For all that have followed the lively debate, here or other places, I think I am heading back toward the direction that the GT-R (ringer!) that achieved the 7:29 N'Ring time is not just slightly under-rated but substantially under-rated. Keep in mind anyone paying attention will realize that the GT-Rs that have been tested vary quite drastically. This is intentional, it can not be purely by accident or tolerances.

**What I am speaking to in the first analysis in this post is THE PARTICULAR CAR that achieved the 7:29 Nurburgring Nordschleife time.**
Let's forget for a moment about the GT-R being faster through corners than a 997TT, or having a better AWD hardware and software and generally exiting corners faster than many competitors. Let's also forget that in some straight line competitions it bests some of its well known competitors but in others it loses. Let's simply consider the raw acceleration of this car when exiting a fast corner (around 100 mph at Schwalbenschwanz, at around km 16.5) and on to the long stretch (Döttinger Höhe). We surely can all agree that this is nothing but a speed contest, a rolling start drag (granted a pretty fast rolling start) and a hp war.

I used the following videos to grab some distance vs. time results and speeds where available (others have obviously found this particular car as suspiciously fast as I have...).

- ZR1 vs. GT-R vs. Zonda (Long Straight): Link.
- Viper ACR vs. ZR1. Link.
- Viper ACR. Link.
- GT-R "official" 7:29 video. Link.

All of this action for my analysis begins around 6:30 by the timer in the ZR1. Thanks to Chevrolet for providing more data than the other folks discussed herein!

The times are gathered for time to achieve known distance markers along the track consisting of a banner, various signs on the RHS of the track and the first bridge. I estimate the worst uncertainty in these estimates to be only about +/- 0.3 seconds. Go full screen, use quick mouse double clicks and take the data yourself, you will find you can get good precision. Do note

**I am NOT using youtube video times** but the recorded times from the accurate in car timers. If you really want to follow along open the ZR1... spreadsheet attached in the zip file below and look at the first table. It is immediately apparent that all cars are accelerating quite closely. You barely need my analysis that follows but here we go...

It is VERY unfortunate that neither Dodge nor Nissan provided a speedometer in their videos but we can still do some basic calculations, modeling and predictions. We will begin with the ZR1. I ran some CarTest simulations for all of these vehicles. For those of you who have not read my previous posts CarTest is a physics based vehicle simulation software which includes a great deal of factors and phenomena such as engine power curves, parasitic losses, gear ratios, shift times, tire sizes, environmental conditions, aero drag, clutch drop/launch, etc.). Specifically for the ZR1 I used a total drivetrain loss of 15% which reproduced 0-100 mph, 1/4 mi time and traps within the range of various actual test values. The only other parameter I altered was shift time and I chose 0.3 s with .05 s for clutch activation. Since the ZR1 has the speed data along with the times in the second set of tables I can do some strong validation of this model. First I used CarTest to calculate a speed vs. time trace beginning at the known corner exit speed. I compared this to the known pairs of (speed, time). Coming out with a significant error and wondering why, I observed the difference between Vmax on this lap and the reported/observed/simulated top speed of the car (all within 1 mph of each other! at 206 mph). I read a bit more about this lap and GM was reporting significant winds. My first guess of a head wind on that straight was 15 mph. Placing this into CarTest my predicted times all fell within 2% of the recorded results (one slight outlier point had a mere 4% error). Pure luck on this guess.

Feeling quite confident with this model I moved along to the ACR. The ZR1 can outgun the ACR in a straight line test of raw acceleration based on both power to weight and simulation as well. However the ACR does corner like a race car and generates over 600 lb of downforce at around 100 mph. I estimated where the ZR1 exited at 109 the ACR was probably more like 113 mph (a bit more about justifying this number later). Simulating the ACR with no headwind finds the two cars very close, just like the video and extracted times. Since it was not supplied, I calculated both speeds and times for the ACR and in general was within about 5% accuracy. Finally on the the GT-R...

I concluded this from data in the Car and Driver Lightining Lap 2008 (Link

here that the GT-R probably exits this corner closer to or slower than the ZR1. In that test, on one particular corner at VIR with exit speeds quite close to this one, the ACR blasted out at 113 mph and the GT-R trailed a bit at 107 mph. An exit value of 107 for this exit produced results that made the CarTest simulations consistent with an almost dead even acceleration to the ZR1 (again with the 15 mph head wind) but lagging slightly behind it. This is very evident when you watch the signs fly by on the RHS in the first video above.

**The KEY ASSUMPTIONS on the GT-R model is that it was simulated WITH 550 crank hp AND identical drivetrain losses to both other RWD vehicles (15% in this case)**. Here I am being generous and assuming a 100% transfer of power to the rear wheels by the GT-Rs ATTESA-ETS AWD system thus leaving any additional AWD losses zeroed out of the simulation.

Again the full data tables are included in the first worksheet of the attached/zipped Excel file. A graph showing distance vs. time of all of these vehicles is on the second worksheet and finally the CarTest tabular data is on the last worksheet. What we see from the graph is how similar a 550 hp "RWD" GT-R is to these other vehicles and how a GT-R with factory specified power is simply left in the dust. The tabular data shows how well the models predicted the initial burst of acceleration out of the corner compared to observations (the range of ~110 mph - ~145 mph).

