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///M3 Forum
The BMW E46 ///M3 is the M version E46 and puts out an amazing 333 HP and 262 lb-ft of torque at stock specs! There are an amazing amount of modifications for both the coupe and convertible models so read up and get started modifying your cars today!

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Old 06-22-2013, 02:55 PM   #1
BurgundyM3
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Why not use HP/Torque by average over full rev range instead of peak?

just curious

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Old 06-22-2013, 07:56 PM   #2
karl hungus
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Engine power output is proportional to the amount of fuel burned in a given unit time. So, to increase that output you must improve overall volumetric efficiency and try to generate more cycles in the same unit of time. This means increasing engine revs.

This is a quote. If you even wondered why F1 engines are designed to rev at 19,000RPM, this is your answer. With engine capacity and volumeric efficiency being equal, a higher revving engine will generate more power.
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Old 06-23-2013, 03:32 AM   #3
BurgundyM3
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Thanks for the reply. I regret deleting the original text that I wrote. What was left was quite vague.

In short I was speaking of quoted performance figures using only Peak HP and Trq numbers. I think it might be helpful to show what the average output is throughout the full range of revs from idle to redline, an average output for HP and TRQ.

Anyhow thanks for the reply
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Old 06-23-2013, 10:20 AM   #4
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here's my take:
HP is calculated as a product of torque x RPM x a conversion constant. Torque is fairly flat, but obviously HP increases as RPM increases. The combustion rate of fuel along with valve timing, piston stroke & diameter, compression, engine complexity and more affect the output of the engine.

The peak values are surely given because they are bigger; which sells better and wins contests of numbers. Stating average might be OK for torque, but HP is a different matter as it clearly peaks since it is dependent on RPM. At which RPM that peak occurs can indicate engine behavior and driveability.
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Old 06-23-2013, 10:45 AM   #5
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When describing a cars power. It's easy to explain and visualize a number. You can't easily describe how a power band looks when selling a car or just describing it unless you had pictures. Peak numbers is something easily interpreted
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Old 06-23-2013, 09:50 PM   #6
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you're talking about the area under the torque curve, right?
best estimate of all out performance and tractability.

to understand that, you need some background in mathematics. on the showroom floor, its easier to explain a number than a concept.
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Old 06-26-2013, 04:58 PM   #7
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I just figured it a more realistic value than using only the peak power which is...just at peak.
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Old 06-26-2013, 07:31 PM   #8
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The majority of the population of the world doesn't care to know how much a car makes anyways lol
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Old 06-27-2013, 10:55 AM   #9
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Peak horsepower and torque figures are used to advertise and sell cars, but they do not mean what most people think they mean. What most people don't understand is that (1) while the 2 are related, there is a difference between horsepower and torque, and (2) the amount of power generated by an engine isn't as important as how and where it is generated. Horsepower is a measure of the amount of work the engine can produce, while torque is a measure of the force available to perform that work. Horsepower is computed as torque times the rpm at which it is generated divided by 5252. Thus, an engine can generate a lot of power by developing a moderate amount of torque at high revs or by developing large amounts of torque at modest revs. Think of it like 2 athletes, one of whom is a track star and the other of whom is a weight lifter. If the weight lifter can pick up a 500 pound weight and walk it 10 yards in 1 minute, he has accomplished a certain amount of work (ie horsepower). If the track star can run that same 10 yards 10 times in the same minute, while carrying 50 pounds of weight each trip, he has accomplished the same amount of work in the same period of time. Both engines, weight lifter and track star, generate the same horsepower, but the weight lifter generates much more force (torque).

Generating massive torque at high rpms is possible, but can be prohibitively expensive. Forced induction engines tend to have more moderate redlines, because both forced induction and high engine speeds generate a substantial amount of heat, which can lead to turbo failure. Large displacement engines are expensive to get to high revs because bigger parts tend to have more mass to reciprocate. Moreover, there is a sweet spot at about 0.5 litres per cylinder that is optimal for power development, which means that an engine much larger than 3 litres of capacity is better off with more than 6 cylinders. That's why you don't see 4, 5, or 6 litre 6 bangers. That's probably also why the e92 M3 has a V8.

The amount of power and force that an engine can generate depends upon the volume of fuel that it can effectively burn. This volume can be increased by increasing the size of the engine, by forced induction, by improving both intake and exhaust functions, or by boosting the engine's rev capability. Boosting displacement and using forced induction will increase torque because each power pulse is bigger. Increasing rev limits does not increase the size of each power pulse, and while it does increase frequency, the impact on torque is minimal. As most people on this board have realized, the M3 is close to optimized as it came out of the factory. There isn't much that we can do to increase power substantially without going to forced induction.
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Old 06-28-2013, 11:05 PM   #10
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Re: Why not use HP/Torque by average over full rev range instead of peak?

Op, I've thought the same thing before. What's the point in having a high peak HP but its barely usable. I would rather have less power more accessible to me. I wish companies would calculate/report the area (amount of space) (integral - calculus term ) under the power curve. This is a more realistic figure for determining power in my opinion because it says how much power is across the entire RPM band. So its like, how much power can your car produce period instead of how much at one time (peak)

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Old 06-29-2013, 03:30 AM   #11
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Well if you want a good representation of how the car feels, simply knowing the average numbers doesn't help a whole lot. You can have some really low points and some really high points, and that average might still seem reasonable. Area under the torque curve is helpful (or average * rev range), especially if they also supply you with an average slope. Ideally that slope would be near 0

Peak power is actually a pretty decent metric if you have a flat torque curve (or near flat). For the most part, a 300hp car will accelerate like a 300hp car as long as they're have flat curves and are geared properly for their rev limits. Area under the curve would be near identical in a low-torque/high revving car and a high-torque/low revving car. You can see this by comparing M3 and 335 graphs. Calculate a middle Riemann Summation with each partition being ~1000 RPM apart. You'll find the resulting numbers to be really close

Problem with the peak power number is that these days many cars have torque surges in the middle, so you get little idea of how the car behaves down low.

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Old 07-01-2013, 08:24 AM   #12
DSilk56
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Quote:
Originally Posted by TerraPhantm View Post
Well if you want a good representation of how the car feels, simply knowing the average numbers doesn't help a whole lot. You can have some really low points and some really high points, and that average might still seem reasonable. Area under the torque curve is helpful (or average * rev range), especially if they also supply you with an average slope. Ideally that slope would be near 0

Peak power is actually a pretty decent metric if you have a flat torque curve (or near flat). For the most part, a 300hp car will accelerate like a 300hp car as long as they're have flat curves and are geared properly for their rev limits. Area under the curve would be near identical in a low-torque/high revving car and a high-torque/low revving car. You can see this by comparing M3 and 335 graphs. Calculate a middle Riemann Summation with each partition being ~1000 RPM apart. You'll find the resulting numbers to be really close

Problem with the peak power number is that these days many cars have torque surges in the middle, so you get little idea of how the car behaves down low.
That's a very good point, but keep in mind that the launch techniques will differ, since low torque engines need to be launched at a high enough rpm to keep the engine in its power band and keep the engine from bogging down. This will favor the high-torque engine in the hands of an inexperienced driver. It also favors clutch wear. Moving away from drag racing, the opposite is true. Engines that develop power at the upper end tend to be better on high speed circuits.
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