The frictional losses that occur due to the supercharger drawing energy from the engine rather than using its left over wasted energy allows the turbo charger to be more efficient. Whilst a car rated by the manufacturer (e.g. mini cooper s) may have 160bhp, frictional losses mean its output is equivalent to 140bhp.
The frictional losses that occur due to the supercharger drawing energy from the engine rather than using its left over wasted energy allows the turbo charger to be more efficient. Whilst a car rated by the manufacturer (e.g. mini cooper s) may have 160bhp, frictional losses mean its output is equivalent to 140bhp.
Are you implying car manufacturers may fib HP output?? Say it aint so....
Anyways, both turbochargers and superchargers will cause parasitic loss of power. The Turbochrager's loss comes from higher exhaust backpressure. Minimal I'm sure, but still there.
No they just always quote power at the flywheel, whilst their is nothing wrong with that its not the whole story.
Its similar in concept to putting a heavier flywheel on a car, the power developed is unchanged, but a heavier flywheel wont allow a car to rev as fast.
Jeff7181
Lifer
- Aug 21, 2002
- 18,368
- 10
- 81
I'm tempted to dig out my books from college to prove a bunch of people wrong... however I don't have a great enough desire... I will however post my knowledge and anyone who wants to flame me can go ahead and make an ass of themselves, and those who can respect my opinion and have enough faith that I wouldn't spout off crap I don't know to be true, are welcome to comment/ask questions.
Turbo charging and Supercharging are both methods of forced induction. Forced induction is exactly what it sounds like... air is forced into the engine.
A naturally aspirated engine draws air in when the intake valve is open and the piston moves down in it's bore, creating low pressure, which causes atmospheric pressure to fill the low pressure area. This is where the argument comes from about whether air is forced in or sucked in... which will come up later in my explanation of superchargers.
Forced induction is using a device to force air into the cylinders, rather than letting the air flow in naturally due to the vacuum created. This is where the term "blower" came from... air is blown into the engine.
Turbochargers accomplish forced induction by using exhaust gasses to spin a turbine that is connected to another turbine by a shaft.
For simplicity, I'll call the turbine that exhaust turns the driving turbine, and the one it's connected to the driven turbine.
At a normal idle speed, about 800 RPM, there is not enough exhaust gasses exiting the engine to spin the driving turbine with much force, so not much boost is produced... when you increase the engine RPM, more exhaust gasses are exiting, thus increasing the driving force on the driving turbine, and also the speed of it.
The driven turbine is spinning also, and is drawing air in and forcing it into the engine... when more air is being forced in than the engine normally could draw in on it's own, you start to see increased power, which spins the engine faster, moving more air, which drives the driving turbine harder and faster, which spins the driven turbine faster, which forced even more air into the engine and will eventually increase the pressure above atmospheric pressure. This is the point at which we say it is creating boost, measure in PSI.
A turbo charger also uses something called a waste-gate, I'm sure you've heard the term before. The simplest way to explain a waste gate is to call it a pressure relief valve. In it's simplest form, it is operated by a spring, and when the turbo charger creates a certain amount of boost, it overcomes the spring pressure, opening the valve (waste-gate) and relieving some of the pressure. This is necessary because if you allowed it to build up as much boost as possible it would damage the engine in one way or another. (What way isn't really important, but if you want, I can explain some different ways.) When you have a car with a turbo charger that creates a lot of boost, you hear a sort of hissing sound when the car is shifted. This is the waste gate opening as the RPM of the engine drop, which reduces the airflow through the engine, which will create higher pressure in the intake system... so the waste gate opens to bleed off the excess pressure to prevent damage to the engine and turbocharger.
To my knowledge, the only reason turbo chargers are more efficient is due to the lack of frictional losses, being only a couple moving components. Although, when compared to certain types of superchargers, they don't heat the air as much, and cooler air is denser, so you can make more power.
There are several types of superchargers.
