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Yoyo Mama
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Discussion Starter #1
I'm looking for a layman's definition of horsepower vs torque vs torque curve. I hear so many varying opinions and definitions, I'd be interested if someone can put it in the perspective of the e90.

For example: I know the e90 325 has 215 HP and 184 ft-lb torque. What does this actually mean? Any why does it matter that the torque peak is at lower RPMs? I know torque has to do with acceleration from rest and horsepower is "passing on the highway" speed - or so I've been told. But I've never gotten a straight answer from anyone. I'm not looking for a scientific answer with mathematical formulas but just a practical defintion of how this all relates to driving the 3 series.

And how does the torque curve play into this? Does low RPM torque mean that the 325 can out accelerate a higher HP car from the line?

Thanks in advance. :dunno:
 

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Here is a good but lengthy comparison of torque vs horsepower. http://www.g-speed.com/pbh/torque-and-hp.html In short, the torque an engine makes at a given RPM provides the acceleration you feel but high horsepower engines produce good torque at high RPMs which allows gearing to provide greater torque multiplication so overall they can be quicker. A flatter torque curve allows more consistant better overall acceleration instead of a peaky feel.

The way I look at it, a long flat torque curve allows great around town power since you have pulling power at cruising RPMs. A high RPM horsepower peak and close gearing maximize overall acceleration. BMW engines typically allow both flat torque curves and high RPM power.

PS: I suspect that the 325i could easily have greater torque (and more power) but it might end up being peaky.
 

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Yoyo Mama
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Discussion Starter #4
Thanks - these links both post to the same article.

So the conclusion from the author is:

The Only Thing You Really Need to Know

Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :)


Does this then mean that because the 325i makes peak torque at 2750 RPMs (low by most standards) that it's torque-curve drops off sharply at the higher RPMs?
 

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Just think of it as how many horses (hp) you'll get and how strong (torque) they'll be...

More horses and strong = very good
Fewer horses but still strong = also good

More horses but not so strong (weak bastards!) = bad
Few horses, also not so strong = very bad

:angel:
 

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kobechrome said:
Does this then mean that because the 325i makes peak torque at 2750 RPMs (low by most standards) that it's torque-curve drops off sharply at the higher RPMs?
No, the torque curve is actually very flat, from 2750 all the way to 6k. That means you can maintain peak torque throughout the entire rev band. :thumbup:
 

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Can you please post the hp/torque curve for the 2006 330i or link me the site where to look up. I assume the numbers are at the crank, thus it's the the same for both auto and standard. Please post numbers for both standard and auto 330i if possible. I currently own a 330i auto, curious to see where the peak torque and peak hp is is, which will give me an idea of optimum shift point.

Thanks in advance, :thumbup:

mkh said:
No, the torque curve is actually very flat, from 2750 all the way to 6k. That means you can maintain peak torque throughout the entire rev band. :thumbup:
 

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They're in the Official BMWNA E90 Product Info. Sourcebook at the top of forum page.
 

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Yoyo Mama
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Discussion Starter #10 (Edited)
Thanks for all this good info but I have to ask more questions because maybe I'm just dense :)

So because the 325/330 engines hit TP at lower RPMS, doesn't that mean these cars would be slightly faster off the line than even cars with higher HP? If I am interpreting this right then torque is what matters from rest, not HP. Why does everyone then always say that all other cars smoke the e90 from rest?

Is it because the torque itself is only 184 ft-lb? For example, my 2003 TL has 215 torque at 5500 RPM and 225 HP at 6000 RPM. Is there any way I can objectively tell how this will compare to the e90 325?

Also - is a lower TP what gives drivers that "push you back in your seat" feeling? I've always been curious about what causes this...



Thanks!
 

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torque peaking low give the car the ability to accelerate briskly even at low RPM's

cars like an S2000 only accelerate well when at high RPM's

HP= torque*RPM/5252

HP is just a function of torque and RPM
 

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I'll second those remarks about the S2000 - I have owned one for four years. A very measly 153 lb-ft of torque, but it comes on forever. Actually the peak is at 7500 rpm,and the peak horsepower is at 8300 rpm, where the torque is about 152 lb-ft, to create 240 hp. Horsepower is a measure of the rate of doing work, i.e., accelerating the mass of your vehicle up to a hgher speed. The S2000 only puts out a lot of work at screamingly high rpm, while a higher torque engine can accelerate more competently in 5th or 6th gear at modest speeds and rpms.
 

