Sprint booster is a waste of money & does nothing to make the car quicker. It's a feel good thing that just increases the throttle tip in rate to to simulate better performance.
The JB Power box also remaps the throttle for faster tip like the sprint booster but in addition it remaps the cars ECU for more power. That being said the gains are marginal, about 10whp max. On My 330Ci I just stuck with the factory settings as I did not think the gains were worth the price. Overall the 328's are pretty well developed from the factory & its very hard to gain much power without spending a lot of money.
Last edited by bear-avhistory; 01-20-2013 at 08:27 PM.