There is the roots style, which most of you think of when you think of superchargers. They're the large ones that sit on top of the engine, with a carburetor on top, and often some sort of scoop. They use rotors that mesh together and compress the air as they turn. Then are pulley driven from the crankshaft and draw air in from the top, and down. These heat the incoming air as well because the rotors create a lot of friction. Hot incoming air is bad for power, which is why these are typically used on low RPM engines with a power band that peaks around 5000 RPM or lower.
There is the screw type, which is similar to the roots type, but use different style rotors that seal better and create less heat from friction. They are also pulley driven from the crankshaft. They pull air in from the front, and back... a design that allows it to use less vertical space, and allow them to be placed under the hood of a car without a large scoop or cowl built into the hood. This is the type used in Ford's SVT Lightning. These also heat the incoming air, but not as much as the roots style due to their more modern design.
Then there is the centrifugal type, which works a lot like a Turbocharger, but instead of having a turbine that is turned by exhaust gasses, and turns another turbine, it is driven by a belt connected to the crankshaft. These mount the same way an alternator or air conditioner compressor mounts. These are the most efficient type of supercharge due to the low drag of the turbine, as opposed to the rotors in the roots and screw type. Of superchargers, these heat the air the least, and most of the parasitic power loss comes from the friction of the belt and pulleys rather than the heated incoming air.
Now, the point I mentioned about whether air is sucked or pushed into the engine...
Roots and Screw type super chargers are between the intake manifold and the throttle plates (whether they're in a carburetor or throttle body, it doesn't matter). This means the air moving through the throttle plates is under the same pressures as in a naturally aspirated engine... and if a carburetor is only capable of flowing 750 cfm at that pressure, it's not going to flow much more even if you create a stronger vacuum. So... to meet the airflow demands of an engine with a roots or screw type super charger, you must increase the area of the venturi or throttle body, whichever you have. That's why you see a lot of roots style blowers with 2 or 3 carbs sitting on top of them.
A Centrifugal Supercharger and a Turbocharger are located ahead of the throttle plates. This means that the entire induction system is pressurized when the device is creating boost. And if the air is under pressure, it's denser, and more air flows past the throttle plates... this is why it's not necessary to increase the size of the throttle body or carburetor as long as it meets the airflow requirements of the engine.
So to simplify the last two paragraphs... in effect, a roots and screw type supercharger make the engine seem like it has a larger displacement to the carburetor or throttle body & computer, so it needs a larger opening for more air to flow through. The centrifugal supercharger and turbocharger, just pressurize the induction system, allowing more air to flow through the same size opening.
** Please excuse any typos... it's late**
Turbo charging and Supercharging are both methods of forced induction. Forced induction is exactly what it sounds like... air is forced into the engine.
A naturally aspirated engine draws air in when the intake valve is open and the piston moves down in it's bore, creating low pressure, which causes atmospheric pressure to fill the low pressure area. This is where the argument comes from about whether air is forced in or sucked in... which will come up later in my explanation of superchargers.
Forced induction is using a device to force air into the cylinders, rather than letting the air flow in naturally due to the vacuum created. This is where the term "blower" came from... air is blown into the engine.
Turbochargers accomplish forced induction by using exhaust gasses to spin a turbine that is connected to another turbine by a shaft.
For simplicity, I'll call the turbine that exhaust turns the driving turbine, and the one it's connected to the driven turbine.
At a normal idle speed, about 800 RPM, there is not enough exhaust gasses exiting the engine to spin the driving turbine with much force, so not much boost is produced... when you increase the engine RPM, more exhaust gasses are exiting, thus increasing the driving force on the driving turbine, and also the speed of it.
The driven turbine is spinning also, and is drawing air in and forcing it into the engine... when more air is being forced in than the engine normally could draw in on it's own, you start to see increased power, which spins the engine faster, moving more air, which drives the driving turbine harder and faster, which spins the driven turbine faster, which forced even more air into the engine and will eventually increase the pressure above atmospheric pressure. This is the point at which we say it is creating boost, measure in PSI.
