spark plugs heat range

[petejw]

ive been messing around with the spark plugs and noticed the colder the
plug the quieter and smoother the engine ran,
with the bp5's the engine knocked and sounded noisey
under load, with the 6's it quietened down a bit, but with the
7's the engine was fairly quiet and smooth.

i was just wondering if anyone else has messed around or has changed the heat ranges from stock?

[oldyam80sg]

I think the NGK BP6ES plugs i use are the ones recommended by Yamaha.I have always used these and never had any noise from anywhere.Have used the Bosch plugs and didn't like them at all.

[Ivan]

I ran some 8s (I think, it was two ranges cooler than stock) and they did make the engine run smoother, for sure, but I think it lost a little grunt in the process.

[petejw]

i noticed that to ivan,
its a little flatter down low,
but i was still getting that slight knock around 4000rpm
under hard acceleration, the 7's have seem to got rid of it
altogether, and it seems a bit smoother at higher rpms.

[TADracer]

I tried.

Here is my humble two cents.

I have fooled around with heat ranges before but have always stuck with NGK plugs to keep it real. The heat range of the plug is what controls the chamber temperature which should stay between about 930F to 1500F to prevent pre-ignition (on the high side) or fouling (on the low side). From what I gather every heat range step changes the chamber temp. from 150F to 220F. So if you switched to a BP-7ES (which sheds more chamber heat to the cylinder head for removal), you lowered the chamber temp by 150-220F which probably took you out of the pre-ignition range. The flat low end might be because the chamber temp decreased too much at low speeds to get a good flame front on your air/fuel charge until the chamber heated up a bit at higher RPM. So, read your plugs for signs of fouling because lowering the chamber temp below that needed to burn away tip deposits will lead to early fouling.

Alot of stuff affects the plug heat range required. Things like air/fuel mix, timing, engine mods and even riding style can affect the heat range required to keep your motor singing happy. It would be great to have a way to accurately measure the chamber temp but, trial and error is the only way to choose a plug for the average guy. My forays into the matter has always led me back to the BP-6ES stock plug though sometimes during the dead of Winter I switch one range hotter (BP-5ES).

[petejw]

hey mike,
i agree with what you say,
my engine burns a lot of oil, so i thought the hotter plug would
help, but it didnt, my engine also has a main bearing on its way
out, and its winter over here as well, all good indicators for using
a hotter plug but
using the hotter plugs made the valves knock (not pinging more like the piston being hit by a hammer ) using reg unleaded fuel,
the 7's got rid of that knock totally, but like the reasons you said at the exspense of the lower end.
ill go back gto using the6's over winter, and use the 7's for summer.
i was just curious to hear from others that had messed around with it.