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      12-16-2009, 06:22 PM   #221
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Quote:
Originally Posted by Jim Pearce View Post
1. The torque in your equation is not engine torque.
2. Peak torque numbers should come with a disclaimer "subject to gearing".
Indeed not a bad criticism. You have to always separate wheel values from engine values and I was referring all along to T as wheel torque. However, torque at the wheels is simply engine torque x gear ratio x final drive x efficiency, so I could have substituted this relationship and then had one showing a vs. T. There a similar difference (less the gear ratios) in a = P/(m x v) since the power the engine develops is not all available for power that actually is accelerating the vehicle due to parasitic losses. In other words there is still the efficiency factor. OK, that is nitpicking...

Thinking more about this I think I have it figured out a little bit more concisely. But not much... You must speak about what is typical because the physics does not rule out bad designs that may break the "rules". This explanation covers both gearing and torque vs. horsepower.

Single in gear peak acceleration levels across the entire rpm or speed range (not typically how you drive when at full clip obviously!) are governed by peak torque to weight. This is simply a result of Newtons 2nd law when you work out the math. However, the length of time you can remain in any given gear and the peak speed you will obtain is more governed by peak power since a high redline (in a roughly acceleration optimized gear set) is always accompanied by larger gear ratios, more torque multiplication and therefore also speed multiplication from them.

But when driving for peak multi gear performance this potential maximum in gear acceleration (referred to in the first sentence in this section) is never actually even felt (except in 1st gear). This is evident since a graph of drive wheel force vs. speed for all gears (again Newtons laws repeated for each gear) mandates operating well past peak torque and in the upper rpm ranges near or past redline (just pick a speed and follow the graph of force by gear up vertically to find the maximum force). It will always mandate the lowest gear which forces the highest rpm and hence the peak power (again AT THAT speed, not the engines peak power). You can also see this from a = P / (m x v). In short at any given speed using the lowest gear that does not exceed redline both maximizes acceleration and power (total common sense there and consistent with the math).

This just so happens to be right along the lines of Bruce A's old and lengthy "essay" on this topic.

In short to "prove" power to weight is more important than torque to weight you need,

-Newtons law, F=ma
-The definition of power slightly re arranged, a = P/(m x v)
-An understanding that ICE cars are pretty much designed with gearing that is matched to their engines to maximize acceleration

You can't really just say a = P/(m x v)

So maximum potential in gear instantaneous acceleration is governed by peak torque to weight whereas multigear overall acceleration is governed by power to weight.
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      12-16-2009, 06:33 PM   #222
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Quote:
Originally Posted by swamp2 View Post
Indeed not a bad criticism. You have to always separate wheel values from engine values and I was referring all along to T as wheel torque. However, torque at the wheels is simply engine torque x gear ratio x final drive x efficiency, so I could have substituted this relationship and then had one showing a vs. T. There a similar difference (less the gear ratios) in a = P/(m x v) since the power the engine develops is not all available for power that actually is accelerating the vehicle due to parasitic losses. In other words there is still the efficiency factor. OK, that is nitpicking...

Thinking more about this I think I have it figured out a little bit more concisely. But not much... You must speak about what is typical because the physics does not rule out bad designs that may break the "rules". This explanation covers both gearing and torque vs. horsepower.

Single in gear peak acceleration levels across the entire rpm or speed range (not typically how you drive when at full clip obviously!) are governed by peak torque to weight. This is simply a result of Newtons 2nd law when you work out the math. However, the length of time you can remain in any given gear and the peak speed you will obtain is more governed by peak power since a high redline (in a roughly acceleration optimized gear set) is always accompanied by larger gear ratios, more torque multiplication and therefore also speed multiplication from them.

But when driving for peak multi gear performance this potential maximum in gear acceleration (referred to in the first sentence in this section) is never actually even felt (except in 1st gear). This is evident since a graph of drive wheel force vs. speed for all gears (again Newtons laws repeated for each gear) mandates operating well past peak torque and in the upper rpm ranges near or past redline (just pick a speed and follow the graph of force by gear up vertically to find the maximum force). It will always mandate the lowest gear which forces the highest rpm and hence the peak power (again AT THAT speed, not the engines peak power). You can also see this from a = P / (m x v). In short at any given speed using the lowest gear that does not exceed redline both maximizes acceleration and power (total common sense there and consistent with the math).

This just so happens to be right along the lines of Bruce A's old and lengthy "essay" on this topic.

