OS 91FX matched to Mac header and 15cc pipe (aircraft/standard)

[DPeckNSRCA at aol.com]

Hi Guys,    
    Our club sec. is refurbishing his dad's EU-1 and has anew OS .91 FX 2 
stroke.  Drew wants to know what header/pipe length settings to use.  My limited 
Rossi, Picco .60 drawings used measurements from exhaust port to pipe high 
point.  Props then became the flying and "pipe tuning length" factor, to get the 
engine "on the pipe."  
    The MAC Co. is not giving any info. as they "haven't any data."  I told 
Drew maybe he bought the wrong brand.  Seriously, my man Drew is our club's VP 
for 2004 and may very well be our tenth local entry in our Huntsville, AL RCRC 
2004 Sept. Pattern Meet.  I don't want to mislead him with poor info.  All my 
attention has been .91YS 4S using 13.5x10 or 14x10 APC.  I am asking for the 
following advise:

1. Prop size (with muffler) to test fly EU-1 (big 60 size wing CI, 1,200+?)
2. Recommended starting prop size with header/pipe
3. Suggest minimum and maximum pipe length, measuring exaust port to high 
point of pipe.
4. Any RPM specs. you may have on idle and top end of OS .91 2S motor.
5. Comments wanted on use of .91 2S using back pressure from pipe/header to 
pressurize tank.  I have Rossi old pipes with Mac pressure fittings for back 
pressure.  If you do recommend tank back pressure, where do you drill your 
pressure fitting? At approximately what point on pipe, or header, (distance for 
exaust port)?  Some guys ran pressure fitting just in front of the pipe high 
point.  That sure made a long line, however, ducted fan 91's live with the 
pressure!  Seems like our lower RPM's of today are not worth the pipe pressure 
fitting trouble. 

Thanks for your reading time.

The 2nd best "billfold builder" in the Rocket City,
Don Peck
NSRCA 585

    
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