Calling all guys running big bores. Vote!

[rablack21]

I want to know what heat range spark plug you are running in your big bore. I know ESR recommends B9's for theirs or some other makers, but I'm wondering what is really working for people. Do the B9's work or do you use B8's instead? Vote now. Thanks for participating.

(Big bore owners of all sizes only, please!)

[C-Leigh Racing]

B8ES for years & years & have used B7s.
No air leaks & the carb jetted right, pipe sealed up is more important & for God sakes, stay away from the worthless pump gas if you love that 250R.
Neil

[Polonda]

B8 for gas.  9 for Alky.

[etccb]

I last ran the 9 with c12 at 18.

[rablack21]

Wow. The vote so far is exactly 50/50. I am curious about this because i have always used B8's in my stock cylinder with no issue. Since I got my ESR 310 pv, I have always only used the B9's that they recommend. However, i have noticed for quite some time that no matter what I do with the jetting, the plug never really cleans up. I have found decent spots in the jetting by "seat of the pants" feel, but the plug always shows rich. The insulation always is wet and dark colored. It has never looked like my old stocky cylinder plugs looked like. My oem cylinder plugs were always a nice golden brown on the insluation with a good smoke ring. Well, yesterday I decided to put a B8es in my 310 instead of the recommended B9es. I was curious if it would work better or not, but I was very hesitant and concerned about burning up the piston. Well, I warmed it up gently and make a couple of 4-5 gear runs down the road. I got back and checked the plug, and it looked alot cleaner, like the combustion was being burned more completely. The insulation looked still clean and white, but the smoke ring indicated a bit lean. This, I am guessing, is due to me lowering the main jet down to get it to run better with the colder plug. I am guessing that it need several main jet sizes larger, and then it will probably run great and burn clean. However, in the mean time, I was curious as to what others were using in their big bores and if they had any issues with running B8's. That is the purpose of this survey.

Thanks for you guys that posted and voted. If you have any additional comment on this topic, I am happy to hear it.

[Pumashine]

The B9eg or ev are even worse as for cleaning up. Its always got that little tick tick tick. If your bike runs smooth on a 9 great but if not you may actually run better with an 8 for the combustion gets fully used. Never heard of melting a piston with an 8 instead of 9. But then again when I went to Lowes this morning the guy behind the counter told me stainless was softer than mild steel. Unbelievable what people believe.

[rablack21]

The B9eg or ev are even worse as for cleaning up. Its always got that little tick tick tick. If your bike runs smooth on a 9 great but if not you may actually run better with an 8 for the combustion gets fully used. Never heard of melting a piston with an 8 instead of 9. But then again when I went to Lowes this morning the guy behind the counter told me stainless was softer than mild steel. Unbelievable what people believe.

(Falling out of my chair laughing at that last part!) Bless their hearts, I have so little patience for stupidity. My 310 engine runs ok on the B9es, but it has never cleaned up enough that I could get readings for plug chops with, with the exception of when I ran it this weekend just for a short bit. The plug was actually clean and readable. And when I say clean, I mean clean combustion, dry, and not black and wet everywhere.

I was more curious if there would be any negative side effects to running the hotter plug. I also noticed on the B9es that the burned in area on the upper electrode was very short and not quite large enough. That also got me thinking it might be too cold.

[Pumashine]

You should only have to run a 7 when your motor is about toast. But as you can see as Niel said sometimes he has run a 7. Its only usually in a forced situation when the carb is not working right or you have water or contaminates in the fuel, or your oil mixture is too rich.  As for heat ranges the 7 8 or 9 can be run safely. The colder the plug the more power you make.

[rablack21]

You should only have to run a 7 when your motor is about toast. But as you can see as Niel said sometimes he has run a 7. Its only usually in a forced situation when the carb is not working right or you have water or contaminates in the fuel, or your oil mixture is too rich.  As for heat ranges the 7 8 or 9 can be run safely. The colder the plug the more power you make.

Tony, thanks for the input. One question though. Why would you make more power with a colder plug?

[Pumashine]

Tony, thanks for the input. One question though. Why would you make more power with a colder plug?

Its something I learned in Physics in college. The efficiency of an engine is the difference between the energy used and the energy created. As for our application you would have to get someone like rsss396 to explain it to you. It peak temperature  will always be the same in the combustion process. The colder you start out the more power is created. Don't really know if you will feel this out on the track.

[etccb]

You wont hurt it with an 8 to test and see how it works with your combo, setup, jetting etc. Just test and check it out.

[jcs003]

also, dont underestimate the advantages of trying different plug gaps.  i was told .025 gap and my 2001 cr250 ignition will run it best.  the engine always felt like it wasnt crisp or something.  worked my way down to .020 gap and then finished at .022 and it seems to be the best with my engine combo.  has anyone else tried messing with the plug gap?

john

[rsss396]

colder plugs will be less likely to create pre-ignition compared to a hotter plug that just might become like a glow plug in the right situation.
Holding the throttle Wide Open for a long length time will build large amounts of heat in the Piston and dome, this heat in return speeds up the combustion speed which is much like adding more ignition advance, this now adds even more heat to the combustion chamber which just keeps getting hotter and hotter.
The spark plug can now start to get very hot and light off the next compression stroke much sooner than needed possibly leading to detonation eventually.
Varying speeds and engine loads will normally make the piston and combustion chamber run cooler because it is much less efficient because of pipe and port not being optimized during those times but at peak power the motor is most efficient and creating allot of BTU's in the combustion chamber, if held for long lengths of time the plug temps will rise very high.
Problem with cold plugs are they are much more likely to foul than a hotter plug so its all a balance.
I will say its better to choose a plug temp by what you do with the motor not what HP you make with it.
woods-MX guys should run hotter plugs like a 8
TT-duners should run a 9
methanol bikes for drag racing can run 10's

Methanol confuses allot of people because of how cold it makes a motor run, but in reality you but create more BTU's with a methanol motor building more heat in the combustion chamber.
BTU's are what create the expanding gases in the motor thus pushing against the piston giving you more HP, methanol since it can run at very high fuel to air ratio compared to gasoline is why methanol makes more power. methanol actually makes less BTU's per drop of fuel when compared to gasoline but since you can run almost twice the amount of methanol with proper combustion more BTU's are created thus more HP is developed

[rsss396]

plug gaps needs are mostly affected by mixture density in the combustion chamber

Mixture density is affected by outside air density, cylinder filling efficiency and compression ratio, the higher the density, the harder for the voltage to jump the gap.

most engines that have been modified for more performance tend to need smaller spark plug gaps in order to properly fire even though it would possibly make better power if the plug gaps were wider but had a stronger ignition to jump the gap.

[RIDE-RED 350r]

I run a 9 regularly in my ESR 78 bore (350) running on Sunoco 110oct mixed 32:1 with Maxima Castor oil. I ride gravel roads, long straights/sweeping turns. I do some long pulls on the throttle on a pretty regular basis, and don't want the engine to retain alot of heat in the combustion chamber on those pulls.... It's jetted in nicely and for the most part,  I only change plugs as part of maintenance, not because it fouls them.

My understanding of the heat range of plugs is the rate the plug sinks heat into the head. I guess that's my dumbed down, and much less detailed idea about it compared to rsss396. Thanks for that info BTW rsss396!

I have never felt the need to run a hotter plug...