[zmo]

Searched and found nothing in the F87 forums, but found this at the F80 one: http://f80.bimmerpost.com/forums/sho....php?t=1044799

Googled the torque curve for the M2, but there's no graph taking in mind the overboost extra torque (this is easily solved just by adding the extra 50nm, however, I don't know how will the slope in the graph evolve at the end of the overboost, which at that point intersects with the peak power output // I mean if it's a linear or an exponential negative slope, I'm sure it's linear when it kicks in, not so sure when it wears off). Anyways, which are the optimal shifting points, factorizing the overboost variable, for maximum acceleration? Sport+ (MDM) or DSC off?

[mrcheezle19]

if you don't bang limiter in every gear you're not revving high enough.

[J3STER]

Get a dyno of your car and you will know when to shift. But from that graph peak power comes in very late so redline shift would be ideal.

[oj34]

Red line shift is only optimal for 1st and 2nd gear.
Attached image shows wheelpower (not considering overboost because I found no reliable torque chart showing overboost).

So without considering overboost:
1st : red line
2nd : red line
3rd : approx. 6800 (almost red line)
4th : approx. 6500
5th : approx. 6500
6th : well - no 7th gear

Of course everything here is 6 MT. 7 DKG would need another chart. Too tired for that

[6734202]

I was literally just wondering about this. Awesome thread for us 6MTs!

[SeanWRT]

Don't look too much at torque curve which can be misleading, you will not want to shift early just because torque is there. You lose torque when going a gear up.

You will want to shift where rpm is kept in the range of maximum WHP output.

That being said, with modded cars earlier shift make less difference because they like to crank up boost down low and max out turbo in middle, so push you back to seat can be felt, which is perceived by many as fun in street, and good torque number can be advertised. There is much less gain in top end though due to turbo flow limitation, especially with m2 on stock turbo. When aggressively tuned, sometimes HP just starts to fall as early as 6000rpm.

Do a dyno run to check out.

[twboy1999]

red line
always red line

the lower rpm you shift, the longer it will take to get back to the optimal range

[arquitecto]

[oj34]

Originally Posted by twboy1999

red line
always red line

the lower rpm you shift, the longer it will take to get back to the optimal range

that's certainly not true. Pls. look at the very good video shared by arquitecto!
You want to shift whenever the next higher gear provides more wheel force than the lower one.
The diagram posted by me above is a wheel force diagram for each gear. So it is pretty obvious that you have to shift whenever the wheel force line of previous gear crosses the one of the next gear.

[Destroya]

Originally Posted by oj34

that's certainly not true. Pls. look at the very good video shared by arquitecto!
You want to shift whenever the next higher gear provides more wheel force than the lower one.
The diagram posted by me above is a wheel force diagram for each gear. So it is pretty obvious that you have to shift whenever the wheel force line of previous gear crosses the one of the next gear.

Great post, thank you. Interesting that the video explains that for maximum speed in most cars you shift at red line in all gears but not the M2. Why was the M2 engineered differently?

[J3STER]

Originally Posted by Destroya

Great post, thank you. Interesting that the video explains that for maximum speed in most cars you shift at red line in all gears but not the M2. Why was the M2 engineered differently?

Its not that it was engineered differently. Its just normal behavior for boosted cars since factory turbo's tend to be small to spool quick and they loose efficiency at higher rpm's.

Naturally aspirated cars tend to make peak power closer to redline just because of the physics of how a engine makes power. But then you have to take into consideration how efficient the air is getting into the cylinder. So real world results will always be slightly different from theoretical results. And even with the wheel power calculations provided by the other member it is still an estimate.

Nothing will beat a dyno plus some drag passes to see what provides the best results.

[oj34]

Originally Posted by J3STER

And even with the wheel power calculations provided by the other member it is still an estimate.

Definitely. First of all the torque chart from BMW is smoothed - a real dyno chart looks different. Another very important point is traction. In the real world traction is limited - especially in 1st and 2nd gear. So depending on tires and surface you want be able to use all the available wheel force.
But besides from that wheel force diagrams are a very good indicator when to shift if you dont care about +/- 50 RPM.

[J3STER]

Originally Posted by oj34

Definitely. First of all the torque chart from BMW is smoothed - a real dyno chart looks different. Another very important point is traction. In the real world traction is limited - especially in 1st and 2nd gear. So depending on tires and surface you want be able to use all the available wheel force.
But besides from that wheel force diagrams are a very good indicator when to shift if you dont care about +/- 50 RPM.

I agree, its just like everything else just a tool to point you in the right direction. Lots of variables.

[arquitecto]

Originally Posted by Destroya

Great post, thank you. Interesting that the video explains that for maximum speed in most cars you shift at red line in all gears but not the M2. Why was the M2 engineered differently?

You got me intrigued so I decided to give it a shot. Using these numbers from BMW and the method in the video I linked it would show the following for the M2:

The theory states that maximum acceleration happens when maximum wheel torque is achieved. To simplify the calculation we can focus on the only variables in the calculation. These are engine rpm and the gear ratios of the transmission.

