Hello Paul

Measured the sound levels coming off the engine yesterday. Here's what
we recorded:

2500rpm - 97db
5500rpm - 112db

Sound levels were measured at a distance of 20 feet off the port side
of the cowling in line with the muffler. C weighting, slow response.

Mark (Rocky Mtn high)

Thanks for the data Mark.

That is not too bad for 20 feet.
Our standard is 30 feet so it should be be below 100 db at 5500 RPM at 30
feet.
We have recorded worse than 112 db at 30 feet.

As I recall you have a 2 inch down pipe. Area 3.14 square inch.

If you want to get it lower with no increase in back pressure
try two 1.5 diameter inch down pipes. Total area 3.5 square inches.

Do you have a blast tube on the muffler cooling pipe yet?
That tube might burn through if you don't get a blast tube
on it.

Paul Lamar


We are planning on how to get the blast tube on there right now.  Neither
end of the muffler cooling pipe is obstructed right now.  Seems like
convection ought to move enough air through there to prevent it from burning
through, though I suppose that could be wrong.

Mark (Rocky Mtn High)