Mystery Solved: Complete correlation between S55 Dyno's, Simulations, and Real World

[CanAutM3]

Originally Posted by Boss330

Just to add to the 1/4 mile trap speed on the M4 with MT 6:

R&T got a 12,3 @ 114,9MPH

http://www.roadandtrack.com/features...group-a-bmw-m3

Even on the generic and not especially scientific trap speed calculators, that doesn't have the capability to consider the plateau power curve and higher average power of the S55, this result equates to a 437hp engine.

Consider how the power curve and high average power of the S55 throws off the generic online trap speed calculators and we realize that the car R&T tested certainly couldnt have more than 425hp...

Note that the simulations were done with the assumption of DCT shift times while the R&T road test was done with a 6MT.

[Boss330]

Originally Posted by CanAutM3

Note that the simulations were done with the assumption of DCT shift times while the R&T road test was done with a 6MT.

Which is why I started the post with specifying that the R&T car was a MT6

As far as trap speed goes, isn't that more dependent on engine power than outright shift speeds? At least not a major influence?

[CanAutM3]

Originally Posted by Boss330

Which is why I started the post with specifying that the R&T car was a MT6

As far as trap speed goes, isn't that more dependent on engine power than outright shift speeds? At least not a major influence?

I would guess that shift speed will make a difference. There are two shifts in an F8X over a ¼ mile run, hence a DCT car spends .4~.8 seconds more time accelerating than a 6MT. That is certainly worth a few mph. This probably could be demonstrated through simulation.

[Boss330]

Originally Posted by CanAutM3

I would guess that shift speed will make a difference. There are two shifts in an F8X over a mile run, hence a DCT car spends .4~.8 seconds more time accelerating than a 6MT. That is certainly worth a few mph. This probably could be demonstrated through simulation.

The MT 6 did the 1/4 mile in 12,3s while most DCT cars have been around 12,1s IIRC. That is only 2/10ths of a second difference. Would that be good for a few MPH extra?

Or am I missing your point here?

EDIT:

Since the car doesn't stop during a shift but keeps rolling towards the finish line, the 0,2s difference, doesn't necessarily mean it spends just 0,2s less time accelerating. A average manual shift is probably around 0,3-0,4s.

R&T compared a MT with a paddle shift and found that each gear change took 0,37s on average (in that car) and dropped 0,9MPH on the paddle shifted car.

http://www.roadandtrack.com/go/news/...hift-gearboxes

[CanAutM3]

Originally Posted by Boss330

The MT 6 did the 1/4 mile in 12,3s while most DCT cars have been around 12,1s IIRC. That is only 2/10ths of a second difference. Would that be good for a few MPH extra?

Or am I missing your point here?

EDIT:

Since the car doesn't stop during a shift but keeps rolling towards the finish line, the 0,2s difference, doesn't necessarily mean it spends just 0,2s less time accelerating. A average manual shift is probably around 0,3-0,4s.

R&T compared a MT with a paddle shift and found that each gear change took 0,37s on average (in that car) and dropped 0,9MPH on the paddle shifted car.

http://www.roadandtrack.com/go/news/...hift-gearboxes

Let me try to explain my point with an example:

Let's assume that, as you stated, the DCT equipped M4 is 0.2 sec faster through the quarter mile compared to the 6MT, so the DCT has 0.2 sec LESS time to accelerate.

However, since the manual car needs to shift twice over the quarter mile run, it stops accelerating twice for a period of 0.3~0.4 sec each (the time it takes to execute the shift). The DCT does not stop accelerating during the shifts so it gains back 0.6~0.8 sec of acceleration time.

According to the R&T article, the 6MT M4 needs 2.1 sec to accelerate from 110 to 120mph. Hence the 0.4~0,6 sec of additional acceleration time that the DCT gets is worth 2~3mph.

It is that additional speed that allows the DCT to cross the line 0.2 sec before the 6MT... (that 0,2 sec at 117mph is worth about 30 feet, that is considerable).

[Boss330]

Originally Posted by CanAutM3

Let me try to explain my point with an example:

Let's assume that, as you stated, the DCT equipped M4 is 0.2 sec faster through the quarter mile compared to the 6MT, so the DCT has 0.2 sec LESS time to accelerate.

However, since the manual car needs to shift twice over the quarter mile run, it stops accelerating twice for a period of 0.3~0.4 sec each (the time it takes to execute the shift). The DCT does not stop accelerating during the shifts so it gains back 0.6~0.8 sec of acceleration time.

According to the R&T article, the 6MT M4 needs 2.1 sec to accelerate from 110 to 120mph. Hence the 0.4~0,6 sec of additional acceleration time that the DCT gets is worth 2~3mph.

It is that additional speed that allows the DCT to cross the line 0.2 sec before the 6MT... (that 0,2 sec at 117mph is worth about 30 feet, that is considerable).

Great explanation of a very simple concept (it must have been my day off ).

This also points to one other significant advantage that needs to be accounted for when using simple trap speed calculators online. I'm not sure they are set up for 80ms shift times...?

IIRC the OP didn't want to share which shift times they used in their simulation... That is a point I haven't really thought to much about, but it might be a factor that will influence simulation results.

[CanAutM3]

Originally Posted by Boss330

IIRC the OP didn't want to share which shift times they used in their simulation... That is a point I haven't really thought to much about, but it might be a factor that will influence simulation results.

The OP refrained from posting the shift times they used earlier in the thread, but, IIRC, they later posted they used 50ms. Since in a simulator, the shift time represents the period of time when acceleration is interrupted, I believe that a shift time of 0ms should be used for DCT.