In short to "prove" power to weight is more important than torque to weight you need,

-Newtons law, F=ma
-The definition of power slightly re arranged, a = P/(m x v)
-An understanding that ICE cars are pretty much designed with gearing that is matched to their engines to maximize acceleration

You can't really just say a = P/(m x v)

So maximum potential in gear instantaneous acceleration is governed by peak torque to weight whereas multigear overall acceleration is governed by power to weight.
I think we're in complete agreement at this point swamp, and this is quite an elegant explanation in my opinion. I was - in a droll and trollish fashion - simply making the point that there are certain characteristics of vehicle dynamics that aren't relative to the hardware that delivers the power.
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      12-16-2009, 06:52 PM   #223
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Quote:
Originally Posted by Jim Pearce View Post
I think we're in complete agreement at this point swamp, and this is quite an elegant explanation in my opinion. I was - in a droll and trollish fashion - simply making the point that there are certain characteristics of vehicle dynamics that aren't relative to the hardware that delivers the power.
Cool, I agree, that's great. Too bad more discussions and debates don't end this way. You helped keep me honest and helped me look for better ways to say things.
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      12-17-2009, 02:28 AM   #224
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      12-17-2009, 03:29 AM   #225
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This discussion is too heavy for holidays, but here's a quote from BMW Exec

Quote:
Still, BMW's North America president, Jim O'Donnell, isn't sure about a durable change in consumer culture. "I have it in the back of my mind that consumers are saying in interviews that they'll change habits, but I'm yet to be convinced," he said. In case the change turns out to be more ephemeral than it now appears, BMW's "joy of driving" campaign could morph into a theme that's more hedonistic. BMW looks at "joy" as a flexible concept. "You can twist" the idea, Mr. O'Donnell said.
BMW has a heavy marketing machine that can't be stopped. So to those who drinks the kool-aid I can only say drink with moderation. In the end it's not my money, spend it wisely.
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      12-17-2009, 04:28 AM   #226
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Let me show you what BMW and others that manufacture in Europe will have to get their overall emissions down to by 2015 and might go some way to explaining the switch to smaller FI units instead of maintaining the larger capacity motor of old.

2015 European Co2 emissions regulations

So what I am saying and have been saying for heaven knows how long is that the switch is coming whether you like it or not and with the M3 is more of an issue because of the sales volume than than it is will other rival brands.
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      12-17-2009, 04:53 AM   #227
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      12-17-2009, 08:17 AM   #228
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I love my ///M
I love my M, too...except for the lack of torque, of course

Just kidding. Happy holidays everyone.
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      12-17-2009, 09:57 AM   #229
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I thought I should mention here what the advantages of a normally aspirated engine over a forced induction engine are, or more to the point a flat, wide torque curve vs. a peaky, high, narrow torque curve. Just so everyone is on the same page.

In either case the designers and engineers will match the gearing to the engine's characteristics. So, in the end both types can be equivalent in a drag race. However, with a wide torque curve with a lower maximum torque, the whole drive-train need only be designed to handle this lower maximum torque. Therefore, it can be smaller and lighter. That's not only lighter but it is rotating mass that is lighter. This has benefit for engine response and control, and even handling. The difference might seem small but for those who really want to maximize all aspects of a cars performance then it adds up.

Another aspect of a high revving, flat torque engine is that this type of engine is usually associated with racing, since you spend more of your time near red-line in a race. Although the M3 (and all the M cars) are street cars first, the whole M concept started out as racing cars that could be put on the road. As time went on the disparity between what is required for a road car and a race car grew wider -- airbags, cats, etc. are required for a road car but just add weight and complexity to a race car. So its really not feasible to make a car just for racing and have it be road-legal (and give most drivers what they want for daily driving) too. Especially if you're considering selling a lot of them. I'm sure BMW still wants to make money. BTW, an M3 still makes a good car for tracking (among the other road-legal cars). But I see the M3 as rather a road car that is exceptional at practically everything anyone would ask of a road car.

So, that is why many prefer a normally aspirated engine with a wide, flat torque curve over an engine that has the same horsepower but more (maximum) torque.

