ben in lj

so the 430 with R compound tires is faster than the enzo (and CGT which has pretty near R equivalent on the outter 1/3 of the tire - where you'd need it)? mark me down as skeptical.

MetalSolid

I had the Pirelli P-Zero Corsa System - same tire as Stradale - on my GT3, while they have more grip than most regular street performance tires, I wouldn't call them R-compound. The difference between a true R-comp tire, the MPSC that I have now and the Corsa System is night and day.

ben in lj

that's kinda my feeling too. these tires act more in between street and R tires.

Philip in AL

I take delivery of a new 430 in May/June. Our local Porsche club should have a PDE at Barber Motorsports Park shortly afterwards. I intend to take my GT3 and the new 430 to the track for testing. You know what would be really cool; I wonder if any of the magazines would be interested in coming here to do a comparison of the GT3 and the 430, using my cars. I don't know why they wouldn't; BMSP is a premier race track. Both cars will be availble at the track. Hurley Haywood could be the driver (it could be scheduled for a day after he teaches class at the track for Porsche Driving Experience). Anyone know who I could call?

NJ-GT

The 300lbs penalty on the F430 is offset by the amount of torque available on the new engine. That car will be faster than the 360CS at any racetrack. It will be faster than the GT3 as well. It just need the right tires.

The problem is that there are not r-comps available on 19", but they will come. Viper, Z06, 997S, and plenty of other high performance cars are coming with 19".

On my Boxster S I was turning Pocono North at 65 secs average on GForce KD. These are one of the fastest street tires (no r-comps) out there. Same car on MPSC was running 63 secs.

On a 45 seconds lap autocross, the Hoosier A3S04 is 0.7 secs faster than the Kumho V700. The V700 is 0.4 faster than the MPSC. The MPSC is almost one second faster than the MPS2.

At Pocono Full course with the two infields, the R3S04 Hoosier is almost 2 seconds faster than the MPSC.

There are plenty of threads on the Racing forum that compare tires.

I'm planning to attend the 2005 Porsche Parade at Hershey, PA. The new class S13 is for the GT3, GT2 and Carrera GT. You will see Boxsters and 911 on r-comps turning faster laps than the CGT on street tires at that event.

tdf360

Well, couple things here. One, Fiorano is a short track, so probably 1.5 to 2 sec/lap for the R tires. Two, unless you are testing on the same day, there will be differences in grip levels, temperature affecting hp, etc, so it's difficult to compare lap times from different weeks much less different years. In controlled conditions, I believe the differences I quoted between street and R tires are pretty accurate.

Gary

tdf360

Yeah, there is a grey area with the Corsa System. I'd like to see some back-to-back tests, my feeling is they would fall about halfway between R and street.

Gary

The_Phantom

It's not just rear engine cars. Both rear engine rear wheel drive cars and front engine front wheel drive cars have lower drivetrain losses because they don't have to have long heavy driveshafts, etc. which is in large part what creates the drivetrain losses. That's why one of the commonly touted advantages of front wheel drive is that front engine rear wheel drive cars typically have a drivetrain loss of 20% while a front engine front wheel drive car will typically have a drivetrain loss of 15%. The same is true for a 911 which, of course, is rear engine rear wheel drive. As far as proving it to you, I can't find any reputable web sites that describe this concept, but I have read about it multiple times in various places (one of which was European Car Magazine). The reason why there is an aftermarket for lightweight driveshafts is because people have found that a lighter driveshaft reduces drivetrain losses and thus increases hp at the wheels (and this has been dyno tested by import tuners types). Basically, 911s have a defacto lightweight driveshaft because they don't have a long drive shaft like a Corvette does and therefore lower drivetrain losses. At least that is what I've been led to believe. Does that make sense to anyone else?

Z06

As much as there may be a slight increase in drive train loss with the Corvette,
the 405 HP Z06 from 02 - 04 makes 353+ rwhp.

Greg Fishman

Long, heavy driveshaft has nothing to do with drivetrain loss. It affects acceleration (inertia) but the weight and size of components is not a factor in loss. Drivetrain loss is a function of friction. The transmission gears, bearings, etc add to the loss. The U-Joints in a driveshaft create friction. Gears, bearings, etc in the diff do the same. Wheel bearings too. With independent suspension, the CV joints add drag as well.

So all told, the FWD or Rear engine package has a very slight advantage as it has eliminated 2 U-Joints for the driveshaft and any additional bearings. It is no where near the 5% loss you have claimed.

The_Phantom

The dynos appear to show otherwise. They are 5% or more. Here is a chart which shows a 320 bhp 911 with 295 hp at the wheels which is approx. a 7% loss. (This dyno is taken from the Evo website evoms.com, a highly respected tuner of Porsches that have an interest in downplaying the factory hp reading if anything since their job is to improve it). The Corvette Dynos are from a website which has the stock dyno results from a series of Z06 Corvettes: http://www.dynoperformance.com/ The drivetrain losses for the Corvettes were more like 15%. There is a big difference in drivetrain loss between the two cars.

e6tme

Fishman, your examples don't seem to help your argument.

