YOUR ENGINE'S VACUUM

Air is needed in the engine's cylinders to burn with fuel when the spark ignites. However, an air filter is necessary as we cannot have dirt in the engine as dirt would cause damage and clog up sensors. This filter cleans the air but results in a loss of air intake velocity, so much so that often air comes in later than the fuel feed that is increased by opening the throttle quickly (this results in momentary air pollution as much unburnt fuel exits the exhaust, and can be smelled even in modern cars on the move).

How does air get into the engine? The answer is that moving pistons fill and empty cylinders of air, and the flow causes a vacuum, and air must flow continually into that vacuum. By using a Surbo (air-Suction turbo) to aid the engine's vacuum externally and in series, this net vacuum can be deepened and torque spread and power increased.

Since the filter is connected to the air intake, and suction is required to overcome the filter loss (resistance of filter paper material and dirt trapped) to get air through, part of the engine's vacuum is used up is getting air through the filter. The rest of vacuum is needed to carry this cleaned air past the throttle into the cylinders. The Surbo can improve the air passage through the filter so a smaller throttle opening is reqd to get the air past the filter (therefore more of the engine's vacuum can be used to carry air past the throttle and into the cylinders).

Surbo between the filter and throttle: Surbo's inlet vacuum pulls air across the filter and its outlet pressure forces air through the throttle opening.

Surbo before filter: Surbo's inlet vacuum aids inflow of atmospheric air and its pressurized outlet forces air through the filter and the throttle.

Surbo's requirements: air-tight installation, resulting in max vacuum through the filter, and all air passes through and is processed by the Surbo.

Scenarios:
When all the vacuum is used up: throttle opened all the way (accelerator floored); engine speed cannot increase any more, gear must be changed (up/down):
Up: for example, at the rev limit, during a change up, the throttle is closed relatively for a lower rpm and higher gear ratio. When the throttle is closed, the manifold vacuum is increased again so air can be drawn in increasingly, so raising rpm again and thus vehicle speed. The Surbo enables the engine to get to higher rpms with the same throttle travel (observed red line by half throttle), so for any given rpm, the throttle is more closed so there is more spare vacuum to cart the air promptly to the cylinders, or to accelerate some more. A more-closed throttle due to Surbo usage also means less excess fuel is induced so preventing flat spots due to overfuelling. These improve the engine's torque spread over the rpm range.

Down: At the other extreme, when the gear used is too high for the vehicle speed, so that rpm is very low, and in order to induce more air, the throttle has to be opened more (so all vacuum is used up) and speed cannot increase. A lower gear must be selected, so that rpm goes up as the moving car pushes against a lower gear (vacuum increased) and air intake velocity increases, and the vehicle picks up speed. The Surbo, which gives better low rpm torque, allows the car to get to a lower speed on a given gear, as the throttle is more relatively closed so that the manifold vacuum is still sufficient to draw in air. There is less of a need to change the gear, indicating increased engine flexibility.

In general, when the accelerator is nearly floored, and most of the vacuum used up, the engine will slow down because there will not be enough vacuum to draw the air through the filter, or to carry any more air into the cylinders. ie, max engine speed is reached. Also, at extreme throttle openings, the fuel induced is the maximum, but air that goes in is curtailed due to the above reasons, and the resultant overfueling can have an extinguishing effect on the combustion. The increased air flow from the Surbo at any rpm mops up any excess fuel and burns it more completely. Therefore the surbo gives more power throughout the entire rpm range.