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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > General E90 Sedan / E91 Wagon / E92 Coupe / E93 Cabrio > Why BMW needs turbo for E54 engine to acheive 306hp?



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      03-01-2006, 10:25 AM   #133
Durbrain
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One final reply from me.

Too many people say that:
"Torque = acceleration and Power = top speed". That's such a gross over simplification that it becomes a stupid statement.

What do people mean when they say 'acceleration'. Do they mean the *instantaneous* acceleration (which varies with RPM), or do they mean *average* acceleration (which is constant)?

The "push you feel in the back" when you mash the pedal is *instantaneous acceleration* - and this is what Garrett refers to. The *instantaneous* acceleration correlates to the torque curve of the engine. So if the torque curve rises from 100Nm at 2000rpm to 200Nm at 4000 rpm, you will feel twice the 'push' (ie the force) and hence twice the (instantaneous) acceleration at 4000 rpm than you do at 2000 rpm.

But when people talk about 0-60 times, this is a measure of the *average* acceleration. The *average* acceleration of a car is constant.

But ppl don't make this distinction when they say stupid phrases like "Torque = acceleration, Power = top speed".

A more accurate statement would be "Torque = *instantaneous acceleration*, Peak Torque = *max instantaneous acceleration* and Power = *average acceleration*". Taking this perspective into account, *both* torque and power relate to acceleration, it just depends on whether you are speaking of *instantaneous* acceleration or *average* acceleration.

That being said, *average* acceleration is the key to an engine's performance. So if you want a car to be accelerate quickly to high speeds, look at power, not torque.
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      03-01-2006, 04:59 PM   #134
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Quote:
Originally Posted by Durbrain
I'm not confusing the issue. I'm not disagreeing with what you're saying. And yes, I know what 'acceleration' is - any junior high school student knows what that is!

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.


Yes..YES and YES. But NO !!!

I KNOW it's irrelevant. If I tell you that my car has 4 tires, that is also irrelevant, but is also TRUE.

Torque=Acceleration

Your trying to put words in my mouth and teach me something I am fully aware of. Also, your "intantanious acceleration" is not my words or my analogy. I'm talking about the RATE of acceleration. As infatesmol or irrelevant as it is in dealing with the overall acceleration of a car. Never-the-less, the rate of acceleration is fastest at the highest torque point within the engine. Albiet, minus anomolies such as torque converter, clutch and limited slip...etc.

Now there are many small discrepancies in CARS that will alter that formula somehwhat.... but those are irrelevant to the overall debate at hand. In which your in agreeance with me on.

"Average acceleration" was in quotes... because it was something you (or another said) Not my words. Meaning, but you can have an engine with a torque curve like a bell (Peaky) or one thats more smoother and more of a perfect curve like the top of a basketball.

If the bell curve has 400 ft-lbs and the Ball curve has 350 ft-lbs i would chose the Ball curve. Because overlaying the two, the ball curve has more torque when compairng their delta's.

*BUT THAT IS NOT THE TOPIC OF THIS DISCUSSION*

Just because I didn't discuss it earlier or add any other benifits from torque doesnt mean I'm unknowladgeable, I'm just trying to keep this debate on track... and if you havn't read this whole thread let me remind you what we were dealing with.



Quote:
Originally Posted by Saintor
Turbo (x2) is a stupid stupid idea for only 300HP. Even Audi abandonned it. They just had to throw in the "old tech" M3 engine and they would got... 333HP. In the end, these double-turbo engines takes as much fuel as larger engines and they would have been better with a larger displacement at the beginning. I owned 2 turbo cars. Harder to resell at high mileage, too.

Crazy move from BMW.
.
Quote:
Originally Posted by Saintor
Completely FALSE. HP is what matter for acceleration. You can have a big engine with top torque figures that will be slow as hell. Not its definition, but HP shows how quickly an engine will change RPM under load.
.
Quote:
Originally Posted by Saintor
No, no, no, no.

Ever tried a 1.8T? 100% of torque at 1600rpm. I can tell you that at 1600rpm, this engine has no trust and not much happens under 2500-3000much

Power is what ultimately will determine acceleration, at any speed.
.



Quote:
Originally Posted by Saintor
No, I am not wrong. You are.

Don't believe one site because you'll get another one that says the contrary on this subject.

Fact is that an engine pulls quicker on peak HP over all gears, NOT on peak torque.

If you have an engine with the following specs, 200HP at 5400rpm and 200lbs.ft at 3500rpm. According your logic, you would have to shift to keep an average close on 3500rpm.

I can tell you right away that the guy shifting at redline, will get you easily, no context. Because he is optimising the average RPM close to the 5400rpm - at peak HP.

