A little more info on a true Killer Bee....

1995 Killer Bee 049 (Cat#340 - Manufactured 1995-1996)
The Killer Bee was an attempt at making a fast reed valve 049 engine from information that had been learned over the years of racing and competition. It had a tapered cylinder with SPI and lighter piston similar to the Tee Dee, a stronger balanced crankshaft and a new reed valve shape. They had a Yellow plastic needle valve. Later in 2002 Estes produced a Killer Bee that had none of these features but looked like the original Killer Bee except for the needle valve. Beware of fakes! Some unscrupulous people are producing fakes and selling them. Check to make sure the engine is the "real deal" before purchasing.

1996 Killer Bee 051 (Cat#360 - Manufactured 1996)
The Killer Bee 051 existed so that modellers could fly the same plane in two competition classes (i.e. A and 1/2A) simply by changing the engine. This engine has exactly the same performance as the 049. There is a legend that two thin lines (or grooves) in the piston skirt are for positive identification but this is incorrect. The grooves were intentionally designed to bleed off just enough power so that the 4% increase in displacement does not necessitate trim changes to a free flight model when switching the model from an 049 to the 051 to fly in the higher "A" class.[15] The benefit of the grooves as a visual identifier was accidental.