Think LOGICALLY about the M5 performance data - Page 8

HBRAMSTEDT · 21st August 2004, 19:20

In the torque versus horsepower discussion, OPINIONS DON'T COUNT!!!

POWER IS THE PRIMARY MEASURE OF A VEHICLES POTENTIAL TO ACCELERATE QUICKLY, NOT TORQUE.

Power is the amount of work (torque's ft./lbs.) multiplied by the rate at which it is done. A fast car in the 1/4-mile will have an engine that by definition has high power, it can do a lot of work in a short time in order to get down the track in the shortest possible time.

Yes, torque (ft./lbs.) is a component of power, but not necessarily needed to create high power. You can also create high power by doing a little bit of work (low torque) very fast. Look at a turbine engine, low torque at high r.p.m.s. I've seen turbine and jet cars turn amazing times at the drags!

Look at this link to help understand the physics of power and work:
http://www.physicsclassroom.com/Class/energy/U5L1e.html

All drag cars are tuned for peak power, NOT PEAK TORQUE. Even top fuel cars turn their big torque numbers at 9000+ r.p.m.

People here sound somewhat lame when even suggesting that high torque is what is needed to go fast or move a car down the drag strip quickly. It is absolutely irritating.

Torque allows for a more flexible power band for driving (less sensitive to what gear you are in) and less energy loss in the powertrain. However, torque multiplication through gearing can be applied to high horsepower vehicles with relatively low torque to obtain the required performance.

Other strange and erroneous claims:

AJ: F1 tires and drag tires share the same design and are functionally equivalent. AJ, I can't believe you actually said that. The construction of the tire carcass is absolutely different on a drag tire and a F1 tire. How can you possibly make such a claim? I've seen the internal construction of both and they are very different.

Richard in NC · 21st August 2004, 20:20

Here are a few points and counter points.
On HP vs torque: They are tied together with HP being a function of torque and RPM. At a given RPM, if you have more torque, you have more HP and vice versa. However, HP is what ultimately determines acceleration. You can prove this by holding 2nd gear from 2000rpm to redline. The torque peak is 3900 rpm but the car accelerates harder above 4000 proving torque isn't the sole factor. BTW, saying that torque gets you off the line is wrong also. Reving the engine is to increase the horsepower at start. In a low power car, one must rev well past the torque peak to break the tires loose hence once again, its power not torque.

On the 7 speed SMG: Proper gearing is what puts the engine in the right RPM range to make max HP. I bet the 7 speeds aren't to do a super low first gear, they are to provide closer ratios to keep the engine at its peak power. And BMW does this better than anyone else. BTW, with SMG, the argument that the Merc automatic is easier to get max acceleration figures no longer applies. Both cars keys to best times is modulating wheel spin off the line and maintaining traction throughout first and 2nd. Manual shift times and clutch skills won't apply.

MEnthusiast · 21st August 2004, 22:49

Ahh Richard, but theres the rub. I can't say regarding SMG3, but my experience with SMG2 is that your better shifting automatics are better at being an automatic and stick shifts are better at being a manual transmission. The book on SMG3 has yet to be publicaly written though. My guestimate- it will be a big improvement and yet for some of us it will be no more or less involving than SMG2.

Enigma · 21st August 2004, 23:31

Quote:

Originally Posted by MEnthusiast

Ahh Richard, but theres the rub. I can't say regarding SMG3, but my experience with SMG2 is that your better shifting automatics are better at being an automatic and stick shifts are better at being a manual transmission.

To each his own, however, from a performance aspect SMG2 is superior to a manual in every aspect except the initial launch.

A manual is only better if you miss you extra pedal and don't want to learn left foot braking.

zzzzMD · 21st August 2004, 23:46

Quote:

Originally Posted by MEnthusiast

Kees,
I know its a figure of speech and all, but isnt everyone here human? I mean, what kind of cars do space aliens like?

Maybe Saturns, Plymouth Satellite, or a Mercury Comet???

Tom_K · 22nd August 2004, 00:15

Quote:

Originally Posted by Erik

Yes they are. The M3 and the CSL is so close its poinless to discuss who is the fastest car in straight line. both are in the high 4 sec 0-100 kph. The E39 M5 is also in that area. Same goes for the 0-200 kph run. the CSL is normaly high 16 sec and the M3 is from high 16 until 18 sec with some ones close to 20 sec.

Do you have any tests from magazines to prove what you are saying about the 0-100 km/h times? Sport Auto tested the M3 at 5.2 s, M3 CSL at 4.8 s and E39 M5 at 5.4 s. Those times are as close to the official numbers as you can get. The CSL was 0,1s better than the official time and the M5 was 0,1s slower but they are very close. I would really like to see proof of anyone achieving a sub 5s time for the 0-100 km/h sprint.

