1/4" NPT to 4AN Turbo Feed Fitting - Restricted 1.8mm - BorgWarner

This fitting is manufactured exclusively for BenzForce.  Made from stainless steel and restricted to 1.8mm.  This will fit the BorgWarner turbos we sell.

PROBLEM/ISSUE:

We had one of our awesome customers install a new BW s362 on a newly rebuilt Mercedes om606 (great oil pressure).  After a couple of test runs, the turbo started to leak oil.  After contacting our BW distributor rep, we were told that if high oil pressure was expected to use an oil pressure regulator.  They would NOT disclose a maximum oil pressure as Holset does nor would they warranty the brand new turbo!

The oil pressure regulator they referred us to was the 40 PSI Turbosmart model which we sell but 99% of the customers will not run it, therefore we used our internal regulator calculator to get the correct size opening for this fitting.

WHAT IS THE RESTRICTOR?

This is a mechanical part used to reduce the oil pressure before entering the turbo, in our case we need to reduce the pressure from 105 PSI to 50 PSI.  The restrictor applies the law of hydraulic losses (Bernoulli equation) to make pressure drop when the oil passes through it.

WHAT DO WE MEAN BY HYDRAULIC LOSSES?

Hydraulic losses are due to two main factors:

1. Friction losses due to flow through a pipe with surface roughness
2. Local losses due to sudden change of pipe area or flow direction.

The restrictor is affected by the local losses as it has a hole with a small diameter, which means a sudden change in the area, and then pressure drops across it.

Note: we can neglect the friction losses as the hole length is not big enough to make a pressure difference and quality machining should limit its impact

FORMULA FOR THE CALCULATION:

1. Frictional losses (major losses):
   

   This is the loss due to the oil friction inside the pipe and it depends on the flow speed and the pipe material, but we will not work on it as we need to see the effect of the restrictor only.  As explained above, we will ignore this.

2. Local losses (minor losses):
   

   This is the pressure drop across the fitting (restrictor) and it depends on the shape and area ratio between the pipe and the connection.

   

   h_L ……………………………. Local head losses (m).
   K_L ...…………………………. Local losses dimensionless coefficient.
   V ……………………………. Flow speed through the restrictor (m/s).
   𝛒  ……………………………. Oil density at 90^oC (15w40) (835.2 kg/m³).
   g ……………………………. Gravitational acceleration (9.81 m/s²).
   𝛥P …………………………. pressure drop across the restrictor (bar).

RESTRICTOR CALCULATION

1. Inputs:
1. The maximum pressure for the turbo.
2. The engine pressure (to get 𝛥P).
3. The oil density.
4. The geometric shape of the restrictor (to get KL).
5. The engine oil flow rate (6 L/min)
2. Outputs:
• The oil velocity through the restrictor.
• The cross-sectional area of the hole / The hole diameter.
3. Calculated values:

Due Diligence:

This restrictor size was selected based on pressure seen in the om606 under constant load.  Make sure your engine has ample pressure at idle as well.  The downside to restrictors is that it will ALWAYS be restricting so restricting weak engine pressure can put your turbo at risk on the low-pressure side.