Dyno Testing with a Sidewinder - baffle in or baffle out?
On some bikes, especially Hayabusa's with modified engines, the air-fuel signal to the pump can be lost during a Dyno run. Truthfully, we are not exactly sure why this happens, and it is very inconsistent between bikes and engine combinations. Probe length, the condition of the air-fuel pump itself, and the power output of the engine all seem to be contributing factors.
Nonetheless, here is what to look for: The air-fuel curve looks normal at first, then suddenly shoots DEAD LEAN (typically between 5000 and 7000 RPM) and stays lean for the remainder of the run. Naturally, the operator's first inclination is to begin to richen the map. Because he is receiving a FALSE reading, this is the wrong direction and soon he will receive a corresponding drop in power while also witnessing the same excessively lean reading. This can become confusing and disorienting, especially to the novice tuner.
The solution: Install the baffle. The increased velocity prevents the lost signal which allows a true air-fuel reading. After tuning as normal, remove the baffle for a final power test. Do not worry if the A/F signal is lost again. Afterward, we typically alter the map at the drag strip after the dyno map is created for maximum performance using a wideband 02 sensor or by making a slight adjustment to the map and watching the corresponding change in MPH. This situation typically only occurs with Sidewinder exhaust, but can also occur with any megaphone base system.
Note: using the O2 sensor directly in the collector of our TiWinder exhaust eliminates this issue.