To simply illustrate: the 2001 Z06 was rated at 385 bhp, and put down 342 bhp, an 11% "loss." The 2003 Z06, rated at 405 bhp put down 335 bhp, a 17% "loss."

If there is such a variance between two cars on the same dyno, how can you honestly compare a different car on an entirely different dyno?

By the way, Evo MS has another dyno plot on their site of a 320 bhp 996 putting down 283 bhp, an 11.5% loss.

The point is that comparing dyno runs is pretty much useless, unless you are comparing the averages of several runs on each car, on the same day, on the same dyno. Even then, it is virtually impossible to determine the actual drivetrain loss without putting the engine on an engine dyno, then measuring the power at the wheels.

People much more technically minded than I have debated this subject to no end, and about the only thing everyone can agree on is that parasitic losses in automatics account for 15-20%, while manual gearboxes are in the range of 10-15%.

As Greg said, the driveshaft affects inertia and thus acceleration, there is no way the two additional U joints can account for 1/4 to 1/3 of the parasitic losses.

Greg Fishman

Do you think it is possible (likely?) that the cars in your example may not make the hp they claim? Were both these tests done on the same dyno?

Only way I can imagine to compare driveline loss between cars would be to engine dyno both cars and then compare it to a chassis dyno (same dynos for both) and then do the caluculations. Without it there are too many variables to give a meaningful comparison and and any results are purely speculation.

E. J. - 993 Alumni

Is there a scientist in the house? Can we get a scientist please?

No offense dude, but this is wacky. Can you get any more unscientific? There is no way to scientifically prove what you are trying to say. There is no dyno that is both a motor dyno and a wheel dyno. WIthout that, your assumptions are nothing more than unscientific guesses.

In order to make it work, you would have to take a car, run it on the wheel dyno, remove the motor, and run just the motor on the same wheel dyno. Oh, and the conditions would have to be the exact same too.

And BTW - a wheel dyno has driveline loss too from the big wheel spinning. Sure, they account for that in their software, but how do we know that is accurate?

Are you starting to understand?

Oh, and its pretty funny that you took stock HP claims from a manufacturer for your baseline numbers. Boy, those are never inflated. Can anyone say Mustang Cobra?

The_Phantom

Sure they do. They tend to show that a rear engine rear wheel drive 911 has a lower drivetrain loss than a front engine rear wheel drive Corvette.

I'm not claiming these dyno results are perfect, the numbers are trivial. Give them a reasonable accuracy plus or minus a few percent to support the general proposition that rear engine rear wheel drive cars and front engine front wheel drive cars have lower drivetrain losses than a front engine rear wheel drive car.

Thank you, 11.5% is another damn low drivetrain loss from a rear engined rear wheel drive car. Do you have even a single dyno of a Corvette with such a low drivetrain loss? No, of course not. The Corvette dynos all tend to be around 15% and the 911s tend to be around 10%.


I'm not citing these dynos results to claim that they are precise. Again, the exavt numbers are trivial. The dynos are cited to support the general proposition that rear engine rear wheel drive cars and front engine front wheel drive cars have lower drivetrain losses than a front engine rear wheel drive car.

I already got Greg to admit that I was right and there was less drivetrain loss

Now the argument is just over how much of a difference does it make. I have not yet found the article in European Car Magazine which stated that it is an advantage in terms of drivetrain losses to have a rear engine rear wheel drive car, but this article from European Car Magazine is just as good:

"On the other hand, a Mustang dyno will correct with a 21% loss figure. Actual over-the-road loss is probably in the 17-20% range. A lot of front-wheel-drive cars do not have any 90-degree gear changes. All gearing is straight transfer. Losses are less; I'm going to guess at 11 to 12%."

http://www.europeancarweb.com/tech/t...02d/index.html.


Here's another article from a different magazine which, although the numbers are different, makes my point:

"A lot of people also don't realise that a FWD has significant benefits over a rear wheel set-up. For a start, a front wheel drive delivers a greater portion of engine power to the wheels. It's widely generalised that there's a 30% power loss through a RWD's drivetrain, while a FWD loses only 20%. Needless to say, 10% is a big difference. That's the kind of power gain you get when you go out and install a high flow exhaust. And, with reduced drivetrain loss, you're also talking improved fuel economy as well."

http://www.autospeed.com/cms/A_697/article.html

Ok, two articles from reputable magazines. I forget, what evidence did you guys have?

My point is proved correct in real world tests as well considering that 911s with less bhp are faster than Corvettes.

Road and Track found that despite having 55 hp less, the new Carerra S was faster than the new Corvette. Click here:

http://roadandtrack.com/article.asp?...&page_number=1

According to Car & Driver which tested both cars, the newest Corvette with 80 hp more than the Carrera 2 only beats it by 0.2 of a second in the quarter mile. Click here:

http://caranddriver.com/article.asp?...&page_number=5

I know that there is more to this than drivetrain losses as 911s also have much better traction than a Corvette, but my original point

was that the fact that other cars have more hp than a 911 is not as big of a deal as it seems since 911s often times are faster with less bhp.

Right or wrong?