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Turbocharger vs Supercharger
Turbochargers vs Superchargers
Turbochargers and superchargers have both been around for many decades - cramming air into engines to squeeze out as much power as possible. The turbocharger vs supercharger debate has raged for just as long as they have existed. There are those who swear by one or the other, but in reality, both turbochargers and superchargers have their own strengths and weaknesses.

The Supercharger
Superchargers are compressors which use power from the engine to compress the intake air. In reality, turbochargers are superchargers which are driven by engine exhaust. Typically, however, when one refers to a supercharger, they mean all superchargers except turbochargers. There are three types of superchargers which are commonly used: the roots blower, centrifugal superchargers, and screw-type superchargers. Each of these superchargers are driven by a pulley system by the engine crankshaft, so the faster the engine speed, the faster the supercharger speed. The roots blower and screw-type superchargers typically operate up to 15,000 RPMS. The centrifugal supercharger can reach speeds exceeding 40,000 RPMS.

The Turbocharger
Turbochargers, however, are driven by the engine's exhaust gases. A turbocharger operates at maximum speeds often reaching 150,000 RPMS. Follow this link to find out more about how a turbo works.

The Comparison: Turbocharger vs Supercharger
Response. Superchargers afford the engine immediate response since the supercharger is always compressing intake air, provided that the engine is rotating. Although this initial boost is very small, it's growth is gradual with increased engine speed, resulting in a smooth increase in power. Turbochargers, on the other hand, suffer from what is refered to as turbo lag. Becuase of the inertia of the turbocharger rotating assembly, the turbo must "spool up" before it is able to compress air, so there is no power increase at low engine speeds, as the turbo impeller starts rotating. At WOT (wide-open throttle), there is usually a very sudden increase in turbo boost at a certain RPM range (typically near 3000 RPM). If you've ever driven a turbocharged vehicle, you probably know what this kick in the pants feels like. Turbochargers can also be sized so that faster response is acheived. For example, diesel engines use turbochargers which are small enough to spool by 1700-2000 RPMS. The trade-off is that maximum power can't be reached with such a small turbocharger.

Parasitic Power Loss. Becuase superchargers are driven by the crankshaft, they draw some of the power which the crankshaft would be producing to compress the intake air. This parasitic power loss can exceed 50 hp. Of course, the supercharger is more than making up for the power it uses by introducing additional air. Turbochargers, however, do not use any of the crankshaft's power in order to operate. Turbos are often described as exhaust restrictions, though. The argument is that the increased exhaust backpressure presented by the turbo also robs power from the crankshaft (since it is now harder to push the piston up to expell the exhaust gases. This argument, however, is overstated. Because the intake air is also under pressure (typically greater pressure until the maximum horsepower engine speed), it pushes the piston down. For the majority of the power band, these two forces cancel on another out. Because turbochargers do not use much of the power output of an engine, the highest power levels are possible when using a turbocharger rather than a suprecharger.

Heat Production. Cooler intake air is denser - which means more oxygen per unit volume. More oxygen means more power. Roots blowers are notorious for their heat production. This heat production is a result of inefficient compression of the intake charge. Turbochargers tend to operate at a much better efficiency than thest upes of superchargers. Centrifugal superchargers can be just as efficient as turbochargers, and offer the advantage of flexibility in placement. Turbochargers must be placed so that the exhaust flows through the turbo's turbine. This brings the hot exhuast pipes closer to the intake pipes - resulting in higher intake temperatures. A well designed centrifugal supercharger installation can reduce this heating, resulting in a cooler intake charge.

Reliability. People often say that superchargers are more reliable than turbochargers. Because turbochargers operate at such high temperatures and are oil lubricated, if they are not allowed to cool down before the engine is turned off, the oil can bake inside the turbocharger. This can result in shorter turbocharger life. However, with proper care and cool down, a turbocharger can last as long as an engine.

Boost Levels. For absolute maximum power applications on stout engines, turbochargers allow much higher boost levels than superchargers. In tractor pulling, to take the example to the extreme, up to three turbochargers are used in series to produce boost levels of up to nearly 200 psi!


Superchargers
Turbochargers Roots Blowers Twin-Screw Superchargers Centrifugal Superchargers
Response 3000 RPM Fast Very Fast 3000 RPM
Power Drain Very Low High High High
Heat Production Moderate Very High Moderate Moderate
Reliability Good Very Good Excellent Very Good
Boost Levels Very High Low Low Moderate
Manufacturers Garrett, Holset, KKK, Mitsubishi Eaton Whipple, Kenne Bell Vortec (Vortech), Paxton


Conclusion: Turbocharger or Supercharger?
You can see that it is difficult to say which is better. The main advantages to supercharging are low-end response (not the case with centrifugal types) and simplicity. The main advantages to turbocharging are efficiency and the realization of maximum power. It is up to the vehicle owner to decide which solution is best for him or her. If you're considering turbocharging your engine, please have a look at our additional technical articles, as well as our product, TurboCalculator, which will aid in the relatively complex task of selecting the proper turbocharger for your engine. We also sell turbos and accessories.


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One thing not mentioned in this article that has been brought up is noise. Superchargers have a whine due to the belt. Turbo Chargers will actually be more quiet than a stock system due to disrupting the exhaust flow. So unless you have a blow off valve, a turbo would be more stealth.

 

superchargers come with a bov

 

Let me restate, disregarding BOV, the turbo will be quieter than the super charger.

 

is it necessary to have a blow off valve for the turbo charger or is it ok without one?
does the valve let it cool down faster?

Quick Robin... TO THE BATMOBILE.

 

In my opinion a BOV is necessary for both a supercharger AND a turbo setup. It's really not good on the system to make the pressurized air find its own way to escape.

But keep in mind that unless you're building boost there's nothing to blow off. The BOV only makes the quick "pissshhhhh" noise if you've just let off the throttle (or shifted gears) after getting on it.

The exception to that, I guess, is the Vortech "bypass valve" that has an audible whistle even when you're not under boost.

--Steve

 

This isn't a funtion of Vortech's bypass valve but the fact that at low to mid part throttle applications the manifold/plenum still sees vacuum as not enough of the pressureized air in the intake pipes can seep past the throttle to match or exceed the airflow the motor is trying to pull in. Since the bypass valve works off the pressure differential in the manifold and the intake pipe, it opens as the supercharger is not reactive to loads like a turbo is. A supercharger running of the engine's 6000 RPM will flow just about as much air at closed or open throttle(the difference being that there is more resistance at closed throttle). If the bypass valve didn't stay open, the compressor would be experiencing surge and there would be an extreme amount of pressure in the intake pipes.

I'm not sure it is absolutely necessary to run a BOV on a supercharger as I am not sure if the supercharger's bearings are more suited to handle higher thrust loads(associated with compressor surge). It would probably be a good idea anyways, but turbos need BOV's to prevent surge. Especially with standard sleeve bearings which are not the most durable when it comes to handling thrust loads.