Turbo Vs. Super

[2strokebloke]

I guess I'm the first one to post in here. So I thought I'd start off with a thread to discuss the differences between super charging, and turbo charging.
Anybody want to enlighten me (and others) as to what the pros and cons of the different systems are?

[ccc880]

I want to be second to post... I like superchargers better

[Sluttypatton]

I guess that makes me third.

The differences between turbo and supercharging depend on the type of supercharger one compares it to.

CENTRIFUGAL

If you were to compare a turbocharger to a centrifugal supercharger the differences would be small, after all a centrifugal supercharger is simply the compressor half of a turbocharger that is belt driven from the crank. The issue with these types of compressors is that they produce boost in a non-linear fashion, further compounding the issue that superchargers have with not being able to produce full boost until redline. This is because the supercharger is crank driven, so when the supercharger produces maximum boost must be directly synchronized with the engines redline, because if the supercharger were to produce full boost at half of the engines possible RPM, then in the other half of the engines RPM range the supercharger would choke and actually produce less CFM than before. When compared to a turbo, the turbo can build to its maximum potential very quickly in the RPM range and then be controlled by the wastegate to stay there.

I will address the other different types of superchargers in a bit, but I have run out of time so I will post again later.

[Neutrino]

SWWWWWWEEEEEEEEEEETTTTTTTTTTTT.......we got a general FI forum............



Go Igor

[SaabJohan]

In general there are two types of compressors, displacement compressors (roots, screw) and dynamic compressors. Dynamic compressors are also called turbomachines and the centrifugal compressor is of this type.

Displacement compressors work by reducing the volume of the trapped gas and hence increasing its pressure. The gasflow is proportional to the rotational speed of the shaft and the flow is almost independent on the pressure increase.

The centrifugal compressor works by increasing the velocity of the flowing fluid with the impeller, and therefore its kinetic energy. In the following diffusor the velocity is reduced and the kinetic energy is transfered into a static pressure.

When the pressure is increased thermodynamic laws says that the temperature will rise, if no heat is supplied to or rejected from the working fluid (no friction, heat radiation, cooling and so on) the process is called adibatic. In reality this is not the case for any compressor, therefore there’s something called adiabatic efficiency which relate how much the temperature will rise in reality compared to what thermodynamic laws says. If the adiabatic efficiency is 100% it's an adiabatic process.

Compressors are doing a negative work, this means that they require power from an external source. This source can be an exhaust driven turbine or the engine itself, in any case the amount of power required depends on a few things. The power needed is the enthalpy change over the compressor multiplied with the mass flow per second, this can be written as:

P=delta h * m, where delta h is:

delta h = h outlet - h inlet

or if we consider the fluid to be thermally perfect:

delta h = (cT outlet)-(cT inlet)

where c is specific heat and T the absolute temperature

If we consider that the compression is an adiabatic process the outlet temperature would be:

T outlet = T inlet * PR^((g-1)/g)

Where g is gamma, specific heat ratio and PR is the pressure ratio defined below

PR = pressure outlet/pressure inlet

As we now can se the power needed to drive the compressor depends on the adiabatic efficiency, pressure ratio and mass flow.

The centrifugal compressor is one of the compressor types which has a high adiabatic efficiency, the ones in modern turbochargers have up to 80% efficiency while the ones that are engine driven usually have a little lower efficiency (I think this is because they use lower rpms). Other compressors like roots compressors have an extremely low efficiency, which usually is below 50%.

If we use and exhaust driven turbine to power the compressor we will use the heat in the exhausts which had otherwise been wasted. The power delivered by the turbine can be written, similar to the power needed by the compressor:

P = ((cT inlet)-(cT outlet)) * m

Under ideal conditions a turbocharger robs almost no power from the crankshaft, this means that the power output and engine efficiency can be higher with a turbocharger than with an engine driven compressor. However, exhaust flow and temperature is too low to at low speeds for the turbine to produce enough power to create a boost pressure, and if a smaller turbine is used it will cause a restriction at high speeds/loads and therefore a drop in peak power. But if variable nozzle area (usually called VNT or VGT) is used on the turbine we can increase the width of the turbines range so it will work earlier and cause less restriction at high speeds/loads, sadly it can only be used in diesels because of their lower exhaust temperature, at least yet.

