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Why BMW needs turbo for E54 engine to acheive 306hp?
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02-28-2006, 07:48 AM | #111 | |
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02-28-2006, 09:24 AM | #112 | |
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I agree with your points. Except you are referring to *instantaneous acceleration*. The maximum *instantaneous* acceleration of any car in any one gear is at its maximum torque - no dispute about that. *But*, when people talk about and measure the acceleration of a car, they are not measuring the *maximum instantaneous accleration*! The 0-60 times are a measure of the *average acceleration* up to a certain speed. And for this reason the torque rating for any car (which is the *maximum instantaneous torque*) is *not* a measure of how fast the car will accelerate (by this we mean *average acceleration over a range of speeds). All the torque rating for any car will give you is a measure of the maximum torque, or maximum instantaneous acceleration at any one point in the engine's rev range. You *cannot* estimate how fast a car will accelerate over a wide range of speeds with just a torque rating. All you can say from a torque rating is "At a certain rpm, the engine will have its maximum instantaneous accelration". So what is the best measure of how fast a car really accelerates (ie not *instantaneous* but *average accleration*)? Well, the best is to see the torque curve. But what does the torque curve really tell you? It tells you the torque of the engine over the entire engine's RPM range. And if we were to compute this data into a single number - that would be the *power* of the car. "Power" (from basic physics) is simply the energy expended by the engine over a period of time. This factors in the entire torque curve of the engine over the entire RPM range. To reiterate, you are correct to say that an engine with a greater max torque would have the greatest *instantaneous acceleration* at a certain point in time. But this is useless information. We don't know how the car acclerates at any other point in the rev range. A 530d will have a much greater *instantaneous* maximum accleration than a 530i. But who cares? When you race the car, you aren't at max torque the whole time...the rev range of the engine and the torque characteristics of the engine at 'non-peak' parts of the range are just as important to *overall average acceleration* (ie the acceleration that will get you from 0-60!) To say that power has nothing to do with acceleration is ignorant. It has nothing to do with *instantaneous* acceleration is true! But it is a far greater predictor of average acceleration, which is what everyone talks about when they say "How fast is your car from 0-60?) And yes, greater power = greater speed. But this is simply because the terminal velocity of a a more powerful car is higher because the engine can expend more energy by providing more overall force to overcome air resistance! |
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02-28-2006, 09:36 AM | #113 |
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A quick summary to sum everything up:
Torque rating: Relates to a car's maximum instantaneous acceleration Power rating: Relates to a car's average acceleration over a range of speeds If you had to cars equal in all respects and had to choose between two engines, one with higher torque and the other with higher power, which would you choose for a race from 0-60? (Or 0-100 or any test of average acceleration over a wide range of speeds)? The car with the greater power. If you *really* want to know how a car will *feel* like to drive, what do you need? The torque curve. As Garrett says, this will exactly mirror the instantaneous acceleration of a car at any RPM point and it will tell you how wide a range you have to extend the car. In any case, the new 335i's engine looks fantastic. Especially for everyday driving, which is in the < 3500 RPM range (where the torque of this car is optimised). For this reason it may well 'feel' faster than an E46 M3 in everyday driving (the M3 has far less torque than the 335i in the < 3500 RPM range). But don't kid yourselves, if you were to race the two cars - the E46 M3 would rip the 335i to shreds. |
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02-28-2006, 09:49 AM | #114 |
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What a refreshing post Durbrain, I was beginning to wonder if anyone could express themselves clearly and without vitriol on this subject.