I fully expect you could repeat a similar analysis for many straight sections of the track and find similar results. I'd wager on 530-560 hp WITH a drivetrain loss of a RWD vehicle (or 560-590 hp with a 20% drivetrain loss).

**Conclusion #1. The 7:29 GT-R accelerated from around 100 mph, on to Döttinger Höhe, neck and neck with the ACR and ZR1. To do so at its stated weight it was producing approximately 550 hp and and had a conservative drivetrain loss comparable to the 2WD ACR and ZR1 cars. If the car has a drivetrain loss closer to 20% it was producing closer to 580 hp.**
Next, just to be thorough, I revisited the power to weight vs. lap time regression armed with this result (see thread

here). Again all tables and regressions are included the other Excel file in the attached zip file. We now find the GT-R with the new 7:29 time (and factory specified power) to be an outlier by a whopping 33 seconds which corresponds to 3.4 standard deviations outside of the model. This means there is about a 0.1% chance that this result is consistent with the model. It simply means something else is going on with the GT-R compared to all of the other cars. Again this is the single largest outlier in the model and is so by an enormous margin (it was already an enormous outlier with the previous time of 7:38). The next best over performers are both a bit less than 2 standard deviations better than the regression; the Porsche GT2 (and it was driven by Roehrl, not Horst) and E46 M3 CSL. (Note: I am not counting the Audi S3 here as I suspect a typo or some other anomaly contributing to it being a large outlier). If we simply give Tochio Suzuki's GT-R 550 hp the amount the car is an outlier is decreased to about 26 seconds better than the regression, which is 2.8 standard deviations. 550 hp finally gets us just inside the 3 standard deviation "rule" or the so called "3 sigma" rule. Still evidence of a very fast and capable car, even at this power to weight ratio. Also, a vastly more believable result. Those still suspicious of the regression and why we can't just use the linear formula to calculate this GT-Rs power keep in mind there are plenty of deterministic effects here contributing to the car over performing. These include but are not limited to: a suspension slightly tweaked by Nissan, fantastic rubber, tremendous practice of the track by Suzuki, the DCT system (which was conservatively modeled with 15 ms shift times), the advanced AWD and traction/stability control system, the car being generally accepted as being very easy to drive and push to the limit, potentially favorable track conditons and temperature, etc., etc.). Look at the existing variation in the chart, there are a lot of data points and many under and over performers. Many of which make perfect intuitive sense.

Not satisfied with just a regression for the Nurburgring I also did one for the Car and Driver Lightning Lap at VIR and for the Top Gear Track. For the Top Gear Track I deleted many cars I could not find data for or that were sort of "odd balls" as they have tested some rare not generally available cars (at least in the US). For the Lightning Lap the GT-R with stated power is still the largest outlier in the group, outperforming the regression by 7 seconds out of approximately 1.25 minutes. The interesting thing is that although it was again the single largest outlier it was "only" an outlier by 1.6 standard deviations. So much more believable than the 7:29 N'Ring result. The MoslerMT900S and Viper ACR being such "poorly tuned" track vehicles were "only" outliers by 1.3 standard deviations. It took adjusting the power of this GT-R to 500 hp to match the same level of over performance of the ACR and Mosler. Once again at the Top Gear Track the GT-R was the largest outlier and was so by 2.1 standard deviations. With the Top Gear data set it took the assumption that particular car was making 520 hp to bring the car in between the next two best over performers, the Cayman and Pagani Zonda F. Again real slouches in the handling/track department (immense sarcasm there for those who didn't pick that up).

Note that all three tracks while all exhibiting good R^2 values (0.83, 0.84. 0.70) exhibit predicted slopes that are drastically different, 16.7, 8.3, 3.0. Why? Just as I have theorized previously a faster track will have more time spent in drag like conditions (of course not meaning from 0 speed but still like a rolling start drag). For such tracks handling and cornering are less important as compared to what wins drag races for you - power to weight! Of course the slopes are ordered exactly the same way the tracks average speeds are. Power to weight matters on all tracks, even on a very tight non road course such as an autocross track, but how much faster you will go per additional hp (or per reduced lb), all else equal, is clearly less. Here the physics clearly agree with the regressions in terms of regression slope vs. average track speed.

So my conclusion #2 from this further regression analysis. A GT-R with 550 crank hp and a real ace driver producing a 7:29 N'Ring lap time is just within the 3 sigma realm of the regression model. The amount that the particular cars used in the Lightning Lap and by Top Gear for their tests were under-rated is not nearly as much as the car used for the 7:29 N'Ring run. This is consistent with the cars history of inconsistent performance.

I think most of us agree that an under rated car, a very practiced and top notch driver, favorable conditions and a tremendous track support team and marketing effort all contributed to this fantastic time for this fantastic car. Nonetheless, given the gut feeling from watching these videos and examining the times achieved by these other cars we can pretty quickly tell that this particular 7:29 GT-R was a real ringer, both in terms of power to weight and perhaps other favorable factors.

I will leave you with this great article with a balanced perspective on this whole issue. As if my analysis and post was not long enough! Do have a look

here at Speedsportlife.com if you are at all interested in this particular "achievement" by Nissan, the ensuing Porsche-Nissan battle and to better understand the changing role of the Nurburgring.