Currently looking into aftermarket exhausts. Mod goal is to replace the stock exhaust with a significantly lighter unit but want to retain low dB level and low/mid rpm torque.
I am under the impression that the smaller (shorter) the can is, the louder it becomes... and the more low-end and/or mid rpm torque is lost. is this somewhat correct?
Short large bore cans will be outrageously loud, period. (when on the boil)
Longer smaller bore cans will be quieter, but there is a wide range of result, depending upon the level of silencer design sophistication.
Noise does not equate to power, be it Torque or BHP.
Generally speaking, the cans are not part of the interference wave tuning inherent with any kind of "timed" exhaust system.
The cans can bottle things up, in other words become a flow restriction. Proper dyno work will uncover this and allow mapping to compensate for.
More resistant gas flow cans will reduce the total gas flow from inlet to exhaust, thus triggering the need for less fuel for any given map co-oridinate.
The cans can bump the peak Torque and peak HP position on the RPM curve, as well as their values. Good cans will not move the RPMs at which peak T and HP occur by much if any, and instead should result in some T and HP gain.