I have heard that some owners have raised the red line on their engines, as high as 7,000 rpm, in an effort to make more horsepower. This is not advisable for engine longevity and may not actually improve performance. The reason is the oil supply. At higher rpms there is so much oil being pumped through the engine that little active oil scavenging occurs. As a result, a considerable amount of oil remains in the engine. This is because of air getting into the oil the pump and it becoming foamy. This puts the main bearings/rod bearings at risk because they do not like oil with air in it. But even if the mains/rods survive, what happens is that power actually falls off (Note- This can be seen on a dyno where the horsepower curve flattens or falls at higher RPMs concurrent with low oil pressure). The pressure falls off because the air in the oil causes the hydraulic lifters to become "soft" and this affects breathing at higher RPMs. If you must raise your maximum rpm, the best advice is to give your engine an extra margin of safety by keeping your oil level topped off and fresh, since "old" oil is more prone to foaming.