BC

If you noticed, they did mention the GT2, and that the price would have been more realistic in comparison to the other two. They, if I can recall correctly, said that the GT2 would have been no faster then the GT3, and that the "Value" ideal would have been reduced. I cannot say that I agree with that. I think the GT2 may have been a TRUE comparison. 180k, right?

I think they will have a BUNCH of letters on this one.

tdf360

To me the result that stood out as unbelievable was the Ford GT. No way does a 500 hp, 3400 lb car put down numbers like that. It tested basically the same as the Enzo, which has another 150 hp at the same weight. It is also MUCH faster than the Viper SRT-10 with 500 hp and maybe 100 lbs more weight. And, just to add to the mystery, the C&D test numbers were way faster than R&T's of the same car, on the order of 0.6 sec faster in the 1/4. Something fishy.

Gary

Bob Rouleau

what a great thread! A few data points:
The Stradale comes std. with "Launch Control" - this may help the standing start!
They criticized the handling of the GT3 which is a bit sensitive on street tires. As others have pointed out, a set of P0 Corsa ties would have improved things a lot.
911's in general are lousy drag racers. Hard to launch too much traction back there and you get axle hop.
Wait a while and when it becomes known that the Ceramic brakes and pads on the Ferrari also require frequent replacement CD may change their minds. The pads cost 3200 (f) and 3000(r). Don't ask about the rotors! A guy with an Enzo had to replace his brakes at 5000 miles at a cost of 20K.
I'm starting to like PCCB better.

bob_dallas

John, thanks for the physics review - saved me from looking all that stuff back up. My point (I think ) is that your HP figure maybe close but "artificial".

Don't worry - I'm not disputing Newton. But this is too simplistic of a view. The basic formulas basically assume a 1:1 transfer of power. An automobile does not typically allow a 1:1 transfer of power - they have pesky things called gear ratios and final drive ratios (among other things) that either enhance or detract from the power transfer.

Try this example - same 3200 lb car with 361 rwhp - except the driver shifts from 1st to 3rd to 6th. Same weight, same HP but a dramatically different ET. If you were calculating the HP based on the work done with the weight and time to go 1/4 mile the HP number wouldn't be too impressive. Granted this is not very realistic but lower gear ratios are. Gear ratios and other factors make a difference, and could be a huge difference in leveraging that HP and making it seem like it's much higher.

Comparing the Ferrari and the Porsche you see some decent differences in ratios - overall ratios

Gear GT3 Stradale
1st 13.14 14.56
2nd 7.396 9.546
3rd 5.3664 7.104


If the GT3 was geared the same as the stradale it would have likely turned in better acceleration numbers, right? Same HP but the actual newtonian power would have increased because of the gearing multiplier. For the GT3, the proper gear ratio for a 1/4 mile run is probably not the same as the gear ratio that gets them to the magical 190 mph number that they wanted as well so they made a compromise in acceleration.


To take it even further, as you say this doesn't account for losses either - tire friction, etc. but I'm not going there.

Make sense? Again, I'm not trying to repeal the laws of physics but am trying to point out the limitation of applying a basic law to a much more complex equation. Not sure what else I proved though...

bob_dallas

Agree with most of the other comments on the C&D article so I won't rehash. Brendan - their point was that it would not have been sufficiently faster to compensate for costing almost twice as much, not that it would not have been faster at all. This is debatable since most of the comparison factors were very subjective but another key point is that the GT2 is harder to drive at the limit than the GT3. If the test driver couldn't figure out how to drive a rear-engine car with the GT3 then I'd guess that the GT2 would have really gotten away from him. In the end though - I'd guess that they wanted to rank it lower as you alluded to...in their words "it came down to the cachet of the two others. If ever a 911 could feel plain it does in the company of the Stradale and Ford GT"

bob_dallas

BTW - if the Porsche could have been faster with equivalent gearing...I might be proving that the HP is much higher than 380 if you compare it to the Stradale, but then we have the F1 transmission factor, shift times, launch and everything else to muddy it back up again.

Time to hit the sack - enjoy...

GuyR

'The GT2 wouldn't be faster' - what a load of rubbish………

Lets look at the facts from the Porsche website:

GT2 vs GT3

483bhp vs 381bhp

640nM vs 385 nM

1420kg vs 1380kg

So the GT2 has an extra 98bhp (27%) and an extra 255 nM of torque (66%) with which to carry an extra 40kg (3%). Mmmmmmmm I wonder if that might work……….

