In short, the harder you push the motor the colder the plug.

I think you have that the wrong way round. "Hot" plugs advance ignition, "Cold" plugs retard ignition. Higher Nitro content in fuel retards ignition. Therefore the higher Nitro in the fuel requires a"Hot" plug to restore the desired ignition timing.

ORIGINAL: HighPlains

Insane prices on plugs. Not so long ago, a card of 1S or 1L K&B plugs was $6

I've found that pushing an engine harder with more nitro and a pipe raises the overall stress and operating temperature of the engine to include the plug. This in turn requires a colder (and sturdier) plug to reduce timing and extend plug life to an acceptable level.

Colder plugs often include a "lighter" element that often does not hold up well when stressed beyond "normal" sport flying. For example, I would not try running an OS A3 or F plug in a boat with 65% nitro or heli with 30%.

Colder plugs often include a "lighter" element that often does not hold up well when stressed beyond "normal" sport flying. For example, I would not try running an OS A3 or F plug in a boat with 65% nitro or heli with 30%. [quote/]

So in this quote you would not us a "Cold" plug in a high nitro engine

A little ambigious?.

I quote from a knowledgable source

High Nitro fuel is a relatively slow burning fuel.

Remember the original question concerned a Thunder Tiger 40 sport engine, Not High nitro, Pipes and different element thicknesses.

I am finished here.

ORIGINAL: wjvail

Sorry... You've caught me. That should have said "HOTTER (not colder) plugs often include a "lighter" element that often does not hold up well when stressed beyond "normal" sport flying. For example, I would not try running an OS A3 or F plug in a boat with 65% nitro or heli with 30%." You are correct, it didn't make much sense the way it was written. I have edited my post and made the correction. I'm sure you can forgive my carelessness. We all need an attention to detail lecture in our posting![:@] You've misspelled ambiguous and knowledgeable.



Who?



True; however, its addition in model two stroke fuels above about 15% is usually for performance reasons. Included with these performance goals usually comes higher cylinder pressures either though the use of a pipe, more nitro or higher compression. That implies a colder plug.



Not forgotten... but... nitro content was not mentioned at all... nor was the exhaust system or head shims. I would remind YOU the question was in reference to Q-500 which would suggest the engine was not mounted in a Cub. I stick by my answer in post #2.


Hmmm... I though we were just getting started


Bill Vail

Sorry ED! the more Nitro the colder plug you have to use.
This is what every pylonracer knows.

I want to thank both of you guys for your input. It is knowledgeable poeple like yourself that help others, myself included, to learn new things about going fast. I read these threads to learn and I really appreciate the good input in these threads.

K&B 1S plugs for $2