Torque

[southlight]

Originally Posted by mkoesel

Its like asking - So, on a racetrack, which one is better: speed or acceleration? Um hello?

Cool comparison since without acceleration there's no speed.


Best regards, south

[bruce.augenstein@comcast.]

Originally Posted by rldzhao

ok i have been thinking about this problem more and here is my answer:

Let's assume two identical M3's are side by side doing a drag race. Car A starts out in 1st gear, and Car B starts out in 2nd gear.

Obviously, Car A will accelerate faster than B, because it is in 1st gear, which means more torque at the wheels.

Now think about HP, it is the same at the wheels for both cars (because gearing does not change power (assuming 100% efficiency); it only changes torque).

Hence, this simple scenario shows that wheel torque is what matters in acceleration.

Of course, the M3 does benefit greatly from being a high-rev engine, since you do not need to shift as much because of the wider torque/power band.

I say car A accelerates faster than car B at that point because car A is making more power at that point, period. No matter the gearing, no matter the torque, the car making more power in any given instant will accelerate harder than the car with less power, because making more power means you are making more torque at the drive wheels.

Bruce

[footie]

The basic maths explains the relationship between torque and power but doesn't explain why some engines produce them at different speeds and in differing amounts. The is most to it than pure mathematics.

The difference in the way diesels accelerate compared to a petrol proves that the gearing both in the gearbox and the diff determine how these figures relate to forward motion. I understand that one is connected to the other but have always felt that there is more to it than pure figures can explain.

Take the new Audi 3.0TFSI engine, it peak power and torque figures are at the same 4850rpm, the peak power is lower than the 335i and it's producing slightly more torque, the Audi's peak revs are 6500rpm and the 335i I believe is 7000rpm which should mean the Audi has taller gearing in comparison but I reckon they will accelerate all but identically. This may be a bit premature to know if this is indeed the case but I would say that Audi have tested the A6 which will receive this engine against it's closest rival (535i) and I doubt they will have the BMW being decidedly quicker.

[J08M3]

Originally Posted by bruce.augenstein@comcast.

I say car A accelerates faster than car B at that point because car A is making more power at that point, period. No matter the gearing, no matter the torque, the car making more power in any given instant will accelerate harder than the car with less power, because making more power means you are making more torque at the drive wheels.

Bruce

Power is torque. Power in a specific time is horsepower

[bruce.augenstein@comcast.]

Originally Posted by J08M3

Power is torque. Power in a specific time is horsepower

Nope. Read back up the string for better definitions.

[lucid]

Originally Posted by J08M3

Power is torque. Power in a specific time is horsepower

Sorry, but that is really off.

[ArtPE]

an engines output is fully described by the following:

M = V pe/(4 Pi)
M = moment or torque
V = volume, displacement
pe = mean effective cylinder pressure (mainly Cr and/or turbo boost, with some volumetric efficiency influence)

that is all that influences torque generation...rpm is no factor

P = M w
P = HP
M = torque
w = engine speed, angular = 2 Pi n, n = rev/sec

the science is easy & clearcut...the engineering, not so

[jm1234]

Originally Posted by lucid

Wow, your plots are cool.

Where did you get the torque data from?

You might want to add the RS4.

Another suggestion is to normalize by weight although that can be tricky as published numbers don't seem to be obtained by using the same methodology...

Therein lies the rub. Some of the data is more accurate (from actual plots) and some is less so (interpolation from published power points or dyno). I can't upload the spreadsheet but here is the power curve data I used. Adding the RS4 wouldn't be hard, if you have that data (or more accurate data for these cars) can you push it to me and I'll add it. The modified 335 was the Dinan tune. The worst data is for the C63 as I could only find two points (max HP and max Torque) from which I got the torque at two RPM values. Luckily, the engines are mostly between both values for max acceleration so the plot should be "mostly" correct.

335i Stock 335i Modified M3 C63
RPM Torque Torque Torque Torque
0 000.00 000.00 000.00 000.00
500 073.76 073.76 162.26 310.00
1000 236.02 236.02 184.39 335.00
1500 295.02 295.02 210.21 350.00
2000 295.02 331.90 244.87 369.00
2500 295.02 349.07 261.83 385.00
3000 295.02 354.56 280.27 400.00
3500 295.02 365.83 293.55 410.00
4000 295.02 383.16 293.55 420.00
4500 295.02 371.31 291.34 430.00
5000 295.02 355.47 291.34 443.00
5500 283.96 323.50 293.55 400.00
6000 258.15 292.09 293.55 369.00
6500 239.71 266.76 291.34 357.00
7000 206.52 213.99 287.65 345.00
7500 000.00 000.00 280.27 000.00
8000 000.00 000.00 269.21 000.00
8500 000.00 000.00 254.46 000.00

[J08M3]

Originally Posted by bruce.augenstein@comcast.

Nope. Read back up the string for better definitions.

well I don't agree with many of the posts in this string. How can you say power isn't torque? Well maybe I should've used the word Force instead of power. Torque = http://dictionary.reference.com/browse/torque

[lucid]

Originally Posted by jm1234

Adding the RS4 wouldn't be hard, if you have that data (or more accurate data for these cars) can you push it to me and I'll add it.

