Palting

At least your trying.

You already got a quote from SRC4S and here's a reprint. Click the link at the end for the source, and the full article.

"'We have given up an almost imperceptible tick in acceleration against the Carrera in favor of more grip and better brakes,” says project engineer Georg Wahl. Measured by a lap on the old Nurburgring’s north loop, the C4S shaves four seconds from the C2’s time, according to Wahl. Stat freaks note: The C4S runs the 12.8-mile Nordschleife in 8:16 seconds (92.9 mph), the Turbo in 7:56 (96.8 mph) and the damn-the-electronics, 456-hp, two-wheel-drive GT2 in 7:44 (99.3 mph).'" mag one

Enjoy.

AlexT

This site tracks all Ring times. They don't post it until verified. The 997 TT is already on the list and it matched the CGT's time.

http://www.supercars.net/PitLane?vie...ID=0&tID=10073

Just so you know, the normal torque split for the C4S is 5% Front 95% rear. I was getting rid of my tires one day and was able to burn off all of the rear tires while the front was untouched. Video anyone?

Now toque steer has nothing to do with HP. As the phrase said, it's torque that plays the part. Now a rear engine awd car, essentially a backwards Audi quattro, there won't be any of that.

I love my C4S. It's a perfect every day car. But after driving the 997, I just love the trans so much. It almost switched me over to 997CS. Finally, I talk myself out of it with the depreciation hit I already took with my C4S. Didn't want to face it again.

TT Surgeon

Nice pics, that site doesn't even spell Walter Rohrl's name right.

SRC4S

From those pics, one would never think that the C4S is awd! I've actually seen a number of shots of 996TTs tail wagging. I've had more instances where the tail will happily step out. Makes you wonder when does the front actually engage? Alex, have you felt the fronts pull at all during your tire disposal process?

Sanjeevan

Alex T, awesome pictures...you've got PSM right?

Riad

PSM comes standard with the C4S. If you turn it off you'd never know you were in an AWD car.

AlexT

There is so much torque going to the rear, it overwhelms the viscous coupling. No front pull at all. Here is a video of the burn. It's clear that the front is not doing anything.

http://www.lotususa.com/Alex/911Carr...oMuchFun01.WMV

Yes. PSM off at the time of burn. I was really amazed at how easily the tires light up. These are Contis Sport Contcact 2. I now have Mich PS2. It's much harder to even do a burn.

Sanjeevan

Exactly, the old schoolers refuse to believe that......, the proof is in the pictures...I just wantd to make sure he did'nt somehow totally disable it prior to showing the pictures to them old schoolers who refuse to believe such things can be done on a PSM/AWD car.


P.S: Ok, ok I cave in from getting into trouble in the past...old timers=hardcore trackies.

bowmanm98

I'd have to go 997. Newer body style and the new interior is pretty nice.

Palting

Amazing pics and vid!! With rear spin, the VC is supposed to deliver up to 45% of the torque to the front wheels. You must have just overwhelmed the thing!! Holy smoke.! Literally!

Bullet

My impression is that the car is delivering lots of torque to the front axle, but the huge amount of power oversteer is overcoming that. I would imagine that that puts alot of stress on the AWD viscous coupling unit.

Also, the smoke is usually coming from the one wheel that is spinning much much faster than the other wheel - the inside wheel has lost grip and is spinning much faster than the outside wheel, which has grip, so the car turns. This exaggerated example nicely illustrates what a LSD is for. On the track, wheel spinning is a no no - it makes you slower.

SRC4S

LOL. How bad did the car smell after that?

I had read on the PCA Tech section that PSM equipped cars DO NOT have LSD (996 C2 and/or C4. That would include the C4S). The GT2 and GT3 do have it though. Reason is that powering through with LSD with PSM on triggers the system to think it wants to direct the car in a different way:

Here's the quote:

When Porsche came out with the C4 for Model Year 2000, they said: "As a standard feature, the 911 Carrera 4 has Porsche Stability Management (PSM). A mechanical limited-slip differential would have a detrimental effect on the functioning of the PSM. The 911 Carrera 4 cannot be fitted with a mechanical limited-slip differential."

