12-13-2010, 10:41 AM | #45 |
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You're right ... curb weight was too low. Just to mention: it was the same (wrong) value for both 1M simulations. Wrong but fair
I fully agree that the area under the HP curve is important. What the CarTest simulations also don't take into account is the fact that an FI engine increases torque at a quite limited rate (turbos need to spool up) and therefore in low gears peak torque is more at the upper rev-band. |
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12-13-2010, 02:32 PM | #46 | |
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BMW has said 332 ft lb from 1500-4500 rpm. If you allow the actual peak to be all the way up at 4500 (or simply truly 100% flat across this band) you'll have a really hard time having a truly physically realizable power and torque curve and one that has the peak hp quoted by BMW.
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12-13-2010, 02:42 PM | #47 |
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Sure it matters, but again NOTHING matters as much as power to weight. Not the peak torque to the wheel per weight nor shape of the torque curve nor anything else...
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12-13-2010, 03:42 PM | #48 | |
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Effective torque at the wheels is actually more useful than horsepower, as it considers the actual gearing and tire size. Horsepower is great for a rough idea of how a car with a given weight will accelerate, but it's not as precise as torque at the wheels. P.S. Early on you were talking about centrifugal forces causing tire diameter to expand, but that has no where near the effect that deformation from the weight of the car (i.e. contact patch) and the longitudinal slip ratio (The tire bunches up right before the contact patch and stretches after it when being acted on by a longitudinal force). The tire size is actually always smaller than it's static diameter (although it gets closer the higher the speed). Calculating this stuff, though, requires much more info than you have, and ultimately it's not worth it when you're using such a basic simulator. You're better off making sure you've got the basic stuff right; worry about the complicated stuff much later (same goes for parasitic loss; it's much more complicated than you're assuming it to be, and you'll probably be way off). |
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12-13-2010, 05:33 PM | #49 | ||
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For street radials this isn't an issue, and I turned that off in my sim.
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12-13-2010, 06:03 PM | #50 | |
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As far as I can tell you had this concept in your head, and when I posted results showing otherwise you strongly disagreed. What this shows, though, is that it's the area under the curve in the particular gear you are using that is important. In 1st gear the whole rev range is used, so while the peak power to weight favors the M3, the average power to weight of what's used favors the 1M due to the huge low-end torque. In higher gears a smaller and smaller slice of the rev range is used, and there the average and peak power to weight ratios converge, so there a car with a higher peak power to weight has a more of an advantage... Of course if you're driving a caterham with an awsome power to weight ratio, higher gears are also where aero begins to catch up, so it's not that simple either.
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12-13-2010, 06:08 PM | #51 | |
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Oh, and the effective radius is closer to the loaded radius the fatter the tire (and both of these cars have relatively fat tires for street cars). Long story short, this stuff has much more of an effect than tire expansion due to centripetal acceleration. |
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12-13-2010, 06:19 PM | #52 |
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Since we are talking about the diff (LSD) and transmision... I wonder IF BMW will say that the 1M needs to have its trans and diff fluids (AND oil and filter) changed at 1,200 miles - first service.
BMW still requires this for other M models like the M3. I have also seen on the M3 forum where guys were doing ED with their M3's and had the service done at a German dealer. Even though its free in the states over here the dealers charge about 500 euros ($700) for this first "oil" service. I also saw where BMW NA will reimburse you IF you pay for this service over here while on ED. So... I wonder what the //M stance on this will be? Since the car has a N54 but has a LSD and different trans. ? Dackel |
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12-13-2010, 06:21 PM | #53 |
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I've read several of your posts, in various threads, and it appears you're extremely skeptical of the 1M, even insecure about its very existence.
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12-13-2010, 06:34 PM | #54 |
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My point is that statement is not true of drag tires/ wrinkle walled slicks. They can grow in diameter 30% when designed too. For street radials I agree completely.
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12-13-2010, 07:03 PM | #55 | |
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Drag radials are completely different beasts. |
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12-13-2010, 07:18 PM | #56 | ||
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The ONLY curve you need bother with is HP; torque naturally relates, but isn't "it".
