View Single Post
      05-31-2013, 06:35 PM   #1
swamp2
Lieutenant General
swamp2's Avatar
United_States
609
Rep
10,407
Posts

Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

iTrader: (3)

Lightbulb Updated BMW F82 M4 Performance Simulations-Predictions - Even Faster...

BIMMERPOST
     Featured on BIMMERPOST.com
Many of the regulars here will recall my advocacy of the principles of science/math (engineering really) to the enjoyment and understanding of vehicles. Some time ago I made some detailed predictions about the performance of the upcoming M3/M4. If you want to refresh your memory have a look at that thread from way back in late 2010 here. It showed a very quick new M3/M4!

With the new rumors on weight, redline and the not so new rumors on the torque and power I thought it was time to update my predictions. Stay tuned (or skip the details near the end if you are not so inclined) as I'm reasonably confident the car will be even faster than my prior predictions. No real surprise there as the new inputs to my physics based simulations are in essence more power and less weight. However, you'll probably be able to glean some things about the effect of the shapes of the power/torque curves on vehicle performance, the advantage of a high redline (disadvantage of a lower one...) and how we can extrapolate changes from the E60 M5 to F10 M5 to better understand what likely lies in store with the next generation M3/M4.

Relatively high torque, low (or even high) power, low redline engines as compared to low torque, high power high redline engines simply must be geared differently. The cars must delicately balance acceleration, peak speed in gears and utilizing the full rpm range. The former cars are great for more lazy driving with adequate torque to pass in higher gears whereas the latter have an addictive linear power band that is noisy, thrilling and takes more shifting to extract the total available performance. The new Ms are heading in the former direction, however, with good news that the new motor may rev “close to 8000 rpm”, they are not going to totally Corvette style power on us.

We can should be able extrapolate some of the changes from the E60 M5 to the F10 M5 to the M3, even though the new M4 will likely be lighter than its predecessor, unlike the progression of more weight in the M5. As far as engine and transmission we can extrapolate quite a bit. Both engine and transmission changes must go hand in hand and the changes for the M3/M4 are thus likely to be right in line with what happened with the M5 to accompany the lower displacement and forced induction. A bit unexpectedly the F10 M5 has more gear multiplication down low and less in its top gear. A wider overall range that impacts both off the line acceleration as well as providing increased fuel economy with a 7th a bit more like an overdrive gear. The F10 has about 5% lower gearing (higher gear ratio/torque multiplication) in first gear combined with a whopping 30% higher 7th gear (lower combined gear multiplication). Because the new M3/M4 will also have much more torque and peak torque will arrive at a much lower rpm its gearing should change in a very similar fashion.

I’m not also going to recall my prior statement that the new M3/M4 will require shifting at redline in all gears to extract maximum performance. The new M5 does not, only the first three shifts are done so in the M5. The rapidly falling torque curve means that you can get more thrust in a lower gear by shifting earlier for the higher gears. Basically when the force vs. speed graphs (second set below) cross before redline then the ideal shift will also be before redline. The higher the redline is, combined with this falling torque and 7 close spaced gears all lead to an inability to utilize the full rpm range in all gears. This obviously was not a problem in the current M3 because of the very flat torque curve up to high rpms (equivalently its very linear power curve). Based on this effort I also do not believe the car will have a redline "very close" to 8000 rpm. Or perhaps a slightly weaker but more confident statement is that the combination of power and torque curves that look like the ones in the M5, along with similar gearing changes like the ones I’ve chosen, do not yield significant performance improvements with a redline above about 7600. Thus my best guess is 7500-7700 tops. I really think “close to 8000” is more BMW marketing speak for a figure like I’ve mentioned.

