spiral_72,

I feel your pain.

Really, engine tuning is an art, and it takes practice. I've been doing it for quite a while, and since I do a lot of flight instruction, I spend time tuning not just my own engines, but other guy's as well.

You're right, differnet engines will behave differently. There are tons and tons of factors. Glow plugs can be confusing as well, as you've noticed. The reason for all the plugs is that differnet engines will "like" different plugs.

Also, the fuel you use will affect your plug choice. Nitro is the obvious one, but oil percent can also affect engine running.

Your prop choice can also affect what plug is "best". And as we know, prop choices vary by person and airframe, even for the same engine. The exhaust system also has an effect on how your engine runs, though getting in to tuned exhausts is probably beyond the "beginners" forum.

Add in different ways of putting together an engine (ABC, Ringed), and engine design issues like the bore/stroke ratio, compression ratio, age of the engine and so on.

Oh, and don't forget the weather and where you are. There's a big difference between running and engine in Flordia in the summer and Denver in the early spring.

So, yeah, there's no "one answer". No one "best plug", "best prop", "best fuel".

There ARE techniques that generally work the majority of the time, and you can use to get your engine running well enough to fly and learn with.

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The reason a lot of guys like the OS 8 and the OS A3 is that they are reliable plugs with a medium heat range, and are a tad shorter than some, though technially still a "long plug". So they work well in most engines most of the time. I use the OS #8 in my Mosquito twin engine plane in a pair of OS .46AX engines. I'm not looking for peak power on those engines, but an engine out on take off will wipe out the plane, so reliability is everything.

On the other hand, in my combat planes where I'm running mousse cans for extra RPM, sometimes use extra nitro, use small props and wind the engines up to high RPM, I use K&B 7300 plugs because they work for me and do what I want in those engines. That K&B plug in a new OS .46AX will often cause it to run badly, I've seen that happen myself.