Muffler Theory

[W MacDonald]

The attached photo shows the muffler pieces as-received with my ca. 1912 Little Giant bus. The four shells are 4, 5, 6, and 7 inches in diameter and 20 inches long. The exhaust enters the inner shell through two 1 3/8" diameter pipes (one from each cylinder) and gets from one shell to the next though nine 3/8" diameter holes. Doing the math, that's 2.97 square inches inlet and 0.99 square inches outlet. Having no experience with this type of muffler, that seems like a LOT of restriction. In my case, the engine is a 2 cylinder, 5" bore and 4" stroke which works out to 157 cubic inches.

Does anyone know how this type of muffler is supposed to work, and how the hole size and number is determined?

Thanks,

Wayne MacDonald

[Steve Braverman]

My father has a Sears with a similar but much smaller muffler. There are only two shells though, not four and it's pretty quiet.

I'd love to see what the rest of the bus looks like.

[Guest malonemach@aol.com]

your outlet needs to be larger than the inlet!

[Seldenguy]

I really think it should be the other way around. I have owned many autos and all of them had larger exhaust pipes than the tail pipes. Some authoritys may comment but I believe backpressure has some cooling effect on the engines exhaust valves. Look at the millions of model T Fords all have a larger exhaust pipe than the little tail pipe.--Bob

[Guest malonemach@aol.com]

the smaller the outlet the more back presser you have thus less horse power !!!!!!!!!!

[Richard Lichtfel]

My 1909 Mason, 5 x 5 two cylinder, has a large muffler but only a 3/4 inch pipe outlet, and this is the original shown in the manual. That's why I run with the cut out open and only close it in QUIET ZONES like the manual says.

[Restorer32]

That's how mufflers work, by slowing down the exhaust.

[Layden B]

Mufflers kind of average the exhaust, it comes puffing down the exhaust pipe from the cylinders and gets smoothed out to a more even flow out the tail pipe. The exhaust pipe gets sized for the puffs and the tail pipe sized for the averaged flow, hence smaller size. At least that is my story and I am sticking to it!