In all fairness, it was a while ago.

http://www.youtube.com/watch?v=9HS3gz1M6GU...feature=related

This is very 80's propaganda video by Audi.

They won the championship with Shirley, um, Hurley Haywood. Hans Stuck and Walter Roehl were maybe a little more impressive behind the wheel, but would get into trouble here and there.

Manufacturers (obviously) have to optimise a wide range of performance figures including launch and top speed - neither of which have anything to do with 60-100 acceleration.

Yes.

Most gearboxes are wider spaced in the lower gears (where there is usually plenty of acceleration - perhaps even traction limited) with progressively closer spacings as you go up through the gears. If you ignore this for a moment (for simplicity) and assume that the gearbox has constant (geometric) spacing, you will find that the engine rpm drops by a fixed percentage every time you shift up - regardless of final drive. If you're still not getting the picture - consider a box with constant (say 30%) spacing. For simplicity let's say 1-2 shift occurs at 60, then the 2-3 shift will occur at 78 and the 3-4 shift at 101.4. So the 60-100 can be done in 2 gears - 2nd and 3rd. Now change the final drive by 30% -either way. The shift points will still occur at 78 and 101.4, the engine revs will still be the same at those points (and everywhere else between 60 and 100) as will the overall gear ratio (everywhere between 60 and 100). The acceleration will be identical. So - provided the ratio spacings are close enough to keep the engine close to its power band, the 60-100 test will be largely unaffected by choice of final drive.

Thinking about it, I suspect that gearchange time is also an issue. The 997TT.2 has PDK, which is effectively a seamless shift (pipe down at the back, I know it's not the same technology as F1 robotised manual seamless shift, OK?); the McLaren was a conventional manual. A clue might be that the 997TT.1 tiptronic is faster to 100 than the manual, not because the gearshift is fast (I have one and can tell you that it isn't) but because it's a five-speed, so there might be one fewer gear change involved. Ratios and other data for 997TT.1 Tip (3.7s to 60, 7.8s to 100) as follows:



Wheel/tyre combination F 235/35/19 and R 305/30/19
Redline 6750rpm
353kw@6000
620nm@1950-5000 (flat, so gearing not critical to hitting peak torque)
680nm@2100-4000 with overboost (so previous poster was right about overboost)

"Hitting peak torque" is irrelevant to the 60-100 time. The revs need to be maintained in a band that maximises power.

So--- both cars are side by side doing 60 mph,then both then accelerate flat out in their best gears,the Mc Laren reaches 100mph half a second before the Porsche.Doesn't sound like much,but if you were in the Porsche you'd feel blitzed because the Mc Laren would be 73 feet ahead of you !

Probably much worse than that if both cars are doing steady 60 then nail the throttle. The Porsche would lose extra metres due to turbo lag.

Don't forget you can cheat a little with a turbo car, by left-foot braking to load the engine and so turbo up before starting to accelerate. Done that in a few turbo cars with good success.

Gold for Canada ! but gruntguru, mcguire and other axis of evil members seem to have signed a peace pact.

Guess that only works if there's a torque convertor in the middle?

Surely what you are doing is spooling the turbo up to max, rather than cruise speed, thereby giving maximum boost at the instant of accelerating - no lag.

No it works fine with a manual gearbox, but you have to work the brakes quite hard for a few seconds. It can be difficult to get balance with the pedals in some cars.

True.

My son has a 2,600 lb front wheel drive car with 333 turbo charged WHP. Wathcing him pull away from a stop is nearly a popcorn level event...sometimes pretty and sometimes not. But I'll pass on the technique above...maybe he'll have better luck.

BTCC and similar race series in the nineties when Audi ran an A4 Quattro. They conserved their tires well, low speed acceleration was good and during braking the four wheel drive prevented lock up of any single wheel.

power to weight to traction seems pretty basic but how about using torque instead, pound per feet on the wheels to car weight because it does come down to that for acceleration.

Sure - if you don't mind the extra work - I mean effort - no, I meant calculation time - Oh what the hell. Do it whatever way you want.

Trouble-maker.

"pound per feet on the wheels" your wheels have feet?
No offence but if you want to be taken seriously at least quote the correct units for torque.

Actually it comes down to pounds (tractive effort) at the contact patch and car weight.

And the power determine the tractive effort for any given car velocity.

well, we drove the new 997 turbo with PDK, and according to the race logic telemetry, quite a lot of us went under the Porsche's 0-100 km/h claims... fastest time of the day was 3.09x sec...

and, the car drives very well for a flawed concept..

I'll get my data from race logic unit (I forgot my USB key in portugal..) and hopefully get some acceleration graphs for 0-200 km/ runs.. might be interesting..

One thing you all have missed out is air drag. At 100mph both cars are probably putting a large part of their power into this.
Assuming both cars are fairly equal in their drag this power will be the same regardless of the weight of the cars.

