911, 911 Porsche, 993TT, 997TT, engine builder, engine rebuild, Forced induction, supercharger, turbo, turbo Porsche, Uncategorized

To turbo, or supercharge that is the question

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Which came first the chicken or the egg? Which is better the Turbocharger or the Supercharger? They both are very similar. The mechanics of these systems is where the difference is found. They both offer their own advantages and disadvantages but it depends on you, the driver.

So what’s the difference?

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The Turbo-charger uses exhaust gases to drive it and the supercharger uses a belt that runs off the crank shaft to drive it. They both increase the speed of a car significantly. I spent many months researching this topic. The similarities and differences are stunning. These performance parts force the novice mechanic to graduate to the next level of planning and paying for that matter. These systems are not cheap. But for those who enjoy racing down the ¼ mile drag strip at top speed. This may be for you.

Similarities

Both superchargers and turbochargers are forced induction systems and thus have the same objective – to compress air and force more air into the engine’s combustion chamber. The benefit of forcing more air into the combustion chambers is that it allows your engine to burn more fuel per power stroke. Using an internal combustion engine, burning more fuel means that you convert more fuel into energy and power. For this reason, supercharged and turbocharged engines normally produce 40% to 100%%2B more power than normally aspirated engines.

How They Work

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A supercharger is mounted to the engine and is driven by a pulley that is inline with the crank (or accessory) belt. Thus, the supercharger robs horsepower from the engine in order to multiply horsepower, giving it back to the engine. Kind of in a circular fashion. (For example, I give you 5 dollars and you give me back 25 dollars) this is how the power multiplies within the supercharger. Air is drawn into the supercharger and compressed by either an impeller (centrifugal-style supercharger), twin rotating screws (screw-type supercharger), or counter-rotating rotors (roots-type supercharger). The air is then discharged into the engine’s intake. Faster crank speed (more engine rpm) spins the supercharger faster and allows the supercharger to produce more boost (normally 6 to 9 psi for a street vehicle). Typical peak operating speeds for a supercharger are around 15,000 rpm (screw-type and roots style superchargers) and 40,000 rpm (centrifugal-style superchargers). Thus a supercharger is easier to tune because the speed of the supercharger directly relates to the speed of the crankshaft.A turbocharger operates in much the same way as a centrifugal (internal impeller) supercharger, except it is not driven by pulleys and belts attached to the engine’s crank. A turbo is instead driven by exhaust gasses that have been expelled by the engine and are traveling through the exhaust manifold. The exhaust gas flows through one half of the turbocharger’s turbine, which drives the impeller that compresses the air. Typical operating speeds of a turbocharger are between 70,000 and 160,000 rpm. 

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Let’s look at the 2 side by sideTurbocharger vs. Supercharger Cost

The cost of supercharger and a turbocharger system is basically the same. However, if you are deciding which to use. First, determine your mechanical ability and the accessibility of special pipe benders and welders. If you don’t have access to these tools then a supercharger will be more reasonable because you will likely be able to do all of the work saving on the cost of labor. Turbochargers require special pipe benders because of the extensive exhaust set up.

Lag vs NO Lag

The supercharger can very easily boast that the biggest advantage it has over the turbo charger is NO LAG. Turbochargers are driven by exhaust gas. The turbocharger’s turbine spools up first before it even begins to turn the compressor’s impeller. The result is what we call “lag time”. This is the time needed for the turbine to reach its full throttle from an intermediate rotational speed state. During this lag time, the turbocharger is creating little to no boost, which means little to no power gains during this time. It is common knowledge that smaller turbochargers spool up quicker, which reduces some of the lag. Turbochargers use what is called a “waste-gate”. The waste-gate is a valve that allows exhaust to bypass the turbine blades. The waste-gate senses boost pressure, if it gets too high, it could be an indicator that the turbine is spinning too quickly. In this situation the waste-gate avoids some of the exhaust around the turbine blades, allowing the blades to slow. Therefore, a waste-gate allows a smaller turbocharger to eliminate some of the lag time while preventing it from spinning too quickly at high engine speeds. A waste-gate is a crucial part of the Turbocharger.On the other hand, a Supercharger is connected directly to the crank, so there is “NO LAG”. Superchargers are able to produce boost at a very low revolutions per minute (RPM).

