Hey,

I have OS 95 AX in break in level
I bought Mac muffled tuned pipe (1290) for this engine with long header.
this engine mounted on phoenix 7 of Hangar 9
i use 11x12 apc prop (plans to stay with this kind of load or change a bit to 12x11-12x12 apc)
i want to hear from experience of tunning this engine with macs pipes with this kind of RPM (os91fx and OS95ax)
i want to say that i have lot of experince with macs pipse and various of engines.
i need to have a good start point with this tunning (header length)

appreciate your time
Guy

There aren't any published figures that I could find for your engine and pipe combo, so I'd recommend tuning the pipe the way Macs Products recommends. Break-in the engine for 30 minutes on the included muffler. Then run the engine with open exhaust on your intended prop to get a baseline rpm figure using a tach. Then start cutting off the header in small increments noting the peak rpm each time until you don't get a change in peak rpm between two header cuttings.

See here: http://www.macspro.com/tuning.asp

Hey 1QwkSport2.5r,

thank you for your answer,
yes i know, there is no much information for this engine with Tuned Pipe.
maybe some experience with the 91FX can help cause theoretically the calculation this semilar enouth (same exhaust port dimension - almost same angles for for open port and close port).
the Macs manual is familiar to me.. try to find kind of compare for my results

if anyone have more information, i will appreciate
thanks

Guy

that is what you do to tune the pipe to the engine. just what macs says to do. don't cut it to short about 1/4 in at a time.also the prop can affect rpm so go with a smaller prop. don't load it down with to much pitch. you want (rpm) also tuned pipes are hard on glo plugs. back in the day ,guys used tuned pipes all the time....but glo plugs cost 1.50 then. 8.00 now. so if you went through 2 plugs a week no biggie. now were talking 16.00 for two.i recently took the tuned pipe off a ys .45 sf two stroke that is made for a pipe because of this.i put a os muffler on it instead. the motor ran 15,000 rpm on the pipe and now runs about 13.400. the plane is 95% more reliable this way too. no needle friggin around flight after flight either. also uses less fuel. plane flies about 70 mph now and it flew close to 90mph with the pipe.i like fast planes but not paying that much for the few mph. just my thought on this . but i love the sound of tuned pipes and miss that.. also consider a jet muffler made by dub jet of jet engineering.

I have two engines on full pipes - a Jett 56LX and SuperTigre S29. The S29 isn't fussy at all, runs a season or more on a single plug (5% nitro). The Jett is a little bit more high strung. It's still pretty new, so peaking it is a no-no. I've gotten close to peak a couple times and torched a few plugs. Not blown - still operable. Just distorted the element. I doubt an OS AX engine is timed anywhere near hot enough to worry much about plugs. It's the high timed and high nitro engines that are hard on plugs. Usually anyway.