Muffler hole size versus exhaust port.

[Kiwioilboiler]

Gents I've been playing around with my 288. Removed the front deflector to find a part flap hiding in the outlet.
I filed the flap down, and then continued until the outlet basically matched the deflectors inlet dimension, about 30x20mm, up from around 30x15.
Thinking I was the ducks nuts I pre-assembled the muffler only to note that the deflector really only has around 30x12mm opening to atmosphere.
Interest now at an all time high, the exhaust port itself measured as an oval 33x16mm. Area of port and muffler outlet are therefore pretty much equal.

So the question is, does it really matter that the deflector outlet is the smallest dimension?
It's a 288, so it's not like it didn't go alright to begin with.

Adam.

 

[mdavlee]

Gents I've been playing around with my 288. Removed the front deflector to find a part flap hiding in the outlet.
I filed the flap down, and then continued until the outlet basically matched the deflectors inlet dimension, about 30x20mm, up from around 30x15.
Thinking I was the ducks nuts I pre-assembled the muffler only to note that the deflector really only has around 30x12mm opening to atmosphere.
Interest now at an all time high, the exhaust port itself measured as an oval 33x16mm. Area of port and muffler outlet are therefore pretty much equal.

So the question is, does it really matter that the deflector outlet is the smallest dimension?
It's a 288, so it's not like it didn't go alright to begin with.

Adam.View attachment 242984 View attachment 242985

It depends. I always opened the area up under the big deflector and welded the front part of the stock opening shut. Going as big as that one would cover

 

[Al Smith]

They say about 80 to 85 percent of the area of the engine exhaust port area is optimum on a chainsaw with a pressure can muffler . I suppose on something like a kart engine with multiple carbs it could be more .In the day they did use giant megaphone pipes that really moved some air but with the large fuel delivery capacity it worked .It just wasn't very efficient because it blew out a lot of unburned fuel .
I remember those days well .The racers toward the back of the pack looked liked oil field workers from the castor oil residue all over them .They used layers of cellophane over their face shields that could be torn off when visibility was hindered .Sheets of plastic floating everywhere .