Which is more economical?

Some say the turbocharger is more economical. It all depends on your level of mechanical ability and your ability to access good quality welders and pipe benders. Some feel that the turbocharger is more economical to operate because it is driven primarily by potential energy in the exhaust gasses. The gas would normally be lost out of your exhaust pipes. However, the supercharger draws power from the crank, which is normally used to turn the wheels. One positive, is that the turbocharger’s impeller is powered only under boost conditions, so there is less internal drag when the impeller is not spinning. The turbocharger does create additional exhaust backpressure and exhaust flow interruption which can be viewed as less than positive. If you are looking to save money and have the tools handy that you will need to complete this installation successfully then this may be for you

.Very Hot vs Not so Hot

The turbocharger is mounted to the exhaust manifold which is extremely hot. Turbocharger boost may experience additional heating through the turbocharger’s hot casing. Hot air expands which is the exact opposite of what happens in a turbocharger or supercharger, therefore an intercooler becomes necessary on almost all turbocharged applications to cool the air charge before it is released into the engine. Remember, when we discussed the special pipe benders. This is where the complexity of the installation can be a challenge. A centrifugal supercharger on the other hand creates a cooler air discharge, so an intercooler is often not necessary at boost levels below 10psi. However, some superchargers (especially roots-type superchargers) create hotter discharge temperatures, which also make an intercooler necessary even on fairly low-boost applications.

Surge

Turbochargers spool up before its boost is delivered to the engine, when this happens there is a surge of power that is immediately delivered. This happens when the waste-gate opens at approximately (2500-3000 rpm). The surge can cause extreme damage to the engine and drivetrain, and make the vehicle difficult to drive or lose traction. Superchargers also experience surge which is why they have a blow-off valve to release the excess pressure during deceleration. (All superchargers should come with this blow-off valve as an accessory)

Exhaust Back Pressure

Remember the supercharger is powered by the crank, thus there is no need to deal with the exhaust gas interruption created by inserting a turbocharger turbine into the exhaust flow. The supercharger creates no additional exhaust back pressure. The amount of power that is lost by a turbocharger’s turbine reduces it’s overall efficiency.

How Loud is it?

The turbocharger is generally quieter than the supercharger. Because the turbo’s turbine is in the exhaust, the turbo can substantially reduce exhaust noise, making the engine run quieter. Some centrifugal superchargers are known to be noisy and may sound like a bird chirp at idle, which annoys some drivers.

Dependability

Normally superchargers are more reliable than a turbocharger. When the engine is turned off (i.e. the turbo is shut off), residual oil inside the turbo’s bearings can be baked by stored engine heat. This, combined with the turbo’s extremely high rpms (up to 150,000rpm) can cause problems with the turbo’s internal bearings and can shorten the life of the turbocharger. In addition, many turbos require aftermarket exhaust manifolds, which are often far less reliable than stock manifolds.

Ease of Installation

Superchargers are substantially easier to install than a turbochargers because they have far fewer components and simpler devices. Turbochargers are complex and require manifold and exhaust modifications, intercoolers, extra oil lines, etc. – most of which is not needed with most superchargers. A novice home mechanic can easily install most supercharger systems, while a turbo installation should be left to a turbo expert.

Peak Power

Turbochargers are known for their unique ability to spin to incredibly high rpms and make outrages peak boost figures (25psi). While operating a turbocharger at very high levels of boost requires major modifications to the rest of the engine, the turbo is capable of producing more peak power than superchargers.

Tuning

Turbochargers, because they are so complex and rely on exhaust pressure, are notoriously difficult to tune. Superchargers, on the other hand, require few fuel and ignition upgrades and normally require little or no engine tuning.

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One thought on “To turbo, or supercharge that is the question

  1. You share interesting things here. I think that your page can go viral easily, but you must give it initial boost and
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