'Correct' heat range

[canyncarvr]

Using the kdx as an example, general knowledge says a '7' plug is closer to correct for the bike than the stock '8'.

What IS the correct temp of a 2 stroke woods bike?

I have access to one of those nifty point-and-detect temp gun things, if I had some º number, I could determine if indeed the '7' heat range plug is 'correct'.

Thanks for the input!
***edit***

I'm familiar with what overheating appearances are.

My bike is jetted correctly using a '7' as the telltale. It's not 'too hot' I'm wondering about, but whether an '8' range plug would cause performance degradation due to subsequent heat reduction.

Thanks for the numbers!!!

 

[Rich Rohrich]

You'd be better off learning to read the signs of overheating by the texture of the insulator because you won't be able to read insulator temps with a non-contact temp gun. either way here are spark plug insulator working temperatures courtesy of Dr. Dave Redszus Precision Automotive Research

Self cleaning threshold 400oC (752oF)
Normal operating range 400-900oC (752-1652oF)
Lower edge of safety zone 900oC (1652oF)
Auto ignition range 1050oC (1922oF)
Spark plug destruction 1500oC (2732oF)

 

[IrishEKU]

I can't reply from knowledge but from experiance. That comes from watching my brother, a fellow KDX rider like yourself. He runs a NGK 8 at 40:1 synthetic, and I have never seen him foul a plug. After riding(Before my YZ decided to go south) we would let the bikes cool and check gap on the plugs. He has yet to have a problem. I am guessing you ride trail and hills. So far this combo has worked well for him and continues to do so. He rides stricktly woods and every once in awhile likes the scrambles. If my opinion counts, work into the machine and dial in what you think you would like or better yet, what works for you. Unless you have a bottemless supply of $ I would fool around with my mix and plug #'s. I wouldn't dial your KDX down to a 7 for wood's running though, a little hot. Remember there is alot of clutching and reving going on.

Hope this helps,
Irish

 

[gooby]

i too run a 8 @ 40:1 all i can say is .....:)

 

[Canadian Dave]

IrishEKU I'm curious about:

I wouldn't dial your KDX down to a 7 for wood's running though, a little hot. Remember there is alot of clutching and reving going on.

Would you mind explaining your response in a little more detail? Why do you feel a NGK with a heat range of 7 is a little too hot?

David

 

[canyncarvr]

Alas. The point hath been completely misseth..........:(

Probably what's REALLY sad is that I can read the original question...and have NO clue as to how it could be misunderstood.

'What we have here is a failure to communicate.......'

 

[Mac]

Ok, I'll ask the question, Is there a website or any articles available on the net which discuss the proper way to read the insulators texture?

I currently run a br8eg and would like to try a br7xx if this would improve throttle response but I'm not sure of the relationship between plug temp and pinging if any.

I ride both ends of the spectrum, sometimes crawling through river beds in 1st gear and sometimes holding WOT in high gear for long periods of time.

 

[BRush]

The Gordon Jennings rule: pick a plug heat range so that the insulator/tip temps run between 700 - 1000 deg F for the kind of riding you do. I don't know how you would get an accurate read with that gun, because by the time you pull out the plug to expose the tip to aim the gun at it, you are no longer at the true operating temp.


http://www.strappe.com/plugs.html

 

[Rich Rohrich]

Originally posted by Mac
I ride both ends of the spectrum, sometimes crawling through river beds in 1st gear and sometimes holding WOT in high gear for long periods of time.

Assuming you have room for it in the combustion chamber it might be worth looking into a projected tip BPR8ES. It's easier to keep this plug clean at lower speeds without the risk of overheating that comes with a 7 series. It's an excellent compromise for woods riders.

 

[G. Gearloose]

I had experienced preignition when I tried a 7. It was just fine in the woods, but after a run down along the corn, it wasn't happy, funny sounds and surging. An 8 never does this for me, same jetting.

The 7 only worked for me as a crutch until I ditched the 1172 (run-fat) needle.

Caynon I remember you saying you experienced overheating with the 7, and not with the 8, and you have one of the better-jetted bikes around. Perhaps the overheating was due to preignition, from the higher tip temp? In summary I think a 7 may be too hot, but of course, stock plug on my '91 is a 9, vs 8 for your model.