The article also states that there's a version of the LSD that was available to cars after 2004 (most likely the 40th Anniversary intro and on). This particular LSD (option IX75) was available to the AWD models as well but only after '04. Lots of debate on whether it's there or not but that's what I've read.

so bullet may be right that we do not have LSD in exchange for PSM. but that would also mean that any PSM equipped car (sans option IX75) would not have LSD as well. BTW, Porsche's option code for LSD has traditionally been M220. So, a C2 w/o PSM would benefit from having M220. The real question is, which is faster around a track? PSM or M220?

Sorry for opening up a can of worms, fellas!

Sanjeevan

I think some of the early 996's had LSD as well, I know none of the 3.6L had any at least until my model yr., 03. (so, it's news to me that it was an option in 04). I know for a fact that the 40th had LSD . It is possiblt that PSM and LSD are mutually exclusive. well, for sure the LSD will be quicker than the PSM car, PSM turned-off is quicker than PSM ON, let alone with LSD. But, when it is off it is NOT overly intrusive, but most trackers who hate PSM don't seem to buy this. So IMO, for tracking LSD is faster, PSM makes it SAFER and if OFF not really in your way. So, the question I may ask is, is a car with no LSD or PSM quicker than the same car with no LSD and PSM turned OFF.

Palting

The ealier PSM was incompatible with LSD. As of 2004, I have seen cars with both PSM and LSD listed on the window stickers.

The earlier cars with PSM without the mechanical LSD have an electronic version called ABD: Automatic Brake Differential. The statement at that time was that with ABD, there is no need for LSD. The mechanical LSD increases rotational load or resistance on the more rapidly spinning axle to force more torque to the slower spinning axle. ABD does the same thing, but rather than using the differential, it uses the brakes. When the sensor senses that the wheel is spinning insensibly, it pulses the brakes to that one specific wheel forcing torque to the more sensible non-slipping wheel. My understanding is that this occurs at all four corners individually on the C4 and C4S since there are 4 separate half-axles.

Now, does a non-PSM car have ABD? My original sticker lists PSM and ABD separately. I assume non-PSM cars would have ABD listed separately as well, if they had it. Check your original stickers, guys, and let us know.

Is ABD better than LSD, that's another can of worms. My opinion, as the unbiased owner of a car with ABD, is that ABD is better heh-heh-heh . We need a tongue-in-cheek emoticon

I think Alex overwhelmed not only the VC, but the ABD, the tires, the road, even the LSD if he had it. Looked like a heck of a lot of fun!!!

AlexT

Um. Total peak torque is 273 at the crank. 5% standard to the front = 13.65 ft lbs add 15% loss I'm left with 11.60. I don't think that is a lot. Even at the max 40% is still only 104 ft lbs. minus 15% loss = 88.4 ft lbs. This is also at 4250 rpm, I was at 7000 rpm most of the time. Where do you get "lots of torque to the front axle"?

Look at it carefully. Both wheel are doing the same amount of smoke. Just the wind is blowing it away which is coming from the left side of the picture. I'm leaving TWO black lines. Both rears were down to belts when I was done. cars with LSD are the cars that would snap the tail or "power oversteer" like I did. Single wheel burn won't do that because one wheel still has grip. I would know, I had a open diff BMW 540is and a few American sedans.

Viscous coupling works by having a liquid material that "drag" the other side to transfer torque. Kind of like a torque converter.

http://auto.howstuffworks.com/differential9.htm

Therefore, no harm's done. Not to mention the car is still moving and the 5% torque split is about enough at 19 to 1 ratio in wheel spin.

Wheel spin doesn't necessarily make you slower. E46 M3s are faster around the track if you drift through corner. (I think it was either Road and Track or European Car that did the test said that) Ruf Yellow Bird did the fastest lap while drifting through all the corners at the Ring. It's how you maintain speed and carry momentum through corners that makes you fast on track or not. Nothing to do with retaining traction at all time.

It smell like burnt rubber for the next 5 days. The belts gave on the way home and send tiny little "needles" flying into the wheelwell. Took the shop a while to get all of them out.

Did I have fun? Read the name of the file.