Supercharger or turbo charger - which one ?

[rf065]

IE; The supercharger only cuts in when the system senses the need.

Probably when the accelerator is pressed then? :lol:

Russ

 

[Splatt]

Probably when the accelerator is pressed then? :lol:

Russ

Yes, but not just tickled :lol:

 

[Myros]

on the SSKs

the blower came in when you floored the throttle, and only stayed in while the throttle was floored. Lovely banshee wail to accompany the overtaking. I think the old blower Bentleys did something similar.

 

[Enigma AMG]

I don't think there is anything wrong with either form of forced induction they are simply different. Fuel efficiency will be reduced if either are used to their maximum potential but no more so than a large capacity NA engine of similar maximum output. Chargers can be cut in and out using a clutch mechanism seen on 55K mercedes. Turbo's have a theoretical advantage in that they produce boost from waste product ie, exhaust gas but in practice they are not that efficient as the the turbo acts as an exhaust restrictor which increases back pressure and reduces power. That said with the money being poured into turbo development by the likes of BMW Iam sure it will become the way forward for speed and economy. I still like the instant hit of the blower tho....

 

[HERBIEMERCMAN]

thankyou everyone for your information, it seems like most things, there are "swings and rounabouts".
my brother's mk4 supra ( 500 bhp),chipped and tuned, runs on for 3 minutes when he turns off the engine, this is obviously as some of you have explained to cool and lubricate the two turbo bearings, it all makes sense.

we visited the IOM, TT races in 2004 in my brother's supra, very few bikes could match it on straight line acceleration, none could keep with it on the corners. herbiemercman.

 

[Number_Cruncher]

For light pressure applications, like a knock limited production petrol engine, the deficiencies of a supercharger diminish to the extent that it becomes a realistic candidate.

A supercharger would be unsuited for use with a diesel engine, because when providing higher levels of boost, the poor efficiency of a supercharger would mean that the engine's output would suffer when compared with a turbocharger.

Particularly at lower engine speeds, the back flow or leakage through a supercharger represents a direct waste of engine power. There is generally a fair amount of leakage in most superchargers - the lobes of a roots blower do not touch - there is no direct seal.

For a diesel, the way that the thermal energy contained in the exhaust gas increases with engine load makes driving a turbocharger an easy match - the intake air mass doesn't change much on a diesel engine at any given engine speed unlike a throttled petrol engine.

 

[muller1]

the deficiencies of a supercharger diminish to the extent that it becomes a realistic candidate.
A supercharger would be unsuited for use with a diesel engine, because when providing higher levels of boost, the poor efficiency of a supercharger would mean that the engine's output would suffer when compared with a turbocharger.

REPLY= Nearly all (many millions) of GM diesel engines have only a supercharger including the massive EMD engine used in most of the trains in the US and in ships throughtout the world .
Some use a turbo also but not all have a turbo.
The us military tanks use a supercharged engine as did the RAF in most of the aircraft during WW2 as did the Germans

Particularly at lower engine speeds, the back flow or leakage through a supercharger represents a direct waste of engine power. There is generally a fair amount of leakage in most superchargers - the lobes of a roots blower do not touch - there is no direct seal.

REPLY=There is not so much leakage as the tips of the lobes are machined to within a couple of thousandths of an inch much less than the thickness of a human hair, and there is much more clearance in the turbocharger housing to to air compressor side.

For a diesel, the way that the thermal energy contained in the exhaust gas increases with engine load makes driving a turbocharger an easy match - the intake air mass doesn't change much on a diesel engine at any given engine speed unlike a throttled petrol engine.

REPLY= The thermal energy in a petrol engine exhaust increases with the engine load also, and and the injested air mass increases in direct relation to the revs this is why petrol and diesel engines have a Mass Air Flow Meter to measure the varying air flowing in to the engine petrol OR diesel.
If the flow did not vary there would not be a need for a MAF meter. It is not the waste thermal energy that runs the turbocharger it is the VOLUME of gas flow that does the work, hot or cold the turbocharger could not care.
The turbo is not a thermal converting machine the heat is only incedental to the burning of the fuel/air mixture and the turbo would run just as well if the gas flow was cold.
Lastly, ALL the major drag racing cars are supercharged and they run up to 3500 hp and beyond.