Here are my predictions for speeds in gear comparing the existing DCT M3 on the left to the new M4 on the right:



Here are the force at the wheels comparisons. Many talk about the torque at the wheels, almost the same thing but one should really take the next step and convert that to a force. You can get an idea why folks talk about such turbo engines feeling a bit dead up top. It directly affects how much force gets to the wheels and the change to a downward slope can happen quite ubruptly (just like in the dyno itself). This is called jerk or surge and we humans are very tuned to feel this change in acceleration. The left is the existing car and the M4 is on the right.



The next key point is underrating, the 335i was, the 1M was and now the F10 M5 is as well. The M5 is likely to be underrated by about 20-30 hp. Given its weight and performance there really is no other reasonable explanation. I’ve this same CarTest physics based acceleration simulation software to model a plethora of cars performance and I’ve done so using the F10 M5 as a baseline to provide better M3/M4 predictions. Just based on the claimed ~400 ft lb of torque in the new M3/M4 and a redline near 8000 rpm, as well having a torque curve that looks anything like the F10 M5, “about the same power” as the current M3 is just not possible. I’m estimating the quoted power of the car to be 420-430 hp but actual power will be more like 440-460. For the included simulations I’ve decided on 450 hp. I have however, varied the power and weight like in the prior post and effort linked to above to provide a more reasonable range of performance figures. The complete range of simulations I’ve used is certainly not shown.

Here are the torque and power curves I have used:



Here are the basic inputs into the simulation:



Weight: My prior estimate was around 3590 lb (wet without driver). For three reasons, one stronger and two weak I am revising that estimate down.
  1. BMW reports weight in the US with 165 lb (75 kg) added for driver and cargo. 3700 is about right for a typical US E92 M3, which translates to about 3550 (wet without driver). BMW will probably be saving at least 100 lb compared to the current car meaning a figure of about 3450 (wet without driver) is reasonable. The 100 figure is very roughly justified again in the post mentioned near the beginning of this one.
  2. Ongoing rumors insist we’ll see a significantly lightened vehicle.
  3. Less weight = more performance = an more exciting post.

Like I said, one stronger and two weak…

For completeness sake the software has a place to add the drivers weight and I have used 160 lb. Guess 165 might be better from a standards perspective, but what's 5 pounds among friends.

Acceleration curves: turquoise for the new M4 and purple of the E92 M3. These also show a fairly dramatic difference in what you feel at high rpms. First gear is obviously quite dramatic in the new car, a huge overall advantage for the M3. Despite the undesirable roll off in acceleration, even at its worst point (right before shifting) it remains with more acceleration than all except right around the peak of the existing car!



Last but not least the full comparison, first column is E92 M3, second is my initial prediction mentioned above and last is the current effort.



Summary of predictions:
  • 0-60 mph: 3.5 - 3.7 s
  • 0-100 mph: 8.2 - 8.4 s
  • 0-200 kph: 12.4 - 12.6 s (for our metric friends!)
  • 1/4 mi time: 11.9 - 12.1 s
  • 1/4 mi trap: 120 - 123 mph
  • Top speed: 193 - 197 mph (of course true, not indicated, indicated will be over 200 mph)
  • Nurburgring Nordschleife lap time (SportAuto): Low 7:5X (will greatly depend on choice of tires)

Hope you enjoy the predictions. Like all work of this type, garbage in garbage out. There are a lot of assumptions in such simulation. If the actual car differs significantly from these inputs then the predictions will be correspondingly off. However, if the inputs are close to actuals, I'm highly confident the car will indeed have this level of performance. Will this be enough to keep the car on the top of the competitive heap?
__________________
E92 M3 | Space Gray on Fox Red | M-DCT | CF Roof | RAC RG63 Wheels | Brembo 380mm BBK |
| Vorsteiner Ti Exhaust | Matte Black Grilles/Side Gills/Rear Emblem/Mirrors |
| Alekshop Back up Camera | GP Thunders | BMW Aluminum Pedals | Elite Angels |
| XPEL Full Front Wrap | Hardwired V1 | Interior Xenon Light Kit |

Last edited by swamp2; 05-31-2013 at 10:06 PM..
Appreciate 0