I think its been posted before and I measured it and its true: The new B4.1 standard rear arm carrier (the part that adjusts toe in) has more slightly toe-in than the old B4 standard block even though they are both supposed to be 3 degrees.

If you get a B4, I would recommend getting the B4.1 rear block system first and try the 3.0 block. If that doesnt resolve the loose on power feeling, I would suggest the .5 rear hubs.

This is the new part:

http://www.amainhobbies.com/product_...t-Set-25-335-4

Lastly, you may also want to invest in the ballast weight that fits in front of the transmission.