The preluber is just that, a "PRE" luber. Certainly helpful but not everything it can be; where the accusump is an automatic oiler and can be set up as a preluber.
How it works is when the oil pressure drops below a predetermined level it releases pressurized oil back into the engine, when engine oil pressure comes back up the tank refills and is ready to release the next time oil pressure drops; it can also be turned off before engine shut down (preserving the pressurized oil) then turned on before the next start-up (releasing the pressurized oil--prelubing the engine).
People will argue that if the oil level is kept in check there is no need for an Accusump and a preoiler is the better choice, but I feel that it is cheap insurance. Slightly low oil level + WOT + high G corners = drop in oil pressure.
http://www.supramania.com/forums/showthread.php?t=52321
Matt
