SL/R230: Torque Question
02-04-2005, 02:49 PM
#1
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2006 SL600, 2001 S500, 1996 SL320
Torque Question
Still a little confused on Torque!
SL600 - 590 lb-ft @ 1800 to 3500
911 Turbo - 415 lb-ft @ 2700 to 4600
911 Carrera - 273 @ 4250
With these comparisons, why the difference in RPM ranges for the torque. Why would you want it in the lower range like to SL600 versus the higher range for both porsches.
Also why does the one porsche only say 273 @ 4250 and not a range like the others?
SL600 - 590 lb-ft @ 1800 to 3500
911 Turbo - 415 lb-ft @ 2700 to 4600
911 Carrera - 273 @ 4250
With these comparisons, why the difference in RPM ranges for the torque. Why would you want it in the lower range like to SL600 versus the higher range for both porsches.
Also why does the one porsche only say 273 @ 4250 and not a range like the others?
02-04-2005, 03:47 PM
#2
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Some fundamentals. Power is force * distance moved per second. Move to rotating forces and power is torque * angular velocity (not expressed as RPM but as radians per second).
The torque an engine can provide varies across the RPM range and when a rev range is specified, the torque is at or above the quoted figure across the rev range. If specified as a single value, it's illustrative but doesn't tell you as much as a range based figure.
The torque an engine can provide varies across the RPM range and when a rev range is specified, the torque is at or above the quoted figure across the rev range. If specified as a single value, it's illustrative but doesn't tell you as much as a range based figure.
02-05-2005, 10:57 AM
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2006 Gallardo 6-speed, 2005 SL55, BMW X3
Torque 101 (part 2):
Torque is a product of a force exerted against a moment arm, as suggested by the units in which it is measured - the "pound-foot" ( or "foot-pounds" for us older types). If you're tightening lug nuts, the "pounds" comes from your muscles and the "foot" is the length of the wrench. Having stronger arms or a longer wrench (or both) gives you more torque.
When it comes to engines, the "pounds" comes form the expanding gas in the cylinders - which is in proportion to engine displacement (piston bore times stroke times # of cyls) and, if applicable, forced induction (turbo/supercharger). The "foot" comes from the piston stroke, since a longer stroke engine has a longer "lever" with which to turn the crankshaft.
So if you do the math, multiplying displacement by stroke gives you something like "bore times stroke times stoke" or "bore time stroke squared". The fact that torque is proportional to stroke squared means that a 10% increase in stroke yields a 20% increase in torque. This is in contrast to cylinder bore, in which a 10% increase in bore gives only a 10% increase in torque. So, when comparing engines of similar displacement, the longer stroke engine (like the MB V12) willl give you more torque. On the down side, the longer stroke means there's a higher piston velocity (it has to cover a longer distance) at a given RPM, and this will limit the engine's top end.
That being said, the engine designers can optimize the performance of the engine for a given RPM range through valve timing, tricks with the intake manifold, and other engine management techniques. Like blueSL pointed out, you really need to see the torque vs. RPM and HP vs. RPM curves. A single set of numbers doesn't really tell you enough.
So, back to your original question. - why would you want a MB V12 instead of a high-reving Porsche engine? Personal preference. Some people like a quiet engine that produces massive amounts of torque without having to rev to high RPM's. In fact, the SL65 produces so much torque that if you floor it while driving toward the east, you can actually slow the rotation of the Earth.
Torque is a product of a force exerted against a moment arm, as suggested by the units in which it is measured - the "pound-foot" ( or "foot-pounds" for us older types). If you're tightening lug nuts, the "pounds" comes from your muscles and the "foot" is the length of the wrench. Having stronger arms or a longer wrench (or both) gives you more torque.
When it comes to engines, the "pounds" comes form the expanding gas in the cylinders - which is in proportion to engine displacement (piston bore times stroke times # of cyls) and, if applicable, forced induction (turbo/supercharger). The "foot" comes from the piston stroke, since a longer stroke engine has a longer "lever" with which to turn the crankshaft.
So if you do the math, multiplying displacement by stroke gives you something like "bore times stroke times stoke" or "bore time stroke squared". The fact that torque is proportional to stroke squared means that a 10% increase in stroke yields a 20% increase in torque. This is in contrast to cylinder bore, in which a 10% increase in bore gives only a 10% increase in torque. So, when comparing engines of similar displacement, the longer stroke engine (like the MB V12) willl give you more torque. On the down side, the longer stroke means there's a higher piston velocity (it has to cover a longer distance) at a given RPM, and this will limit the engine's top end.
That being said, the engine designers can optimize the performance of the engine for a given RPM range through valve timing, tricks with the intake manifold, and other engine management techniques. Like blueSL pointed out, you really need to see the torque vs. RPM and HP vs. RPM curves. A single set of numbers doesn't really tell you enough.