Wheel torque = Engine Torque x Gear Ratio for that gear

STEP 1
Naturally engines make different amounts of power at different rpms. The M2 has a pretty flat torque curve with a steep drop off right before redline. This is key to understanding when to shift. Here are the key numbers for the M2 based on the info from BMW:

465 Nm up to 5560rpm (This is Peak Torque)
440 Nm at 6000rpm (This is a loss of -5.38%)
400 Nm at 6500rpm (This is a loss of -14.08%)
300 Nm at 7000rpm (This is a loss of -35.48%)

STEP 2
The next part of the equation is calculating the amount of loss that happens when you shift up a gear:
Transmission gearing: http://www.bmwusa.com/Standard/Conte...fications.aspx

M2 6MT Gear Ratios:
1 - 4.11
2 - 2.32
3 - 1.54
4 - 1.18
5 - 1
6 - 0.85

% Loss in Gearing for shifting up:
1st>2nd: -43.55%
2nd>3rd: -33.62%
3rd>4th: -23.38%
4th>5th: -16.74%
5th>6th: -13%

STEP 3
Now, Redline always makes 300Nm but remember that redline in one gear equates to a lower rpm in the next gear. This is important to calculate how much Engine Torque you have once you shift up.

Redline in 1st (300Nm) = 3,934rpm in 2nd (465 Nm) +35.48%
Redline in 2nd (300Nm) = 4,666rpm in 3rd (465 Nm) +35.48%
Redline in 3rd (300Nm) = 5,363rpm in 4th (465 Nm) +35.48%
Redline in 4th (300Nm) = 5,932rpm in 5th (440 Nm) +14.08%
Redline in 5th (300Nm) = 6,090rpm in 6th (440 Nm) +14.08%

STEP 4
When we shift up, we are putting the engine back down into an rpm range where it can make more power. At the same time we take a hit in the gearing since the next gear is a lower ratio.
Remember the relationship is (Wheel torque = Engine Torque x Gear Ratio for that gear) So in order for the shift up to be beneficial the gain in power must be greater than the loss in gearing:

Do we hold to Redline?
1st>2nd: (-43.55% From Gearing) > (+34.48% Torque from Engine) = Hold to Redline
2nd>3rd: (-33.62% From Gearing) < (+34.48% Torque from Engine) = Shift Before Redline
3rd>4th: (-23.38% From Gearing) < (+34.48% Torque from Engine) = Shift Before Redline
4th>5th: (-16.74% From Gearing) > (+14.08% Torque from Engine) = Hold to Redline
5th>6th: (-13% Gearing) < (+14.08% Torque from Engine) = Shift Before Redline

Conclusion:
Based off these numbers, it seems that not every gear should be held to redline. The loss in gearing gets smaller and smaller as you go up each gear but eventually (4th>5th) the engine speed in the next gear (5,932rpm) is already within that drop off at the end of the torque curve. As a result, you are actually better off holding this gear to redline whereas in the other gears the trade off of shifting early is better.

Do we hold to Redline?
1st>2nd: Hold to Redline
2nd>3rd: Shift Before Redline
3rd>4th: Shift Before Redline
4th>5th: Hold to Redline
5th>6th: Shift Before Redline

Feel free to double check my logic and if anyone can provide more detailed numbers then I would be happy to find the exact rpm for each gear. I will run the numbers for the DCT next to see if those have this condition as well.

[J3STER]

When I get through break in I will go to the track and get some real world numbers and will give this a try plus other combinations also to see which one yields the best results.

[ashburyn54]

Originally Posted by zmo

Searched and found nothing in the F87 forums, but found this at the F80 one: http://f80.bimmerpost.com/forums/sho....php?t=1044799

Googled the torque curve for the M2, but there's no graph taking in mind the overboost extra torque (this is easily solved just by adding the extra 50nm, however, I don't know how will the slope in the graph evolve at the end of the overboost, which at that point intersects with the peak power output // I mean if it's a linear or an exponential negative slope, I'm sure it's linear when it kicks in, not so sure when it wears off). Anyways, which are the optimal shifting points, factorizing the overboost variable, for maximum acceleration? Sport+ (MDM) or DSC off?

N54 cars as low as 5500, n55 around 6. The M2 has a little more breathing room. So 6-6.5 is fine.

Tried and true through the years of turbo BMW's since the n54.

I say whatever makes you enjoy the car the most

[rich8566]

Originally Posted by arquitecto

You got me intrigued so I decided to give it a shot. Using these numbers from BMW and the method in the video I linked it would show the following for the M2:

The theory states that maximum acceleration happens when maximum wheel torque is achieved. To simplify the calculation we can focus on the only variables in the calculation. These are engine rpm and the gear ratios of the transmission.