I hope our two experts here (Mr. Swamp and Mr. Pearce) can agree.
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      12-17-2009, 10:36 AM   #230
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Quote:
Originally Posted by ersin View Post
I thought I should mention here what the advantages of a normally aspirated engine over a forced induction engine are, or more to the point a flat, wide torque curve vs. a peaky, high, narrow torque curve.
I'm no expert, but it isn't clear to me that a forced induction engine can't have a relatively flat powerband of 5,000+ rpm. Of course it would start 1,000rpm lower. Actually I think the M engineers will solve both this and the "linear throttle response" fairly easily. More torque at the wheel, on the other hand, is a real challenge in terms of both traction and the effects of weight transfer under maximum acceleration. This is why I'm guessing that the F30 M3 will feature an active differential.
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      12-17-2009, 10:50 AM   #231
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Quote:
Originally Posted by Jim Pearce View Post
I'm no expert, but it isn't clear to me that a forced induction engine can't have a relatively flat powerband of 5,000+ rpm. Of course it would start 1,000rpm lower. Actually I think the M engineers will solve both this and the "linear throttle response" fairly easily.
I would say keep dreaming. That is all wishful thinking, like mentioned plenty of times before. The 5000+ rpm flat powerband is irrelevant when the car only revs up to 6800 - 7000 rpm. Using tall gearing, it does not need any power above 5000 rpm and given the turbo makes all its peak at 1500 - 1800 rpm, the cross over with HP at 5252 rpm dictates that it will never be making more than 60 - 70% of its peak torque above 5252 rpm since the peak HP does not happen until 6500+ rpm. It is physically impossible unless the torque peak gets shifted up in the rpm band.

The linear throttle response is another wishful thinking. Porsche has not been able to remove that because it is a nature of how turbo works and they are currently the leader in terms of getting better throttle response using variable turbine geometry. Even by changing the angle of attack of the turbine blades, it still requires reasonably more time to spool up than say a completely N/A high-revving GT3, which is instantaneous. Still the best throttle response in Porsches are in the GT3 and the older Carrera GT. None of the turbo Porsches come even close.

Yet, in the SUV market, they have been more successful than BMW since the throttle response, although laggy, in the Porsche Cayenne Turbo S is still WAY better than the X5 M because the Turbo S uses Variable turbine geometry while the BMW does not.
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      12-17-2009, 10:54 AM   #232
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Sorry but it's a shame you can't hear the laughter I am having right now. FI engine's don't have flat torque curves I heard you say, ARE YOU SERIOUS.

As a percentage of over the entire rev range you will find that FI units offer a bigger percentage of 'flat' torque compared to any N/A engine, even the M3 which I might add is truly brilliant at this.
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      12-17-2009, 12:32 PM   #233
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Do you really want to get me started again on this?

If you understand how physics works and what torque and HP crossover point means, you will know a car that makes 400 HP and 400 ft-lbs@ only 1500 rpm will have its torque curve nose dive past 5252 rpm and will not be making more than 50 - 70% past 5252 rpm since at this cross over point, that is the maximum a car can achieve in terms of HP. Unless the peak torque in the turbo car somehow gets shifted past 5000 rpm in order to achieve a flat torque curve using different internals, turbos and tune, which is irrelevant to this discussion.

Did you forget how you kept bragging about your beloved Audi and how the supercharged S4 torque curve is flat and after doing some investigation, I burst the bubble when I posted a multitude of dynos of the new S4 where the torque curve plummeted like no tommorow past 5000 rpm?


Quote:
Originally Posted by footie View Post
Sorry but it's a shame you can't hear the laughter I am having right now. FI engine's don't have flat torque curves I heard you say, ARE YOU SERIOUS.

As a percentage of over the entire rev range you will find that FI units offer a bigger percentage of 'flat' torque compared to any N/A engine, even the M3 which I might add is truly brilliant at this.
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      12-17-2009, 12:35 PM   #234
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Quote:
Originally Posted by footie View Post
Let me show you what BMW and others that manufacture in Europe will have to get their overall emissions down to by 2015 and might go some way to explaining the switch to smaller FI units instead of maintaining the larger capacity motor of old.

2015 European Co2 emissions regulations

So what I am saying and have been saying for heaven knows how long is that the switch is coming whether you like it or not and with the M3 is more of an issue because of the sales volume than than it is will other rival brands.
Oh, so that is why BMW, a car company that can't brag enough about its efficient dynamics, felt the need to release two obese gas guzzling DI FI land yachts, weighing in at around 5400 pounds, can attain an amazing 17 mpg highway, going 55mph down hill with a tail wind. Now I am finally a believer in BMW's constant beckon cry for efficient dynamics to meet those difficult emission standards, especially given their higher sales volume over key rivals.
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      12-17-2009, 12:39 PM   #235
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Quote:
Originally Posted by 330CIZHP View Post
Do you really want to get me started again on this?

If you understand how physics works and what torque and HP crossover point means...
I'm game. What is the physical meaning of "torque and horsepower crossover point"?
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      12-17-2009, 12:46 PM   #236
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Quote:
Originally Posted by Jim Pearce View Post
I'm game. What is the physical meaning of "torque and horsepower crossover point"?
On a graph the torque line is falling/staying constant while the horsepower line is rising. So the two lines cross one another. Take a look at a dyno print out.