So, back to your original question. - why would you want a MB V12 instead of a high-reving Porsche engine? Personal preference. Some people like a quiet engine that produces massive amounts of torque without having to rev to high RPM's. In fact, the SL65 produces so much torque that if you floor it while driving toward the east, you can actually slow the rotation of the Earth.
02-05-2005, 11:10 AM
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Originally Posted by doltmo
Torque 101 (part 2):
...In fact, the SL65 produces so much torque that if you floor it while driving toward the east, you can actually slow the rotation of the Earth.
...In fact, the SL65 produces so much torque that if you floor it while driving toward the east, you can actually slow the rotation of the Earth.
02-05-2005, 01:13 PM
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Mercedes-Benz A170 CDI
I'm going to try as best as to explain torque in as little as possible....
Torque is basically the twisting force. In an Internal Combustion engine, ( I assume you know how one works!), when the explosion in a cylinder is created, the force by which it pushes down on the piston is what the twisting force originally comes from...This explosion sends the piston down, turning the crankshaft and voila! You have a twisting force expressed through a simple explosion, neat eh?
Obviously, an engine needs to rev to SUSTAIN this torque. For example, you could apply 200lb/ft of twist through your wrench to undo a bolt, but could you do it 1000-7000 times a minute>? Thats what an engine does...
Most car engines, have a torque curve on the dyno graph that increases, to a point and then starts falling.
Lets look at the SL55....
http://www3.mercedes-benz.com/omb/am...ch_data_06.htm
That means once fully floored, an engine will follow its torque curve, that is maximum kick will come from peak torque, in the SL55's case, approximately 2700-4000rpm, you will get maximum pulling power. When you have a torque curve expressed as a value between 2000-4000rpm, that means the engine is producing a flat torque curve, as in consistent amount of torque for that engine speed range...
Power is a derived value. Yes its not measured! Power is the engine's ability to sustain its torque. HP is basically work done over time. The work is torque and the time is engine speed in rpms. Once an engine has its torque curve (which is measured), FROM this curve we measure power.
Power = torque (lbfts or ft/lbs) X RPM / 5252.
The SL55 V8K has 430lbft @6100rpm or 584NM..
So by inputting into the above equation we get....
430 X 6100rpm /5252 =? 499HP!
The number 5252 is a from a number of calculations, it is irrelevant to explain at the moment. Power being work done over time can only increase if you do a lot of work for a little time, OR little work for a lot of time....
E.G
The 55 V8K makes 516lbft! ( I know your SL6's make much more!) BUT, since the engine can't sustain it for a long enough time as in engine speed and the torque starts dropping by 6100rpm, and the engine only revs to 6500rpm, we get 500HP.
The M5/F430 type cars, have not that much torque (376lbft) , but they can produce it for a longer amount of time, e.g 7000-8500rpm, and they still get that same power.
The reason why the M5 is as fast as the SL55, is not due to its HP..... it is due to its torque curve and gearing. Simply put, what the gearing in a car does and the final axle ratio is multiplies whatever torque the engine produces. The difference in the SL55 vs M5 is, the SL has only 5 gears and these have to be spaced out ie, longer, but to get acceleration, these gears need a lot torque.
The M5 has 7 gears, and can afford to be very short, ie have a higher final drive, the higher the gear ratios (and you need a hgh revving engine to do this) the more torque you can multiply.
The final ratio of the SL55 is 2.82. The M5's is 3.62.
SO, if the 55 puts out 700Nm, if we multiply by its final drive of 2.82, we get...1974.
The M5's torque is 520Nm, so multiplied by its final drive, we get....1882. But because the M5 is lighter, the less torque is advantaged by the lesser weight, hence why the M5 is as quick if not quicker than the AMG Benz.
So, power really depends on a lot of torque over a little rpm range. OR a small amount of torque over a longer RPM band (7-8000rpms), they both essentially get you the same result, HOWEVER, the less torque engine NEEDS quick gearing and a high final drive to be as quick as the monster torque'd car. But with Mercedes, only having a 5 speed auto, and with longer gearing needed for 200mph ability, only a low revving, torquey motor could get you the results, and thats exactly what they did
Turbocharged cars, can have lag but this depends on the exhaust gas or rather amount of it and the size of the turbo. To eliminate this problem, Mercedes decided to use smaller turbos, these have the advantage of spooling up quicker and providing a lot of instant torque, PROVIDED they get a huge amount of exhaust gas, now a 5.5 V12 or a 6.0 AMG V12, isn't exactly short on exhaust gas is it?
And voila! You get insane amounts of torque low down. BUT, smaller turbos are not that efficient at high engine speeds, and therefore the immense torque created drops off in the higher speed ranges....
