Thanks for all your thoughts and input. As Greg said, the original thread was for speed only, not for 3D or flying under a limbo pole. My intent is for top rpm with the correct prop combo. Please dont get the impression I'm a rev head intent on achieving destruction of my motor. I treat all my engines as I would my "crown jewels". The delta model to be used for, shall I say, this experiment, only has a 20mm (just over 3/4 inch) depth at the wing root chord, tips tapering to 12mm (1/2 inch)= for speed only. My son will be flying this model; will be too fast for me "on the pipe". I'm too old but not yet senile (well, I don't think so. I still recognize the bloke looking back at me in the mirror). Pleased me to read in the posts where tuned pipes do actually work on diesels. The reference to an old RCM about ducted fans and diesels really drew my attention. Another field I'm involved with (fans and Rossi's and K & B 7.5). I still get a great kick out of the "newbies" at the strip when they see me start my diesel motors without a glo driver or an electric starter, just using the old digit. The gasps, dropping of jaws. Priceless. But will definately not use that same digit on the 9" prop on the dieselized Vmax 46. Electric starter here. Yes, I know about hydraulic lock. Looks like I take the plunge and dieselize. Glen