I agree with most of your points, although even power is not a true indicator of acceleration since that maximum power may arrive at 7000 revs with nothing much in the way of torque output at anything less than this. Clearly an accelerative powerplant needs plenty of torque spread across a wide range of revs that can then be exploited by well matched gearing. Just to add to your comments here's a post I made on another forum that talks about the 'feel of acceleration'; "Whenever you accelerate in 'any' car, the shove in the back is caused by torque being transferred to the road. The more torque being transferred to the road, the stronger that feeling will be. The second thing you notice is the consistency of that torque output, whether it's even or if it kicks up at some point (as in the VTEC engines). Then thirdly you notice how sustained the torque output is, so rather like a fairground ride, how long the ride continues to accelerate will be another factor in determining how fast it feels. So if I was choosing an engine, I'd be looking at how much torque is produced, how consistently this is delivered and how long it lasts for. Factor in a glance at the gearing, vehicle weight and peak power and I'd have a pretty good idea about how it feels, whether it is effortless and how accesible and usable that performance is. " |
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02-28-2006, 10:30 AM | #118 | |
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Imagine a 10ft giant running against a 6ft athlete. The giant might be stronger, but the athlete can run faster, because he can use his lesser strength to stride forwards more frequently. To be quickest he must be strong and fast |
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02-28-2006, 06:02 PM | #119 | |
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torque is twisting force horse power is measured by the effort needed to move 1 pound, 1 foot up in the air in one minute!
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02-28-2006, 06:27 PM | #121 | |
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When accelerating, HP is what matter most at any RPM. Your Prius example was excellent. It is a car that doesn't pull that much, yet it has a tons of torque. |
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02-28-2006, 06:36 PM | #122 | |
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Horsepower ratings Vehicle 2005 2006 Acura MDX 265 253 Acura RL 300 290 Acura RSX 160 155 Chevrolet Corvette LS7 500 505 Cadillac XLR 440 469 Ford Explorer* 210 210 Honda Civic 200 197 Lexus LS430 290 278 Pontiac G6 200 201 Toyota Corolla 130 126 Scion xB 108 103 I just did a search and found a article titled "Asians oversell horsepower." The numbers above are from that article. (http://www.detnews.com/2005/autosins...A01-283759.htm) Now I know there is only one Lexus mentioned. The trend is what I'm more concerned with. Overall, cars from Japan lost more with the new testing standard. No mention of BMW losing one horse. You may call it bias...I call it a well supported opinion. |
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02-28-2006, 07:41 PM | #123 | |
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Again, we are not talking about a car's acceleration. We are talking about at what point is the the car accelerating at it's fastest rate. And more specifically at what RPM is that ? And even more specifically; is the point in which the car is at is fastest acceleration near or at it peak torque output...? And the answere to this is: YES! -Garrett |
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02-28-2006, 07:49 PM | #124 | |
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I do not look at torque in terms of a # ie.. 256ft-lbs... I do not care what maximum torque is. Thats not even the dabe or an issue. I look at the powerband. But when looking at a POWERBAND, there will be a point in which Torque will be at it maximum. And that is usally listed as Peak Torque... coincidentally at or near this point is when a car will accelerate it's fastest. There is nothing more to my arguement, no amount of you trying to put words into my mouth or suggesting. And it also a FACT. Because of what torque is. Torque is the engines propensity to accelerate motion, while HP is the power to maintain that motion. (In a nuttshell) Last edited by Garrett; 02-28-2006 at 08:07 PM.. |
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02-28-2006, 07:53 PM | #125 | |
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I never said that... I NEVER compaired torque from one car to the next. This is not the arguement at hand. Take any car... I don't car which. Post the Dyno Chart. For now on we will debate at what point THAT car is accelerating is hardest... OK ? |
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02-28-2006, 08:03 PM | #126 | |
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I'm reporting Saintor as a TROLL. He obviously hasn't read anything here and is purposely playing ignorant to incite board members. SAAB does not claim peak torque @1,900rpm's..! I've listed 2 dyno charts yesterday (about 10 post back) from several SAABs. And have repeatedly ask you to produce such a fact. Not only have you ignored every point made, you replies no longer back your original statement and have since started to include arguements which no one is even dabating. Saintor, I repeat, what model and year is the SAAB your talking about. -Garrett |
