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Hi all,

I have a scratch built .60 size pattern plane that currently has an OS 90FX w/ stock muffler and a APC 12x11 prop turning about 11,000 rpm's. I have a Macspro header and tune pipe for this engine. But the Macspro website still has no data on how much length to cut off from the header. Is the anyone out there who has this engine, header and tune pipe combination? If so, how much length, if any did you cut off from you header to get maximum rpm's?

Thanks,

Jeff

Well it's been years playing with a piped motor, but if pipe is to short high rpm and no needle valve adjustment. It will go lean/rich very quick with one or two clicks of adjustment.. You will want to be able to move approx 1/2 turn either way. Also on the OS91FX you'll want to adjust the low end needle to help transition and also 25% nitro helps clean up the mid-range. Well hope some of this helped..

Scott Anderson
Team Castle Creations
Team Tanicpacks.com

Here is some tuning Information you may look through...Just some bookmarked sites I have come across:
http://www.osengines.com/faq/faq-q652.html
http://www.rcaerobats.net/tuned_pipe_info.htm
http://www.jettengineering.com/tech/pipetune.html
http://www.macspro.com/tuning.asp
http://www.mh-aerotools.de/airfoils/...pe_main_en.htm
http://www.prestwich.ndirect.co.uk/tunedpipetheory2.htm
http://rcboat.com/pipe.htm
http://www.*********.org/cars_eng-tuning.htm
http://www.bmaps.net/info/pipes.html
http://engine-analysis-software.com/pipe.htm

Sorry for the Information Overload..he he

Maybe you will find some useful information in there?? I realize it's not engine specific...But hope it helps anyhow??

Have Fun...

Chuck

I don't remember exactly my 90 pipe settings but the FX91 makes it's HP at 15k, ball park pipe setting about 39 cm for that range from glow plug to convergance cone of the pipe measured as the exhaust gas flows (follow the path of ex gas to measure not strait from plug to cone) I ran props like 11-1/2 x 6 11 x 7 11 x 8 to get in the rpm power range, 91FX isn't happy with hi nitro you may have to ad a head shim to run more than 15%. If your test running on the ground you can cut a 1/4 inch at a time and as long as rpms go up your good but go too far it will get finicky and drop rpms, you will need less prop to get back in the sweet spot or put a cut pipe piece back in the coupler. (RPMs go up as the pipe is shortened but you can't overprop or it will not get on pipe and will run hot, set richer than normal for flight it will lean as it comes on the pipe, good luck!

Have you considered a Performance Specialties or Jett muffler which seem to do the same with maybe less effort. They are made for specific engines(Performance Specialties, anyway). http://www.pspec.com/details.asp?ProdID=61&category=8 or http://jettengineering.com/ .

I thought about buying a Jett muffler, but I already have the header and tune pipe. So I'm gonna try to make those work. I know a Jett muffler would be alot easier to install.

Thanks for the info captb, I will definetly give your suggestions a try.