Tom Stangl has a VFAQ on the subject.
The disadvantage to removing the shafts is increased engine noise and vibration. By removing the balance shafts, you are removing the primary mechanism for controlling engine shake. The engine will sound rougher, noisier, and 'buzzier' than normal.
As for the advantages, opinions vary, and the debate is too exhaustive to report in full here. Proponents have the following reasons for removing the shafts:
Of these, only the removal of the balance shaft belt is uncontested, and is most cited as the reason for removing the balance shafts. Owners who have experienced $2000+ in engine damage as a result of a broken balance shaft belt generally don't want to repeat the experience.
Opponents counteract the other claims with arguments that the power increase from the engine might be negligible, and removing the shafts might affect long-term engine durability. Some say that getting the engine balanced and blueprinted will alleviate durability problems, but others disagree with this.
It would seem that claims of increased horsepower from this mod are difficult to make. Todd Day is highly skeptical about any claim of power increase by reducing rotating mass. He points out (quite correctly) that once a rotating mass is spinning, it takes much less energy to keep it spinning than it did to get it spinning in the first place. This makes any static estimate of power difficult to credit.
Overall, the majority of owners who commented on it said they were happy with the mod, and found the increased engine shake quite bearable. Of course, most of these individuals were probably enthusiast drivers or racers, and so don't mind the extra noise.
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