Towing w/ a radix
10-20-2007, 12:10 PM
#61
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However there is a huge metric that is almost always overlooked in these "which is better" debates: Compressors are also rated in terms of mechanical efficiency or the ability to effectively utilize the power being input into the device to gain the desired result (i.e. amount of work left over to actually compress air). Superchargers are actually much more "mechanically" efficient than a turbo as a belt connected to a crankshaft is a much more effective (and efficient) means of transferring power than "air" is.
Turbos are around 60% mechanically efficient, whereas a supercharger (more specifically an Eaton supercharger) is around 70-80% mechanically efficient (again, this is energy going into the device that is left over to compress air). (Blown2300, please correct me on these mech. efficiency numbers if they're wrong).
The turbo does have a leg up in terms of reclaiming energy lost in heat production so the net efficiency isn't that far from a mechanical supercharger. The amount of energy reclaimed can be measured by measuring the temperature of the gases in the inlet and outlet of the turbine and calculating how much the temperature has dropped (delta T) and then calculating how much heat energy was actually recovered. It has been determined that about 6% of the energy is extracted from the heat and used by the turbine to spin the compressor. This still isn't enough to make up the mechanical losses in spinning the compressor wheel (losses from back pressure, leaks in the system, drag from the spinning turbine/compressor wheels and shaft, etc). Furthermore, this 6% is typically only at the most efficient point on the turbine efficiency map.
The largest downside to the turbo is the amount of energy required to spool the compressor and turbine (the mass) to the speeds that they endure (sometimes 100,000RPM or greater). A great amount of energy is required to spool it and that is why there is a waste gate. The waste gate holds exhaust pressure back in order to get this mass spinning and that back pressure is a big load on the engine. Compare the brake specific fuel consumption (BSFC) map of a turbocharged engine during the boost transient phase (time where the turbo is spooling up, but the engine is not yet at max boost pressure and therefore isn't in the "peak efficiency" island of the map) and it will consume a considerably larger amount of fuel during the transient phase than a comparable supercharged engine. A truck towing a trailer will spend more time in this "transient" period than a passenger car.
Real world testing (by large OEMs) has shown that supercharging (more specifically a roots device with bypassing) is actually more fuel efficient than turbocharging. Their engine analysis software all say turbos are more efficient, but the actual real world testing shows that is not the case and has left them scratching their heads as to why the supercharged vehicles have better fuel economy. I believe there is still a lot that is not understood about both turbos and superchargers in terms of where the most energy is wasted in both devices.
I think the only thing that would really convince the mass public that the perceived truth is actually the contrary is to wait and see what the OEs do within the next few years. They are really the only ones with the resources to do the research required to find the real bottom line as to which one is really "more fuel efficient".
And I am done...
10-20-2007, 07:14 PM
#63
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Has ANYONE ran 13.5 psi (190 kpa) of boost threw a lq4 with radix??????
I just would like to know there 1/4 mile times.........
BTW, I pulled the info posted about effciency from here.http://en.wikipedia.org/wiki/Turbo
For answer please read:
O.K, no more joking...
I would like to know where you got your info on turbo vs. Supercharger efficient. I have always been told/taught turbocharging is more efficient. And if that just was not true, I'd like to know before going out and making an a$$ of myself on some forum somewhere........(I do that well enough with-out been wrong)
I just would like to know there 1/4 mile times.........
BTW, I pulled the info posted about effciency from here.http://en.wikipedia.org/wiki/Turbo
Real world testing (by large OEMs) has shown that supercharging (more specifically a roots device with bypassing) is actually more fuel efficient than turbocharging. Their engine analysis software all say turbos are more efficient, but the actual real world testing shows that is not the case and has left them scratching their heads as to why the supercharged vehicles have better fuel economy. I believe there is still a lot that is not understood about both turbos and superchargers in terms of where the most energy is wasted in both devices.
They are really the only ones with the resources to do the research required to find the real bottom line as to which one is really "more fuel efficient".
They are really the only ones with the resources to do the research required to find the real bottom line as to which one is really "more fuel efficient".
For answer please read:
I'm done, Turbos are better, get over it..
O.K, no more joking...
I would like to know where you got your info on turbo vs. Supercharger efficient. I have always been told/taught turbocharging is more efficient. And if that just was not true, I'd like to know before going out and making an a$$ of myself on some forum somewhere........(I do that well enough with-out been wrong)
10-20-2007, 07:31 PM
#64
Let me correct that: Turbochargers are typically 70-85% efficient at "COMPRESSING" air at peak efficiency (i.e. isentropic efficiency). And then add this: 85% efficiency is a stretch for most turbos, but there are some devices that reach that high of efficiency so I won't deny it.
