Does anyone know what size dia. is needed to restrict the oil line
so oil pressure does not drop to much.Have seen it somewhere but can't remember,and where is the best place to locate in the system.

Steve i have a frantz oil filter and the orifice size in that is about 3MM.

Thanks Shane,I thought i read it was 1/8" but was not sure.Where about is it in the system , was on the inlet to the filter or the return into the engine.? Thanks Steve

On the inlet

Have found it,fram filters have a restricted hole in the center tube of the filter,to avoid a large drop in oil pressure.