This fitting is manufactured exclusively for BenzForce. Made from stainless steel and restricted to 2mm. This will fit the T3 Holset turbos we sell.
**Our calculations came to a 1.92mm orifice to achieve 72PSI at the turbo on an engine producing 7 bar of oil pressure. We elected to go up to 2mm. **
PROBLEM/ISSUE:
The T3 Holset series of turbos need a continuous operating pressure lower than 72 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.
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:
- Friction losses due to flow through a pipe with surface roughness
- 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:
- 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.
- 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).
RESTRICTOR CALCULATION
- Inputs:
- The maximum pressure for the turbo.
- The engine pressure (to get 𝛥P).
- The oil density.
- The geometric shape of the restrictor (to get KL).
- The engine oil flow rate (6 L/min)
- Outputs:
- The oil velocity through the restrictor.
- The cross-sectional area of the hole / The hole diameter.
Calculated values:
| Inputs |
Value |
Unit |
| The engine Lube oil pressure |
7 |
bar |
| Engine oil density (15W40) at 90 degrees Celcius |
835.2 |
kg/m3
|
| Turbo Oil pressure needed |
72 |
PSI |
| Engine oil flow rate to the restrictor |
6 |
L/min |
| Local losses coefficient (KL) |
0.41 |
|
| Pressure difference needed across the restrictor |
203578.8206 |
pascal |
| Local losses head loss (HL) |
24.84695086 |
m |
| Oil velocity through the restrictor |
34.48213308 |
m/s |
| Hole area |
2.90005E-06 |
m2 |
| Hole diameter |
1.92157791 |
mm |
CALCULATION STEPS TO CHECK THE CONDITIONS OF 3 BAR ENGINES:
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):
| Inputs |
Value |
Unit |
| The engine Lube oil pressure |
3 |
bar |
| Engine oil density (15W40) at 90 degrees Celcius |
835.2 |
kg/m3
|
| Engine oil flow rate to the restrictor |
3 |
L/min |
| Local losses coefficient (KL) |
0.41 |
|
| Restrictor hole diameter |
1.92157791 |
mm |
| Oil velocity through the restrictor |
17.24106654 |
m/s |
| Hole area |
2.90005E-06 |
m2 |
| pressure difference needed across the restrictor |
50894.70515 |
pascal |
| Input Oil pressure to the turbo |
36.12973375 |
PSI |
Due Diligence:
This restrictor size was selected based on maximum pressure from the Mercedes om617 and the flow and pressure requirements of the Holset T3 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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