I have a small diesel tractor that I added a turbo to. This is a very small engine, but the turbo is matched to it. The engine has a pressure lubrication system. To lubricate the turbo, I removed the oil pressure switch and installed a T fitting. I then ran a -3 line to the turbo with a -4 line draining it. I reinstalled the pressure switch right after the T. The turbo has a very small oiling hole, not much bigger than 1/16". The oil pressure switch is 1/8" mpt. The first time I ran the motor, it ran well, but the -4 drain line was too small. This caused oil to build in the turbo bearing so it blew past the seals. I switched to a -6 drain line and it solved the problem. Now however, the oil pressure light is coming on after the oil heats up. I installed a pressure gauge and found the motor was not putting out more than 10psi of pressure with the oil cold. From other people that have this tractor, I should be seeing 40-50psi. At this time, I don't have a oil pressure reading with out the turbo. I'll get that number shortly. When running, the engine sounds just fine. No dry bearing rattles or lifter clicks. Of course, this is a diesel engine so it's kinda hard to tell. I'm thinking the 1/8" port is having trouble actually building pressure in the line, not that there is a internal engine problem. When you guys add a pair of turbos or a external supercharger to a engine, how is it being lubricated? Does it just tap into the oil pressure sending port? Are these usually 1/4"? Have you ever seen a low pressure reading after adding the blower? If so, how did you solve it?

Cord, on my old boat that is exatly how mine was plumbed. It was a 460 ford with twin turbos. The return lines were at least 1/2"

Thanks Pay.