I am running 30% nitro in my S7II with a Mckoys MC-59 plug. Can someone clear up wether its a hot plug to use with a high nitro content or is it the other way round. I have read a couple of threads about this but both said the opposite high% nitro = hot plug then the other thread said high% nitro = cold plug? What are the effects of changing plugs?

Typically,
High nitro = cold plug
low nitro = hot plug

the mc-59 is med to hot,
I use that plug with 20% nitro in my .12 engines
I think it will fire early with 30% in that engne

Thanks for that, I might have to change the plug by the sounds of it then, although it is a modded engine. Im thinking of going down to an RB 6 plug?

...last I heard, you match the ambient temperature to the plug rating, ie cold plugs for cold outside temperatures.

I think thats how its shown on the back of OS plug boxes, and I think thats what Rody said on the RB forum.

so unless I/we are wrong then I would the plug rating to the ambient temperature, more than nitro content

What he said...

And also depending on what you want from your engine.... hot plug, more ignition advance, more bottom end less top end... and vice versa...

Many more factors involved other than just ambient air temp.

this the best tutorial I've seen
http://www.rcnitro.com/rn/articles/glowplugs.asp

as the engine gets bigger or nitro content higher its recomended to use cooler plugs and visa versa ..

true, i just couldnt get the explanation into words without rambling into an essay. nice webpage.