The big battel around here is weather the noise is a result of the exhaust or the engine speed or mechanical or whatever.  TM 5-6115-323-14 says that after you build your generator pit, line the outside with sandbags and a roof you are supposed to attach flexible pipe to the exhaust line and construct a passage out of the revetment along with a exhaust chimney. So looks like they can tolerate some back pressure.

You have to admit, discussing late sixties vintage military generators is an interesting subject.

Ray F/KA3EKH

From: MARK DORNEY <[email protected]>
Sent: Thursday, June 1, 2023 2:03 PM
To: Doran Platt <[email protected]>
Cc: Ray Fantini <[email protected]>; [email protected]
Subject: Re: [MRCA] BC-224 vs BC-348

You create exhaust back pressure problems when a muffler not designed for the engine in use is used. May result in a lost of power and/or mechanical problems with the engine. 

Mark D. 

WW2RDO

“In matters of style, float with the current. In matters of Principle, stand like a rock. “.   -   Thomas Jefferson 

Sent from my iPhone

On Jun 1, 2023, at 10:49 AM, Doran Platt <[email protected]> wrote:

FWIW, in CAP we put small automotive mufflers on all the 1.5KW PE-108s we got as new surplus. I am currently having a flange welded up so that I can silence my mogas 10kw home generator. Noise is always an issue. 3600 rpm types are worse. The 1800 types can be better and certainly longer lasting.

Jeep K3HVG

On 06/01/2023 10:33 AM EDT Ray Fantini <[email protected]> wrote:

For what it is the MEP-25 1.5 kW may be the loudest generators built. Fail to understand why they are so loud. Its not the exhaust or a muffler issue but something to do with them screaming along at thirty six hundred RPM, looked at a newer MEP-531 2 kW diesel unit at Hagerstown but upon trying discovered that it was loud too and had the added benefit of producing a cloud of black diesel smoke.

Almost half the manual for the MEP-025/015 TM 5-6115-323-14 is on building a pit or revetment and lining it with sand bags to try to cut down on the noise.

Ray F/KA3EKH