A turbo charger also uses something called a waste-gate, I'm sure you've heard the term before. The simplest way to explain a waste gate is to call it a pressure relief valve. In it's simplest form, it is operated by a spring, and when the turbo charger creates a certain amount of boost, it overcomes the spring pressure, opening the valve (waste-gate) and relieving some of the pressure. This is necessary because if you allowed it to build up as much boost as possible it would damage the engine in one way or another. (What way isn't really important, but if you want, I can explain some different ways.) When you have a car with a turbo charger that creates a lot of boost, you hear a sort of hissing sound when the car is shifted. This is the waste gate opening as the RPM of the engine drop, which reduces the airflow through the engine, which will create higher pressure in the intake system... so the waste gate opens to bleed off the excess pressure to prevent damage to the engine and turbocharger.
To my knowledge, the only reason turbo chargers are more efficient is due to the lack of frictional losses, being only a couple moving components. Although, when compared to certain types of superchargers, they don't heat the air as much, and cooler air is denser, so you can make more power.
There are several types of superchargers.
There is the roots style, which most of you think of when you think of superchargers. They're the large ones that sit on top of the engine, with a carburetor on top, and often some sort of scoop. They use rotors that mesh together and compress the air as they turn. Then are pulley driven from the crankshaft and draw air in from the top, and down. These heat the incoming air as well because the rotors create a lot of friction. Hot incoming air is bad for power, which is why these are typically used on low RPM engines with a power band that peaks around 5000 RPM or lower.
There is the screw type, which is similar to the roots type, but use different style rotors that seal better and create less heat from friction. They are also pulley driven from the crankshaft. They pull air in from the front, and back... a design that allows it to use less vertical space, and allow them to be placed under the hood of a car without a large scoop or cowl built into the hood. This is the type used in Ford's SVT Lightning. These also heat the incoming air, but not as much as the roots style due to their more modern design.
Then there is the centrifugal type, which works a lot like a Turbocharger, but instead of having a turbine that is turned by exhaust gasses, and turns another turbine, it is driven by a belt connected to the crankshaft. These mount the same way an alternator or air conditioner compressor mounts. These are the most efficient type of supercharge due to the low drag of the turbine, as opposed to the rotors in the roots and screw type. Of superchargers, these heat the air the least, and most of the parasitic power loss comes from the friction of the belt and pulleys rather than the heated incoming air.
Now, the point I mentioned about whether air is sucked or pushed into the engine...
Roots and Screw type super chargers are between the intake manifold and the throttle plates (whether they're in a carburetor or throttle body, it doesn't matter). This means the air moving through the throttle plates is under the same pressures as in a naturally aspirated engine... and if a carburetor is only capable of flowing 750 cfm at that pressure, it's not going to flow much more even if you create a stronger vacuum. So... to meet the airflow demands of an engine with a roots or screw type super charger, you must increase the area of the venturi or throttle body, whichever you have. That's why you see a lot of roots style blowers with 2 or 3 carbs sitting on top of them.
A Centrifugal Supercharger and a Turbocharger are located ahead of the throttle plates. This means that the entire induction system is pressurized when the device is creating boost. And if the air is under pressure, it's denser, and more air flows past the throttle plates... this is why it's not necessary to increase the size of the throttle body or carburetor as long as it meets the airflow requirements of the engine.
So to simplify the last two paragraphs... in effect, a roots and screw type supercharger make the engine seem like it has a larger displacement to the carburetor or throttle body & computer, so it needs a larger opening for more air to flow through. The centrifugal supercharger and turbocharger, just pressurize the induction system, allowing more air to flow through the same size opening.
** Please excuse any typos... it's late
**
Jeff7181
Lifer
- Aug 21, 2002
- 18,368
- 10
- 81
Won't rev as fast, but the RPM also won't drop as much when you shift... if you have an engine with a narrow power band in a heavy car, you definately want a heavy flywheel. Idle quality can also be effected, as the flywheel is heavy for more than one reason... it's inertia is used to keep the engine spinning in the right direction... with an automatic transmission, the torque converter's weight provides that inertia... and engine WILL NOT run correctly without a flywheel or torque converter.