However there is a huge metric that is almost always overlooked in these "which is better" debates: Compressors are also rated in terms of mechanical efficiency or the ability to effectively utilize the power being input into the device to gain the desired result (i.e. amount of work left over to actually compress air). Superchargers are actually much more "mechanically" efficient than a turbo as a belt connected to a crankshaft is a much more effective (and efficient) means of transferring power than "air" is.
Turbos are around 60% mechanically efficient, whereas a supercharger (more specifically an Eaton supercharger) is around 70-80% mechanically efficient (again, this is energy going into the device that is left over to compress air). (Blown2300, please correct me on these mech. efficiency numbers if they're wrong).
The turbo does have a leg up in terms of reclaiming energy lost in heat production so the net efficiency isn't that far from a mechanical supercharger. The amount of energy reclaimed can be measured by measuring the temperature of the gases in the inlet and outlet of the turbine and calculating how much the temperature has dropped (delta T) and then calculating how much heat energy was actually recovered. It has been determined that about 6% of the energy is extracted from the heat and used by the turbine to spin the compressor. This still isn't enough to make up the mechanical losses in spinning the compressor wheel (losses from back pressure, leaks in the system, drag from the spinning turbine/compressor wheels and shaft, etc). Furthermore, this 6% is typically only at the most efficient point on the turbine efficiency map.
The largest downside to the turbo is the amount of energy required to spool the compressor and turbine (the mass) to the speeds that they endure (sometimes 100,000RPM or greater). A great amount of energy is required to spool it and that is why there is a waste gate. The waste gate holds exhaust pressure back in order to get this mass spinning and that back pressure is a big load on the engine. Compare the brake specific fuel consumption (BSFC) map of a turbocharged engine during the boost transient phase (time where the turbo is spooling up, but the engine is not yet at max boost pressure and therefore isn't in the "peak efficiency" island of the map) and it will consume a considerably larger amount of fuel during the transient phase than a comparable supercharged engine. A truck towing a trailer will spend more time in this "transient" period than a passenger car.
Real world testing (by large OEMs) has shown that supercharging (more specifically a roots device with bypassing) is actually more fuel efficient than turbocharging. Their engine analysis software all say turbos are more efficient, but the actual real world testing shows that is not the case and has left them scratching their heads as to why the supercharged vehicles have better fuel economy. I believe there is still a lot that is not understood about both turbos and superchargers in terms of where the most energy is wasted in both devices.
I think the only thing that would really convince the mass public that the perceived truth is actually the contrary is to wait and see what the OEs do within the next few years. They are really the only ones with the resources to do the research required to find the real bottom line as to which one is really "more fuel efficient".
And I am done...
However there is a huge metric that is almost always overlooked in these "which is better" debates: Compressors are also rated in terms of mechanical efficiency or the ability to effectively utilize the power being input into the device to gain the desired result (i.e. amount of work left over to actually compress air). Superchargers are actually much more "mechanically" efficient than a turbo as a belt connected to a crankshaft is a much more effective (and efficient) means of transferring power than "air" is.
Turbos are around 60% mechanically efficient, whereas a supercharger (more specifically an Eaton supercharger) is around 70-80% mechanically efficient (again, this is energy going into the device that is left over to compress air). (Blown2300, please correct me on these mech. efficiency numbers if they're wrong).
The turbo does have a leg up in terms of reclaiming energy lost in heat production so the net efficiency isn't that far from a mechanical supercharger. The amount of energy reclaimed can be measured by measuring the temperature of the gases in the inlet and outlet of the turbine and calculating how much the temperature has dropped (delta T) and then calculating how much heat energy was actually recovered. It has been determined that about 6% of the energy is extracted from the heat and used by the turbine to spin the compressor. This still isn't enough to make up the mechanical losses in spinning the compressor wheel (losses from back pressure, leaks in the system, drag from the spinning turbine/compressor wheels and shaft, etc). Furthermore, this 6% is typically only at the most efficient point on the turbine efficiency map.
