Quote:
Originally Posted by coloradoe92m3
Gearing :
E92 dct
Final-3.154
1-4.78
2-2.933
3-2.153
4-1.678
5-1.39
6-1.2
7-1.0
F80-
Final-3.46--9% shorter
1-4.8 --same-----9% shorter overall
2-2.593 14% taller------6% overall tall
3-1.7. 21% taller_------12% overall tall
4-1.27----25% taller---16% tall overall
5. 1.0-----29%_--------21% tall overall
6. .84-----30% taller----21% overall
7. 0.67...---32% taller----24% overall
So check my math but 1st bear choice is crazy. I can't use 1st in my e92 due to traction limitations so talk about hard to launch. F80 will be really tough to put power down in first. 2nd gear is going to be downright freight train. But e92 is quite a bit shorter gearing from 2nd on.
So you can't only compare dyno plot as gears are the other half. If someone wants to create a plot with gear ratio differences taken in to account, the f80 will be way faster but not quite as much as it has seemed thus far.
Keep in mind at WOT you don't see below 6500 ROMs in e92 dct so you can't draw a line straight up as they do as you need to account for e92 power band .
So love to see area under curve of each cars WOT power band with gearing taken into account
|
A few things to keep in mind:
1) Gearing doesn't directly effect power, it effects torque. However, side-effects of gear selection can still have an effect on
measured horsepower, but that effect is spread over the entire power curve, so relative comparisons of the curve shape (like the one in the chart) remain valid. It also depends on the dyno. An inertia chassis dyno is more susceptible to these fluctuations than a load dyno, so you can still work around those inaccuracies by choosing the right chassis dyno.
2) Most chassis dyno runs are conducted in the gear ratio closest to 1:1. Differences in final drive will affect torque output, but this is easily corrected by compensating for final drive with a percentage.
3) It's unlikely that BMW used a chassis dyno for that plot anyway. Manufacturers typically have access to an engine dyno, where the engine is placed in a mount and connected directly to the dynamometer.
I don't mean to talk down to you. You probably know all of these, but sometimes things like this get overlooked because we (as enthusiasts) spend so much time looking at the information that is available to us, which is usually chassis dyno information.
Your point regarding RPM offset is well made, but if you calculate the area under curve for the S55 from 5500 to 7300 RPM, it's still going to be greater than the S65 from 6500 to 8300 RPM. I get the sense that your point isn't that the S65 would win that comparison though, just that it's not nearly as lop sided as it first appears. You can't simply draw straight lines like that.
I wish BMW provided the raw data for those charts
Also, I reformatted your gear comparison in to an
MultiMarkdown ASCII table in case anyone wants it:
Code:
# Gear ratio comparison - E92 M3 DCT vs F80 M3
| Gear | E92 DCT | F80 | Relative Gear | Relative Overall |
| --- | --- | --- | --- | --- |
| Final | 3.154 | 3.46 | 9% shorter | |
| 1 | 4.78 | 4.8 | same-ish | 9% shorter overall |
| 2 | 2.933 | 2.593 | 14% taller | 6% overall tall |
| 3 | 2.153 | 1.7 | 21% taller | 12% overall tall |
| 4 | 1.678 | 1.27 | 25% taller | 16% tall overall |
| 5 | 1.39 | 1.0 | 29% taller | 21% tall overall |
| 6 | 1.2 | 0.84 | 30% taller | 21% overall |
| 7 | 1.0 | 0.67 | 32% taller | 24% overall |