80-120 kph times and very long explanation (more) (archive)

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The difference in the M5/M3 80-120 times is totally reasonable given the motors of these two cars.

If the M3 has a 3.7 rear (which I believe it will, to match the mph shiftpoints the same) the following is true:
speed rpm(M5) rpm(M3)
80kph 2640 3100
120kph 3960 4600

If you look at the torque curve of the M5 motor, it generates its peak torque at 3500rpm, so its torque over this rev range goes from ~350 (-5%) to ~365 (~peak), for a rear wheel torque of 1356ft-lbs to 1414ft-lbs

The M3 motor (see my previous posts on this motor) will generate (in US trim) about ~225ft-lbs at 3100rpm and ~250 @ 4600rpm. Giving a rearwheel torque of
1024ft-lbs and 1138ft-lbs respectively

With the M5 weight @ 4024lbs (www.bmwusa.com) and the M3 weight at 3450lbs (1560kg) the torque to weight figures are the following
speed M5 M3
80kph 0.339 0.296
120kph 0.353 0.329

The M3 has a 12.5% deficit in torque-weight to the M5 @ 80, and a 6.8% deficit @ 120, for an average of 9.65%.

Now, the important part.
Neglecting Aerodynamics (since the two cars have VERY similar drag forces) and since the cars are rolling, the time requird to go from 80-120 is directly proportional to the torque-weight ratio of the car. So the M3 will go 80-120 9.65% slower than the M5. If the M5 time is 4.8s, the corresponding M3 time would be 5.31. The euroM3 with ~6% more torque should be around 5.1-5.2. If bmw instead used a 3.64:1 rear, the time for the euro would be ~5.4 (so maybe, the rear is a 3.64, or this number for the M3 is more conservative than the M5, which is more likely)

The reason the M3 is as fast 0-60 is drag-type contests are typically high rpm (or at least chosen rpm) contests. If the M3 and the M5 did 80-120 in the fastest mode possible
(2nd and 3rd for both) (assuming Euro M3 E46)
the M3 would be going from 6360rpm to 8000rpm (2nd) with an a torque of 248 228ft-lbs respectively then shifting at 63-64mph or so to 3rd and going from 5300rpm to 6300rpm with a torque of 265 to 248ft-lbs respectively

The M5 would be going from 5400 to 6800 in 2nd with a torque of 335 to 305ft-lbs and 4500 to 5360rpm in 3rd wit ha torque of 354 to 335ft-lbs.

Since both cars have to shift, we can neglect that time as a factor. Looking at the average acceleration of the cars in each gear, the M3 has a small ~1.5% advantage. If we keep the same correction factor that changed the 5.2 to a 5.4 (like a 3.64 ratio rear end or something), the M5 has a ~1.5% advantage, much smaller than the 12.5% advantage it has in 4th gear 80-120kph times.

SUMMARY!!!!!!
In summary:
The reason the M3 lags the M5 so much in the 4th gear test (by ~12.5%), is the M5 engine is PERFECT for this test with the ratio's given. The M3 is a high revving engine, and we all knew that. IF you compare the two cars (with a few easy assumptions) in the proper environment where the drivers can choose the optimal gear, (since I believe the cars will redline in each gear at roughly the same speeds) the M5's advantage erodes to ~1-2%, well within the error margins of this test. The reason the EuroM3 E36 is faster than the E46, is since this test is done below the torque peak of the E46 and (see my earlier post) the two engine I believe to be quite similar, the ligher E36Euro will be faster:
assuming the rear ratio of the E36Euro is 3.23 (I don't know this for sure), the average torque to weight for the 3250lb E36M3 Euro will be 0.305 ft-lbs/lb very similar to the E46!

Note, this is not to say the new M3 motor doesn't have low-end torque. The US M3 E36 in the 4th gear 80-120kph test would have (the rpm's in question would be 2750 to 4000 or so) a average torque-weight of 0.289, or roughly 10% less than the heavier E46. (so the new M3 will pull roughly 10% harder in every gear/speed combination than the current US M3)

whew, thanks for the bandwith
before anyone flames, the nubmers for torques, rpms, and weights are taken directly off www.bmwusa.com and www.bmw.com. The torque-vs rpm dyno data is from actual dyno tests where possible, and in the case of the E46 (again see earlier posts), computed using the peak torque and peakhp points with a linear fit between. Low rpm behavior of the E46 is calculated using a combination of stage-4 Dinan E36M3 data (high-rpm high flow related mods) and EuroM3 E36 data.

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