Jeff7181
Lifer
- Aug 21, 2002
- 18,368
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Brake Horsepower is measured at the crankshaft... all parasitic power losses IN THE ENGINE reduce the power before it is measured... so BHP is a true indication of the usable power output of the engine. What BHP doesn't take into consideration is parasitic losses through the drive line... this is where you get your net horsepower figure from. Normally this is measured at the output of the transmission with all accessories operating, meaning, A/C compressor on, power steering pump pumping, and alternator charging at it's full capacity. Horsepower can also be measured at the wheels, which takes into consideration EVERY frictional power loss, even down to the wheel bearings themselves.
Jeff7181
Lifer
- Aug 21, 2002
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Originally posted by: Priit
Nothing much, I'm still lurking here most of the time, I just haven't had much to say lately
Engine braking isn't why horsepowers are needed
Extremly powerful per displacement engines tend to have really bad turbo lag: I've seen Ford Sierra with heavy truck turbocharger mounted on it that made 509 RWHp out of 2L 4-banger (most of the engine was stock!). It ran low 12sec times on track but start was always very slow and turbo really kicked in after about 2-4 seconds. I have also seen finns ~600HP 1,5L russian IZ-412 and about as powerful 1,3L Toyota Starlet.
Acceleration and the "feel" of the power has to do with torque as well... a high horsepower engine doesn't necessarily produce a lot of torque, which is require to overcome the vehicle's inertia and get it moving.
*EDIT* Sorry for all these posts in a row =)
Jeff...
Good layout of the basics of it all. Nice
But...How does that really prove anyone wrong here? Nobody has really said much otherwise, the major argument seems to be which is a better option, t-chargers or s-chargers.
But again, good info!
Good layout of the basics of it all. Nice
But...How does that really prove anyone wrong here? Nobody has really said much otherwise, the major argument seems to be which is a better option, t-chargers or s-chargers.
But again, good info!
Although the revs will drop off, the road speed will mean accelleration will continue once the clutch has resynced the transmission/engine speed. I was only comparing the effect of a heavy flywheel to the frictional lossess from the supercharger. so the rest whilst true is moot.
Sorry have to disagree, most are sold based on output at the crank or the flywheel, not power at the wheels. Accelleration times are also done on miserly amounts of petrol, a/c off and lights / radio etc. off by manufacturers at least not car magazines.
No argument their, but by using forced induction you get a fairly linear increase in power and torque.
AH! Ok, well then... Good job! You should have specified it was in regards to the original poster.
Yeah, I was rather suprised myself we made it this far on the subject.
You were saying that crankshaft BHP numbers don't take into account parasitic loss from the supercharger, and that's not true.. assuming the supercharger was used in the process of getting the BHP numbers.. but it would be pretty pointless to have a supercharger belted up and not actually blowing the engine, no?
Jeff7181
Lifer
- Aug 21, 2002
- 18,368
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Doesn't matter what figure is advertised... parasitic losses from power adders occurr before anything is measured, and thus already accounted for in any HP figure you see.
And just to be clear on another point... horsepower is not measured, torque and RPM are measured, and horsepower is calculated from those figures.
HP = (torque x RPM) / 5252
If you know much about math, based on that formula, you will see that horsepower is a function of torque and RPM... and at 5252 RPM, horsepower and torque will ALWAYS be the same. If you see a dyno graph that shows otherwise, it's a bogus graph... simple math.
*edited for clarity*
yep.. should've mentioned this earlier in the thread..
It's amazing how many people don't realize this.. lol..
I wouldn't doubt that we eventually start measuring engine power simply as torque/RPM, instead of a rather arbitrary number like "horsepower".. lol
Jeff7181
Lifer
- Aug 21, 2002
- 18,368
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Actually horsepower isn't just an arbitrary number... there actually is a method to the madness... that's how they came up with using 5252 in the calculation. Like I said, if I cared enough I could get my books and show you that formula, or look it up online, but to be honest, I just don't care =) And I doubt anyone else cares exactly where 5252 came from either =) And if they do... too bad, because it's off topic, lol.
Oh, I know.. I was just trying to convey that it's like old world stuff that doesen't really mean much anymore, except in reference to other cars.
