I have never looked into it in a way that you might, but in dealing with mostly LA.25, FP-25, and Brodak .25 engines I have used on stunt models and casually looked at heads and plug fits, a standard plug (long reach) would have the body just flush with the combustion chamber. I use mostly R/C plugs with idle bars largely to help protect the element and it gives carbon some place to grow instead of inside and over the element chamber. I use 10% nitro content fuel with 20% total oil generally, as 10% usually gives a pretty consistent needle setting over the temperature range that I usually fly at. I'll drop to 5% for more run time if I can't do anything else to increase tank capacity and generally I don't like to add stuff to the fuel to stretch out the run. Head shape would be anybody's guess. hemi heads of varying dimensions are used on bigger engines to soften the break and help combustion. You see Fox .35 heads in slant plug configuration in combination with a slight hemi chamber, both from the read and from the side, but I haven't ever heard or read any explanations of theory for this. Just not much experimentation with .25s in stunt. Lots of club racing with them, especially down under in Australia and New Zealand, so maybe one of those guys will chime in, or if you have any contacts there you might ask them directly. I hope this helps.
Type at you later,
Dan McEntee
Topic: Plug depth (Read 794 times)
