Ball bearing turbos

[sunsetR33]

Hi all.

Been a while but things are moving along.
I just have something that I am wondering about. Since I will use OEM turbo oil pumbing, I got myself a new bolt, the one that goes into the engine block oil feed.
As I recall (and see visually) this bolt comes restricted with I think a 1.7mm hole? Not quite sure but it was something around that size.
The turbos have 1mm restrictor bolts installed, as necessary due to ball bearings and my higher oil pressures.

Can I now just use that OEM bolt with the 1.7mm hole in for the engine block or will this actually be too much oil flow restriction and I have to drill it out first?
In my head it would make sense for the bolt to be at least 2mm wide as both turbos take "1mm of oil flow". Do let me know if my logic is flawed here, I just want to make sure I don't kill my turbo bearings with too little oil. Don't know if I can trust the saying I read somewhere that ball bearing turbos essentially only need an oil mist

Edited July 10 by sunsetR33
typo

[GTSBoy]

The cross sectional area of a circular hole scales with the square of diameter. So a 2mm diameter hole is 4x the area of a 1mm hole. Not double.

The 1.7mm hole is nearly 3x the area of a 1mm hole.

You do not need restrictors at both ends of the oil supply line. If you have new, additional restrictors at the turbo end, that you did not have before, then you do not need a restrictor at the inlet end.

[sunsetR33]

On 10/07/2025 at 11:19 PM, GTSBoy said:

The cross sectional area of a circular hole scales with the square of diameter. So a 2mm diameter hole is 4x the area of a 1mm hole. Not double.

The 1.7mm hole is nearly 3x the area of a 1mm hole.

You do not need restrictors at both ends of the oil supply line. If you have new, additional restrictors at the turbo end, that you did not have before, then you do not need a restrictor at the inlet end.

I didn't think about how a circle works before, dumb. 
Before, I had .9mm restrictor bolts but I can't use these cause they were shorter aluminium bolts that just tear off their threads when tightening since the OEM lines are thicker than the shitty braided one that was installed previously. Now I use longer 1mm stainless steel restrictor bolts.
I think the difference will not affect the health of the turbos, but I guess I'll have to drill out the main feed bolt as I agree multiple restrictions sound dodgy. The one that was installed with the braided line was just too short, but completely without a restrictive hole.

Edited July 12 by sunsetR33