| Hi
Nelly has covered the main points, piston weight is very important and i would recommend a full balance (but it is loads more labour). Also setting squish clearance and piston to valve clearance's is vital. If you do need to change the squish by then you need to re-time the cams.
Hi comp pistons can be a bolt on item but its pretty rare that none of the above needs to be done.
Can't say i remember fitting them without re-timing, balancing etc. its usually done as a package.
Pistal pistons are very good, Call John at JHP who will certainly have fitted these to the 996R/998S motor so he will know the weight and clearance details.
If you are looking for a cheap upgrade 'while its apart', hi comp pistons may not be it. Be prepared to get the whole lot done so you dont get caught with a big bill you weren't expecting.
Having said that, it is a VERY good mod, the 996R motor is ideal for it and is much sharper after the upgrade. dialed in cams, balanced bottom end, squish set and hi comp pistons make for a fantastic motor indeed!  |