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JR-Spektrum . Gyro Hobbies . E-flite

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Engines Plugs Mufflers Fuel > Monster Engines and Tuned Pipe Length
 
 
dchinww
Senior Heliman
Location: Seattle, Washington

In one of their older catalogs, Vario published a canned formula for calculating the length for their tuned pipes:

{(Exhaust Port Timing in Degrees) X (41,900)} / Engine RPM = Tuned Pipe Length in mm

For example, a popular (modified) port timing for the OS 61SX-H WC is 165 degrees:

(165 X 41,900) / 16,000 = 432 mm

This formula is simplified for 60 size engines. Does anyone know how the relationship changes as the displacement is increased? Yes it gets longer but is it a linear increase, is it based on pipe volume? Anyone in the know???
03-02-2002 Over year old.
 
 
Michigan PI
Senior Heliman
Location: St Clair Shores, MI

The formula should remain the same, just run a larger volume expansion chamber. For a given RPM, the frequency of the pressure wave will remain the same regardless of displacement.
Thanks for the formula BTW.
03-02-2002 Over year old.
HOMEPAGE  
 
 
GMPheli
Veteran
Location: W. Bridgewater, MA USA

432mm = 17". Isn't that on the long side?

Alan Angus
03-03-2002 Over year old.
 
 
Conrod
Veteran
Location: Melbourne, Florida

length

It's a starting point. You can work in from there. Alot of variables will affect the length. Measuring from center of piston to first reflector, exhaust gas temp., how fast the pipe dissipates the heat, the density of the gas in the pipe, measuring from the exhaust port to first reflector.
conrad got plenty of pipes for sale mingledorff
03-03-2002 Over year old.
 
 
dchinww
Senior Heliman
Location: Seattle, Washington

Recommended tuned pipe lengths are always on the long side (kinda like the slobbery rich initial needle settings for new engines). The measurement from the Vario formula is from the glow plug all the way to the widest cone of the pipe or the first reflector disk.

Back to the original question. All other factors being equal (fuel, plugs, air density, etc.), doesn't tuned pipe length increase with the displacement of the engine? For example tuned pipes that are designed for 60 size engines are bigger in volume and longer in tuned length than similar tuned pipes for 30 size engines.
03-04-2002 Over year old.
 
 
Conrod
Veteran
Location: Melbourne, Florida

tuned pipes

From all the formulas that I've seen and from experience: NO!
You do have to have more volume on the pipe as the displacement is increased to handle the extra exhaust or else you will get a choking effect and motor will run hotter and less consistent. The formulas have nothing in them that I have seen to indicate displacement as being a factor of tuned length. The main functions of the formula are "speed of sound at a given atmospheric pressure", "exhaust port duration", and "rpm's" which give you the ballpark tuned pipe length.
conrad
ps..I hope this answers your question
03-04-2002 Over year old.
 
 
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Engines Plugs Mufflers Fuel > Monster Engines and Tuned Pipe Length
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