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... a glorious V8 that screamed and hollered as the revs rose and then howled in an orgy of what sounded like BDSM ecstasy as it neared the red line.
Well, you can forget all that. The new car is fitted with a turbocharged straight six. Turbocharging? In an M car? That’s like putting gravy on an ice cream. - Jeremy Clarkson, discussing the S65 and then S55 M3 engines. |
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12-13-2010, 07:30 PM | #57 |
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I think I would say, if you know one then you can figure out the other. Since Hp is a function of torque and rpm, if you know one you can calculate the other. Knowing this, is one really more important than the other?
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12-13-2010, 07:40 PM | #58 |
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How do you calculate the HP at a given speed without taking into account the gearing? Do you have examples of the curves you're thinking about?
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12-13-2010, 07:45 PM | #59 |
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HP is not affected by gearing.
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... a glorious V8 that screamed and hollered as the revs rose and then howled in an orgy of what sounded like BDSM ecstasy as it neared the red line.
Well, you can forget all that. The new car is fitted with a turbocharged straight six. Turbocharging? In an M car? That’s like putting gravy on an ice cream. - Jeremy Clarkson, discussing the S65 and then S55 M3 engines. |
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12-13-2010, 07:49 PM | #60 | |
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So to say "torque matters for X, whereas HP matters more for Y" is absolute nonsense.
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... a glorious V8 that screamed and hollered as the revs rose and then howled in an orgy of what sounded like BDSM ecstasy as it neared the red line.
Well, you can forget all that. The new car is fitted with a turbocharged straight six. Turbocharging? In an M car? That’s like putting gravy on an ice cream. - Jeremy Clarkson, discussing the S65 and then S55 M3 engines. |
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12-13-2010, 08:07 PM | #61 |
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I think if you look at HP alone you are missing part of the information. Meaning, I think it would be hard to compare 2 different vehicles on a WOT run just looking at a HP curve as it runs through the gears.
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12-13-2010, 08:08 PM | #62 | |
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F=ma. In a rotational sense, T=m*alpha (angular acceleration). For a given mass, it is instantaneous torque that determines how fast that object accelerates at any given second. Torque at the wheels = engine torque * gearing/tire size. Torque at the wheels, which is directly related to acceleration, is directly related to gearing. That means acceleration is directly related to gearing. Ultimately it's the area under the torque at the wheels curve vs. speed which determines how fast something accelerates. |
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12-13-2010, 08:28 PM | #63 |
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The definition of Horsepower.
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... a glorious V8 that screamed and hollered as the revs rose and then howled in an orgy of what sounded like BDSM ecstasy as it neared the red line.
Well, you can forget all that. The new car is fitted with a turbocharged straight six. Turbocharging? In an M car? That’s like putting gravy on an ice cream. - Jeremy Clarkson, discussing the S65 and then S55 M3 engines. |
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12-13-2010, 08:33 PM | #64 |
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BUT, we're kinda headed off topic anyway. Originally the discussion was about the gearing specs of the 1M. Then I commented regarding my preference for a higher numerical final drive ratio.
I've participated as much as anyone else in the tangent, but I'd prefer to get back to the prior discussion if possible. Another poster stated that the higher numerical gear would result in slower acceleration. I continue to disagree, especially when we're talking about WITHIN a gear, or across a contrived set of time/speed/distance measurements that favor the lower numerical gearing.
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... a glorious V8 that screamed and hollered as the revs rose and then howled in an orgy of what sounded like BDSM ecstasy as it neared the red line.
Well, you can forget all that. The new car is fitted with a turbocharged straight six. Turbocharging? In an M car? That’s like putting gravy on an ice cream. - Jeremy Clarkson, discussing the S65 and then S55 M3 engines. |
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12-13-2010, 08:40 PM | #65 |
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HP at a given speed is. I.E. what is the 1M's hp at 60 mph?
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12-13-2010, 08:41 PM | #66 | |
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