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      02-17-2012, 03:29 PM   #45
adc
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Originally Posted by jamze132 View Post
Couldn't agree more about the shift times. The DCT shifts ridiculously fast, especially when you have it floored. I don't think there is a human alive who can shift as fast as that car can when it's being pushed hard.
I don't think it's the speed of the shifts per se that matters, but rather the lack of interruption in the power delivery and in this context, the extra gear ratio.

I don't recall SMG cars being quicker than their manual counterparts.
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      02-17-2012, 08:15 PM   #46
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Originally Posted by bruce.augenstein@comcast. View Post
At a guess, the new GT500 will likely be turning trap speeds in the 125-126 mph range, given decent traction, but with traction control off. This estimate is based on an ancient (but tried and true) formula for estimating horsepower based on quarter mile trap speeds.

Take the trap speed, divide it by the constant 234, cube the result, and multiply that figure by car weight with driver. The result is a reasonable horsepower estimate. As an example, Car & Driver ran a ZL-1 Camaro to a trap speed of 119 mph, so assuming a 4300 pound curb weight with driver (4120 empty), we get:

119/234 = .508547, times .508547, times .508547 = .1315, times 4300 = 565 HP. Close enough to the rated 580.

Doing the same thing with the Mustang at 4100 pounds, trapping at 126 mph, one gets a result of 625 HP. Again, close enough.

ET? A goal for front-engine, rear-wheel-drive street cars on stock rubber is that ET times mph should equal about 1400 or so, or as close as you can get. This is easy with low-powered cars, but gets tougher as power goes up. Using this as a guideline, the new Mustang could likely be in the very low 11s in the quarter mile.

Doubt it, though. Consider the ZL-1 at 12.3 @ 119 mph. That product is about 1464, so assuming the Mustang could hook up as well as the Camaro, 126 mph gets you in the mid 11s.

With well-warmed slicks? High 10s, I think.

Bruce

PS - Its not as if the goal of ET times mph equaling 1400 is unobtainable in higher powered street cars, though. I have watched a stock ZR-1 Vette go 10.75 at 130 mph at a carefully sprayed drag strip on a perfect day, so it's possible. Of course, the Vette has better weight distribution, and extremely aggressive street meats on it right from the factory.
wowww!!!! ur the boss.... thank you.... that was a good bit of information....love this forum
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      02-18-2012, 01:21 PM   #47
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Originally Posted by swamp2 View Post
...The Getrag designed M-DCT is rated for 443 ft lb and 9000 rpm. It was not specifically designed for the M3 but did have it's debut in that. Thus is was not specifically designed for the relatively low 295 ft lb torque in the M3 and certainly has a much greater capacity than the S65 generates.
I have no specific knowledge of this transmission, but I'm willing to bet it comes in more than one flavor. I'm also willing to bet that specific engineering and parts went into this transmission for M3 use. The fact is, nobody designs transmissions for a single use any more. As an example, the six-speed that GM uses for its higher-powered cars comes in several flavors, each with differing torque ratings, and although they all look the same from the outside, transmission weights vary from around 110 to around 125 pounds, depending on application. Gearing also varies depending on application.

I don't doubt that whatever version of the Getrag box installed for the M3 has an overall torque rating a good deal higher than what the M3 generates, but am equally sure that it is an M3-specific model.

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Also I've never seen a transmission speced based on torque per cylinder. It is always dynamic torque or torque which is not measured per firing or per cylinder. It would be the same way an electric motors torque would be measured.
The fact that you've never seen a transmission rated on a torque-per-cylinder basis is of little consequence to me. I first saw this referred to back in the sixties, when Chrysler arrived late to the four-speed game with their own box. There were several articles in the nutbooks at the time, and if memory serves, the Mopar engineering folks rated their new pride and joy at 50 foot-pounds per cylinder, continuous duty. I thought that 50 foot pounds per cylinder wasn't very high, given the engines coming into being at the time, but "continuous duty" clearly spells out something pretty rigorous. Another early reference was with the front-engine, rwd, transaxle-equipped Pontiac Tempest from the early '60s. That car came with a ropey driveshaft connecting engine to transaxle, with a 195 cubic inch straight four (half of a Pontiac 389 V8) providing a magic fingers massage to all riders . When Pontiac installed a 326 cubic inch V8 in that car in '63 with the same ropey driveshaft, the nutbook scribes were aghast, thinking the V8 would twist up that driveshaft like a rubber band. Not to worry, said Pontiac engineering. The 326 V8 was actually easier on driveline parts than the four, again referring to torque-per-cylinder.

Nowadays, dual-mass flywheels will tend to dampen individual power pulses more than single-mass models do (along with traditional sprung clutch hubs), but I guarantee you that somewhere in the specs is a torque-per-cylinder rating. If you consider the difference between, say, a V8 at 443 pound feet versus a single-cylinder engine at 443 pound feet, you can clearly see why the torque-per-cylinder number is of clear consequence. The single-cylinder engine will pound hell out of the drive train in comparison to an eight-cylinder.

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Also from way back you said:

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Originally Posted by bruce.augenstein@comcast.
we well know that German cars use flywheels that may as well have been liberated from old Panzer tanks, or U-boats.


Which is it in the M3, super light flywheel or tank like heavy? You can't have it both ways.
What part of "reduced (by German standards) engine flywheel weight" didn't you get. Just let me know, and I'll break it down for you.

You think my two statements are somehow at odds with each other?

Huh.

In point of fact, at last-year's New York auto show a BMW guy with heavy German accent told me that the M3 dual-mass flywheel weighed "around 13 Kilos" . He could have been just BSing me around my queries regarding seemingly low overall rotational inertia of the M3 engine and driveline, but whatever. That's just another data point, providing you agree with me that around 29 pounds is pretty damned light for a German flywheel.

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Originally Posted by swamp2 View Post
One key reason the M3 is an overachiever is because of its fairly low total drive train parasitic loss. The most accurate measurement of this is done by Rototest Research Institute (rri.se). They found only an 11% loss (less tire losses). This is not comparable to other loss specs that do often include tire losses.
Not arguing with anything here other than I doubt this is a "key" reason. We're very, very far from orders of magnitude here.

Last edited by bruce.augenstein@comcast.; 02-18-2012 at 02:14 PM. Reason: Spelling
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      02-18-2012, 02:06 PM   #48
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I don't think it's the speed of the shifts per se that matters, but rather the lack of interruption in the power delivery and in this context, the extra gear ratio.

I don't recall SMG cars being quicker than their manual counterparts.
Well you would be wrong in thinking that way. Shift times directly relate to improved times for any given performance metric of time for speed x to speed y. Draw yourself a curve of velocity vs. time, add a very long shift time and then contrast that with a zero shift time. This will illustrate the point perfectly. The non interruption of power is basically the same thing as a short (near zero) shift time.

SMG shifted substantially slower than the DCT. The data was posted here on the forum long ago (I posted it and we discussed) but I can't seem to quickly locate it right now. IIRC typical SMG shift times are on the order of 0.2 - 0.3 seconds. Perhaps as fast as the fastest human with a really good transmission mechanism/throw/lever.
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