ORIGINAL: AndyW
CP,
Thanks for the additional input. I'll get me a few 4.2 X 4 APCs and play around with the idea. Please confrim that all this discussion is about open exhaust? Also, what's the oil type and content in combat/speed fuel?
I have the Picco, a GZ that I re-worked over ten years ago,(never ran it) and the Picco/Brodak hybrid. No KBs though. But with the Cox engine, isn't the ball socket conrod the serious weak point? Castor helps but 28K? Geez, how many flights before you need to tighten the socket in the pin?
About head buttons wearing out. I wonder if they would last longer if they were anodized? Even colour anodizing is far harder than stock and the pores hold oil that would surely help.
Oh,yes,the GZ has a newly installed button to take a turbo. Any recos on the brand and heat range? On 25% nitro?
Andy, combat fuel is anything you want to run. IDK about speed classes, you have AMA, Canadian and FAI speed rules [and future rules] to consider.
You would have to sign into the North American Speed Society and the MACA websites to get the low down about fuel.
Set the engine up so it will run strong on 0% nitro and let the end user shim it to his liking [or modify the head button] for higher nitro. The G&Z and most likely the Picco could use larger screws to clamp down the head. Anodizing the head sounds like a good idea. As for plugs, I like the massiveness and perfect sealing of the Nelson plug.
Speed engines need heavy elements regardless of nitro content..so no need to worry about heat ranges.
Cox engines...if you can make the piston light enough it takes a huge load off the other parts.
I do not honestly remember failing a crankpin or a ball socket after lightening a Cox piston. Piston / liner wear ends up becoming the next weakest link IIRC.