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Old 01-26-2013, 09:52 PM   #48
TerraPhantm
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Join Date: Feb 2008
Location: Mountain Top
Posts: 5,983
My Ride: 2005 M3 Coupe
Quote:
Originally Posted by DSilk56 View Post
The M3 is not a torque monster by any stretch of the imagination. Saying that it has more torque than a Honda Accord is like saying that Justin Bieber weighs more than Natalie Portman. It may be true, but it doesn't make either of them heavyweights.

As a general rule, normally aspirated engines need large displacement to generate large torque numbers. It's relatively simple. Torque is a measure of the twisting force exerted on the crankshaft by the connecting rods, and this is limited by the amount of explosive force harnessed in each cylinder. The more fuel effectively exploded, the more force available.

Unless you use forced induction, it is tough to get a lot of torque from a relatively small engine. 263 lbs./ft. from 3.2 litres is good, but doesn't compare to the 290 lbs./ft. that the 2.0 litre turbocharged engine in the Subaru WRX-STi makes or the 390 lbs./ft. that the 5 litre V8 in the Mustang GT makes.

Horsepower is a more complicated matter, as it is a measure of work done over a set period of time, as opposed to a measure of force. To put it in more pedestrian terms, a weightlifter who can pick up a barbell with 500 lbs. of weight and move it 10 yards in 1 minute has performed the same amount of work as the sprinter who can make the same trip 10 times in the same minute laden with 50 lbs of weight each trip. The weightlifter performs the work by exerting substantially more force at a slower speed than the sprinter. In our example, the M3 is the sprinter. It relies upon its ability to rev to very high rotational speeds while still developing usable torque, while the larger displacement Mustang relies upon brute force, and doesn't need to rev to particularly high speeds to get the work done.
Forced induction is essentially increasing displacement. More pressure = more oxygen = greater volumetric efficiency (which is what matters moreso than displacement for torque).

My point was that 262-269 (depending on which variant you're talking about) lb-ft torque out of a 3.2L is not low by any means. And the fact that this car has a very flat torque curve (unlike the STi and other boosted vehicles) is important to consider. The only reason I even mentioned the accord engine is because you brought it up.

Finally, it's the torque at the wheels and not the crank that matters. You're not taking gear multiplication into account. Consider... an E46 M3 and an E9x 335i. M3 makes 262 lb-ft and 335 makes 300 lb-ft. M3 has a 3.62 final drive ratio, while the 335 has a 3.08. The gear ratios of the transmissions are pretty similar, and iirc the tire diameters are about the same as well.

262 * 3.62 = 948.44; 300 * 3.08 = 924. Hey, what do you know, the gear multiplication actually gives the M3 more effective torque. And since the M3 can rev considerably higher, it can still reach higher speeds in the same gear.

The STi actually does have pretty aggressive gear ratios, but it still has a low redline. So it has to shift considerably earlier than an M3 would. The net result is that the STi might be faster for rather contrived scenarios, but it would be slower across multiple gears (until tuned anyway... but I'm just considering stock vs stock here)

All that said, I don't know what you're trying to get at. It's no big secret that the M3 has a 3.2L engine and makes ~260 lb-ft torque. If you're expecting it to make as much torque as a 5.0L V8 or 2.5L engine w/ 20 lbs boost... then you're expecting too much. Torque by itself is a useless metric anyway -- you need to know gear ratios, area under the curve, and rev limits to make any real judgments. Despite popular opinion, horsepower is a much better tool than torque for judging the capabilities of an engine.

Last edited by TerraPhantm; 01-26-2013 at 09:59 PM.
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