...or just a different dyno.
I've seen dynos vary by as much as 10% because there is NO SET STANDARD used in calibrating them. Some dynos have shorter rulers then others so even comparing dynojet to dynojet is only getting in a close ball park. Unless it is the same dyno it is not going to be an very accurate comparison.
A dyno is for tuning and not bench racing. When used like it should be it is an excellent tool. This is the main reason why Mustang dynos are so popular with tuners. They give a more consistent reading and a more accurate representation of power at any given throttle position and rpm point.
