For my HP 40 ( RPR ) I used 1 1/4 Dia. Alumn. , about 2 in. long .
Put 10 ? 2 mm holes in it outboard aft . X pattern Square .
Fairly Quite and mellow . Equiviant area to one bigHole .
bin Racking the brain for which muffler I used in the Spit for the worlds best engine run , on the G-51 . !
Thinking it was the ST Sausage thing , with the outlet bunged . And 10 holes outboard aft , as above .
Like toungue muffler holes .
Theory on the big muffler is theyre differant ( not ONE ) distance from the ' source ' of the ' pulse ';
Thus not one shock wave , acoustically . And also a broadening of the powerband , de sensitising
of the needle . Thats my theory & Im sticking to it .
Will drag it out for next weekend .P -51 may need the nose weight .
below a pic. of That Type of MUFFLER , un modded . ( Bung outlet & drill Sq Pattern ( 4 x 3 ? ) x 2 m.m.