 

[Mac]

Great tip Rich, I'll pick one up and see if it fits.

Anyone out there in KDX land try a BPR8ES?

 

[canyncarvr]

Gearloose:
Overheating, yes. Too hot a plug, no. No evidence of a too hot plug (I looked)...but a hissing, spitting radiator. Yes, it was a hot day. Yes, the hill climb I was on was a clutch-slipping, throttle twisting thing that noone ever got to the top of.

Pre-ignition or detonation..neither one was happening.

My question regarded correct heat range for the BIKE..not so much the plug.

From the numbers RR posted (750-1600º) and what BRush posted I can get an idea. What the kdx cooling system would do, say with an engine running a plug tip @ 1200º I don't know. Has to do with amount of air moving thru the rads, coolant makeup..all sorts of stuff.

Wonder about a BPR8EG (or some other fine wire plug)?....Guess I'll look it up.

oh..the '..the risk of overheating that comes with a 7 series...' THAT's the sort of information I'm looking for. If a '7' tends to run toward hot (regardless of how much less trouble it is..how much cleaner it runs than, say an 8), then an 8 may well be what to stick with.

...with jetting to suit the cooler running bike.

Mac:

Several of them. Some better than others.

Here's one with some decent pics (plug condition in general):

http://www.atlanticjetsports.com/_techtalk/00000005.htm

Do a search for 'spark plug color' on the web, and you'll find a number of references...some in BLACK AND WHITE! ;)

Then, there's always this:

First of all, nobody is going to be able to quote you jetting specs without fully understanding the mechanical condition of your bike and the conditions where you ride. Don't worry about seizing the engine. It will bog real bad before it seizes. Forget about trying to jet a two-stroke dirt bike by spark plug color, that doesn't work. Try using a hotter spark plug. That serves to lean the whole range only slightly and poses no threat to seizing. Also try experimenting with leaner premix ratios, like change from 40:1 to 50:1 That is nearly the same as the spark plug trick.

Do I understand this to say that changing from 40:1 to 50:1 is 'leaning ..slightly'?

uh....oops? The quote is from an expert in the field. It makes me feel better!

 

[Rich Rohrich]

Originally posted by canyncarvr
Do I understand this to say that changing from 40:1 to 50:1 is 'leaning ..slightly'?

YES, Leaner in terms of oil quantity, but not in terms of air/fuel ratio. The word "lean" was probably a poor choice of words in this case. When you get a million or so words published you're bound to have a few that can be taken more than one way.

As for not jetting by plug color Eric was referring to the color of the nose of the insulator. Again maybe not the best choice of words. Brevity has a way of leading to mis-communication at times.

 

[BRush]

Originally posted by canyncarvr


oh..the '..the risk of overheating that comes with a 7 series...' THAT's the sort of information I'm looking for. If a '7' tends to run toward hot (regardless of how much less trouble it is..how much cleaner it runs than, say an 8), then an 8 may well be what to stick with.

...with jetting to suit the cooler running bike.

Yes a hissing radiator is a different thing from a too-hot plug. The quote that has always stayed with me from that Gordon Jennings article I posted above is

“We must emphasize that it is the engine that puts heat into the plug, and not the reverse. A "hot" plug does not make an engine run hotter; neither does a "cold" plug make if run cooler.”

If it is fouling you’re trying to minimize then you have to pick a plug that is going to keep temps above the “self cleaning threshold temp” that Rich mentioned above. The advantage to the fine wire plug is that they require less voltage to form a spark. All things being equal (jetting, environmental factors) I would not think it has as much an effect on fouling – which is primarily a phenomenon whereby the insulator nose becomes coated with a foreign substance such as fuel, oil, or carbon and allows current to flow along the insulator surface instead of sparking across the air gap. You need to keep nose temps up to burn these deposits off. The BR8ES is marginal for that when you start plonking along tight single track (in my opinion).

The BPR8ES that Rich mentioned is interesting and I may give it a try. That said, I have a lot of hours on BR7ES plugs and for me at least they are a better pick. I ran one last year at an enduro on 95 deg day with several WOT sections and it was fine (no pinging, no surging or other signs of preignition from a too-hot plug) – but that’s my engine (jetting, porting, fuel, etc) your experience could be different.

