Mr Q 7th May 2019

So in our first installment of Let’s Get Technical, we discussed the 4-stroke cycle and how exactly that noisy lump in the nose (or tail in some cases) of your car actually works. So today we’re going to take a brief look at how you actually control it! (If you haven’t read that first installment, please do so HERE, as the rest will make much more sense if you understand the basics of how an engine works.)

Some engines are fitted with Individual Throttle Bodies, or ITB’s. This means you have one throttle body for each cylinder. This pictures shows ITB’s for a V8 Engine.

Obviously, if you want to make the car go faster, you step on the accelerator pedal and whoosh! Off you go. But what actually happens to make all that possible? The popular narrative seems to be that stepping on the loud pedal, pumps more petrol into the engine, making a bigger bang and therefore more power. Now, although that is “somewhat” true, it’s not actually as simple as that – in fact many people would be extremely surprised to learn that the throttle pedal, actually has NO direct control over how much fuel goes into the engine.

For simplicity, we’ll look at a fuel injected engine today and handle carburetors another time.

A fuel injector has a connector at the back where it connects to the fuel rail, which supplies it with petrol under pressure. On the side there is an electrical connector through which the ECU triggers the injectors to fire.

In its simplest form, a fuel injector is kind of like a squirt gun for petrol. It sprays a fine mist of fuel into the intake, or in some cases, directly into the cylinder. They are controlled by a small computer, called the ECU, or Engine Control Unit (AKA Engine Management System). When your engine is running, the ECU takes readings from sensors in the engine, and the exhaust of the car to determine how much fuel to inject, and it tells the injectors how much fuel to inject by telling them how long to operate for (we’re talking a few milliseconds here).

What this means is that the driver, technically has NO CONTROL over how much fuel is injected into the engine, it is all determined by the ECU, based on information gathered from its sensors. What the driver DOES control is the airflow into the engine.

This is what your car’s throttle probably looks like. The Throttle cable attaches to the cam on the left of this shot, and when pulled, rotates the valve blade to open the throttle and allow more air through.

You see your throttle pedal is connected to a big butterfly valve inside the air intake, and all it actually controls is how much air is allowed into the engine. The more air enters the engine, the more fuel the ECU will allow the injectors to squirt and the more power the engine will ultimately produce.

It looks a lot more complicated than it really is, but this diagram shows how the ECU controls the engine’s various functions to make it run and control the amount of fuel going into the engine.

And that, in a nutshell, is how we control the power output of our engines! Post your questions in the comments, or let us know what part of your car you would like to understand better – we’ll do the research and write it up!

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