No experience with the AFE spacer referenced here.

However, any device that claims to increase horsepower and torque by creating a swirl in the intake manifold is flaky by definition. You have to start with the assumption that it is a scam and then try to disprove that. If you don't do baseline dyno readings, your experiment won't necessarily help answer that question.

I have read about studies of throttle body spacers tested in a lab, which showed that it was possible to increase power, but not until the spacer was over one meter long. And at that length, there was very poor throttle response, apart from the packaging issues.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue