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


Paul,

Can you send a drawing of what the exhaust manifold looks like internally?

Yes, I've seen it on the CAD drawing but still curious to see the internal
structure. This will also help me with your comment about using two 1.5"
pipes rather than a 2".

I'm mentally trying to picture this, as my gascolator drain will located
in relation the the exhaust pipe.

Oh we have City Buses at 115db from 30 ft, so I'm impressed!

Thanks,

Tom


There is nothing inside it except the cooling pipe.

Paul Lamar