Gabri343

SportAuto
BMW: 1.16,8 min
Maserati: 1.17,5 min
Porsche: 1.16,6 min

Improviz

Micah

I have the 2004 AMG catalog and it states that the CLK55 redline is 6700rpm. I also think that the power is dependent on break-in. From what I have seen, MBs gain more power after 5 or 10K miles of running.

AMG///Merc

And it shifts at what appears to be awfully darn close to 7000 rpm, which would lend credence to the 6700 rev-limit, but this was just going by the factory tachometer, which may or may not be all that accurate...

As far as Improviz's statement about gearing not helping with trap speeds, I'm confused by that. If a car is geared too high (Numerically low), doesn't it stand to reason that if the car is not accelerating at its maximim potential, it won't reach it maximim potential trap speed? If a car is accelerating faster through any given distance, let's say in this case, a half mile, wouldn't its trap speed be higher at the 1/4 mile point (Or right before it where trap speed is measured?) than if it's not accelerating to its maximum potential? I can't see how that's not possible, but by no means am I saying that I can't be wrong. I'd appreciate your input...


Best regards,
Matt



p.s.) Speaking of acceleration, I had my new wheels mounted recently, and I was surprised to see that my rear P-zero's were worn almost all the way to the wear indicators with only 9500 miles!! I guess I ought to stay away from the "ESP off" button!

Improviz

I really can't get too into this without Calculus and lots of boring stuff, but the reason that you have to gain more power to accelerate to a given speed over a given distance is basically dictated by the rules of Physics.

Torque is actually the force being applied here. Horsepower is meaningless from a Physics perspective and is nothing more than a derivation of torque: horsepower is defined as torque*rpm/5252, which is why torque always equals horsepower at 5252 rpm.

The main equation in Physics that explains the trap speed thing is basically F=ma, Force = mass*acceleration. So, the force a body exerts is equal to its mass times its acceleration.

Well, using algebra, solving for acceleration gives a=F/m. Meaning that acceleration is directly proportional to force (torque in this case) and inversely proportional to mass (weight).

So, to increase the rate of accleration, you must either increase power or decrease weight, which we all know. And the only thing which will increase the terminal velocity of a car at the end of a 1/4 mile strip is to do one or the other.

Unfortunately, gearing won't do this; gearing is passive, and does not increase the force. Nor will raising the redline: there must be an increase in force (torque) across the rpm range. Since torque increases horsepower, your horsepower must go up for your trap speed to increase.

In math terms, velocity is defined as the integral of acceleration by the Fundamental Theorem of Calculus. So, for constant acceleration, v(t), velocity as a function of time, is equal to v(0) + acceleration*T, where v(0) is the velocity of the vehicle at time = 0, and T is the time at which you're measuring the speed.

In a standing-start race, v(0) is 0, so velocity at the end of the 1/4 mile will be acceleration*T. So, you're stuck: you have to increase acceleration, by either increasing power or decreasing mass.

For all of you math whizzes: yes, I understand that acceleration isn't constant in this case, but it works out the same in terms of applied force even when acceleration isn't constant.

Sheesh, I didn't mean for this to turn into an essay!! Hope it explains this stuff a bit, and sorry about the boring math!!

MidniteBluBenz

Improviz,

The fact that the 209's are redlined at 6700 vs. 6000 is enough of an increase to account for the difference in 0 - 60 and q/m even though peak power is only up by 20hp.

Look at the time slips of a M3. Magazines usually get 0 - 60 times around 4.8 and q/m in the low - mid 13's, even though the car is down on hp and torque (compared to a C32 or CLK55). Sure it has a manual so there is less driveline loss, but its trap speed is higher "than it should be" b/c of its powerband. An M3's powerband is considerably larger and the car is geared so that it stays in the strongest part of the powerband. Ditto for the 209. Although the gearing is identical to a 208, the higher redline lets the car stay in its powerband longer. Additionally, the power band of the 209 engine may have been reworked to compliment the raised redline.

Even though the peak power is at 5750, it makes more sense to let the engine rev to 6700. A 6000 redline would result in the engine rpm dropping to between 4.5 and 5K in the next gear. At 6700, the rev's may only drop to 5500, closer to peak power. Additionally, the engine may be producing more power between 6000 and 6700 vs 4.5 to 5K where it would be if redlined at 6K.

Improviz

Horsepower is *defined* as torque*rpm/5252. You can't have an increase in power without an increase in torque, *unless* you extend the torque curve to higher rpms, which has not been done. Here is MB's torque/hp curve for the 362 hp 5.5l motor . It clearly shows that 1) horsepower peaks below 6,000 rpm, and 2) torque drops off above 6,000 rpm.

I.e., there *is* no more power at higher rpms. This is why we discussed earlier that it is odd that MB raised the redline without changing the torque curve. Raising the redline alone will help a bit, but it simply will not increase the trap speed, and is not going to shave nearly 1/2 second off a car's 1/4 mile or increase its trap speed by 3 mph.

Plus, while it is true that the 209's horsepower is up by 20, its weight is also up by 200 pounds, which means that its weight/horsepower is the same as the 208's, so the only factor which would help it in acceleration is the gearing.

The E46 M3 is not a valid comparison, because its power peak is at 7,900 rpm, just below redline, so it will, in fact, be making increased power right up to its redline. This is not the case with the 209; its power peak is about 900 rpm below its redline. This can also be verified by looking at both engines' torque curves. And while the early M3s did test with trap speeds in the 106.5-107 mph range, the more recent tests are trapping at 105, which is exactly what you should get with that weight and horsepower. The first ones were Euro versions, and were lighter than typical production versions.

We currently have one datapoint on this forum from a 209 CLK55 at the strip, and as mentioned in an earlier post in this thread, his four best times averaged out to an altitude-corrected 13.7. This is a pretty far cry from a 13.1, and I don't think that car will hit a 13.1 on 245's any more than the 208 would, because to get that time you need a low 60', and the torque of the engine overwhelms the skinny stock tires, which won't allow much below a 2.1 60' time, and you'd need a 1.9 or so for a low 13.

With more traction, based upon the fact that both cars' weight/hp ratio is the same and on my results at the strip, I'm quite certain that both of these cars could hit low 13's, but it's not going to happen on stock rubber unless you're launching on sandpaper.

Thai

Good discussions! Keep up the argument...i am learning....

Kain

Can someone please tell me why the hell were they comparing an AMG to a non-M BMW??

Thai

I think that they based it on PRICE. The future M6 will be quite expensive.

Improviz

1) the prices of the two cars are both about the same;

2) there is no M variant of the 6-series available--yet.