 

[canyncarvr]

Mr. Rohrich:
You're a bit hasty sometimes. Brusque if you will. Has always seemed to me that people tend to run in fear of such responses. Guess I'm stupid ;) .....

re:

BTW people who live in glass forums should be careful of how they quote.

?? I cut, pasted, asked a question. What is it I should be careful of?

The point in the quote was changing air/fuel ratio. The question concerned jetting, not premix ratios. The point of changing to a hotter plug was in reference to 'leaning the whole range.' Not effecting premix. The ratio change comment was intended to attend to the same issue.

You're defensive for no reason. Hell..I'll be the first to admit you've forgotten more in the last 24 hours than I'll ever know about the subject. Mr. Gorr the same I'm sure. That's primarily the reason casual readers/posters on these forums quake at your responses.

I thought it interesting to read that intellectually superior people don't get it quite right sometimes. Hey!...it gives the rest of us, the plebes, a bit of hope. ;)

BRush:
It is not fouling I'm trying to minimize, but wanting to maximize the output (and health) of my bike (or any 2-stroke...which is why the question was posted in the hi-perf forum) by running it at optimum temperature.

Ah!...as long as I'm pi$$ing people off:

A "hot" plug does not make an engine run hotter...

Kinda. It ALLOWS it to run hotter...how's that? One plug range# is reportedly good for a 25-40º increase in engine temperature. True, that one# change doesn't ADD btu's anywhere, but engine temperature does go up.

Flush me... :uh: I'm done!!!

Have a great weekend y'all! This saturday (6-1-02) is 'trail cleanup day 'round here. Going to a media meet with a bunch of sierra clubbers and tree huggers just to show them that 'we care!!'

....maybe get a roost or two in!!

 

[Rich Rohrich]

Originally posted by canyncarvr
Mr. Rohrich:
You're a bit hasty sometimes. Brusque if you will.

For once I agree with you.

I get really annoyed when I think people are taking shots at Eric or his writing. Probably an overreaction on my part. It can be difficult to determine intent in ASCII.

Either way after I posted that it dawned on to consider the source, this might just be your way. Eric is smart enough to not care when internet experts take shots at his writing so there is no reason for me to get bent about it if that was your intention. Besides you are CDave's problem ultimately :)


Enough stupid crap, time for this thread to get back on track.

One last thought to ponder. Oil has an air/fuel ratio as does fuel (they tend not to be the same), so changing the amount of oil that passes through the jet doesn't necessarily have the linear effect on air/fuel ratio in the combustion chamber that might seem intuitively obvious. Combustion chamber temps and ultimately plug temps are also impacted by these changes. There's always another layer isn't there? :D

 

[BRush]

Originally posted by canyncarvr
.Kinda. It ALLOWS it to run hotter...how's that? One plug range# is reportedly good for a 25-40º increase in engine temperature. True, that one# change doesn't ADD btu's anywhere, but engine temperature does go up..

I still don't follow. Same fuel, same temp and elevation. How is changing from a plug with a shorter insulator nose (B8) to one with a slightly longer nose (B7) going to raise engine temps? Assuming pre-ignition is not a factor, I don't understand the physics. Both plugs are going to spark at the same time. Ignite the fuel charge at the same time. The fuel charge (representing the fuel btu input), combustion speed , and resulting temp rise in the combustion chamber would all be the same. So if the 25-40 deg increase truly exists and is not just an old wives tale, what factor is responsible for it?

 

[gooby]

this is a great thread i'm interested big time.i've been all wet about this subject i guess .i always thought the diff from 9,8,7 etc was a longer nose,internal make up of the plug was diff allowing for a stronger charge(from the same coil and other factors) to more efficiently ignite fuel to create a greater boom.seemingly making more power and as a result would have to generate greater heat.that's what i thought burned pistons.i'de like to understand this ,i hope someone replies with a clear answer cause i'm lost now .sorry for bein too dense to get it lol

 

[G. Gearloose]

Originally posted by BRush
So if the 25-40 deg increase truly exists and is not just an old wives tale, what factor is responsible for it?

I suspect, the more exposed insulator (read: insulator not set in the metal of the plug base) of the hotter plugs, the hotter the tip temperature, because the longer the heat in the tip has to travel to be dissapated through the insulator, the plug base, into the head, water jacket, etc. Conversley, the less exposed insulator, the better the heat transfer, and thus lower tip temperatures.