Wheel torque = Engine Torque x Gear Ratio for that gear

STEP 1
Naturally engines make different amounts of power at different rpms. The M2 has a pretty flat torque curve with a steep drop off right before redline. This is key to understanding when to shift. Here are the key numbers for the M2 based on the info from BMW:

465 Nm up to 5560rpm (This is Peak Torque)
440 Nm at 6000rpm (This is a loss of -5.38%)
400 Nm at 6500rpm (This is a loss of -14.08%)
300 Nm at 7000rpm (This is a loss of -35.48%)

STEP 2
The next part of the equation is calculating the amount of loss that happens when you shift up a gear:
Transmission gearing: http://www.bmwusa.com/Standard/Conte...fications.aspx

M2 6MT Gear Ratios:
1 - 4.11
2 - 2.32
3 - 1.54
4 - 1.18
5 - 1
6 - 0.85

% Loss in Gearing for shifting up:
1st>2nd: -43.55%
2nd>3rd: -33.62%
3rd>4th: -23.38%
4th>5th: -16.74%
5th>6th: -13%

STEP 3
Now, Redline always makes 300Nm but remember that redline in one gear equates to a lower rpm in the next gear. This is important to calculate how much Engine Torque you have once you shift up.

Redline in 1st (300Nm) = 3,934rpm in 2nd (465 Nm) +35.48%
Redline in 2nd (300Nm) = 4,666rpm in 3rd (465 Nm) +35.48%
Redline in 3rd (300Nm) = 5,363rpm in 4th (465 Nm) +35.48%
Redline in 4th (300Nm) = 5,932rpm in 5th (440 Nm) +14.08%
Redline in 5th (300Nm) = 6,090rpm in 6th (440 Nm) +14.08%

STEP 4
When we shift up, we are putting the engine back down into an rpm range where it can make more power. At the same time we take a hit in the gearing since the next gear is a lower ratio.
Remember the relationship is (Wheel torque = Engine Torque x Gear Ratio for that gear) So in order for the shift up to be beneficial the gain in power must be greater than the loss in gearing:

Do we hold to Redline?
1st>2nd: (-43.55% From Gearing) > (+34.48% Torque from Engine) = Hold to Redline
2nd>3rd: (-33.62% From Gearing) < (+34.48% Torque from Engine) = Shift Before Redline
3rd>4th: (-23.38% From Gearing) < (+34.48% Torque from Engine) = Shift Before Redline
4th>5th: (-16.74% From Gearing) > (+14.08% Torque from Engine) = Hold to Redline
5th>6th: (-13% Gearing) < (+14.08% Torque from Engine) = Shift Before Redline

Conclusion:
Based off these numbers, it seems that not every gear should be held to redline. The loss in gearing gets smaller and smaller as you go up each gear but eventually (4th>5th) the engine speed in the next gear (5,932rpm) is already within that drop off at the end of the torque curve. As a result, you are actually better off holding this gear to redline whereas in the other gears the trade off of shifting early is better.

Do we hold to Redline?
1st>2nd: Hold to Redline
2nd>3rd: Shift Before Redline
3rd>4th: Shift Before Redline
4th>5th: Hold to Redline
5th>6th: Shift Before Redline

Feel free to double check my logic and if anyone can provide more detailed numbers then I would be happy to find the exact rpm for each gear. I will run the numbers for the DCT next to see if those have this condition as well.

Very nice analysis, but I do have one question - given the mathematics here, exactly when should I shift "before" redline? Can you compute the exact rpm of the upshift which would maximize acceleration?

[oj34]

Originally Posted by arquitecto

STEP 3
Now, Redline always makes 300Nm but remember that redline in one gear equates to a lower rpm in the next gear.

I've not checked your calculations, but you have to consider that the Torque/Power chart you used is wrong (although being official from BMW).
It shows 300 Nm at 7000 RPM on the torque curve and approx. 260 kW at 7000 RPM at the power curve. One of these values MUST be wrong because:

P = M * n * 2 * PI * 1/60 = 300 Nm * 7000 1/min * 2 * 3,1416 * 1/60 = 219912 Nm/s = 219,912 kW

If anyone bothers he should write this to BMW

However, my wheelforce diagram posted above is using 350 Nm at 7000 RPM which leads to the correct power - assuming that the shown power curve is correct.

[oj34]

Update: When using your values (300 Nm at 7000 RPM) the below chart matches almost your conclusion:

Originally Posted by arquitecto

Do we hold to Redline?
1st>2nd: Hold to Redline - yes
2nd>3rd: Shift Before Redline ~ 6900 RPM
3rd>4th: Shift Before Redline ~ 6300 RPM
4th>5th: Hold to Redline ~ no, shift at ~ 6500 RPM
5th>6th: Shift Before Redline ~ 6500 RPM

[oj34]

Update for DKG (using 300 Nm at 7000 RPM):

almost identical because gear ratios differ not very much. 7th gear is a classical overdrive good enough for 380 km/h

[Robin_NL]

Nice info guys.
But practically even driving wot/ fast I shift at 6000/6500rpm max. It just feels faster than redlining at 7000rpm. Which is fun, redlining, but not the fastest way for our N55 as already stated here.

I need an S55

Cheers
Robin

[Artemis]

Akrapovič tested a stock M2. Their test results (see here):

• max output: 284.3 kW or 386.5 hp (metric) or 381.2 hp (mech) @ 5500 rpm;
• max torque: 558.8 Nm or 412.1 lb-ft @ 2500 rpm.

Don't forget that the M2 also features an overboost function.