RE: HPI RS4 Upgrades...
The idea behind the machined aluminum fly wheel is reducing rotating weight.
The first things I would change are the clutch, and brake disk. Then consider
a good quality radio set.
The racing clutch will hold up much better than the stock one. The fiber disk
will increace stopping power greatly. Even a mid-range radio will give better
control and reliability than the stock unit. Reliabilty is the key in a car that can
go 50+ mph.