But yes, BRush, I still don't see how a plug can raise engine temps, and if it does, certainly curious how.

 

[canyncarvr]

Heck..you think I'm going to come up with something like that by myself??

from http://www.edelbrock.com/automotive/sparkplugs.html :

The terms (hot/cold) actually refer to the heat rating or thermal characteristics of the plug; more specifically, the plug's ability to dissipate heat from its firing end into the engine cooling system. A cold plug transfers heat rapidly away from its firing end into the cooling system and is used to avoid core nose heat saturation where combustion chamber or cylinder head temperatures are relatively high. A hot spark plug has a much slower rate of heat transfer and is used to avoid fouling where combustion chamber or cylinder head temperatures are relatively low

**see the note on the above page regarding 'Y' tip (projected tip) plugs, as mr. rohrich brought up.

from http://www.ngksparkplugs.com/techinfo/spark_plugs/overview.asp :

It is important to remember that spark plugs do not create heat, they can only remove heat. The spark plug works as a heat exchanger by pulling unwanted thermal energy away from the combustion chamber, and transferring the heat to the engine's cooling system. The heat range is defined as a plug's ability to dissipate heat.

from http://www.ngksparkplugs.com/techinfo/spark_plugs/overviewp2.asp :

In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber.

** All emphasis above inserted by myself.***

So, pretty much as I read gearloose to say, colder=faster hotter=slower, and as I read me to say

It ALLOWS it to run hotter

meaning a HOT plug dissipates LESS heat.

The 25-40º is a number I read on DRN. I recall it coming from mr. gorr, but don't quote me on that, cuz I haven't found it (yet..but then, I'm not really looking for it, either ;) ).

re: pot shots at mr. gorr. Sheesh..Thanks for taking me for a complete and absolute moron. re: 'consider the source...' now THAT was funny :)

 

[canyncarvr]

gearloose and brush:

Where's this situation sit?

Does 'It ALLOWS it to run hotter' acceptable, or not? If a plug heat range change effects the amount of heat removal, isn't that an acceptable explanation for:
'I still don't see how a plug can raise engine temps, and if it does, certainly curious how.'

 

[G. Gearloose]

Hi CC,

But I still lean toward 'no'; because the effect of heat dissapation is in the opposite direction of the suggestion that hot plug = hot engine ...

I think within the third quote, on the NGK site is in err, somehow.
from http://www.ngksparkplugs.com/techin.../overviewp2.asp :

Quote:
In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber.

Removing 70-100 degrees C from 'the combustion chamber' is an enormous amount of energy, whether they are talking 'bout the just the chamber, nor the 'burn', or both, and would be apparent via 'seat-of-the pants performance. If that were true the effects of this engine temp raising phenonomon would be dramatic and more tangible. I suspect they are talking about just electrode tip temperature.

If switching from 7 to a 9 lowered combustion temps 140-200C, we'd all be running 6's :D .

to digress, please humor me...
If a 7 or 'Hot' plug were to make an engine hotter than an 8, it would have to absorb more heat, but it doesn't. Its tip is hotter because the electrode is less conductive to heat, and that results in higher electode tip temps yada yada...

So, the difference in engine temps (if it exists) is going in the wrong direction to explain a hotter plug raising engine temps. I mean if the cool plug dissapates more heat in order to cool its electrode, then if this were the correct mechanism, the cooler plug would raise engine temps compared to a 'hot' plug, because its sucking more heat out of the electode area and combustion chamber, eventually into the water jacket, but nobody has suggested this (effect) (read cooler plug = hotter engine).

I think the difference in heat absorbed/ plug vs plug is negligible compared to the mass of the engine and water. In terms of calories or joules absorbed, the 40-100 degrees C difference in electrode tip temperature, with orders of magnitude less mass, is likely insignificant.; and in the wrong direction of heat flux. (always wanted to use that word ;) )

ouch, I think I hurt something...

 

[canyncarvr]

I think within the third quote, on the NGK site is in err, somehow.