The largest downside to the turbo is the amount of energy required to spool the compressor and turbine (the mass) to the speeds that they endure (sometimes 100,000RPM or greater). A great amount of energy is required to spool it and that is why there is a waste gate. The waste gate holds exhaust pressure back in order to get this mass spinning and that back pressure is a big load on the engine. Compare the brake specific fuel consumption (BSFC) map of a turbocharged engine during the boost transient phase (time where the turbo is spooling up, but the engine is not yet at max boost pressure and therefore isn't in the "peak efficiency" island of the map) and it will consume a considerably larger amount of fuel during the transient phase than a comparable supercharged engine. A truck towing a trailer will spend more time in this "transient" period than a passenger car.
Real world testing (by large OEMs) has shown that supercharging (more specifically a roots device with bypassing) is actually more fuel efficient than turbocharging. Their engine analysis software all say turbos are more efficient, but the actual real world testing shows that is not the case and has left them scratching their heads as to why the supercharged vehicles have better fuel economy. I believe there is still a lot that is not understood about both turbos and superchargers in terms of where the most energy is wasted in both devices.
I think the only thing that would really convince the mass public that the perceived truth is actually the contrary is to wait and see what the OEs do within the next few years. They are really the only ones with the resources to do the research required to find the real bottom line as to which one is really "more fuel efficient".
And I am done...
10-21-2007, 08:34 AM
#66
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O.K, no more joking...
I would like to know where you got your info on turbo vs. Supercharger efficient. I have always been told/taught turbocharging is more efficient. And if that just was not true, I'd like to know before going out and making an a$$ of myself on some forum somewhere........(I do that well enough with-out been wrong)
I would like to know where you got your info on turbo vs. Supercharger efficient. I have always been told/taught turbocharging is more efficient. And if that just was not true, I'd like to know before going out and making an a$$ of myself on some forum somewhere........(I do that well enough with-out been wrong)
In reality, the difference in efficiency is almost a wash. Supercharging is undoubtedly much better at the transient boost. Turbocharging has a leg up on the ability to reach higher pressure ratios and is slightly more efficient once the turbo has been spooled and has reached max boost. However, in normal driving a person is going to spend very little time there and won't really be able to take advantage of the turbo's efficiencies that much...
And don't forget: in order to take advantage of the "free energy" that the turbo is so famous for it really needs to be placed as close to the heat source as possible. The further you place the turbo from the engine the more the gases have cooled and the more you have to rely on back pressure alone to spool the turbo. It was previously stated in this thread that this is a costly means of providing boost since engine back pressure undoubtedly costs power.
The ideal situation would be to have a super-turbo setup where the supercharger takes care of the transient boost and the turbo handles the higher pressure once it is spooled. VW has a gasoline car in Europe that makes something like 170hp and gets 42MPG... I think we'll see more of this in the future, but it'll be awhile before we get anything like that in the US.
10-21-2007, 11:09 AM
#67
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So how do you feel about STS's statment?
I like FACTS, even if it means I'm wrong.
A "supercharger engineer" makes me wonder if the facts you picked up are bias at all. WONDER that's all. I'm not by no means calling you a liar. But for me, they are very interesting theories yet to be proven beyond a doubt.
Here is something else I just found on STS's revamped web site.
This graph appeared in "Battle of the Boost", Hot Rod Magazine in the August 2003 issue. Turbo systems are the clear choice if you are looking to generate usable horsepower between 2500 and 5000 rpm.
"Given equivalent vehicles, the turbo would easily motor away from the centrifugal in an acceleration contest......The turbo offered massive midrange torque production, the only system to exceed 600 lb-ft. Need more convincing? At 4,000 rpm, the turbo was more than 100 lb-ft. stronger than either the Roots or centrifugal." Richard Holdener, "Battle of the Boost"
Due to our significantly lower Intake Air Temperatures, STS remote mounted turbo systems many times see more horsepower per pound of boost than even front mounted turbo systems
.
Denser exhaust gasses drive the turbo turbine wheel more efficiently
A "supercharger engineer" makes me wonder if the facts you picked up are bias at all. WONDER that's all. I'm not by no means calling you a liar. But for me, they are very interesting theories yet to be proven beyond a doubt.
Here is something else I just found on STS's revamped web site.
This graph appeared in "Battle of the Boost", Hot Rod Magazine in the August 2003 issue. Turbo systems are the clear choice if you are looking to generate usable horsepower between 2500 and 5000 rpm.