Guy

johnfm

bob

my point in establishing the minimum power required to shift a mass 1/4 mile in a given time was intended to show how fundamental the physics is. They are simplistic, and this is a good thing. We can, without ANY doubt whatsoever, determine the MINIMUM power needed to produce certain performance. This is a great tool in itself, and allows anyone to determine what sort of power/weight combination they would require AS A MINIMUM to achieve a certain figure.


If you then add into this other fundamental (and known) physics for losses due to wind resistance, mechanical losses due to power transfer, thermal losses, tyre slip, gear change time etc etc, you get software which is actually extremely accurate. This is borne out by the fact that virtually every branch of engineering utilises computer modelling to a huge extent.

BUT, all computer models depend entirely on the accuracy of the data they are fed. If you could be bothered (I'm too busy today) a simple spreadsheet with the above HP formula could show how sensitive the formula is to the data.

There is no substitute for real world testing, BUT all designers & manufacturers realise that they can very accurately assess design changes in a computer before spending money on a single component. THe people who design the software use real world testing to validate their computer models. Good computer models are frighteningly accurate. One of the areas where they currently fall short are in complex aerodynamics, where there currently isn't the computing power to deal with all the equations. AS an example, golf ball manufacturers cannot model a ***** performance by computer - too many variables. Its cheaper to make a mould, make the new ball & test it. If it goes further, or higher or spins more or less (or whatever they are trying to achieve) they then stick with that design.

Mr. RS

Funny, I often think the same thing.

Hello? Hello? is this thing on....

bob_dallas

Right - completely agree with this point. However, weight and HP are truly objective measurements so using real-world power/weight numbers to come up with an estimated ET is one thing. Using a real-world, subjective ET to reverse engineer to HP is, however, flawed.


Exactly - and way beyond me to calculate in my head or on paper.

Already aware of this - no debate here. Might build a spreadsheet if I have time to try out this and a couple of other variables and do some comparisons. I'll repost if I do.

Absolutely in agreement here. My point, which I think has been made, is that absolute determinations of power based on easily flawed inputs (some drivers ET), that do not take into account many important variables (gearing, tire slip, gear change time, wind, etc) are inherently flawed. Rephrasing one of your statements above - The output is only as good as the inputs.

bob_dallas

this might be a fun program to play with and fairly cheap

http://www.quarterjr.com/quarter_jr.htm

or this if you want to be more precise (and spend more $$)

http://www.quarterjr.com/quarter_pro.htm

johnfm

I recently found a spreadsheet for engine modelling, done by a guy called Jim Roal - its VERY basic, but take into account aerodynamic drag losses etc. I cannot upload an Excel file, but it is at this link:


Jim Roal's Engine power/injector spreadsheet

have fun!

bob_dallas

Thanks - just what I needed was more things to spend my time on...

BTW - his home page has some excellent links if you dig around

Sun Ra

in my slow and posing view, the GT3 is the ultimate sleeper. Karl's car clearly has over 400 HP per dyno; mine feels way too strong and fast for a small peak to 380 HP as shewn in the factory HP graph.

and Bob-Dallas's:

" Gear ratios and other factors make a difference, and could be a huge difference in leveraging that HP and making it seem like it's much higher.

Comparing the Ferrari and the Porsche you see some decent differences in ratios - overall ratios

Gear GT3 Stradale
1st 13.14 14.56
2nd 7.396 9.546
3rd 5.3664 7.104


If the GT3 was geared the same as the stradale it would have likely turned in better acceleration numbers, right? Same HP but the actual newtonian power would have increased because of the gearing multiplier. For the GT3, the proper gear ratio for a 1/4 mile run is probably not the same as the gear ratio that gets them to the magical 190 mph number that they wanted as well so they made a compromise in acceleration."

these comments are appropriate. GT3 is similar to an early 911 where it is appropriate to "airport" gear the car for maximum acceleration in your daily usage. If I decide not to use this car for ORR, i no longer need to exceed 150, and will regear. Hillclimbing in Malibu was greatly improved when i regeared my 70S, and a MK II GT3 geared to 150 redline in 6th would be rather sporty around town.


PS: Mr. RS: you're still paying the price for that McDonald's comment; the colonials remain vituperative!

PPS: the suspension improvements in the Mk II vs my 02 GT2 are so remarkable, i am thinking the 04 GT2 may actually be worth 15 under... and my dream car is evolving into a narrow body GT2 that feels as light and quick as the MK II......

bob_dallas

Hey Watt - no reason why you can't do that with your existing car... Twin turbos on a GT3 would be quite a package

WRT ORR - would be interesting to evaluate the class where the GT3 would be competitive and whether gearing with a topspeed in the 170s would help even that. I admittedly have no experience with ORR but just a thought.