I know diddly squat about turbos or superchargers but can you not adjust, (lower) the boost from the charger?
GKD Superchargers
- Thread starter Faheem
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- Dec 8, 2011
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The objective in super/turbocharging is to increase the "effective" capacity of the engine.
A 3.0 litre engine is more powerful than a 2.0 litre engine because it can burn 50% more fuel at the same RPM. It does this by "sucking" in 50% more air.
But a 3.0 litre engine is bigger and heavier than a 2.0 litre engine.
In an ideal world (with no energy losses), if we can squeeze 50% more air into the 2.0 litre engine, we can get the same power as a 3.0 litre engine, but without the weight / size penalties.
You can use a supercharger or a turbocharger to squeeze the extra air into the engine.
The extra air is squeezed by the piston into the combustion chamber. There will be 50% more molecules of air in the combustion chamber than the engine was designed for. The pressure will be 50% higher.
Assuming that the compression ratio of the 2.0 litre engine is 10:1, the total volume of the combustion chambers is 222cc.
Keeping the total combustion chamber volume the same, but compressing 3.0 litres will give a compression ratio of 14.5:1.
The maximum CR is around 11.5:1.
The only way to reduce the CR is to make the combustion chamber bigger. This will reduce the nominal CR (based on a 2.0 litre engine).
To keep the CR below 11.5:1, the total combustion chamber volume would need to be below 285cc
The nominal CR of the supercharged 2.0 litre engine would be 8:1
I understand the maths, but can't you control the amount of air going into the combustion chamber from the turbo or supercharger. Is there no way to slow/reduce the airflow rate? Is the charger on a direct drive from the crankshaft?
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That is what the wastegate on a turbocharger does. I guess that there is a similar gate on a supercharger.
The pressure of the pump will increase as the engine speed (supercharger) or exhaust speed (turbocharger).
A simple pressure valve wastegate will just allow a certain maximum pressure to go into the engine. The excess is usually dumped into the exhaust.
A more complicated wastegate will allow the optimised pressure to go into the engine.
Yes, a supercharger is powered from the crankshaft.
I have an Eaton M21 laying around somewhere. It has an internal bypass controlled by an actuator on the side. It diverts some of the outlet air back to the inlet side to control pressure. The air is recirculated since it is already passed through the air filter and MAF sensor. If it was just wasted it would completely throw the air fuel ratios out the window.
Why doesn't the extra air make the mixture too lean?
The MAF is measuring engine air before anything else and the ECU adds air accordingly. If you wasted part of this air then the ECU would be adding fuel at the wrong rate.
The internal circulation on the Eaton supercharger is very simple. It is just a little flap like the one in a carb that allows the boosted air to go back to the inlet side of the supercharger.
The internal circulation on the Eaton supercharger is very simple. It is just a little flap like the one in a carb that allows the boosted air to go back to the inlet side of the supercharger.