Well...if it's wrong, then the whole idea is out the window of course. I'm approaching the issue from the standpoint of supplied information being correct.

to digress, please humor me...
If a 7 or 'Hot' plug were to make an engine hotter than an 8, it would have to absorb more heat, but it doesn't. Its tip is hotter because the electrode is less conductive to heat, and that results in higher electode tip temps yada yada...

to digress summore then.... 'If a 7..make hotter ...would have to absorb more heat...' It doesn't make things hotter by absorbing more heat, it makes things hotter by sinking less, which in turn ALLOWS (that word's important) the engine to run hotter.

Your point of the temp difference being huge...and it 'would be apparent' is part of my point all along.

It would NOT be correct to jet to a plug (using color as a guide) that is NOT operating at 'correct' temperature. And what I read says that the large temp change should make plug selection a significant issue.

I understand the points of mass of the engine/water and all. I keep pinging on this because it seems an issue of import (the web sites being correct)..and I haven't ever seen it addressed from this perspective. The 'run a 7' mantra in newer kdxs seems more an attempt to run a given mixture without problems than being 'correct' heat-wise.

I mean if the cool plug dissapates more heat in order to cool its electrode, then if this were the correct mechanism, the cooler plug would raise engine temps compared to a 'hot' plug

I guess my one brain cell is stuck...cuz it seems exactly so that: A cool plug dissipates more heat, so the engine temps will lower compared to a 'hot' plug.

There's some semantics issue here I'm sure. After all, if the plug dissipates more (or less) heat, where does it dissipate (or not) it TO? The head? Isn't the head attached rather securely to the cylinder? Don't they all get to whatever temperature based pretty much on combustion temps and the effectiveness of the cooling system?

I still think the 'correct' plug is important...and I don't know what that is,yet. Other than measuring the actual tip temp, how you gonna know? If indeed an 8 is the correct plug, then a kdx jetted using a 7 for color check is wrong..it's STILL too rich.

Thanks for the response.

Hope your owee gets better;)

 

[23jayhawk]

Guys, if I remember correctly from the only internal combustion class I had, spark plug design is a balancing act between wet fouling at low cylinder loading, and preignition at high cylinder loading. If the electrode tip temp exceeds spontaneous combustion temps, presto you get combustion as the inlet charge hits the plug. Dirt bikes create the greatest challenge, due to the tremendous range of loading situations that we put the engine under - plonking along in 1st gear woods, or pinned WOT doing Barstow to Vegas.

As far as raising the engine temp, heat transfer rate is a linear function of temperature differential. So if the plug temp increases relative to the temp of the combustion gases, the rate of heat transfer through the electrode, to the head, to the cooling water is reduced, resulting in increased cylinder temps.

It would seem that if you are not fouling a plug at slow speeds or pinging at the highest, you have no problem. But that assumes that plugs are pretty much indifferent in that 'middle region'.

There is the issue of flame propagation rates, but that is another story altogether... Time to start a new thread!!!

 

[BRush]

My interpretation of the NGK text was the same as Gearloose. The text seems make more sense when taken to mean heat transfer as it affects electrode tip / insulator nose temps, not engine temps. The idea that the plug is so much more conductive than the cylinder head, cylinder, & water jacket etc, that it can control engine temps just does not compute. One heat range resulting in "approximately 70°C to 100°" of engine temp difference? It just does not pass my built-in engineering smell test. I'll readily admit that sometimes these things are counterintuitive, so my conclusions could be wrong, but I'm going to need more data before I'm convinced .

I think that while reading insulator color out near the tip is not good for determining mixture or jetting, is it a valid means for judging proper heat range selection for the type of riding and the as-running jetting. Change either and you would need to re-evaluate.

I do think that the BR8 OEM recommendation is on the cold side - for the same reason that the stock jetting is so rich. Kawasaki is considering the worst-case scenario and acts to minimize potential warranty claims at the expense of best performance, which is only rational behavior on their part.

I am of the opinion that the BR7 is a better all-around choice for woods riders (desert guys that spend 95% if the time at WOT may want to rethink ;) ). Do a lot of riders drop to a BR7 to compensate for too-rich jetting? Sure. Won't change the fact that the bike is running rich, but it will usually help with the plug fouling situation - and there is really nothing wrong with that. There are a lot of riders that just don't want to mess with jetting, they just want to stop fouling plugs when plonking around in the woods. Maybe not the approach that you or I might take, but if that solves the problem then why not?