Back-pressure

[Guest Honolulu Dick]

Aloha,

On the early 4-bangers [mine is a 1917 touring by name of the Honolulu Lulu] the inlet end of the muffler is considerably larger than the 1 1/2-inch exhaust pipe end. This difference in size suggests that back-pressure is necessary for optimum performance and/or to extend engine life [valves?]. Would care to learn more about this subject. Therefore, I'm seeking comments from the collective wisdom of our good Brotherhood concerning this topic.

In the Hawaiian language, mahalo = thank you.

Take good care -------------------------------------------

Mahalo,

Honolulu Dick

[Rusty_OToole]

Practically all cars have a tailpipe smaller than the head pipe. By the time the exhaust gets that far it has cooled considerably and does not have as much volume. I don't believe the smaller tailpipe per se is a back pressure problem.

Back pressure was an unwanted byproduct of quieting the motor. In those days they did not know about using acoustics. The only effective mufflers had more or less backpressure.

Some cars in the pre WW1 era came with cutouts. This was a valve ahead of the muffler that could be opened to release the exhaust straight to the atmosphere.

Back pressure was taken into account for things like carburetor jetting, timing etc. If you change the muffler you may have to retune the engine.

Back in the 20s you could squeeze a few miles of top speed out of a car by removing the muffler. But today I doubt very much that you want to do this. If you are in that much of a hurry you could ride a bicycle lol.

[Rusty_OToole]

Another fad of the twenties was to build a sport model roadster with a copper exhaust pipe. The exhaust came straight out the side of the hood and ran back along the body at elbow level. Supposedly the copper gave a deep tone to the exhaust that no other material could give. It also looked sporty when polished up. As long as you didn't burn yourself on it you were the bee's knees.