Forced Induction : Boost Secrets Unveiled
Forced induction compresses air molecules to fit more air inside a given Space/cylinder size. The way a combustion engine makes power is by burning an air-fuel mixture. To make more power you need to increase the amount of air intake and fuel mixture. There is a perfect ratio for Air to fuel mixture where combustion is most efficient. This ratio is 14.7:1 and is called the stoichiometric ratio. 14.7 parts air to 1 part fuel. Now you can always spray more fuel into the cylinder but what about air? Here is where forced induction comes into play. Forced induction allows you to fit more dense air in at a higher rate of flow for increased power. This is what we call boost. In this article, let’s better understand the various ways that air can be compressed for more power!
What you will learn:
Turbocharging vs Supercharging
Two primary ways of forced induction are using a turbocharger or a supercharger. Both of these systems compress air to feed the air intake to your engine’s cylinder. However, they both do the same job differently. Your engine’s exhaust drives a turbocharger whereas a supercharger is belt driven. To explain the difference we need to look at two parts of an engine namely exhaust and crankshaft.
Forced Induction by exhaust
In a combustion engine after combustion takes place the exhaust from that combustion gets pushed out the cylinder into the exhaust manifold into the rest of the exhaust system which then exists the vehicle. Now there is energy in movement. In a non-turbocharged engine, (naturally aspirated) that exhaust flow is a moment, that is wasted. In a turbocharged engine that exhaust flow is utilised with a mechanism called a turbo. The exhaust enters this mechanism on what is called the hot side, causing rotational force on a turbine. This turbine is connected to another on the flip side (cold side) that spins also. The cold side turbine sucks in the air into the unit designed to condense the air and shoots it towards an intercooler. Condensed air gets hot and cooler air is more oxygen-rich, which is great for combustion. After the intercooler cools down the air, it travels to the intake manifold into the cylinders, thus boosting the air pressure of the engine. Once more air gets taken in more fuel gets added and more power is born!
Forced Induction by crankshaft
A supercharger is a belt-driven mechanism. It uses the rotational force created by an engine from the crankshaft. Usually attached to the top of the engine it is connected by a pulley system driven by a belt. This robs some rotation energy created by the engine, however, the supercharger has to be able to account for that. Once the crankshaft is spinning the supercharged works at the same time. The pulley system spins, which is connected to a unit with specifically shaped lobed rotors that spins and sucks in air into the intake for the cylinders.
Types of Superchargers
There are a few types of supercharger designs out there that get the job done in different ways. Here are some supercharger designs you might have already heard of:
Centrifugal
This design is very similar to a turbocharger design. The difference is there is no hot side because it’s belt-driven. The hot side is replaced but a belt and pulley system with gears that spin the turbine connected, sucking in air and compressing it for the intake. The thermal capacity is generally very good on this type of supercharger as well. Your engine power also increases exponentially the higher you rev, so this setup makes a full boost at high RPMs.
Roots
Roots are your traditionally designed superchargers that have two opposing lobed rotors sucking in the air and then exiting through the exit port. It essentially blows air into the intake. This is why some superchargers are referred to as blowers. Your power is instant and more consistent across your power curve.
Twin screw
Twin screw superchargers have specifically shaped opposing rotors that suck and compress air as opposed to a roots design. This setup also has instant power but can be more efficient in building boost consistently.
Electric superchargers
Electric superchargers use an electric motor powered by the engine to generate power. In this design, your boost isn’t dependent on the engine rpm. This “air compressor” is connected to a battery and with enough energy you can be in more control of your power curves. You can have more power in your low, mid, or high ranges depending on your preference. The electric motor will already have the turbine spooled and ready at your service.
Benefits of ProChargers
Pro-chargers tend to be a more compact design. As opposed to roots or twin screw design which takes up hood space because it sits on top of the engine, pro chargers do not. This compactness gives you more flexibility in the engine bay on where you can place this system.
prochargers also allow for higher boost pressures because of how it is designed. Although pro-chargers use intercoolers to cool the condensed air, their thermal capacity is pretty good, making it easier to get good-quality air for power.
Associated Technologies
In the process of compressing air things get hot, so in most forced induction engines an intercooler is often needed. This is basically a radiator for the turbocharged air. Once the air gets compressed from the turbocharger, ProCharger, or superchargers, before it gets to the intake and the cylinders, it passes through an intercooler. This system is a separator with slats and fines for air to pass through cooling down the air being compressed within. This system is called an “Air to Air” intercooler. There are also less popular methods like an air-to-water intercooler where the system uses water or coolant to cool down the compressed air.
Choosing Between Turbochargers and Superchargers
When it comes to choosing between these various forms of forced induction, it’s good to know their characteristics for your desired outcome. Knowing how turbochargers are set up to where it needs exhaust pressure to spool the turbos, turbo engines experience lag. This is because once the exhaust pressure is sufficient enough the turbo spins. After the turbo spins, it compresses the air which gets hot, then sends it on its way to the intercooler before it gets to the cylinders. This process takes time, so the time from when you press the accelerator pedal to when you feel the boost kick in isn’t aligned. Whereas a supercharger you feel in an instant because it is connected the the crankshaft. As the engine spins the supercharger spins. In this case, you have an accurate pedal simulation of power.
However, turbochargers are smart in the way that it is designed. Using otherwise wasted exhaust gases to create better quality air for combustion. The engine displacement doesn’t change, so you have the benefit of a smaller engine, which is great for gas mileage. They have the simulated power of a bigger engine with the benefits of a smaller engine. Although superchargers don’t have to deal with lag they do however have other complications when it comes to packaging. Superchargers often take up more hood space because of how it’s placed on top of the engine. Different designs will vary.
Prochargers on the other hand seem like a good mix between a supercharger and a turbocharger. Pro chargers share a similar design as turbochargers making them more compact and flexible in the engine bay. It also provides instant power that builds consistently across the rev range. All of these different characteristics can show you which direction to go in when choosing between the different variations of forced induction.
FAQs:
What are the differences between turbocharging and supercharging?
The main difference between turbocharging and supercharging is their power source. Although they both do the same job of forced induction they are powered differently. Turbochargers are powered by an engine’s exhaust output while superchargers are belt driven by the engine’s crankshaft through a system of pulleys. Other differences spawn from this main difference. Other differences like placement flexibility, like where they can be placed in an engine bay.
Can forced induction improve fuel efficiency?
In some instances, it can. The point of forced induction is to fit more air into an engine’s cylinder to make more power. However, to make more power your engine uses more fuel. Smaller engines usually use turbochargers to simulate the power of a bigger engine. That being said, it is still a smaller engine so once the turbos aren’t necessarily being used, it will still benefit from the lightweight and smaller engine characteristics with better gas mileage than a bigger engine.
How does forced induction affect engine performance?
Forced induction is the process of condensing air to fit more of it into the engine. With more air-fuel mixture fitted into an engine the more power an engine can make. With more power available the better your engine can perform under multiple scenarios.
What are the benefits of intercooling in forced induction systems?
In forced induction air is being compressed to pack more of it into a given cylinder size. The process of condensing air itself makes it hot. Cooler air is dense, it has more oxygen molecules which is better for combustion. Intercooler systems are designed to cool condensed air down for combustion. Intercoolers provide better quality air so your engine can make more power.
