yes it increases the oil flow onto the cam lobes and lifter base contact area. yes it cuts a groove in the lower lifter bore from the oil feed hole to the bottom of the lifter bore (it cuts about a .040 wide and .007-.010 thousands deep groove) you must do this on a block before cleaning it the final time and before installing the cam bearings for best results because it scrapes small metal filings from the lifter bores you don't want in your engine. you insert the handle from the top of the lifter bore, hook onto the cutter that you insert from inside the block from the cam tunnel and pull the cutter up and slide it down in the same spot several times, the cutter scrapes the groove,[b] you must be careful to cut the grove on the side of the lifter bore that sprays oil onto the cam lobe as it starts to spin under the lifter not after it passes the lifter, look at diagram closely and figure out how your cam turns http://www.compcams.com/catalog/335.html this has little effect on oil pressure because the oil volume is low compared to the total amount moving through the engine but its one reason I always use a high volume oil pump. btw IT COSTS ABOUT $140 IF I REMEMBER CORRECTLY well worth the price because of the lower cam failure rates the extra oil flow promotes. yes both solid and hydraulic cams benefit, yes it slightly increases the oil falling on the spinning rotating assembly but thats what a milodon style windage screen is designed to handle by quickly returning that oil to the sump. now if you think about it drilling a small hole in the lifter base to feed oil to the contact areas is also a good idea (they already make those)your referring to both crower and comp cams lifters(I use both in addition to the groves)look, under lifters pg 107 http://www.crower.com/misc/m_cat.shtml now some people say grinding a 3 thousands flat spot on the lower lifter circumference helps,true but that groove idea helps during about 1/4 of the lifters rotation, but since the lifter spins in its bore about 270 degrees of the lifters spin adds oil flow the crank must handle as windage yet throws little or no oil on the lobe surface the groove ALWAYS sprays oil directly on the lobes contact point, the lifters with the lazer bored oil feed hole are a great idea that works but only flow a small amount of oil and can get plugged up where the lifter groove tends to self clean due to the lifters constant movement Dave.... HybridZ The Home of High Performance Datsuns http://www.hybridz.org When Stock Don't Cut It http://www.linfoot.net Home of The LSD Brace