This is the torque curve of AMG's 65 engine but is very similar to your 5.5L V12's....
http://www3.mercedes-benz.com/omb/am...ch_data_06.htm
This type of engine gets is power from a LOT of torque over a little speed range. Because the engine can't sustain that immense 1000Nm for very long, and the torque starts dropping off, you don't get as much power as you liked.
Porsche engines or any other kind of naturally aspirated motors try to put all their torque in the higher speed ranges, this gets you the same power, but robs you of low down torque. Floor a F360 and not a huge kick until way past 6000rpm, floor an SL600 and you get massive urge lower down. The engine that produces its torque lower down doesn't need to rev that much and is easier to drive around town, without having to rev that much as in the N/A engine.
The problem with low down torque is traction. The majority of the engine's ooomph is wasted tyre shredding or through the over-active ESP...
Solution? Fit an LSD and wider rubber for more traction, put bigger turbos, and put an electronic restriction on the torque up to 2000rpm, and then see the engine's power output!
I hope I explained as best I could, any Q's and I'll be glad to answer...
Torque is basically the twisting force. In an Internal Combustion engine, ( I assume you know how one works!), when the explosion in a cylinder is created, the force by which it pushes down on the piston is what the twisting force originally comes from...This explosion sends the piston down, turning the crankshaft and voila! You have a twisting force expressed through a simple explosion, neat eh?
Obviously, an engine needs to rev to SUSTAIN this torque. For example, you could apply 200lb/ft of twist through your wrench to undo a bolt, but could you do it 1000-7000 times a minute>? Thats what an engine does...
Most car engines, have a torque curve on the dyno graph that increases, to a point and then starts falling.
Lets look at the SL55....
http://www3.mercedes-benz.com/omb/am...ch_data_06.htm
That means once fully floored, an engine will follow its torque curve, that is maximum kick will come from peak torque, in the SL55's case, approximately 2700-4000rpm, you will get maximum pulling power. When you have a torque curve expressed as a value between 2000-4000rpm, that means the engine is producing a flat torque curve, as in consistent amount of torque for that engine speed range...
Power is a derived value. Yes its not measured! Power is the engine's ability to sustain its torque. HP is basically work done over time. The work is torque and the time is engine speed in rpms. Once an engine has its torque curve (which is measured), FROM this curve we measure power.
Power = torque (lbfts or ft/lbs) X RPM / 5252.
The SL55 V8K has 430lbft @6100rpm or 584NM..
So by inputting into the above equation we get....
430 X 6100rpm /5252 =? 499HP!
The number 5252 is a from a number of calculations, it is irrelevant to explain at the moment. Power being work done over time can only increase if you do a lot of work for a little time, OR little work for a lot of time....
E.G
The 55 V8K makes 516lbft! ( I know your SL6's make much more!) BUT, since the engine can't sustain it for a long enough time as in engine speed and the torque starts dropping by 6100rpm, and the engine only revs to 6500rpm, we get 500HP.
The M5/F430 type cars, have not that much torque (376lbft) , but they can produce it for a longer amount of time, e.g 7000-8500rpm, and they still get that same power.
The reason why the M5 is as fast as the SL55, is not due to its HP..... it is due to its torque curve and gearing. Simply put, what the gearing in a car does and the final axle ratio is multiplies whatever torque the engine produces. The difference in the SL55 vs M5 is, the SL has only 5 gears and these have to be spaced out ie, longer, but to get acceleration, these gears need a lot torque.
The M5 has 7 gears, and can afford to be very short, ie have a higher final drive, the higher the gear ratios (and you need a hgh revving engine to do this) the more torque you can multiply.
The final ratio of the SL55 is 2.82. The M5's is 3.62.
SO, if the 55 puts out 700Nm, if we multiply by its final drive of 2.82, we get...1974.
The M5's torque is 520Nm, so multiplied by its final drive, we get....1882. But because the M5 is lighter, the less torque is advantaged by the lesser weight, hence why the M5 is as quick if not quicker than the AMG Benz.
So, power really depends on a lot of torque over a little rpm range. OR a small amount of torque over a longer RPM band (7-8000rpms), they both essentially get you the same result, HOWEVER, the less torque engine NEEDS quick gearing and a high final drive to be as quick as the monster torque'd car. But with Mercedes, only having a 5 speed auto, and with longer gearing needed for 200mph ability, only a low revving, torquey motor could get you the results, and thats exactly what they did
Turbocharged cars, can have lag but this depends on the exhaust gas or rather amount of it and the size of the turbo. To eliminate this problem, Mercedes decided to use smaller turbos, these have the advantage of spooling up quicker and providing a lot of instant torque, PROVIDED they get a huge amount of exhaust gas, now a 5.5 V12 or a 6.0 AMG V12, isn't exactly short on exhaust gas is it?
