ORIGINAL: Tired Old Man
But NO engine is sold packaged with a tuned exhaust. All are sold with a cheap exhaust diverter or nothing for the exhaust at all. So which tuned system does one rate an engine with? As you noted, a decent exhaust system is a power multiplier, so those willing to spend many, many hundreds of dollars (likely more than the engine cost) could easily stack the power deck by finding and experimenting with the exhaust.
So what exhaust should be used for an accurate power comparison? Logically it would be none for a baseline comparison. Those wanting the most power are dependant on those that have already spent the time and money or need to be willing to toss the dice with their own time and money. Realistically they will need to buy a few different engines and do a lot of exhaust work to find ''the one''.
It's how you look at it
Iwould not consider a noisy setup
and making quiet power requires expansion
so grab a pipe
as for open port comparisons Not really very good as some open port setups spill the mix badly and others do not. ANY of em run better with a pipe or some type expansion setup
the rub is that setting up a decent exhaust system is apparanly a daunting task for some . So the hunt goes on for a setup which is the best with no good system - when the results can never be the best . a conundrum