This was taken from Torquecars = Quote" It is better to fit a supercharger to a Naturally aspirated engine than going for a turbo because you will have much more control over the power and it will be delivered in a more consistent manner establishing a good base for ECU tuning to take full advantage of the power. " Unquote

Hope this helps to understand the workings of superchargers V turbochargers a little better, as I spent over 40 years working with both supercharged and turbocharged engines and some with both in my job as marine engineer.
ps I also raced supercharged cars in my youth.

Regards.

Mike

 

[rf065]

the poor efficiency of a supercharger would mean that the engine's output would suffer when compared with a turbocharger.

It is said that 20% of the engines power is consumed driving the supercharger.
Not very efficient.

http://auto.howstuffworks.com/supercharger6.htm

Russ

 

[muller1]

Give the whole story

It is said that 20% of the engines power is consumed driving the supercharger.
Not very efficient.

http://auto.howstuffworks.com/supercharger6.htm

Russ

Come on Russ tell it as it is and gon't keep the good bits to yourself.
The article says "can consume up to" and goes on to say the bit you missed out.
Quote "But because a supercharger can generate as much as 46 percent additional horsepower, most think the trade-off is worth it."
When you give the whols story it begins to make mors sense as most manufacturers can find a easier way of reducing the engine hp without adding a supercharger.

The addition of a supercharger means that if you had a 100 hp car the supercharger COULD take up to to hp but can give you 146 Prety good gain I would say.

Mike

 

[rf065]

Come on Russ tell it as it is and gon't keep the good bits to yourself.

I put the link up for anyone to read for themselves.

If Superchargers were efficient, and that is what car manufacturers are striving for to meet ever increasing engine regulations, Mercedes would not be dropping them in favour of turbo's.

Russ

 

[Number_Cruncher]

REPLY=There is not so much leakage as the tips of the lobes are machined to within a couple of thousandths of an inch much less than the thickness of a human hair, and there is much more clearance in the turbocharger housing to to air compressor side.

If you look at a performance map for a supercharger, you'll see the effect that leakage has.

REPLY= The thermal energy in a petrol engine exhaust increases with the engine load also, and and the injested air mass increases in direct relation to the revs this is why petrol and diesel engines have a Mass Air Flow Meter to measure the varying air flowing in to the engine petrol OR diesel.

Injested air mass in a petrol is NOT purely related to engine speed. The MAF on a petrol serves a much greater role on a petrol engine. On a diesel, the injested air mass is purely a function of engine speed and air temperature.


>>If the flow did not vary there would not be a need for a MAF meter. It is not the waste thermal energy that runs the turbocharger it is the VOLUME of gas flow that does the work, hot or cold the turbocharger could not care.
The turbo is not a thermal converting machine the heat is only incedental to the burning of the fuel/air mixture and the turbo would run just as well if the gas flow was cold.

The turbo is driven by the energy in the exhaust gas - not the volume. There's an energy balance between the energy lost in the turbine and that used in the compressor. The energy of the exhaust gas stream is made up of two contributions, pressure (potential) energy and thermal energy. The turbo would not run just as well if cold - far from it. Going one step further, the ability of a diesel's exhaust stream to power a turbine is directly related to its temperature - if you compare exhaust gas temperature upstream of a turbine, and the boost produced by the turbo (excepting when the wastegate is operating), you'll find they change in sympathy.

>>Lastly, ALL the major drag racing cars are supercharged and they run up to 3500 hp and beyond.

Yes, because they aren't at all worried about engine longevity - which comes back to my statement about road going petrol engines being kept away from knocking.

 

[type49]

It is said that 20% of the engines power is consumed driving the supercharger.
Not very efficient.

http://auto.howstuffworks.com/supercharger6.htm

Russ

I have read somewhere that the 5.5AMG supercharger takes up to 120 bhp to drive it. In theory then, if it were driven by another means, the engine could produce 620 bhp, as opposed to 500-odd. :lol:

 

[rf065]

I have read somewhere that the 5.5AMG supercharger takes up to 120 bhp to drive it.

I read that too quite recently.
No way would a turbo take that amount of power out of an engine.

