]

heat range, some are hotter than others

https://www.denso.com/global/en/product ... 950%C2%B0C.

The question is "how is the plug made differently to handle the different temperatures?"

[Rockburner]

The heat range is set by the insulator - the ceramic white bit. The plus gets feckin' hot (duh!) and it's primarily coolant route is conduction into the cylinder head. By changing the design of the white bit you can change how 'big' the conductive path is between the plug and the head.

EDIT: What porter said

Ah, so it's s slight difference in the makeup of the ceramic insulator?

Ok, that's what i was wanting to know.

[JackyJoll]

heat range, some are hotter than others

https://www.denso.com/global/en/product ... 950%C2%B0C.

The question is "how is the plug made differently to handle the different temperatures?"

You can see the difference visually, if you have some plugs.





https://www.denso.com/global/en/product ... heatrange/

[Mr. Dazzle]

I love the "it only functions in this temperature window of ±30%" statement. I dunno why, but that tickles me.

If you're AFR, tyre pressure or clutch slip was off by 30% you'd be all over the place.

[Yorick]

.https://www.ngkntk.in/importance-of-hea ... der%20type.

[Yorick]

https://www.google.co.uk/search?q=spark ... nZ3I2oIhVM

[Rockburner]

.https://www.ngkntk.in/importance-of-hea ... der%20type.

I love simple diagrams like that. Good resource, cheers!

[JackyJoll]

I love the "it only functions in this temperature window of ±30%" statement. I dunno why, but that tickles me.

If you're AFR, tyre pressure or clutch slip was off by 30% you'd be all over the place.

I’m not AFR.

I’d be happy with zero clutch slip +/- 30%.

[Demannu]

I love the "it only functions in this temperature window of ±30%" statement. I dunno why, but that tickles me.

If you're AFR, tyre pressure or clutch slip was off by 30% you'd be all over the place.

It's one of the things we take for granted, yet operates in one the most hostile environments we have created.
Plugs and chains, wonderful bits of engineering.

[Mr. Dazzle]

It's exhaust valves which get me. Operate in the same environment with the added bonus of being slammed into the valve seats 100 times a second

[roadster]

The physical differences providing different heat ranges have been well covered above but it might be worth mentioning the effects of using the wrong heat range. In engines near the limit such as racing two-strokes a plug which gets too hot will very quickly overheat the top of the piston through pre-ignition/detonation which will then melt a hole right through it. Damage is more likely to occur in multicylinder engines because if detonation occurs in only one cylinder the engine will keep running and the rider/driver may be unaware of it. Running a spark plug which is too cold creates the more obvious but less dangerous condition where the dirty plug will make the engine difficult to start and/or cause a misfire.

The quality of the spark produced by different design or metallurgy and if/how this affects the engine is a complete can of worms best avoided. But modern electronic ignition and fuelling controls have allowed far more sophisticated methods of managing combustion.

[Mr. Dazzle]

I imagine RB is asking 'cause he's having fun with his JAP engine

[Rockburner]

I imagine RB is asking 'cause he's having fun with his JAP engine

Yeah - that.

I've not really run it up properly yet, so the plug is oiling up a bit, will see what happens if I ever get to ride it and run it for more than a moment or two.

Currently it's a Champion L86C, so I might try to find the next hotter/cooler plugs to try.

[Mr. Dazzle]

Been/going through the same thing with the Bonnie.

I've given it back the high comp pistons and cleaned all the fuel system up. Also has new rings, rebuilt head and a rebore. All of which means the combustion should be hotter and cleaner than it was before and I need different plugs.

Had 8s in there, s'now got 9s.

[roadster]

I should also have mentioned that another way of keeping a spark plug cooler is to recess the electrodes inside the body. This can be seen in some racing plugs but they foul up very easily if the engine is not being thrashed at high rpm. It also doesn't promote the best kind of initiation of the flame front through the combustion chamber.

[kevinduke]

The major difference is heat range and longevity. Iridium spark plugs are best, and they last for over 100,000 miles, while copper spark plugs last only 15,000 to 20,000 miles.

Also, iridium spark plugs generate powerful sparks and ignite the fuel instantly. You might notice power output difference and gas mileage with a good quality plug. This guide explains many different types of the spark plugs. You should read that.