I mean, do you really care that your Mustang can raise 99,000 pounds of coal 100 feet in a minute, or 9,900 pounds of coal 1,000 feet in one minute, or 300,000 pounds 33 feet in one minute?
(@ 300hp)
Jeff7181
Lifer
- Aug 21, 2002
- 18,368
- 10
- 81
Originally posted by: Eli
Oh, I know.. I was just trying to convey that it's like old world stuff that doesen't really mean much anymore, except in reference to other cars.
I mean, do you really care that your Mustang can raise 99,000 pounds of coal 100 feet in a minute, or 9,900 pounds of coal 1,000 feet in one minute, or 300,000 pounds 33 feet in one minute?
Sure it matters... when you rip emissions devices off your "five-oh" you'll still need to haul around all the carbon that builds up in the CAT. =)
Nice posts, Jeff7181. Low-end torque really feels more powerful for most of the people, but that hasn't much to do with cars performance: with proper gearing, you can get just as much power to the wheels with not-so-torquery engine. What's needed to overcome car's inertia is power, torque alone doesn't help One more thing: superchargers aren't always belt-driven, for example older racing engines used gears
One more thing: superchargers aren't always belt-driven, for example older racing engines used gears Originally posted by: Shockwave
I cant believe no one has mentioned that turbo's are for rice and blowers are for MEN.
Nah, both are for pussies, nothing beats the cubic inches
Jeff7181
Lifer
- Aug 21, 2002
- 18,368
- 10
- 81
Originally posted by: Shockwave
I cant believe no one has mentioned that turbo's are for rice and blowers are for MEN.
Tell that to the guy in this video... : drool :
Or maybe this guy... more drooling...
LOL, damn a TON of BS went on in this thread.
IT'S BY APPLICATION YOU DUMBA$$'S!!
Until you bolt on and tune your OWN vehicle why do you even post. If you can't list a pro or a con it just means you best friend told you what was cool at the local hangout parkinglot (ricefest)
IT'S BY APPLICATION YOU DUMBA$$'S!!
Until you bolt on and tune your OWN vehicle why do you even post. If you can't list a pro or a con it just means you best friend told you what was cool at the local hangout parkinglot (ricefest)
Don't mind if I do..
See this is the sh!t that I am talking about. This is kind of half true, let me explain.
The wastegate is a device that bleeds energy away from the hot side of the turbocharger. It prevents you from cramming too much boost into the engine buy opening a valve at a specified boost pressure that diverts some of the exhaust away from the turbine. They come in two flavors: Internal or integral to the cast housing that the turbine spins in, or external meaning a seperate wastegate welded on the manifold somewhere before the turbo. You also have two choices of what to do with the diverted exhaust, send it back into the downpipe(99% of cars do this) or run a "divorced" wastegate which sends it on a short path to atmosphere. Divorced wastegates make slightly more power, but they are LOUD AS HELL.
Now, as for the noise during shifting that you said was the wastegate, this is the Blow off valve, a completely different system. A Blow off valve works on the fresh air side of the system. It is situated before the throttle plate, it bleeds off pressure that can be vented to the atmosphere or recirculated back into the intake before the compressor. Why would you want to do this? Well imagine the turbo is spinning at 150,000 RPM and sending massive quantities of air into the engine, then all of the sudden you shift gears and close the throttle as you do so. Instantly there is a wall in front of the flow path and this sends a reverse pressure wave back down the intake tubes INTO the exit of the compressor this wave can seize the turbo momentarily and put major stress on the fan blades and bearings. Equiping the vehicle with a Blow off valve helps to avoid this situation during shifts and when you suddenly let off the throttle.
Schools out.
Given enough room in the engine bay, could you have both a super charge and a turbo charger on a car? A belt driven super charger that shoves all the air into the chamber at between like 100-4k rpm and then a large turbo that takes off at like 4000 rpm?
EDIT: Found this on google: http://www.supercars.net/garages/PeP/76v2.html
A rally car with both a turbo and supercharger.
EDIT: Found this on google: http://www.supercars.net/garages/PeP/76v2.html
A rally car with both a turbo and supercharger.
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