Best 2-stroke spark plug

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KCvale

Well-Known Member
Feb 28, 2010
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Phoenix,AZ
With the countless expensive parts and tweaks we do to get the most out of our little Chinese 2-stroke motors it is easy to overlook the spark plug even though nothing you do will help with a crappy spark.

There are 3 important parts of a spark plug, the sparking tip, the ground electrode, and the insulator.

Until recently, Platinum was considered the best material to use on the top of an electrode because of its durability. However, Iridium is 6 times harder, 8 times stronger, and has a melting point 1200 degrees higher than platinum.

Put that into a harsh environment such as a 2-stroke engine piston chamber, and you have a spark plug that can resist wear much better than platinum. Additionally it is so durable it allowed engineers to produce the world?s smallest center electrode (.4mm) which reduces the voltage requirements, concentrating its sparking power.

For 2 strokes that means even a weak CDI should have a good spark and a good CDI with everything the magneto has via better wiring and you not only get a whopper of a spark, the Iridium can take it.

Also, its smaller size, combined with the tapered ground electrode, allows more room for the flame kernel to develop and produce a more efficient combustion.

The flat ground electrode design of ordinary spark plugs crush the spark, inhibiting its growth; this effect is known as a 'quenching effect.' The simple, but efficient, U-Groove or tapered ground electrode results in better fuel efficiency, improved throttle response, and greater firing energy.

Besides NGK, Champion and Bosh also make Iridium plugs but the one I know that works in most of our 2-stroke China engines is the NGK BPR?HIX Iridium IX.

The ? in the part number is the heat range, which equates to how much insulator material the plug has and refereed to as how Hot or Cold the plug runs.



Part of your spark plug's responsibilities, in addition to firing a spark, is to remove heat from the combustion chamber. This is accomplished by channeling the heat through the insulator material and metal housing. From there, the heat is transferred to the cylinder head where the engine cooling system can go to work.

A spark plug's heat range is its ability to dissipate heat. The 'colder' (higher number) the plug, the more heat it can channel out of the combustion chamber. In a performance application, colder heat ranges may be necessary to handle the extreme temperatures brought on by higher compression ratios, forced induction, and high RPM?s.

While 'Colder' plugs may seem to be the way to go, please remember that the spark plug must achieve its 'self-cleaning' temperature where it can burn off fuel and carbon deposits. Otherwise, the plug could 'foul out' where it is prone to misfiring and poor acceleration.
A plug that is too 'hot' on the other hand can overheat, also causing power loss, detonation, pre-ignition, and possible engine damage.

Here in Arizona I put BPR7HIX's in all my new builds, I can feel the difference and never had to replace a plug yet.

They are hard to find but SBP has them for $9.

One more note, do NOT attempt to gap them, you will snap the tiny Iridium tip off and they come pre-gaped with a cardboard tube around the end to protect it in shipping.

I have been saying I could feel the difference for years, now we all know why ;-}
 
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mew905

New Member
Sep 24, 2012
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Moose Jaw
great advice, but a note on spark plug heat ranges, the plug itself is not designed nor capable of removing heat from the combustion chamber unless you count the plug itself, hotter plugs protrude more into the chamber to retain more heat from the combustion, colder plugs will tend to be shorter. they can cause detonation and all that jive if you pick one too hot but it will not cool the motor, only itself. Higher RPM's require a colder plug because less time to dissipate heat, low RPM's require a hotter plug to retain more heat, and as mentioned you're aiming for that self-cleaning temperature. Your heat range will depend on the kind of motor you run (2 or 4 stroke), what RPM's you'll be running at, ambient temperatures, cooling method (air, liquid or other) and your gas mix (rich will need a hotter plug, lean will need a cooler one). If you're not sure what your needs are, start cold, the worst that can happen as far as I am aware is the plug will eventually foul.
 
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KCvale

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Feb 28, 2010
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hotter plugs protrude more into the chamber to retain more heat from the combustion, colder plugs will tend to be shorter.
That is not really accurate, a plug size is meant to fit a given engine, if you look at the image the only thing that changes is the amount of white insulator in contact with the plugs outside metal case, the more insulator (colder the plug) the less pink tip left in the same overall plug lenth.
 

KCvale

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Feb 28, 2010
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Phoenix,AZ
Unless most everyone knew this I am bit surprised how few didn't realize what this one cheap improvement actually makes and comment.
 

xseler

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Apr 14, 2013
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OKC, OK
My bike really smoothed out with an improved NGK plug and plug wire. Since I live where it gets almost as hot as Phoenix, I also went with the "7" heat range. I gained about 2mph on the top end just with this simple/cheap/easy upgrade.


Anybody want these 3 pronged pariahs that came with my kit?
 

mew905

New Member
Sep 24, 2012
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Moose Jaw
so apparently after some testing, spark plug ranges DO in fact affect engine temps (or at least head temperatures). According to the thermal diodes, 1 NGK heat range (that is going from #5 to #6) will be the difference of approximately 38 degrees C at the plug, and 20 degrees C at the head bolts. crazy.
 

Huffydavidson

STREETRACER/MANUFACTURER
Jan 29, 2012
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st.louis,mo.
So true, I run BPR6HIX when its under 60 regress, normally #8 , and like now I run a #10 the coldest Iradium NGK makes. I have no problem getting there from my NAPA Auto parts Store . I call them and the next day it at my Store . Don't even have to pay first, just call in the order!!!! O'YAA, their also guaranteed for 2 years .
 

xseler

Well-Known Member
Apr 14, 2013
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NGK has a 'backward' numbering system compared to the norm.

