We thought we would share some information regarding oil restrictor bolts to help clarify our views on them…

Restricting the oil supply to Turbos is not a new idea or fad; turbo conversion companies have been doing this as instructed by Garret since the early 1990s.

It is true that a number of Vauxhalls have suffered from this smoking due to oil washing past the turbo oil seals.

It is true that changing the oil to a heavier weight of oil helps with this by allowing the oil to drain quicker as it is more resistant to any frothing or foaming (call it what you will) in the turbo core.

It is true that journal bearing turbos do need a very good supply of oil.

It is also true that too much oil can and will swamp the seals and in this case… the use of careful oil restriction will help; Vauxhall has also done this in production of the later K04 units.

Now we believe the original Vauxhall KO4 oil restrictor bolt was developed by Ian Percival AKA Percy (vxronline) before GM Modified the core. Ian is very knowledgeable by all accounts. He carefully calculated then made a restrictor as part of the bolt so it can be retro fitted to cure this lack of oil restriction in very early units. Our reluctance to recommend oil restrictor bolts comes not from what Ian did but from the fact that many other individuals and “ebayers” alike have jumped on the oil restrictor bolt bandwagon and produced some very inferior imitations. To this end we have been handed a number to fit, made of some very dubious soft material and we have seen some with a pressed in restrictor plug complete with a loose and rattling swarf built in, which would have killed a new turbo almost immediately! Plus we have removed many others that have been over restricted.

We hope people can now see why a number of suppliers, turbo manufactures and re-manufacturers are reluctant to recommend them. To be clear it’s not the principle or the original execution that is the problem but the others that have come along after, which when fitted can damage what was a perfectly good turbo unit, leaving the supplier / manufacture liable.

The later VXR turbochargers already have the oil flow control built into the oil gallery in the turbo itself, as is evident from the picture below centre:

If a turbocharger is smoking due to worn turbo oil seals, then the turbo already has a problem. A restrictor bolt will not repair worn turbo oil seals.