Originally Posted by Pablo
I know you are not running a stock exhaust. I read that. I was writing in general terms for the general reader.
Here's a conceptual view of what I think you are experiencing. At low rpms BEFORE an expansion chamber can have full effect, it is possible that a straight larger diameter pipe will produce slightly more power. Especially detectable in a single speed bike. Now there is no way physically such a set-up will produce overall higher peak power within the most efficient powerband of a 2-stroke engine. In such a situation it would be basically trading off a nice torquey mid-high peaky on pipe powerband for a slightly more torque in an RPM range where the engine is not the happiest. This of course would not be a good choice for a bike with gearing where one could match that power band as needed with gears.
'Fraid he's right, Map. That expansion chamber is good for giving you torque where torque is usually lacking, but only at a certain RPM. In order for it to cover a RANGE of RPMs from high to low, it would need to change size, or to maybe work like a slide trombone (HEY! there's an idea! Maybe add a bi-metallic linkage to make it automatic! Hmmm...I wonder if there's money in that?) Anyhoo, it's still a good pipe, it's just not real adaptable.