M10x1.25 to 4AN Turbo Feed Fitting - Restricted 1.68mm - HE200, HE221
M10x1.25 to 4AN Turbo Feed Fitting - Restricted 1.68mm - HE200, HE221
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M10x1.25 to 4AN Turbo Feed Fitting - Restricted 1.68mm - HE200, HE221

This fitting is manufactured exclusively for BenzForce.  Made from stainless steel and restricted to 1.68mm.  This...

M10x1.25 to 4AN Turbo Feed Fitting - Restricted 1.68mm - HE200, HE221

This fitting is manufactured exclusively for BenzForce.  Made from stainless steel and restricted to 1.68mm.  This will fit the HE200 and HE221 Holset turbos we sell.


    The HE200 series Holset turbos need a continuous operating pressure lower than 50 PSI, but the engine's oil pump can generate as much as 105 PSI, which will damage the turbo sealing if we didn’t reduce it, and this is what a restrictor will do.


      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.


      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


      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.

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


      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.
        1. Calculated values:
        2.  Turbo max pressure (PSI) 


          Restrictor hole diameter (mm)




          If we reverse all our calculations, and we get the pressure drop using the hole diameter above we get the values in the table below (we assume that the flow rate become 3 L/min): 

          Turbo max pressure (PSI)


          Actual pressure (psi) as engine pressure become (3bar) 30.63

          Due Diligence:

          This restrictor size was selected based on maximum pressure from the Mercedes om617 and the flow and pressure requirements of the Holset HE series.  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.


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