With NGK, the lower the #, the hotter. The higher the #, the colder the plug. All other brands are the opposite.
 

KCvale

Well-Known Member
Feb 28, 2010
3,966
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Phoenix,AZ
I knew I couldn't be the only one that can actually feel the difference a simple plug makes and how they work.
The dead on accurate from the box gap, material, the tiny yet amazing parts that make such a huge spark and seem to last forever are why.

The heat number info is just a reference to pick the best heat number for
your conditions.
NGK has a 'backward' numbering system compared to the norm.

With NGK, the lower the #, the hotter. The higher the #, the colder the plug. All other brands are the opposite.
Hotter means how hot your combustion chamber runs.

The lower the number the less heat is transferred out via the plug to the head which is pretty much all combustion chamber heat, hence a hotter running engine.

The higher the number the more the plug can transfer heat out to the head so it runs cooler, the cooler you can run the better until it is so cool you foul plugs because you won't get hot enough to the natural ~200Fish temp to burn off deposits and burn all the fuel.

With water cooled engines this is easy, the water system has a thermostat and a great heat dissipation system, our 2-stroke air cooled bikes are at the mercy of of how much air you move past the fins via motion and what temperature that air is.

For example running an air cooled 2-stroke wide open in freezing temps the engine simply would not stay hot enough (ever 'warm up') for the fuel to burn efficiently as you have a lot of cold air flow and little heat retention will foul plugs, and overall run pretty crappy.
You want as hot a plug (lower NGK number) as you can get to keep the heat in.

On the other hand you want as cool a plug as you can get in stop and go high ambient use (higher number) as your motor pretty much 'warms up' in a heartbeat and you don't want to keep that extra heat in it.

The fine line is how cool can your engine can run before it is not hot enough to burn all the fuel but not hotter which is directly related to the load and how fast you go which is directly related to how much cooling air passes by the heads cooling fins.

It is like rocket science but pretty darn simple for our little 2-stroke motors with this given plug.

If it's cold air and you ride fast use a lower number (hotter) plug just not so low you toast your engine form too much heat.

If you ride fast or in high temps get a higher number (cooler) plug just not so cool you foul plugs and it runs better.

I haven't tried 8's yet here in AZ but with temps we have been having this summer I'll add some to my next order. 7's though seem to work just dandy even in winter though I can see where a 6 might be better if I see fouling.

Thanks to all of you guys that know first hand how crucial this one cheap little item is to performance, I just figured I would try to make sense of it all so everyone else can benefit and make it easy to pick the plug and number that best suites there riding habit and conditions as they are vast between all of us.

I also have several dozen various brand new kit supplied plugs if anyone wants to buy them by the dozen for dirt cheap as my big box of them is overflowing ;-}
 
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dodge dude94

New Member
Jun 8, 2012
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East Texas
I'm currently running a B7HS. Since most of my riding is in the summer, it runs VERY well and was a huge improvement over the stocker. So if I were to get an HIX what heat range would I get? I would think that since the Iridium is a stronger spark I would be able to keep my current heat range without issue, correct?
 

Henshooter

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Feb 10, 2014
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Melbourne au
I'm going to sound quite dumb when asking this but I have the standard 80cc ( or 66 as would be) china girl kit with the regular cheapo spark plug , never really looked at cheap mods and such but am getting an exhaust with exp chamber soon ,now if one with little or no knowledge on spark plugs and their effectiveness went to get a better one where would I go and what would I ask for .
I know the saying there's no stupid questions but I feel somewhat stupid when asking this from very knowledgable members , also having the same issue with a Cdi unit what do I ask for with regards to better performance
Cheers Henshooter
 

KCvale

Well-Known Member
Feb 28, 2010
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Phoenix,AZ
Well, I can't get the BPR7HIX from O'reillys (where I do my parts purchases). So what about the BP7HS? Pluses minuses for that one?
The NGK BP7HS is a non-resistor that uses a standard electrode and works fine as a stock replacement, it's just not an Iridium electrode.

You can buy the BPR7HIX for $8 direct from NGK http://www.ngk.com/product.aspx?zpid=9496

http://sickBikeParts.com has them as well.
I get mine there in 4-packs when I order other stuff like shift kits and dual-pull brakes levers so they pretty much ship free.
 

BarelyAWake

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Jul 21, 2009
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Today, 98.2% of the production output of Unobtainium is used to create GigaWidget technologies.
 

KCvale

Well-Known Member
Feb 28, 2010
3,966
57
48
Phoenix,AZ
Hehehe, good one BA.
All I care about is do I feel at least a slight performance difference and have less problems like fouling of a plug and I do so that's what I use.
 

dodge dude94

New Member
Jun 8, 2012
1,017
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East Texas
I'm running an NGK BPR7HIX (it's in mah sig down ther) and it gave me a marked improvement in performance over the NGK B7HS I had previous.
 

rustycase

Gutter Rider
May 26, 2011
2,746
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Left coast
I'm a cheapskate but still can't run the Great Master! Young Master... whatever..
I run the ngk b6.

here in Kalifornia they dump tons of alcohol in our gas and I've been told platinum is particularly good for dealing with alcohol fuel...

Question...
Is iridium also good with alcohol loaded fuels?
...as compared to platinum???

Yikes!
It would bring tears to spring $9 for a plug in my chinagirls !!!

Best
rc