What is the best, Turbo or Supercharger?

Why more power with boost?

So why will the engine make more power with boost(Compressed air)? It is not the fact that there is more air than the engine makes more power. Being able to burn more fuel, that is the thing that gives you more power. More power equals more fuel burnt. Now some people will ask “If you set your engine running richer(more fuel) that is also burning more fuel”. Well, you need to have the mixing ratio right to get more energy out of the flame.

The most efficient air to fuel ratio is 14.7 air parts to 1 fuel part. This ratio will give you the best fuel consumption and cleanest combustion. This is not a fuel ratio that you can run under power. It does show you that by just increasing the fuel will not increase your power from the standard.

Supercharging

Supercharging is one of the oldest forms of forced induction. The first roots-style supercharger was brought out between 1848 and 1849. As you can see superchargers as come a long way. Most supercharger applications only give low boost levels. Most of the time it will be boost levels below 1 bar boost (14.5psi). The problem with supercharges is that they are driven off the crank of the engine. This means they use the power that is produced by the engine to generate the boost. With this boost, it makes more power.

Fuel consumption

So what does this mean, it means the amount of fuel used to create the shaft power of the engine is higher. If you take a naturally aspirated engine that makes 200Hp in the flywheel and take a smaller supercharged engine that also makes 200Hp on the flywheel the supercharged engine will use more fuel. The reason for that is the supercharged engine actually makes more than 200Hp but the rest of the power is consumed by the supercharger.

How much power can a supercharger consume?

To give you an idea of how much power a supercharger can consume on a very high-performance engine look at the top fuel dragster. A stock Dodge Hemi V8 cannot produce enough power to drive the supercharger for the dragster. You can make higher power levels with a supercharger but will give fuel economy up to do so.

Engine internals

On the upside, you will get boost from almost idle to redline. The boost will start low and climb as the revs go up, giving you a smooth power gain that is not so violent on the components. Going over certain boost levels you will still need to look at upgrading rods and piston and fitting some kind of boost cooling.

Boost cooling is needed a compressing air heats up the air and no engine like hot air. The hotter the air the more engines will be prone to knock.

The amount of boost that a stock engine can take differs from engine model to engine model.

Supercharger types

These days you get a lot of different makes and types of supercharges. In the end it comes down to the same thing they all use engine power to create boost. The amount of power they consume may vary but consuming power is consuming power.

Turbo Chargers

Turbochargers have also been around a long time but have only taken off a few years ago on a petrol passenger car. Turbos have been around since 1915.

What is nice about a turbocharger is it does not use engine power to drive it. A turbo is driven off the energy that leaves the engine via the exhaust gas. This is energy normally wasted.

Where the issue comes in with turbos is the size of the turbo. At low revs the volume of gas (energy) leaving the engine is low. This means you need a small turbo to get a usable power and torque curve for the engine. This is the reason why most OEM turbos are small in production cars.

With OEM turbos even with aftermarket software on cars, you will see the max torque is low in the RPM range and rapidly drops off to redline. If you look at the boost curve you will also see a drop in the boost from max torque to redline. This is because the turbo’s efficiency drops off. The turbo just can’t cope with the high volume of gas and starts to choke the engine.

On OEM cars this isn’t an issue because how much time do you really spend full throttle at high revs?

So what will happen if you do fit a big turbo?

Fitting a big turbo will give you the ability to run higher boost making more top-end power but at a cost, the position at which the turbo will start to generate usable boost will be higher up in the RPM range. This is known as turbo lag.

You can fit a bigger turbo but fitting the biggest you can find is not the right way. What you need to look at is what amount of power you want to make and then choose a turbo accordingly. You may need to lower the max power if you find the spool starting point is too high for your application.

Maximum power isn’t always the way to go, getting a usable torque curve is a lot better. There is a saying “Horsepower sells cars but Torque wins races”. If you can get a turbo setup that gives you good torque and gives you great horsepower, well that is the way to go.

Fuel consumption

The fuel consumption on turbo cars is usually very good. The power the engine makes is what goes to the gearbox. The fuel consumption on a turbo car is more related to how far the gas pedal gets pushed down. Like I said earlier power equals the amount of fuel you can burn at a given time.

You can have an engine that may be lighter on gas off boost that the same engine without a turbo. Just because the turbo is already feeding the engine with air although it is not on boost yet. With the air being fed to the engine it helps to get the burnt gas out of the cylinder giving you a cleaner mixture for combustion. On naturally aspirated cars you do get a bit of exhaust gas recalculation. This means there is exhaust gas that stays behind and gets mixed into the new combustion mix. This lowers the engine power by a bit.