Re: Does an engine really back pressure??
It more or less comes down to the effect of the exhaust piping and mufflers on the gas flow leaving the cylinders. A well designed system will set up some waves that assist in scavenging the spent gas out of the cylinder. Theres a bunch of gas flow and fluid dynamics involved and a good bit of trial and error. On a HD there are only two cylinders, so they are somewhat more sensitive to the effect of pipe length, shape, etc, that say a V8. As noted, even exhaust sound can vary from annoying to wonderful on the same engine with just a muffler or pipe change.
Note that turbos do add some impediment to free flow, but do recover some otherwise wasted energy to make more power. This stuff is fascinating, but being an ME took another level of calculus over civil, so I settled for being a civil and doing roads not cars.
66 Malibu Coupe, home rebuilt 350. Took me 39 years to get her!
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