I suggest using the following source for steady-state torque at the hubs for a variety of cars, which is where I got the numbers for my spreadsheet.

http://www.rri.se/index.php?DN=29

They seem to be a reputable tester. More importantly, all cars are tested with the same equipment, and if you download the spreadsheet for each car, you can see a column for the corrected outputs according to ISO 1595 standards. That takes care of the test conditions, but if you are curious, those are documented as well.

[bruce.augenstein@comcast.]

Originally Posted by J08M3

well I don't agree with many of the posts in this string. How can you say power isn't torque? Well maybe I should've used the word Force instead of power. Torque = http://dictionary.reference.com/browse/torque

Yes. Torque is a force. It isn't power.

Power means something happens as a result of that force. Meaning work gets done. Specifically in this context, it means something actually moves as a result of that force.

Bruce

[malter2.0]

Originally Posted by J08M3

well I don't agree with many of the posts in this string. How can you say power isn't torque? Well maybe I should've used the word Force instead of power. Torque = http://dictionary.reference.com/browse/torque

You are trying to think intuitively about this, which doesn't always work. Torque pushes you in the car seat just like when somebody pushes you in the chest and exerts force on your body.

Without knowing any physics, simply look at the units if you aren't sure. HP is measured in units of power (albeit non SI). Torque is a force and is not expressed in units of power.

[rzm3]

Originally Posted by bruce.augenstein@comcast.

I say car A accelerates faster than car B at that point because car A is making more power at that point, period. No matter the gearing, no matter the torque, the car making more power in any given instant will accelerate harder than the car with less power, because making more power means you are making more torque at the drive wheels.

Bruce

power is the same because they are identical cars. whatever is produced at the engine is what is transferred to the wheels. gearing does not change power!

[arefog]

You are all being far too technical. If you have an M3, you gotta believe that hp is all that matters. If you have a C63, torque is clearly more important. Simple....................

Dick Fogg

[bruce.augenstein@comcast.]

Originally Posted by rldzhao

power is the same because they are identical cars. whatever is produced at the engine is what is transferred to the wheels. gearing does not change power!

Please try to understand that car A is running at a higher rpm than car B in that side-by-side scenario, and is thus closer to its power peak. Therefore it's making more power and will accelerate faster.

If you do the math, you'll see it's also making more torque at the drivewheels, which is a by-product of making more power.

Bruce

[jm1234]

Originally Posted by lucid

I suggest using the following source for steady-state torque at the hubs for a variety of cars, which is where I got the numbers for my spreadsheet.

http://www.rri.se/index.php?DN=29

They seem to be a reputable tester. More importantly, all cars are tested with the same equipment, and if you download the spreadsheet for each car, you can see a column for the corrected outputs according to ISO 1595 standards. That takes care of the test conditions, but if you are curious, those are documented as well.

Good Data, thanks.

The data looks mostly like what you would expect. Sometimes the M3 has more power sometimes the C63 does, the RS4 is mostly behind but has a few area's where it shines too. On average the C63 has more power but not always so. The RS4 (according to that data) doesn't have the same HP as the M3 and when you scale it by the cars weight that makes it even worse. Second gear in the RS4 looks off, I have 2.05 but maybe I plugged in the wrong number? I'm done for the night though.

[mixja]

Well done - can you factor in the M3 DCT to your graph

[Hammer]

[BMW-videos.com]

Originally Posted by mattwhite

Go do a track day in your C6 Vette with 400 ft/lbs of torque (or more?). When you get passed by a Lotus Elise with 138 ft/lbs of torque, ask yourself if torque is so important.

Torque is great for the street if you don't feel like downshifting. It also can mask lots of mistakes on a racetrack. In the way it is being discussed here, it does not inherently make a car faster.

That's extremely questionable. First off the lotus elise advantage is its weight, it can fling itself around those turns might quickly. Being so small probably requires it to have a less powerful and most likely less torquey engine as well. If the track was autocross, or all short stopping twists and turns all the way I can see where you're coming from, and it's a joke to think that the c6's torque won't help it get moving after those sharp turns (if it's setup properly for traction). Now if this track had enough decent stop to go straits I can see your premonition going dry very quickly. Torque with grip is an advantage, stop denying the obvious. Why is it that a vette z06 or nto can easily beat a lotus exige, when it weights what 500 pounds plus more? It's the horse power, torque and the platform, not that it has super powers.

How else does this ford mustang gt even come close to a lotus? 320 foot pounds of torque might help that pig get out of a turn no?

[jm1234]

Originally Posted by BMW-videos.com

How else does this ford mustang gt even come close to a lotus? 320 foot pounds of torque might help that pig get out of a turn no?

Dude, it's the Stig not the torque!

[jm1234]

Originally Posted by mixja

Well done - can you factor in the M3 DCT to your graph

I could but it would just be a squiggly line around the 6MT. The MDCTs main benefit is that it shifts faster. It's still the exact same engine and same car weight so the different gearing is there to take into account a faster shift mechanism more than anything else.

I couldn't find the ratios, if you post them I'll graph them.

[armyav8tor]

Can't believe this is still going on. Again, torque is for towing, HP is for racing. As simple as that. There's no need to go into a technical discussion or the math equation on which HP is calculated. In the real world, HP is what matters because we have something called a "transmission" with 6 - 7 speeds that creates what is referred to as "gear ratios" to optimize the engine's powerband.