Marauderjack
08-29-2009, 01:36 PM
This is a post regarding Helmholtz Resonators from www.fordmuscle.com ....
Try searching for variations with "airbox" as one of the terms. Motorcycle guys are up on the aircleaner helmholtz tuning.
this is something I found some time ago. I think the formula may be for a 2-stroke, so you would have to cut the number of cyl in half for a 4 stroke.
"Use the Helmholz resonance formula,
rpm = (a/(2xPI))* ((((D*0.01/2)^2*PI)/(I*0.01*B*0.001))^0.5)*60/n
where
rpm = resonant rpm for the engine
a = speed of sound in m/s (usually around 340)
PI = 3.1415 etc.
D = intake pipe diameter in cm
I = intake pipe length in cm
B = airbox volume in litres
n = number of cylinders or carburetors connected to the airbox
Use the formula to calculate the desired rpm where the airbox resonances will aid in increasing the air pressure.
The intake pipe should look like a resonance pipe for a loudspeaker with a rounded mouth.
The bigger the airbox, the better it works. Modern bikes have even 10 litres airboxes. With more cylinders,
you take advantage of smaller boxes, i.e. there is no need to increase airbox volume for more cylinders,
rather the opposite.
This is the same formula to use for calculating boost bottles.
Example:
A 3 cylinder engine, I choose a 5 liter air box, 8 cm long pipe with 11 cm diameter and ends up with a resonant
rpm peak at 5300 rpm.
I would choose the intake pipe to be at least as large as the total intake area to the carburetors.
Then it is easy to adjust the rpm by shortening the intake pipe to the box."
Try searching for variations with "airbox" as one of the terms. Motorcycle guys are up on the aircleaner helmholtz tuning.
this is something I found some time ago. I think the formula may be for a 2-stroke, so you would have to cut the number of cyl in half for a 4 stroke.
"Use the Helmholz resonance formula,
rpm = (a/(2xPI))* ((((D*0.01/2)^2*PI)/(I*0.01*B*0.001))^0.5)*60/n
where
rpm = resonant rpm for the engine
a = speed of sound in m/s (usually around 340)
PI = 3.1415 etc.
D = intake pipe diameter in cm
I = intake pipe length in cm
B = airbox volume in litres
n = number of cylinders or carburetors connected to the airbox
Use the formula to calculate the desired rpm where the airbox resonances will aid in increasing the air pressure.
The intake pipe should look like a resonance pipe for a loudspeaker with a rounded mouth.
The bigger the airbox, the better it works. Modern bikes have even 10 litres airboxes. With more cylinders,
you take advantage of smaller boxes, i.e. there is no need to increase airbox volume for more cylinders,
rather the opposite.
This is the same formula to use for calculating boost bottles.
Example:
A 3 cylinder engine, I choose a 5 liter air box, 8 cm long pipe with 11 cm diameter and ends up with a resonant
rpm peak at 5300 rpm.
I would choose the intake pipe to be at least as large as the total intake area to the carburetors.
Then it is easy to adjust the rpm by shortening the intake pipe to the box."