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kobechrome said:
So because the 325/330 engines hit TP at lower RPMS, doesn't that mean these cars would be slightly faster off the line than even cars with higher HP? If I am interpreting this right then torque is what matters from rest, not HP. Why does everyone then always say that all other cars smoke the e90 from rest?
Different cars with different torque/hp profile requires different launching for the fastest start off the line. For S2000, for example, you need to rev it way up and dump the clutch. E90, on the other hand, you don't have to rev as high. Clutch slip can add gearing effect as well, and some wheel spin can make the launch faster. So, as you can see, it's not a staight matter of torque at lower RPM, though that could mean it's a bit easier to launch fast.
 

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S2k2Bmw330i said:
Can you please post the hp/torque curve for the 2006 330i or link me the site where to look up. I assume the numbers are at the crank, thus it's the the same for both auto and standard. Please post numbers for both standard and auto 330i if possible. I currently own a 330i auto, curious to see where the peak torque and peak hp is is, which will give me an idea of optimum shift point.

Thanks in advance, :thumbup:
Here it is....
 

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I had a S2000 also (1st Gen) and dynoed it. You've never seen such a flat torque curve with a subtle bump up at VTEC. The push in your seat from acceleration is longer than a peakier torque curve from, say, a last-generation Mustang GT. Just about everyone who tries both would swear the Mustang would beat the S2000 because the push is much stronger but they're wrong because the S2000 just keeps on pushing longer (area under the dyno curve).

I notice the 330i's peak HP is close to redline so I can't wait to finish break-in and start wringing it out.
 

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Gearing also has a big influence on performance....proper gearing allows you to take advantage of the engine`s powerband, and keep that power available as needed. Except for the HUGE gap between first & second, the 330i`s 6-speed manual is pretty well suited to performance driving. An auto-trans equipped car will enjoy a brief period where the torque converter will double the torque output, which can make for some interesting launches (next time the dealer gives you that 325i Step loaner, shut off the traction control on your favorite back road, and do a Raceway Park-style tire-smoking start :)

Regards,
Bob
 

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Thanks, I appreciate it. Happy New Year

The torque curve explained it all. My 330i is a dog below 2k rpm and really picks up near 3k rpm. I feel as if VTEC just kicks in like my 2004 S2000. Looks like I don't have to wind it all the way to redline, optimum shift points seems to be at/around 6.6k rpm.

I see many of you were once an S2k owners :thumbup: . I was this || of purchasing the IS350 until I test drove the 330i. Warrup S2K owners... :thumbup:


mkh said:
Here it is....
 

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S2000 is a great car, and unfortunately for BMW their Z4: costs $10K more, performs no better, is much more expensive to maintain. That new E90 engine is great in the 325i/330i, but does not produce the same fun factor in a sports car.
 

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Rest in peace, Coach
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kobechrome said:
Thanks for all this good info but I have to ask more questions because maybe I'm just dense :)

So because the 325/330 engines hit TP at lower RPMS, doesn't that mean these cars would be slightly faster off the line than even cars with higher HP? If I am interpreting this right then torque is what matters from rest, not HP. Why does everyone then always say that all other cars smoke the e90 from rest?

Is it because the torque itself is only 184 ft-lb? For example, my 2003 TL has 215 torque at 5500 RPM and 225 HP at 6000 RPM. Is there any way I can objectively tell how this will compare to the e90 325?

Also - is a lower TP what gives drivers that "push you back in your seat" feeling? I've always been curious about what causes this...



Thanks!
Stop right there. You have got the whole thing confused beyond repair if you ask me.

Let's start you fresh. It doesnt matter how much peak torque you make. It doesn't matter how much HP you make. What matters is the amount of AREA underneath the torque graph throughout the RPM range.

Let's take your Acrua TL example. It makes 215 #ft of torque at 5,500 RPM, but if it makes little next to no torque from idle to 5,500 RPM but spikes up at 5,500 then drops off immediately after that, then the Acura TL would be virtually UNDRIVABLE. However, Honda has engineered their engine to make plenty of torque all the way up the torque band, so that even if it makes the peak up high at 215 #ft at 5,500 RPM, if it makes 90% of that torque at 1,000 RPM, it'll still take off like a bat out of hell. Same as the BMW engines, they may make torque peak relatively low, but the torque continues to plateau thus allowing the engine to continue to make horsepower as the RPM climbs.

At the end of the day, for your daily driving needs it doesn't matter where the torque peaks, it matters more how much it peaks and how much it plateaus before and after the peak. If it's a spikey curve vs. a very flat curve, the flat curve will win everyday. Where torque peak matters is in racing applications. For example, F1 engines probably has less torque than your average V-8 engine, but if it makes that peak at 19,000 RPM, you're looking at 900+ hp. Torque is the force being applied, and at higher the revolution, the more TIMES it's being applied therefore more WORK being done. In an F1 or most racing engine you don't want the peak to be too low.
 
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