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Old 03-30-2008, 08:46 PM   #16
graywolf624
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I don't think you understand. We aren't talking about the ability to adjust bias based on slipage, which is what the nissan currently has. It does not have the ability to adjust based on gs and other inputs. The same system is in the 911 and its not some huge leap. Which brings us back to my point re: historical inference does not backup the assumption that a huge jump in bhp will occur.

Essentially what your trying to argue is that when going from a 95 percent lockup to a 50/50 lockup your getting more driveline loss. While true, its not historically true that it would be as high as your thinking. While coupling the rollers would eliminate this issue entirely, even seperate your not going to lose massive amounts of power.

Heres a good writeup to what im refering too:
http://www.nissanforums.com/nissan-g...a-ets-pro.html

Speaking of which, the whole 25 percent driveline loss bit is a bit of a farce anyway. Take a 1000 bhp car. Theres no way in hell it could lose 250 through the driveline. The losses go to heat. Could you imagine how hot the axles and transmission would be? RC mentioned a number for the z06. Im not even sure I buy it honestly. If we go purely on the sae certified number of 505 bhp and an observed dyno of 450-460 by most owners, that nets out to a 10 percent drive train loss. It would make sense that a 505 bhp skyline, assuming a 5 percent variance in output from the stated 480 bhp which happens alot actually, would have 430 bhp due to the inherint extra friction as part of a two axle system. The difference in this two axle system, if information from the 911, lambo, et all bear as examples, would actually come close to reflecting a 430 bhp output. Under that situation switching to rear bias should only get you back up to the z06s rwhp. It should not allow a trip beyond significant enough to overcome driving around rosie odonnel and two of her fat friends in the trunk (aka the gtr). Which again proves the point the car does not have significantly more power then the z06, despite significantly more weight. Which begs the question, how are cd seeing the acceleration they claim? And why is road and track hushing up the slower traps they saw?
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Old 03-30-2008, 09:09 PM   #17
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I guess I've done a poor job making a point here, but on the dyno shouldn't it be basically a rwd car and not speculated on as a awd car. Therefore wouldn't the idea that it has 570hp be a improbability.
But the comp systems would then give better acceleration times then a rwd car with similar horsepower due to better use of that power.
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Old 03-30-2008, 09:15 PM   #18
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A dyno simply measures the force exerted by the wheels over a given time interval. With that, horsepower is calculated (force x distance / time . . . power). Being awd, the GTR will lose a higher percentage of power through the drivetrain than a rwd car would.
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Old 03-30-2008, 10:10 PM   #19
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I guess I've done a poor job making a point here, but on the dyno shouldn't it be basically a rwd car and not speculated on as a awd car. Therefore wouldn't the idea that it has 570hp be a improbability.
But the comp systems would then give better acceleration times then a rwd car with similar horsepower due to better use of that power.
In a straight line it only would in terms of grip off the line. Unless one set of tires are spinning there is no gain by applying torque to the other set of wheels. Hence the GTR should beat the z06 off the line, but should be roasted anywhere else (again see the r and t times).

Being awd, the GTR will lose a higher percentage of power through the drivetrain than a rwd car would.
This is true, but the point is the switch between the two will not generate a huge increase in bhp when the car switches modes. If you assume the rear portion of the awd system has a drivetrain loss similar to the rwd that means the awd portion should at least in theory lead to increase much less then half the drivetrain loss of the rwd. Why? Because you don't factor in the transmission loss twice.

If we assume a bhp of the gtr of 507 bhp, thats 2 bhp more then the vette. Now unless some miracle occur we can also assume similar driveline losses. So we can essentially estimate the bhp in rwd mode is probably close to that of the z06. We can also pretty assuredly say its not going to result in bhp well beyond that. Which again begs the question of how to move 700 extra pounds.
This basic discussion, granted with the assumptions being assumptions, applies to all manner of other awd cars. Cars like the 911 and lambo have not seen a miraculous jump between the various modes. You would expect similar experiences since the systems are relatively similar (other then the gay ass double driveshaft).
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Old 03-31-2008, 02:14 AM   #20
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It has been quite accurately determined over many many many thousandsof dynos that the C5/C6 drivetrain has an approx. 12% power loss when measured on DynoJet rolling road dynos.

385bhp = ~335rwhp
405bhp = ~355rwhp
436bhp = ~390rwhp
505bhp = ~450rwhp

The %age may be slightly reduced as the crank HP increases - but on a 1000bhp setup, there is close to a 120hp power loss to the wheels.

I would not be surprised that in the end, once someone takes the GT-R motor to an engine dyno, theyw will find that there is closer to a 20% or higher drive train loss on a static dyno setup, but that by conventional calculaiton this loss is less and also variable under load on the road.

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Old 03-31-2008, 10:58 AM   #21
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Originally Posted by 79TA View Post
A dyno simply measures the force exerted by the wheels over a given time interval. With that, horsepower is calculated (force x distance / time . . . power). Being awd, the GTR will lose a higher percentage of power through the drivetrain than a rwd car would.

Ok, new day new attempt to get my point across. The GTR is under normal conditions a rwd car that uses power to the front wheels in trouble situations. So unless it was slipping on the dyno there was no awd drivetrain loss meaning the idea of 570hp is not practical.
As for the power distribution system I agree the gains are only going to coming during slippy periods like launch and that the z06 should run it down fairly quickly thereafter, but I don't doubt it beats it to 60 as through this new system not only does it have that extra grip of awd when it needs it, but it has it without the awd bog theoretically.
I've said it before and I'll say it again the gtr is an off the line/time attack performer that is too heavy to do well in the long run, but this whole conspiracy theory about an extra 100 horsepower is a witch hunt. Technology has moved forward you can't just look at power/weight ratios when talking about this new super computer of a car.
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Old 03-31-2008, 11:02 AM   #22
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^^ Nice post Madpony.
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Old 03-31-2008, 11:05 AM   #23
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Madpony, you are assuming that on the dyno, the front wheels aren't exerting force on the dyno, and that isn't the case
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Old 03-31-2008, 11:09 AM   #24
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I'm going off that assumption based off the fact that from what I've heard they wouldn't be.

edit:
Ok, just looked it up and found out apparently the least it'll put the front is 2% so yes there would be some awd drivetrain loss. I blame Plato's slight overstatement on 5th gear for the mix up.

