Well the 10cm length of hose stopped the subwoofer effect, but I suppose now that I've identified the cause of plenty of noise, its worthwhile trying to minimise it by experimenting with different lengths of hose and mufflers.
I was thinking that an automotive muffler on the intake might be effective for its passive noise cancelling, but it may restrict airflow too much. Any thoughts on that idea?
Barney
Easy to measure Barney.
Assuming you did´nt change anything and the boat is in running condition, you put the hose on and have a ride in calm waters. If there is no smoke, continue. Set the throttle fix and put the hose off. Any change in rpm ?
Remember the setting.
Now put the (cheap) Rover air filter on it and do the same run, same rpm, and get it off while running.
Watch for smoke while the filter is installed, it would be a sign of a choked inlet.
But you can have it easier.
When you are fine with 10cm of hose for a wide range of resonance, you need just another diameter of any length to get rid of almost all of the rest. A plain metal mesh "airfilter" (in fact they hold just mice, rags, and t- shirts out), wider than the inner diam. of your hose, does it.
The Rover "oil" air filter has the same effect, but I assume the inner diameter is smaller than your inlet. then forget it.
And if there is a 90° or worse change in the direction of airflow it is not the way to go. I do´nt have the data at hand, but I remember that a 90° knee is about 20% or more restriction in air flow!
The muffler idea is one you should quickly forget. Exhaust gas pressure has no problem to overcome resistance of some severe amount. The same resistance on the inlet chokes your engine to death.
Regards
Richard
