Quote:
Originally Posted by bruce.augenstein@comcast.
Can't argue any of these points, at least not conceptually. There may in fact be a minor mitigating concept a la Audi's SAE paper way back when, showing that driven wheels have lower rolling resistance than those that are just along for the ride. However, AWD cars will in fact have more restance to the engine's urges, can't deny it.
OK, back to the drawing board.
I fire Quarter, Jr. up, and plug in the numbers from the C & D 911 Turbo Tiptronic "Short Takes" test last year. They got an 11.6 @ 122, 0-60 in 3.4 seconds.
Result: The simulation shows an 11.62 ET, crossing the finish line at 121.5 mph, with an 0-60 time of 3.39 seconds. Wow!
Doing my sums, the Porsche may be underrated by (TA DA!) about six horsepower, as opposed to the 12 horsepower I calculated that those bastards at Nissan weren't telling us about.
Swamp, this is all approximate stuff, and I'm not waxing poetic about Quarter, Jr. (it is in fact the cheapie loss leader from RSA, after all). The thing is, there are some items out there (as previously mentioned and as this lightweight testing seems to show), indicating that the GT-R may not be as "MASSIVELY under-rated" as you are saying.
I know that once you take a stand, dynamite won't blow you off that perch, but I'm thinking that's a precarious perch indeed.
As I said, the jury still seems to be out.
Bruce
PS - Once the GT-R is available in the U.S. with published numbers, I'm thinking that Nissan will have to be doing some very interesting things to fool the SAE guy who is hawkishky watching the dyno tests. Once the SAE observer signs off, then and only then does Nissan get to advertise the results.
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OK first of all MASSIVE and in all caps may have been a bit dramatic/overstated, maybe even a bit premature. There is, however, multiple forms of evidence pointing to an under-rating. Part of the reason for my word choice was based on the dyno results showing basically the claimed crank output
at the wheels. I was a bit short sighted on the subtleties of that particular dyno in that it typically gives figures much higher than other dynos. However, even if it rates things about 10% too high with a 20% total drivetrain loss, the GT-R still comes in at 530+ crank hp, and I guess I would still call that massive. The N'Ring regression analysis also points to the possibility of a fairly substantial under-rating (or a variety of other effects working in tandem such as great driver+DCT+great tires ... or alien technology of you prefer that explanation
...). The last piece of evidence is the 1/4 mi time and it too point to under-rating (the number I have heard is 11.7s). I'm not sure how much more evidence we will need.
Back to the simulations. Getting fantastic agreement from a simulation vs. test results may happen but it may also be a case of getting it right for the wrong reasons. I'm fairly sure this is the case for your 911 Turbo results. If Q. Jr. can predict RWD times in a reasonably well validated fashion and it has absolutely no wasy to account for AWD, then it simply (almost by definition) can not also get AWD performance figures accurate
for the right reasons. Doesn't this make fundamental sense? We all know and understand that AWD cars get a harder launch but then suffer much greater parasitic drivetrain losses which hurts the cars performance more at higher speeds. You can not just rely on a simulation tool blindly and rely on it as a black box to just turn the crank, get the answer and not question the results in any way. It appears that this is what you are doing here. "Responsible" and intelligent use of simulation DEMANDS contstant questioning of the model, the inputs and results. CarTest offers complete control of a huge number of input variables including FWD, RWD, AWD and a plethora of other user defined inputs (you can see some screen grabs of the amazing number of inputs possible in CarTest on other threads here on the forum). One reason I am a bit hesitant to use and post results for cars like the 911 and GT-R is that I have not had great luck simulating Turbo charged cars yet. I will probably work a bit more on the 335i and making sure I can get good results for known/justifiable reasons before relying on CarTest too much for such cases. In any case I think my preliminary runs with CarTest for the GT-R showed it required about 520 hp to get a 3.5s 0-60 and 11.7 1/4 mi. I did use very short 0.03 s shifts as we can expect from its dual clutch system and of course the AWD option.