just thought I would share this info. have blue head zdz 80rv, ks 1080 pipe and 28mm header, did the math for header lenght to hit at 6000.

with msc 27-10 got 5800-5900. flyable in a 35% yak54 (32lb) but not outrageous, did have unlimited vertical, but no jump out of hover capability. on line thrust calculator at LCRC.net says aprox 52 lb thrust (1.62 to 1). plane did not have appreciable change in power above half throttle, prop load keeping pipe from kicking in?.

switched to Vess 27a prop, getting 6500 -6600 same day , same fuel, same settings etc. havent flown with the new prop, but the LCRC thrust calc says aprox 65 lb now (2.03 to 1), quite a change, the pipe seems to be hitting now. if realy 65 lb, thats comfortably 2 to 1, my experience with flat foamies says 1.7 to one is minimum hoverability, more than 2.25 to one and you probably wont use it all, 2 to one and its pretty good. should be much better vertical with the new prop setup, will try it tomarro.

when setting up and testing the pipe and header, on a test stand with a msc 25-10 on it, without the pipe, just header, got 6000, hook up pipe and it jumped to 6450. from what I have read 450 is a respectable rpm increase with a pipe. engine is mounted upright, header is built of two curves, one that brings the pipe streight "down" and another that turns it streight back, pipe exhaust "nipple" pokes out of bottom of plane near trailing edge location.