Miss Llumar question

[NitroEd]

I haven't had any big problems with my boat. But my motor doesn't seem to have the rpm that my friends does. Mine runs good and starts great, but his will eat mine alive. You can really tell his rev's a lot harder than mine. His is a strait shaft and mine is a flex shaft. I have tried the Octura 435 and 535 props, balanced and sharpened. Someone told me that you can get more rpm out of a motor by moving the expansion chamber closer to the header. True? I tried it and I see no difference. Thanks.

[engineman351]

NitroEd: Whenever two similar boats are compared for speed, yes, the engines may be why there is a difference, but you have to look at other things too. Same fuel? More nitro=more fuel=more speed, provided the prop and pipe are adjusted too. Remember more nitro may require adjusting head shims. How does each boat ride...is yours riding any 'wetter' than his? His straight shaft will have the tendency for the rear to be driven up onto the prop, while the flex shaft set-up may need some adjustment to get the rear of the boat up and clear of the water. Also make sure your flex shaft and teflon liner are in good shape (not binding). (I usually do not run the liners) The shaft needs cleaning and greasing regularly. Has he done any bottom sanding to make sure the ride planes are flat & sharp? Are the turn fins and rudder sharpened? Now for the engine: Same plug? Is your carb barrel opening all the way? On the pipe length, given all other factors remain unchanged, shorter means getting on the pipe later and at a higher rpm. Maybe you are not 'getting on the pipe'. I like to lengthen it first then keep shortening until the power falls off in the corners, then go back out to where it stays on the pipe. If you can, measure his from the center of the exh header flange on the engine, straight back to the seam or fatest part of the pipe. Set yours the same. On tuning, read the plug after a run. If the coil is 'shiny' you are probably too rich and not developng hp/rpm. If the coil is whitish/gray and mangeled or distorted...too lean. Look for the coil to be dull gray and its ok if it looks like the coil is being pulled upward, as this means the pipe is working. You might try different heat range plugs as they can change the timing a bit. The colder plugs retard the firing and the hotter plugs advance the firing. The 'Chianelli' platimum Q plug works pretty well. The McCoy MC8's & MC9's work well too. If all else fails, I think that a Traxxas 3.3 would really wake up a Miss Bud or Miss Llumar. Good luck. RC