Maximum Boost, by Corky Bell Chapter 4 Oil Flow and pressure; Too much oil pressure can create problems with turbos. It is possible to force oil past oil seals that are in perfect condition (note Ive been through two new turbos under 50 miles with leaking oil from the tail pipe) if oil pressure exceeds 65 to 70 psi at the turbo. Problems of oil pressure over powering the seal are evident in frequent if not quite constant smoking problems. Anytime oil pressure exceeds the 65-70 psi and smoking persist, a restrictor or by pass should be installed prior to any other changes." Correct me if I am mistaken for I dont have it in front of me, but a 1980 308gtsi owners manual says something like @ 210F, 6000 rpm oil pressure should be form 70-75 psi. If you have read any of my past posts you know I am using low mounted turbo. I believe now I should use oil by pass with a restrictor to reduce oil volume and pressure at the turbo. Does anyone know where to shop for oil restrictors? I am using -4 oil supply line. Can an oil restrictor be made by partially impeding an Al connecting fitting? Also I don't want to starve my turbo for oil so I wish to confirm oil flow and pressure at the turbo, any ideas how to perform this?
Corky specifies 65-70psi at the turbo. Have you considered the headloss before the turbo? That could be 5psi, which would bring the pressure specified in the manual in to the proper range. Also keep in mind that Corky is speaking generally, and it is very possible that a 5psi increase for some turbos is fine.
"restrictor to reduce oil volume and pressure at the turbo" Just remember oil "volume" and "pressure" are to different things.
Corky is a pal of mine. Give him a call and ask him. He's very approachable. Num is available on his site at bellengineering.net Philip
Do not restrict in any way oil passage to the turbo. That is the worst thing you can make to the durability of the turbo because it would increase delay in feeding the turbo at start and specifically at cold conditions.Furthemore a restricted oil feeding line would be more keen to become occluded by carbon deposits ( temperature related ).The oil flow will adjust by itself unrelated to pressure mainly due to the restriction created by the actual clearances between bearings and shaft. You may instead make sure the oil temperature is always not too high and ( very important ) there is no oil starvation after the turbo; oil must always flow from turbo to oil pan without any obstacle or obstruction, otherways it will submerge the bearing housing and overflow/leak both from compressor and turbine side ( smoke in the exhausts ). Furthemore temperature will increase, carbon will occasionally build up till failure of the bearing system. Remember oil after the turbo is emulsioned with air and looks like mayonnaise or mustard, flowing badly in a small or bent pipe.