Would you like me to explain using some example of dyno of your "awesome" ~380 whp 335 dynosheet?
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      12-17-2009, 12:54 PM   #237
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Quote:
Originally Posted by 330CIZHP View Post
On a graph the torque line is falling/staying constant while the horsepower line is rising. So the two lines cross one another. Take a look at a dyno print out.

Would you like me to explain using some example of dyno of your "awesome" ~380 whp 335 dynosheet?
An artifact of the units chosen and the presentation.
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      12-17-2009, 12:58 PM   #238
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Quote:
Originally Posted by 330CIZHP View Post
Do you really want to get me started again on this?

If you understand how physics works and what torque and HP crossover point means, you will know a car that makes 400 HP and 400 ft-lbs@ only 1500 rpm will have its torque curve nose dive past 5252 rpm and will not be making more than 50 - 70% past 5252 rpm since at this cross over point, that is the maximum a car can achieve in terms of HP. Unless the peak torque in the turbo car somehow gets shifted past 5000 rpm in order to achieve a flat torque curve using different internals, turbos and tune, which is irrelevant to this discussion.

Did you forget how you kept bragging about your beloved Audi and how the supercharged S4 torque curve is flat and after doing some investigation, I burst the bubble when I posted a multitude of dynos of the new S4 where the torque curve plummeted like no tommorow past 5000 rpm?
I suggest you chew on this for a little while. Below is old Audi technology. Current BMW and Audi technology blows this away. Not only does the plain Jane RS6 have a torque plateau over 3600 rpm wide, it has a HP plateau over 700 rpm wide. Not only do both engines surpass your magical 5252 threshold, they blast though it. These are totally understressed 4.2 litre engines built by Cosworth.

BCY, C5 RS6: 331 kilowatts (450 PS; 444 bhp) @ 5,700-6,400 rpm; 560 newton metres (413 ft·lbf) @ 1,950-5,600 rpm
BRV, C5 RS6 Plus: 353 kilowatts (480 PS; 473 bhp) @ 6,000-6,400 rpm; 560 newton metres (413 ft·lbf) @ 1,950-6,000 rpm
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      12-17-2009, 12:58 PM   #239
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Quote:
Originally Posted by Jim Pearce View Post
An artifact of the units chosen and the presentation.
What is that supposed to mean? I simply offered to pick a random dyno sheet of a 380 whp 335 and explain what the cross over means. If you are unable to make arguments that justify your beliefs, why resort to sarcasm?
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      12-17-2009, 01:04 PM   #240
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Can I please look at an actual dynosheet? I would like to see how the curve looks across the entire rev range.

Quote:
Originally Posted by Radiation Joe View Post
I suggest you chew on this for a little while. Below is old Audi technology. Current BMW and Audi technology blows this away. Not only does the plain Jane RS6 have a torque plateau over 3600 rpm wide, it has a HP plateau over 700 rpm wide. Not only do both engines surpass your magical 5252 threshold, they blast though it. These are totally understressed 4.2 litre engines built by Cosworth.

BCY, C5 RS6: 331 kilowatts (450 PS; 444 bhp) @ 5,700-6,400 rpm; 560 newton metres (413 ft·lbf) @ 1,950-5,600 rpm
BRV, C5 RS6 Plus: 353 kilowatts (480 PS; 473 bhp) @ 6,000-6,400 rpm; 560 newton metres (413 ft·lbf) @ 1,950-6,000 rpm
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      12-17-2009, 01:23 PM   #241
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Quote:
Originally Posted by 330CIZHP View Post
Can I please look at an actual dynosheet? I would like to see how the curve looks across the entire rev range.
It's flat as Kansas from 1950 rpm to 5600 rpm. The torque is actually managed by the engine management computer to remain constant. That's why tuners can get way over 500 lb-ft of torque out of those motors.

Somewhere I have the factory dyno chart for the standard RS6 engine. I wanted to post it, because it is very impressive.
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      12-17-2009, 01:34 PM   #242
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I don't doubt it is flat from 1950 - 5600 rpm. It is much like the Porsche 911 Turbo 997 that delivers 500 wheel torque across a similar range. Still that is just a 3600 rpm range.

It was the entire curve across the rev range, cross over points and how the torque curve looks like at the top end of the car that I was interested, which is why I requested the dyno.

Quote:
Originally Posted by Radiation Joe View Post
It's flat as Kansas from 1950 rpm to 5600 rpm. The torque is actually managed by the engine management computer to remain constant. That's why tuners can get way over 500 lb-ft of torque out of those motors.

Somewhere I have the factory dyno chart for the standard RS6 engine. I wanted to post it, because it is very impressive.
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