The Supertrapp design does create system back pressure.
I have seen dynos & 1/4 mile testing on V-8 cars w/gains by adding on their muffler instead of no muffler.
By adding supertrapp mufflers, they were able to fine tune thier cars. Improved low end torque ,driveability.
So I would think it will do the same for an inline engine.
I also have friends that put them on thier motorcycles, w/success.
Problem is sometimes you need to add so many disc's to get them to flow they tend to look a little funny.Plus,, the more disc's you add, the louder it gets.
