If the wheel is coming apart it is most likely a design flaw in that the strength of the wheel is simply too low. The air coming in at an odd angle shouldn't affect it. The loads on it are mainly proportional to the square of the rpm. Reducing the rpm a few thousand rpm takes a lot of the load off of it. But how much is the wheel really under designed? Better materials can help-going to a machined vice a cast wheel- but obviously it isn't enough in this case.. The stresses are simply just too high on this particular compressor wheel design. Options are To make the new wheels out of an even stronger material, will the weight increase? then is the shaft strong enough? Then does the acceleration suffer? Total redesign required..