Under low engine load the turbocharger will run with a low speed, and under high engine load it will run with a high speed. Since there is no connection with the crankshaft we must wait until we have enough exhaust for the turbine to supply enough power to reach a boost pressure. This will cause what is called “lag”, today we can however eliminate lag by using an anti lag system, ALS, but this is very hard on exhaust valves, exhaust manifold, turbocharger and exhaust system and of course very loud so it’s only used on racing cars. VNT turbines, ball bearing turbos and so on are also ways of reducing the lag.

[Polygon]

Well SaabJohan has explained it very well so I will just leave you with my opinion.

i personally prefer Turbocharging to Supercharging or N2O. I feel it has the most upsides and the least downsides. I can explain myself further if you wish.

[Leahcim]

Well I'm not sure I'm able to explain it much better than previously stated but I'll give ya a quick sum up which is basically how I first learned the diffrence.

Turbocharger - Driven by exhaust gas that spins a turbine at high speeds and works the compressor which compressed the air on the intake.

Supercharger - Most common is roots blower, Eaton most notably (used by jackson racing and used on many stock engines for high end cars). Superchargers are connected to the driveshaft by a belt that works the compressor.

Turbochargers are considered more efficient because it doesnt use up any potential energy instead it reuses wasted energy (exhaust gas). The only notable problem is what is known as turbo lag, which is caused by the turbine taking a few seconds to spool up at low RPM if the turbine is too large, or the problem of it overspinning at higher RPM if the turbine is too small for your engine.

Hope my 2 cents helps

[ccc880]

turbos also sound better

[Doug000]

Thank you SaabJohan.....

I am familiar with the principles behind the supercharger and turbocharger, but I have not even seen such a clean comparison of the 2 (err 3?) 'chargers in order for me to learn the differences, advantages, and disadvantages.

[454Casull]

Great work, Johan.

Originally Posted by Doug000

Thank you SaabJohan.....

I am familiar with the principles behind the supercharger and turbocharger, but I have not even seen such a clean comparison of the 2 (err 3?) 'chargers in order for me to learn the differences, advantages, and disadvantages.

There seem to be two types of mechanically-driven superchargers on the market now: the Roots type (Eaton makes Roots superchargers, though they've added a few modifications to the lobes and other things), and the twin-screw AKA Lysholm type. Mechanically-driven superchargers have the advantage of infinitely-small boost lag (Roots superchargers do leak a bit of air at very low RPMs due to their design, not sure about twin-screws), but they use up some power. Lysholm superchargers are more efficient than the Roots type but less than a turbine-driven supercharger.

A fun tidbit - the supercharger on a Top Fuel dragster can take more than 600HP to drive.

[Kurtdg19]

I wouldn't say I'm close to as knowledgable in the comparisions of turbo chargers vs. superchargers. Let me chip in my 2 cents and see if you guys think im on a right track.

A Turbo charger is a exhaust driven turbine that compresses intake air by a compresser.

A Supercharger is a belt driven turbine that compresses intake air by a compresser.

I heard that due to the fact that a turbocharger works off of the exhaust it tends to produce more heat which theirfore; wears it down faster than a supercharger since its is belt driven.
I do know that turbo chargers are more efficient than superchargers due to the fact their consuming wasted energy to create energy, as to a supercharger, that uses energy to create more.
I think thats why i prefer a supercharger more due to the fact that they don't produce as much heat than turbos so it doesn't wear on your engine as quick as a turbo would.

[454Casull]

The only thing creating heat would be the breaking of the bonds of octane. Turbos don't produce heat, they run off it. Using a turbo merely increasing underhood temps.

[krebs128]

well actually the turbo can produce heat. so many moving parts creates friction and the compression of air *can* actually make the fuel prematurely ignite-and that's called knocking.

[454Casull]

Originally Posted by krebs128

well actually the turbo can produce heat. so many moving parts creates friction and the compression of air *can* actually make the fuel prematurely ignite-and that's called knocking.

I was talking about the turbine section. If you're talking about the compressor section, then turbos create LESS heat than crank-driven SCs because the air is pressurized more efficiently (centrifugal acceleration vs. positive displacement).

[krebs128]

supercharger or turbocharger, they both produce friction which equals heat, now which one produces more heat? idk-i'll just have to take your word.