'Correct' heat range

[23jayhawk]

BR, completely agree with you. The intent of the different ranges is to get the electrode temp right in that 500 to 800C range under the various loading conditions. The effect that a cooler or hotter electrode has on cylinder temps is probably very slight, unless preigntion becomes an issue. I think that plugs transfer somewhere around 10% of the conductive heat losses from the chamber. Not sure what that equates to in terms of temp changes, but probably not 100C.

 

[G. Gearloose]

Well said BRush,

CC, since we are advised to look at the insulator base for color vs tip, that may suggest it may not be super-critical which plug you use to jet, since at the insulator base, the surface temp will be very similar between plugs due to that area's proximity to the plug's metal (heat-conductive) shell? I suspect?

Am I the only only one who dislikes the way a 7-plug works in their bike?
I'm suggesting it may be susceptible to preignition.
If I use a 7, of course its fine and 'normal' in the woods, but then rev it out along the corn, then reduce the throttle or chop it, the bike will surge, ping, etc, not pretty. Its OK under load but I think it leans up a bit as throttle is reduced, and sets it off.
This was jetted at the 'fat' side of optimal, I'm pretty sure,
(45 1173N-2 155 as 5/8, 40:1 YammaLR, delta valve, dg pipe, fresh crank seals, 70F, 400'.....)

Drop in an 8 and it (the glow-plugging) all goes away.

If I had to make a 7 work, I'd have to go much richer, and give up a good chunk of 1/4-3/4 throttle responce. Got my sudco 5- needle set to play with now, but any thoughts or similar experience?

 

[canyncarvr]

If I had to make a 7 work...

I'm not crazy about the 7, either. It's ok...but as gearloose says, twist it to rabbit.....and you have a problem. Also in steep uphills (grades you can't begin to even stand on) fanning the clutch in 1st gear looking for some bite somewhere...it gets hot. An 8 doesn't. The previous not at all any sort of valid testing procedure cuz I didn't make multiple trips up on the same day with nothing but a plug change. More of a general assemblage of feedback over a months' time. The 'g' series of 8 generally works very well. I haven't tired mr. rohrich's idea of the projected tip series. I'd expect good results from it also.

All things considered...it's really not too important. I don't know much more than I did at the start. While words mean things, and 'ability to remove approximately 70°C to 100°C from the combustion chamber' seem pretty clear to me, it also doesn't pass the 'smell test' as brush says. Counterintuitive? Maybe....it still smells funny.

Thank you all for your input. It's fun to 'hear' the thinking of good thinkers. ;)

 

[BRush]

Originally posted by G. Gearloose

Am I the only one who dislikes the way a 7-plug works in their bike?
I'm suggesting it may be susceptible to preignition.
If I use a 7, of course its fine and 'normal' in the woods, but then rev it out along the corn, then reduce the throttle or chop it, the bike will surge, ping, etc, not pretty. Its OK under load but I think it leans up a bit as throttle is reduced, and sets it off.
This was jetted at the 'fat' side of optimal, I'm pretty sure,
(45 1173N-2 155 as 5/8, 40:1 YammaLR, delta valve, dg pipe, fresh crank seals, 70F, 400'.....)

Drop in an 8 and it (the glow-plugging) all goes away.

If I had to make a 7 work, I'd have to go much richer, and give up a good chunk of 1/4-3/4 throttle response. Got my sudco 5- needle set7 to play with now, but any thoughts or similar experience?

My experience is different. I just did a 90+ mile enduro on 6/2, followed by a two-day 200 mile "dual sport" ride last weekend. Temps in the 70's and 80's. Plenty of places to wring it out. I don't get any pinging at all with the BR7. It just runs. My setup is pretty different from stock: big bore, ported, RB carb etc so that's a factor - but I ran 7's before I did the mods. My jetting too, is on the fat side of optimal which is kind of where I'm comfortable. 155,42, AEK-4, #7 slide, AS 1.5, 40:1 MX2T, Boyesen power reeds, mobil premium.