Intake manifolds and organ pipes
Jul 04 2015
Rohan Chaturvedi

A lot of scientific research is going in about intake manifold design and tuning. No matter how much simple it may look, it takes a lot of understanding and knowledge to make one.

For the uninitiated, an intake manifold acts like the respiratory system of your car, allowing air to flow to the engine cylinders, where combustion occurs to release energy.

Intake manifold and lung
Different but serving the same function

Intake tuning is crucial for an engine to be efficient. Though the process might seem like a daunting task at first, thinking of an intake manifold on the lines of an Organ Pipe seems to make this a lot easier!

Organ pipe resonance

Yes. The organ pipe, which is the root of studies on standing waves and resonance. Frequencies at which the response is a relative maximum are the resonant frequencies. In other words, the condition when the system’s natural frequency matches the external frequency is resonance.

The intake manifold tuning should be in accordance with the intake and exhaust valves’ opening/closing timings. Every intake system designed will possess a resonant frequency.

Parts of an intake manifold
Parts of an intake manifold

We want to tune the manifold so that we can gain maximum power from the engine (Duh!). This means that we want to push maximum amount of air-fuel mixture into the engine’s cylinders.

So let’s think... When air enters into the intake manifold, a pressure difference is created as the air flows from the intake to the cylinders. To make this simpler to analyze, we think of this pressure difference as a 'pressure wave'.

pressure wave

If we can come up with a design (runners of a different length?) such that the pressure wave produced in the runners enters the combustion chamber (or strikes the air-fuel mixing junction) at the time when the intake valve is just about to open, it would mean that we’ll have more air per combustion cycle, which increases the power output for the given volume of fuel burnt (a lean mixture).

The intake valve closes after some time and consequently the pressure wave (now hitting a closed valve) will be reflected towards the plenum forcing to another pressure wave to move into another runner where the intake valve is open. For this to work effectively, we need to synchronize the timings when the pressure wave maxima hits the intake valve with the timings when the intake valve opens and closes.

So by synchronising the frequency at which air enters the engine with that of the closing/opening of the intake valve, we’re able to increase the air drawn into the engine.

That’s intake tuning. Similarly this concept can be applied for ejection of maximum volume of exhaust gases during the exhaust stroke.

Leave us a comment if you thought the comparison was interesting!

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