Armilite, where could I get a tuned pipe for a rotax 277? Thank you Tim
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As far as I know, Nobody today is making a Tuned Pipe for the Fan Cooled 277UL, 377UL, 447UL, 503UL, or the Water Cooled 462UL, 532UL, 582UL, 618UL. Rotax Rick makes one for his 670's. There is JAWS, SLP, The Crank Shop, FMF, etc., that make Tuned Pipes. There is a guy in Canada that makes Tuned Pipes for anything, but I forget his name at the moment. I know he makes them for Sled 277F.
There are at least 5-7 Tuned Pipe Builders that make Sled Tuned Pipes, but even they don't make any for these Older Sled Engines like the 277F, 377F, 440F. You might find one for the 503F, and the 521 LC, 580 LC, 617 LC, 670 LC, but most of them don't want anything to do with Airplanes. If you contact them, say it's for an Air Boat or Hover Craft. Custom made Tuned Pipes can Cost $450 to $700.
Material to make your own $25 or less from a Scrap Yard.
Tuned Pipe & Cone Software to make your own anywhere from Free to $40.
Tools needed: Basic Measuring Tool to Measure your Cylinder Exhaust Port, a Tig or Mig Welder, Construction Paper & Tape, Scissors. Once you have your desired Shape laid out in Paper you want, you take them DXF CAD Files to a Shop that has a CNC Laser or Water Jet to cut them out of Metal. A CNC Plasma Cutter will probably work also or a CNC Hobby Router. People have Hand Cut them out also. The same Machine Shop can Roll them pieces also, or Harbor Freight sells a cheap Metal Roller.
You also have the Option to Cut, Turn, Weld, a Sled Tuned Pipe. But you need to know what Engine and it hp@rpm and Exhaust Duration it was Designed for, and your desired Engines original hp@rpm and its Exhaust Duration. There is a Formula to use that you can make up a Chart of the common rpm used.
Like my Skidoo/Rotax 335 Single is rated 20hp@5500rpm with a 155 Duration. A Stock Skidoo 670 is rated 115.7@7750rpm and has a 180 Exhaust Duration. In the Chart I made, you go to Exhaust port Timing 180 and over to 7750rpm and you get a Number 39.5", then go to 155 and Pick what rpm you want to turn it, like say 6500rpm and you get a Number 40.5". So that Info Tells you to Add on 1.0" to the Lenght. The 335 used a Can Muffler that Bolted directly to the Cylinder. Ideally Exhaust should be Mounted with Springs. So make a 1.0" Wye Pipe with Loops for attaching with Springs.
You can choose to use whatever Max rpm you want, Rotax used 26hp@6250rpm, and 28hp@6400rpm, I would use 6500rpm!
You got (3) ways to estimate your Engines hp at rpm.
#1 The PLAN Formula and using BMEP.
The following tables define equations for four stroke reciprocating engines.
www.engineersedge.com
#2 You have the Simple 7cc to make 1hp Rule. That's using 6500rpm, the proper Size Carb, using 11.5cr, with a Good Tuned Pipe. 268cc/7cc = 38.3hp!
#3 You have the Peak Flow/HP Calc. Most Sled Stock Tuned Pipes fall into the 93-95% VE range. The Calc only works with Whole Numbers.
268cc at 6500rpm at 93% VE = 38hp
268cc at 6500rpm at 94% VE = 39hp
268cc at 6500rpm at 93% VE = 39hp
Most people only know what hp the manufacture decided to use, not it's Max hp capability! Skidoo made some Engines in (3) different classes, like the Standard 335(20hp@5500rpm), 340 TNT(26hp@6500rpm), and 340 Blizzard(36hp), same basic Bore & Stroke they just used different rpm to rate them with different Carb Size used and different CR used. The Blizzards used a Tuned Pipe!
Free Tuned Pipe Ap. Exhaust Calc. The bottom Box is 2.0 for Wide Band. That is all the Info you need to Design a Tuned Pipe for your Engine. You need a Cone program to make Bends in the Tuned Pipe.
A simple 3 stage two stroke exhaust calculator based on formulas of G.P. Blair from the book: The Design & Simulation of Two Strokes. You can also save and load the data by using the provided functions. Note: This coefficient Kh is called the horn coefficient, with typical values between one...
play.google.com
For Paid Software, I like this guy's Program, Pipe Designer. His Cone program is Free.
ypvsbox.free.fr