"Given equivalent vehicles, the turbo would easily motor away from the centrifugal in an acceleration contest......The turbo offered massive midrange torque production, the only system to exceed 600 lb-ft. Need more convincing? At 4,000 rpm, the turbo was more than 100 lb-ft. stronger than either the Roots or centrifugal." Richard Holdener, "Battle of the Boost"
Due to our significantly lower Intake Air Temperatures, STS remote mounted turbo systems many times see more horsepower per pound of boost than even front mounted turbo systems
10-21-2007, 12:14 PM
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So how do you feel about STS's statment?
I like FACTS, even if it means I'm wrong.
A "supercharger engineer" makes me wonder if the facts you picked up are bias at all. WONDER that's all. I'm not by no means calling you a liar. But for me, they are very interesting theories yet to be proven beyond a doubt.
Here is something else I just found on STS's revamped web site.
.
I like FACTS, even if it means I'm wrong.
A "supercharger engineer" makes me wonder if the facts you picked up are bias at all. WONDER that's all. I'm not by no means calling you a liar. But for me, they are very interesting theories yet to be proven beyond a doubt.
Here is something else I just found on STS's revamped web site.
.
The rear mount turbo systems definitely work. Are they the best, most efficient configuration out there? Probably not. I'm pretty sure if you measured the exhaust backpressure and compared it to the intake manifold pressure, you would see that the exhaust backpressure is greater than the intake manifold pressure. Compare this to a well designed and packaged front mounted turbo system and you would see that the extra exhaust heat you might achieve a 1:1 or better ratio. They have a product that works and they're very good at marketing it. If it works for you, that's great! Boost is awesome no matter how you get it.
Dyno graphs are kinda like Wikipedia... It's VERY easy to fudge the numbers so I take them with a grain of salt. Furthermore, you don't drive around on a dyno everyday and you can't see how a vehicle is going to respond on the street by looking at a dyno graph.
Case in point: One "trick" that is often employed when doing a dyno test of a turbocharged car is to use the dyno brake to put a load on the engine. In fact, I watched an episode of Hot Rod TV awhile back where they installed a rear-mounted turbo kit on a 2005? Vette. Then they proceeded to dyno it on the chassis dyno. However, they applied the dyno brake at low RPM to put a false load on the engine. This enabled them to load the engine and spool the turbos at a very low RPM (liken this to applying your brakes as you're driving down the road while mashing the gas pedal at the same time). The results "looked" really good, they had the turbos spooled up at around 2000 RPM and THEN they started recording the data from the dyno... But it's all bogus information, and it's very often employed when dynoing vehicles with turbos. How many people actually drive around with their foot on the brake and gas pedal at the same time? But they're marketing this to people and telling them they're going to have full boost by 2000RPM...
If it was as supercharged vehicle, you wouldn't have to do this. The results would be the same every time, and you wouldn't need to put a false load on the engine to achieve it.
Are the facts I discuss with my friends biased? I pickup facts from everywhere and well: facts are facts. I've seen raw data and have been able to make assessments of that data by my own accord.
10-21-2007, 01:07 PM
#69
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However, they applied the dyno brake at low RPM to put a false load on the engine. This enabled them to load the engine and spool the turbos at a very low RPM (liken this to applying your brakes as you're driving down the road while mashing the gas pedal at the same time). The results "looked" really good, they had the turbos spooled up at around 2000 RPM and THEN they started recording the data from the dyno... But it's all bogus information, and it's very often employed when dynoing vehicles with turbos. How many people actually drive around with their foot on the brake and gas pedal at the same time? But they're marketing this to people and telling them they're going to have full boost by 2000RPM...
Well what if you take your foot off the brake and add a trailer?
That's not a false load. That is why turbos are better for towing applications. IMHO
The more they are loaded the better they work.
I usally try and stay out of these kind of threads, they usally go nowhere fast, but the info you are shairing is very different to what I'm use to seeing/reading. Thanks for posting, sorry to keep dragging you back for more......
10-21-2007, 03:40 PM
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You said it yourself, Load a turbo the results look good.......
Well what if you take your foot off the brake and add a trailer? That's not a false load.
That is why turbos are better for towing applications. IMHO
The more they are loaded the better they work.
I usally try and stay out of these kind of threads, they usally go nowhere fast, but the info you are shairing is very different to what I'm use to seeing/reading. Thanks for posting, sorry to keep dragging you back for more......
Well what if you take your foot off the brake and add a trailer?
That's not a false load. That is why turbos are better for towing applications. IMHO
The more they are loaded the better they work.
I usally try and stay out of these kind of threads, they usally go nowhere fast, but the info you are shairing is very different to what I'm use to seeing/reading. Thanks for posting, sorry to keep dragging you back for more......