I wouldn't touch the B20 with a 10 foot pole. The cylinder sleeves are crap. If you plan on boosting this motor, get the B18B, sleeve it and bore it out and you will have a much more reliable motor.

Since everyone will disagree with me on the B20 being garbage, here is how the cylinder sleeves are cast compared to the other B series motors: http://dwolsten.tripod.com/articles/jan96a.html