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03-01-2006, 01:35 AM | #127 | |
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The 330d pulled best from 2500-4000 The E46 M3 from 6000-8000 near or at the highest BHP But that's irl .Theoretically it must be what you are saying. |
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03-01-2006, 02:04 AM | #128 | |
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When people compare specifications of cars, they don't give a crap about the peak acceleration (which, yes, occurs at peak torque) - they care about how well a car accelerates on average! Tell me - what is the usefullness of knowing the peak torque or peak acceleration of an engine? It is completely useless information in isolation and tells you *nothing* about how a car really performs. People look at two specifications when comparing cars: - Power (ie *peak power*) - Torque (ie *peak torque*) The question should be - "Of these two, which is the better measurement of how well a car performs?" The answer is power (ie *peak power*). |
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03-01-2006, 02:06 AM | #129 | |
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03-01-2006, 03:48 AM | #130 | |
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Comparison E46 330d I had first(184BHP/390Nm) vs E46 330i which I had after the diesel(231BHP 300Nm) In real life the 330d with it's TORQUEY engine felt way faster when driving NORMALLY through traffic than the 'lame' 300Nm 330i. But when it came to REAL performance(redlining it)(also on trackdays) the 330d wouldn't stand ANY chance at all. |
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03-01-2006, 06:59 AM | #131 | |
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Exactly, and your intelligent enough to understand. But, what I'm trying to show Saintor has been lost to you. If you press the gas pedal or mash it... the car will accelerate ..! But the car doesnt accelerate at the same rate throughout the entire revband. If you look at the torque curve to any car... THAT car will accelerate almost identically as fast (rate) as the torque curve. Speed is a point in time... acceleration is the rate of speed...!! But you confusing the issue. Saintor claims that Horsepower is what you feel the rush of when a turbo kicks in. Someone corrected him on this. He came back and called him an idoit. So I felt obligated to start his education. It's a simple concept to understand if you accept a few fundemental things. People tend to complicate Torque, thats why I'd like to have a Dyno chart he is familiar with. I am not in disagreance that "average" acceleration is better than "peaky". Thats whi I enjoy and herold pridigous amounts of FLAT torque. But what I like or look for is not the debate or question in hand. All you need to look is extensive studies of acceleration charts or G-Meter reading to see how torque cooralates to acceleration. I am taking a LAYMANS approach to dealing with Saintor because I cannot presume to know what level of knowledge he posseses. -Garrett |
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03-01-2006, 09:13 AM | #132 | |
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But, I *am* pointing out that what you're saying is largely irrelevant when it comes to looking at the specs of a car. No car's specifications come with a torque curve. The only two specifications car manufacturers give us is peak power and peak torque. If we are to choose one which would best represent the performance of the car (ie the 'average' acceleration...since, as you said, acceleration is *not* constant throughout the rev range...unless there is a completely flat torque curve...which never happens) - then you need to look at power. I'm not sure you understand the concept of 'average' acceleration (if you do, forgive me) - so let me explain it. If a car accelerates from 0 - 30 at say 2ms^2, then accelerates from 30-60 at say 4 ms^2, then the *average* acceleration from 0-60 is 3 ms^2. That is, even though the car never actually accelerated at 3 ms^2, the time it took for the car to accelerate from 0-60 is equivalent to the time it would have taken *if it were travelling at 3 ms^2 the entire time). This *average* acceleration is what is important, when discussing the overall performance of a car. And *average* acceleration best correlates with the *peak power* of a car. Hence why *power* is the best marker of the performance of a car. You seem fixated on the fact that the *instantaneous acceleration* (ie the exact acceleration at any point in time) exactly mirrors that of the torque curve. This is true. I am not disputing this. But it is useless information. It tells us very little! If you read the torque curves of two cars, yes, of course you can tell me exactly when each car will accelerate at its maximum. But who cares?! You can't tell me which car is going to be able to perform better overall? When people compare the performance of cars, they don't go "Oh, well my car peaks its acceleration from 2000-4000rpm, wow isn't that great?" No!! They go "My car does 0-60 in 5 seconds". The torque curve is an interesting piece of information if you want to know how a car will feel like to drive. Ie will it feel linear (a flat torque curve, and hence relatively constant acceleration) or will it feel peaky (a torque curve that rises to a peak then drops, with mirroring acceleration rates). But it won't tell you how fast the car will go from 0-60, 0-100, 30-100 etc etc. |
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