I have seen this on the race track with my Ford Falcon 350bhp, against lower powered cars such as WRX. They are much faster on the tricky bits but on the straight I can out accelerate them once past about 60mph. As most people are cautious overtaking on bends I normally get them on the straight and hold them off.

Since the turbo is driven by gas flow,which is driven by piston speed,how do you increase piston speed (thus turbo boost)without increasing road speed unless there is slippage somewhere like a torque convertor ?

turbo boost is a product of the ammount of exhaust gasses "powering" the turbo nad that is not only a result of RPM but load also.. . So even if you do not change the RPM, but just load up the engine (by holding the speed steady on the brakes and holding the throttle flat to the floor) you can easily produce max boost even at low RPM... In fact, if your engine is at lowish rpm you will not need as much turbo RPM to provide big boost as you would at high engine RPM..

Yes you are correct of course. oh the shame mumble mumble

The only recent one I know of is the Corvette that had a tallish 2nd gear to get a better 0-60 time.

The rest worry about 2nd gear crawl performance in city traffic with a tall 3rd for city economy and highway passing (hence the often 'gappy' 2nd to 3rd shift). Then of course the ultra tall 4th and 5th for economy.

How do we make fun of you if you are going to be humble? We have rules here, no humble!

I'm sure you know a lot more than me, jy - except in this specific instance!

I'm taking a guess here...piston speed increasing without increasing car speed might be possible if these cars are down force cars; Aero loaded tires actually reduce gearing...if I am wrong I humbly accept any punishment. If I am correct I want a cookie.

See post#74! Prepare for your punishment...

I sincerely doubt if spooling the turbo with the brake pedal will produce an improvement in acceleration times. On high-powered road cars the best times are usually achieved with an opposite approach, if you will -- carefully modulating the throttle until well into second gear.

he is talking about flooring the throttle at 60 mph, not standstill... and the resultant lag in turbo cars...

when launching from rest, high powered turbo 4x4's will usually cut the ignition at a predetermined point, and use it to have some boost at rest.

Well, I was referring to actual acceleration times.

that might be on 2wd cars, but 4wd ones will put stupid amounts of power on the ground and do benefit from having some way of spooling up the turbo before launching.. 911 turbo will not spin it's wheels while doing a 3.1 sec 0-60.. and it does build up considerable boost before launch.. My 3100 pound and 400 hp Evo gets off the line with almost 1 bar boost while standing still.. and has no traction problems even with modest street tires..

Such systems which build up boost before starting are common on all wrc cars..

The 911 is equipped with comprehensive launch control. Haven't driven the latest one yet, but the way I hear it from those who have you step into the throttle, the tach just hangs there at 5000 rpm and away you go.

All the posts referring to spooling the turbo under brakes, relate to a rolling start contest from 60mph. The Porsche will suffer from turbo lag relative to the McLaren unless the technique of spooling the turbo under brakes is used by the Porsche driver.

Why do I care? That's not how acceleration tests are generally done.

I heard 60-100 was the new 0-60...

We were discussing a rolling start contest between the Porsche and the McLaren. If you don't care, just STFU.

exactly , it is brutal... I just drove it last week..

ok, but if I really wanted to be the fastest from 60-100 I'd load up the engine under brakes.. I'd guess the ECU could be easily programmed to do a similar thing even without the brakes..

The ECU would need an additional input from the driver to let it know he doesn't actually want to accelerate - he just wants to spool the turbo in preparation for an acceleration event. Perhaps light pressure on the brake to actuate the brake light switch, although that would wreak havoc with other left foot braking techniques.

additional "lc" switch.. or something like pit lane speed limiter..

ok, that would be a bit of a cheat, and have no practical purpose but ...

an African swallow maybe, but not a European swallow.

Return to this forum, and I shall taunt you again!

Okay, but wasn't I correct from another vantage point? If aero pushes the car down, the effective rolling circumference of the tires is smaller...I really want a cookie.

This is generally offset by the tire circumference growth due to centripetal acceleration. For many heavily aero cars the tire rolling radius somewhat balances, but for things like a Top Fuel dragster, the tire is still tuned to grow in RR, even though they make massive downforce, to assist in gearing.

So, the correct answer is 'depends'.

Okay...no cookie

I don't think the tread will stretch or compress much, so the circumference should stay more or less the same - even if the radius at the contact patch is slightly less due to compression. Also, from a standing start there is no aero, I don't know when it kicks in, probably fairly early, but it still won't reach significant load untill the speed builds up. I write this with no knowledge of the numbers involved...

Watch a top fuel dragster's rear tires. I'm not sure how much they grow but gheyvstart kit as typical big fat dragvtires and at speed are tall like a tractor's.