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Old 03-31-2008, 05:34 PM   #25
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All right gentlemen, here's something to ease your discussion there (Dyno vs Road power graphs included)


MOTOR TREND: 2009 Nissan GTR Acceleration Test

http://www.motortrend.com/roadtests/...est/index.html

Results:

0-60: 3.2 sec
0-100: 8 sec
Quarter mile: 11.6 sec @ 120.0 mph







WHAT'S THE SECRET?

There are three factors helping the 3879-pound GT-R appear to dodge the laws of physics:

1. Horsepower and torque. Our testing on the four-wheel Dynojet dynamometer at K&N Engineering indicated that the factory ratings of 480 horses and 430 lb-ft are discounted by at least 5 and 14 percent, respectively. To verify the accuracy of the dyno readings we ran a fourth-gear acceleration pull at El Toro and computed the horsepower required to accelerate the mass of the car and driver, plus the power lost to aerodynamic drag and tire friction (using Nissan 's 0.27 drag coefficient, a 22.5-sq-ft frontal area computed per SAE formula and assuming a 0.020 coefficient of rolling friction for the tires). Note how closely the overall shape of the curves match, including the slight plateau from 4000-4500 (intake cam timing change?)

2. Short Gearing. The Nissan GT-R 's overall gearing (including tires) is among the shortest in supercardom. The Porsche 911 Turbo that served as the GT-R 's performance target spins gearing that's taller by an average of 10 percent in the first three ratios, while the Corvette Z06 it competes with most closely on price averages 40 percent taller in the same three gears. Short gearing effectively increases the engine's "leverage" but results in more frequent shifts, which can add time (the Z06's 0-to-60-mph trick is hitting 60 mph in first gear with no time-consuming shifts).

3. Uninterupted torque during shifts. Nissan quotes a 0.2-second time required for shifts, but this is simply the time that elapses between ordering a shift at the steering-wheel paddles and accelerating in the next gear. What isn't mentioned is that rather than coasting with the clutch disengaged during that time (as happens during a 0.10-second Ferrari F1 shift or a 0.15-second BMW SMG shift), power is still flowing through the previous gear. Those precious tenths add up in other cars, but torque interruption is imperceptible in the GT-R. Manual shifts in the Porsche or Corvette consume about a quarter of a second each, and there are at least three of them in a quarter-mile run.

And that, dear GT-R fans, is the science behind the apparent magic that allows this two-ton Godzilla to sprint like a cheetah. Our final installment will dissect the Nissan GT-R's handling performance. Stay tuned.
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Old 03-31-2008, 06:44 PM   #26
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Maybe the Bugatti would be a contender for the GT-R. Maybe.
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Old 03-31-2008, 06:45 PM   #27
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505bhp = ~450rwhp
Thats 11 percent drive line loss.
I would not be surprised that in the end, once someone takes the GT-R motor to an engine dyno, theyw will find that there is closer to a 20% or higher drive train loss on a static dyno setup, but that by conventional calculaiton this loss is less and also variable under load on the road.
I highly doubt it. That would be nearly double the corvette. I cant believe that the transmission portion is 2 percent. 20 percent drive train loss would be greater then 100 bhp drive line loss. Thats alot of heat and I don't buy it.
It appears that last test posted proves my point. Also slower then the z06.

Quarter mile 11.6 sec @ 120.0 mph
Last I checked the best stock time for a Z06 was a 10.9.. and even mag reported times were faster then this report. Motor trends own times for the z06 were "the standing quarter in 11.5 seconds at 127.1 mph". Significantly higher then that of the GTR. These are results I expect.
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Old 03-31-2008, 07:52 PM   #28
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Great stuff toffy.
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Old 04-01-2008, 07:23 AM   #29
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In considering this thread I realized things need to be put into perspective on the GTRs acceleration difference to the Z06.

The Corvette Z51, a great car, my personal car, and 30k less then its bigger brother the z06 (unless you count the discounted z06s - get one for 62k new I saw today) runs a 1/4 of 12.1 at 117-119 mph. Why is this important? Without the launch control the GTR ran a 12.2. Losing to the z51. They state themselves that engaging launch control is difficult. Lets however assume they made it into this mode. The GTR then ran a 11.7 at 116 mph (120 if you ask edmunds and rt, but you get the point). What does this mean? It means the Corvette Z51, a 45k msrp car, is significantly faster then the gtr in the upper mph. In fact it indicates with the right driver/tires/launch the z51 would probably be kneck and kneck with the GTR. That should put the GTR in perspective re the Z06.
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Old 04-01-2008, 09:22 AM   #30
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IMO, acceleration performance of Z06 and GTR shouldn't be measured by 1/4 times as these two cars are very different.

Generally:
0-100 mph: GTR>Z06 (AWD, short gearing, better tires and seamless shifting from DSG overcompensate for the lesser P.W.R & T.W.R);
>100 mph: Z06>>GTR (greater P.W.R & T.W.R becomes critical)
Rolling start (generally): Z06>GTR

And what's all the fascination about straigtline perfomance anyway? I personally don't care if one car does 1/4 faster than another (you can perform approximate calculation and tell that without the actual run anyway). Race track - that's where you learn the true worth of the sportscar!
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