And voila! You get insane amounts of torque low down. BUT, smaller turbos are not that efficient at high engine speeds, and therefore the immense torque created drops off in the higher speed ranges....This is the torque curve of AMG's 65 engine but is very similar to your 5.5L V12's....
http://www3.mercedes-benz.com/omb/am...ch_data_06.htm
This type of engine gets is power from a LOT of torque over a little speed range. Because the engine can't sustain that immense 1000Nm for very long, and the torque starts dropping off, you don't get as much power as you liked.
Porsche engines or any other kind of naturally aspirated motors try to put all their torque in the higher speed ranges, this gets you the same power, but robs you of low down torque. Floor a F360 and not a huge kick until way past 6000rpm, floor an SL600 and you get massive urge lower down. The engine that produces its torque lower down doesn't need to rev that much and is easier to drive around town, without having to rev that much as in the N/A engine.
The problem with low down torque is traction. The majority of the engine's ooomph is wasted tyre shredding or through the over-active ESP...
Solution? Fit an LSD and wider rubber for more traction, put bigger turbos, and put an electronic restriction on the torque up to 2000rpm, and then see the engine's power output!
I hope I explained as best I could, any Q's and I'll be glad to answer...
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02-06-2005, 11:37 AM
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SL500 2003 previous/ E350 2007 actually
[QUOTE=Bilal]I'm going to try as best as to explain torque in as little as possible....
Thanks for your explanation, but what happend right now that the SL 500 has 7 gear regarding the torque? Did the car improve or stay equal?
Thanks for your explanation, but what happend right now that the SL 500 has 7 gear regarding the torque? Did the car improve or stay equal?
02-06-2005, 04:01 PM
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Mercedes-Benz A170 CDI
Carlos I understand what you're trying to ask. You want to know if the 7 gears has made a difference in acceleration. Well I don't know that much about this new gearbox, but one thing I can tell you, it is NOT like the M5's 7 Speed SMG. By that I mean, the gears are not spaced equally with a high final drive, like they SHOULD be, rather they are very non-linear. 1st gear is relatviely short, 2nd is absurdly short, 3/4 are equally spaced 5th/6th quite long and 7th is mostly overdrive....
http://www.car-videos.com/tools/spee...B1=Recalculate
I have provided the link for the SLK55 AMG which uses this gearbox, as you can see, the engine revs to 6700rpm, and the diagram shows what speed each gear pulls, if you scroll right to the bottom. Now the SL500 and other cars may be different, I just used the SLK55 because I could find its gear ratios.
As you can tell, look at the spacing of 1-3 vs 4-6, they are very strange in spacing. BUT, the higher final drive has improved the acceleration. All cars which use this gearbox have cut their 0-60 time by 0.3 seconds, and in-gear acceleration is 1-2 seconds quicker from any speed to any speed. Very impressive in this respect, and you will be pleased to know that from 50-110mph or 80-180km/hr, the SLK55 is quicker than the M5 if both use 4th gear! Hows that for an auto gearbox and 360hp?
While I am not a fan of the 7 speed, mostly due to weird spacing between gears, that distorts the engine noise, no doubt though, it is a superior gearbox to the old 5 speeder in every aspect. The SLK55 is quicker by 1 second from 0-100mph than the CLK55/C55 which use the old 5 speeder and quicker by 2 seconds to 124mph! (0-200km/hr) that the aforementioned AMG's.
So the SL500 should be a better car than the 5 speed, but I have been told American cars have a different shift logic, so you may get weird responses, test drive to see if that is the case....
7 G Tronic + 500bhp engine.....now we're talking
http://www.car-videos.com/tools/spee...B1=Recalculate
I have provided the link for the SLK55 AMG which uses this gearbox, as you can see, the engine revs to 6700rpm, and the diagram shows what speed each gear pulls, if you scroll right to the bottom. Now the SL500 and other cars may be different, I just used the SLK55 because I could find its gear ratios.
As you can tell, look at the spacing of 1-3 vs 4-6, they are very strange in spacing. BUT, the higher final drive has improved the acceleration. All cars which use this gearbox have cut their 0-60 time by 0.3 seconds, and in-gear acceleration is 1-2 seconds quicker from any speed to any speed. Very impressive in this respect, and you will be pleased to know that from 50-110mph or 80-180km/hr, the SLK55 is quicker than the M5 if both use 4th gear! Hows that for an auto gearbox and 360hp?
While I am not a fan of the 7 speed, mostly due to weird spacing between gears, that distorts the engine noise, no doubt though, it is a superior gearbox to the old 5 speeder in every aspect. The SLK55 is quicker by 1 second from 0-100mph than the CLK55/C55 which use the old 5 speeder and quicker by 2 seconds to 124mph! (0-200km/hr) that the aforementioned AMG's.
So the SL500 should be a better car than the 5 speed, but I have been told American cars have a different shift logic, so you may get weird responses, test drive to see if that is the case....
7 G Tronic + 500bhp engine.....now we're talking
