The factory oil cooler has nothing to do with pressure spikes. It is a total loss cooler that bypasses oil from the pump to the pan through a cooler to control oil temperature. There is a pressure valve in the tree that only allows oil flow through the cooler when there is sufficient pressure IE when the engine is above idle. The restrictor is in the oil cooler line to control the volume of flow through the cooler. If the cooler circuit was open at idle, you wouldn't have much oil pressure. That whole system was designed to adequately control oil temp on a stock engine, not really useful to those of us who are producing a lot more power than stock. Personally I prefer to have higher than stock oil pressure at high rpm with the VG due to its crap crank oiling design. In my opinion, if you go full flow cooling, the factory setup needs to totally be removed.