Russ

 

[muller1]

Not everyone wants the most efficient vehicle.
Superchargers are efficient if you want more power as they give at least a 46% in power output
The supercharger was designed to give more power not more mpg.
If we all wanted the most efficient cars I think we would not be running our nice Mercs but some Jap three cylinder two seater golf cart thingie.
I personaly do not want to go down that route I enjoy power and I feel that if I do not burn the fuel someone else will.
I think that between my Jag and my Merc ML they average out at 31 to 32 mpg which does me just fine at present.
I think if the truth be known the most efficient way to travel in a car would be to throw out the engine and replace it with batteries, solar panels and an electric motor
but it all depends what you want in a car.
Range Rover still make the 5 litre V8 with a Supercharger and Bently make a supercharged model also as do some of the US manufacturers.
You could discuss the pros and cons for ever but in the long run it all depends what you want from the engine.

Regards

Mike

 

[rf065]

Not everyone wants the most efficient vehicle.

If we all wanted the most efficient cars I think we would not be running our nice Mercs but some Jap three cylinder two seater golf cart thingie.

Sometimes it is not what we want that counts.
Mercedes have to build efficient engines to lower the CO2 rating to comply with more stringent regulations every year.
They have already stated that they are going to use turbochargers across the range from now on to get the power they require from their engines.

Russ

 

[HERBIEMERCMAN]

all airflow and gas flow has to follow benui's law. volume is proportional to pressure and inversely proportional to the density (SG) and the pressure drop (resistance) of the system.

Q = CD2 ROOT P/S. so if you increase the volume then the pressure has to increase ? herbiemercman.

 

[muller1]

I have read somewhere that the 5.5AMG supercharger takes up to 120 bhp to drive it. In theory then, if it were driven by another means, the engine could produce 620 bhp, as opposed to 500-odd. :lol:

If the power taken is 120 hp then that seems a lot and there must be a massive drive system to the blower. Quote from the link supplied.

"Despite their disadvantages, superchargers are still the most cost-effective way to increase horsepower. Superchargers can result in power increases of 50 to 100 percent, making them great for racing, towing heavy loads or just adding excitement to the typical driving experience"

As I said earlier I love tham and think they give a lot for a little and run for ever and some other people hate them for little or no reason without ever having run them.
Try a blown or supercharged car then give a true opionion of it.
I am sure a lot of people would get their eyes opened as the saying goes "there is non so blind as those that will not see"

Mike

 

[rf065]

"Despite their disadvantages, superchargers are still the most cost-effective way to increase horsepower. Superchargers can result in power increases of 50 to 100 percent, making them great for racing, towing heavy loads or just adding excitement to the typical driving experience"

I think this is an American quote where they are bought as kits to add to any engine.
They are only the most cost effective as they simply bolt on and are run from a drive belt.

A turbo requires a new exhaust system to be fabricated if fitted as an add on and therefore is more difficult.

This thread has nothing to do with loving or hating them, the question was asked, "what are the differences between the two", that is all.

Russ

 

[Alex M Grieve]

all airflow and gas flow has to follow benui's law. volume is proportional to pressure and inversely proportional to the density (SG) and the pressure drop (resistance) of the system.

Q = CD2 ROOT P/S. so if you increase the volume then the pressure has to increase ? herbiemercman.

No, P1V1=P2V2. Increase the volume, the pressure decreases.

 

[Number_Cruncher]

For some info about how turbines work, although the tutorial is intended for gas turbine engines, the theory of operation for the turbine in a turbocharger is the same as that in a gas turbine engine.

http://www.freestudy.co.uk/thermodynamics/t3201.pdf

In worked examnple number 1, the shaft power obtained from the turbine can be seen to be proportional to the product of the mass flow rate and temperature drop across the turbine. i.e. the turbine would not be anywhere near as effective with cold air.

If you go a bit further into the document, and have a look at the "The basic gas turbine cycle", the ideal operation of the compressor and turbine are discussed;

For a turbo, the power input to drive the compressor (1 - 2) is that produced by the turbine (3 - 4), making sure to use appropriate values for the specific heat for intake air and exhaust gas. [The other 2 equations aren't applicable for turbos, and for the complete picture you would include the petrol or diesel operating cycle as appropriate]