As for understanding torque, I am a registered professional mechanic engineer, thank you.

It is not for nothing that in track races, tech people focus ONLY on HP figures, much much less on torque. Not a mistake.

Get it.
.
Quote:
Originally Posted by Saintor
Don't make stupid assumption and imbecile statements. In an engine, torque is NOTHING without RPM. Both torque *AND* RPM define HP. Over gears and the range of RPM, HP is the determinant factor for acceleration.

Again, the one who is lost is not the one you thought.


So, after all that it's obvious he doesnt understand torque. I know what torque is and does... but I am trying to show him ONE simple thing that almost un-debatable. Once he understand or ackowldge it, then we can go on to educate him the other aspects of it.




-Garrett

Last edited by Garrett; 03-01-2006 at 05:15 PM.
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      03-01-2006, 05:30 PM   #135
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Exclamation

Quote:
Originally Posted by Garrett
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

Garrett, you are such an imbecile with your smart-ass attitude. Get your head out of your ass! You can't even find the standard specs for a 2006 9-5 (it took me 5seconds) on saabusa.com

2.3-LITER 4-CYLINDER HIGH-OUTPUT TURBOCHARGED 260-HP ENGINE
Engine specifications–2.3T
Type–4-cylinder turbo
Displacement–140 cu. in. (2,290 cc)
SAE horsepower rating: 260 hp @ 5300 rpm
SAE peak torque: 258 lb. ft. @ 1900-4500 rpm
(Standard)

Quote:
Originally Posted by Durbrain
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*).
...
e 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.
* Exactly *

Quote:
Saintor claims that Horsepower is what you feel the rush of when a turbo kicks in
Absolutely not. You are so confused and stubborn that you can't even properly report accurately what I wrote. What I said is that HP is determinant for acceleration over a range of RPM - at any RPM.
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      03-01-2006, 06:22 PM   #136
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I think Garrett doesn't want to see the point.

please guys.

F1 is about one thing:POWER.
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      03-01-2006, 07:47 PM   #137
Garrett
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Quote:
Originally Posted by Saintor
Garrett, you are such an imbecile with your smart-ass attitude. Get your head out of your ass! You can't even find the standard specs for a 2006 9-5 (it took me 5seconds) on saabusa.com

RETARD.. not only did I find the specs I actually posted the dyno charts of the SAAB's I found about 20 posts ago. I asked you to look at those Dyno charts (page 5 of this thread) to tell me if that was the SAAB engine you've been talking about. But for the last week nobody has had an ideas of WHAT engine you've been yammering about. I repeatedly asked you to post it. SAAB makes more than 1 car.

It's been almost 1.5 weeks and NOW you finally offer the information ..?



2.3-LITER 4-CYLINDER HIGH-OUTPUT TURBOCHARGED 260-HP ENGINE
Engine specifications–2.3T
Type–4-cylinder turbo
Displacement–140 cu. in. (2,290 cc)
SAE horsepower rating: 260 hp @ 5300 rpm
SAE peak torque: 258 lb. ft. @ 1900-4500 rpm
(Standard)



* Exactly *

*EXACTLY* what ...? Did you even read the quote. He said the question should be..... " "Of these two..." But, that is not the question.



Absolutely not. You are so confused and stubborn that you can't even properly report accurately what I wrote. What I said is that HP is determinant for acceleration over a range of RPM - at any RPM.

Saintor, I am not at all concerned about the SPECs. Spec are a snapshot. Peak torque tells you only 1 thing. A torque curve tells you EVERYTHING. Thus, thats why I have asked for the engine so that we can start discussing why your SAAB doesn't do much at 1,900rpm's.

If you don't understand a what "peak" is or a "revband" which are extremely simply concepts, then it's no wonder why you cannot grasp TORQUE.

Torque = Acceleration

Horsepower does not.. as your so inclined to keep telling people.

Now there are benifits to makng torque higher in the rev range, but that takes nothing away from my statment.

Unlike this:
Quote:
Originally Posted by Saintor
Completely FALSE. HP is what matter for acceleration.
Here study this. Torque is in GREEN


.

Your SAAB's peak torque is 4,500rpm'ish. but that engine has a very flat torque curve and would pull strong all the way threw the revband. However @ approx 4,500 is when the car would be pulling it hardest. IE Fastest acceleration.




-Garrett

Last edited by Garrett; 03-02-2006 at 08:00 AM.
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      03-01-2006, 07:53 PM   #138
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What can't you understand in

"SAE peak torque: 258 lb. ft. @ 1900-4500 rpm"

You are full of it.
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      03-01-2006, 08:08 PM   #139
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Look above at the chart
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