MEnthusiast · 22nd August 2004, 02:01

Youre funny good Doctor.

Enigma,
Theres a performance advantage to SMG, no doubt at all. This is 65% of the reason BMW M is going SMG exclusive. The other factors are warranty costs, the declining % of people who can actually drive a stick shift, etc.

Im saying there will be many people who find the experience less rewarding. You could say this is similar to those who feared the use of ABS and DSC because they felt they would make the experience less rewarding. We all have our own opinions/ preferences. I've made my opinion the old fashioned way- shelling out hard earned money and then realizing that it didn't "do it" for me.

PS- one day BMW will use only 1 transmission for all their vehicles, guess which one it will be?!

digger · 22nd August 2004, 02:57

Quote:

Originally Posted by Richard in NC

Here are a few points and counter points.
On HP vs torque: They are tied together with HP being a function of torque and RPM. At a given RPM, if you have more torque, you have more HP and vice versa. However, HP is what ultimately determines acceleration. You can prove this by holding 2nd gear from 2000rpm to redline. The torque peak is 3900 rpm but the car accelerates harder above 4000 proving torque isn't the sole factor. BTW, saying that torque gets you off the line is wrong also. Reving the engine is to increase the horsepower at start. In a low power car, one must rev well past the torque peak to break the tires loose hence once again, its power not torque.

High engine HP deterines the performance potential. but its the torque at the rear wheels that can be achieved from using a powerful engine that governs acceleration.
Forces give acceleration so its rear wheel torque that physiaclly accelerates the vehicle. If you know the torque at the wheels you can get the acceleration directly. If you know the power you need the speed at which this power is developed to know what acceleration will ensue.

The harder you twist the drive shaft (torque) the more you'll accelerate, if you want to twist it hard at higher speed you need more power to do it.

Think logically (ha ha) you develop peak power in each gear 1st,2nd,3rd etc but your acceleration is highest in first gear (barring traction problems). Why? because torque is highest from gearing you have power but at low speed which gives torque.
The more power you have the faster you will be able to accelerate in each gear, I don't think anyone doubts this fact but physically its due to the torque. So just because you develop alot of power doesn't mean you'll accelerate quickly because you don't accelerate much in top gear.
An excel with its 100hp will accelerate qicker in 1st gear than an 500hp M5 in 7th gear one will be going 30km/h and the other 300km/h though, but like i said before if you increase the power of an excel you will be able to accelerate faster.

People tune their cars for HP so they can increase their rear wheel torque. Tuning a car for torque will give better midrange performance for driving around but to race engine HP is a measure of performance because it enables more torque to be developed. Increasing the power of any car will enable better performance that is fact but this is from increased torque. Power is the measure of engine performance.

Peak acceleration occurs when at peak torque it only feels different because the engine works harder and you are moving faster (even if you remove drag effects). if you attach an accelerometer you will see. At peak torque the power divided by speed is higher so by definition you have more torque twisting the drive shaft.

If you hold 2nd from 2000rpm to redline the peak acceleration will depend on the gear, so it can't be power dependant else why do you accelerate more in 1st than 2nd and 3rd etc. the peak torque (in wheels) only occurs once so thats why there is only one peak acceleration. By your analogy you'd accelerate the same evety time you reached your peak power.

Revving the engine past peak torque is to account for the engine bogging down when a loaded is apllied (as clutch is engaged). When you do a burn out your revs are above peak torque because once the wheels begin to spin it takes less torque to keep them spinning and usually one likes puts his foot near the floor.

I think i've probably siad the same thing over and over and rambled on long enough.

vndkshn · 22nd August 2004, 21:21

Quote:

Originally Posted by Erik

To me the difference of +/- 0,5 in the 0-200 kph run is to me off no importance. The E55 is capable of running 0-200 in less than 15 sec if I am not mistaken. Maybe the M5 will do that in low 14 sec fine but so what. The most important aspect of that is that we can claim back the title as the fastest 4 door car in the world.

Is it just me, or these few sentences contradict each other?

How can you not be concerned about performance, but find the most important aspect to be "we can claim back the title as the fastest 4 door car in the world."

Well, it would seem to me that if you want to make that claim... you have to have something to base it on.

M&M · 22nd August 2004, 22:33

http://www.einszweidrei.de/bmw/m32003-2.htm

Here's Sport Auto's test that got the M3 to 100km/h in 4.8. I think there's another mag that got the same. I'll try to dig it up seeing as some people say it can't be done.