F30 330d 8 speed auto question
Discussion
drmark said:
Welshbeef said:
But given you could hit the same target speed in the lower gear then you are ignoring the zero acceleration time during he gearchange where the still in gear driver is gaining maybe half a car length. This wouldn't be made back in 500rpm 4k to 4.5k
Fact is look at the Derv Le Mans cars how are they driven to extract the maximum performance ? Do they change up at near full revs/just shy of the limiter or as soon as they hit max bhp?
Just back from a party and old advice rings true. Never argue with a fool. I tried but failed. Fact is look at the Derv Le Mans cars how are they driven to extract the maximum performance ? Do they change up at near full revs/just shy of the limiter or as soon as they hit max bhp?
Over and out.
http://www.superchips.co.uk/curves/Focus%20ST%20St...
Something you seem to be omitting from the argument is the gear ratio. The same power/torque in a lower gear will give greater acceleration than in a higher gear.
However, regardless of any arguments regarding what's the best engine speed to change up, if the gear box is in manual mode, it should not change up, end of argument, otherwise it's just another auto mode.
However, regardless of any arguments regarding what's the best engine speed to change up, if the gear box is in manual mode, it should not change up, end of argument, otherwise it's just another auto mode.
This is an amusing thread. There is clearly a lot of misunderstanding of power, torque and acceleration.
'Riding the torque' and changing up so that you hit peak torque in the next gear is not how to maximise acceleration.
The ideal point to change up for maximum acceleration, assuming the power rises, peaks, then falls, is the point at which the power output after the gear change is equal to the power output before the gear change.
No ifs or buts. It's fact. It doesn't matter if the car is powered by petrol, diesel, or the salvaged red wine that welshbeef has spilled down the sofa.
Oh and when you change gear the revs don't drop by a set rpm, they drop by a ratio/percentage (the ratio of the ratios if you will). So if they drop from 3000 to 2500, they would drop from 6000 to 5000.
'Riding the torque' and changing up so that you hit peak torque in the next gear is not how to maximise acceleration.
The ideal point to change up for maximum acceleration, assuming the power rises, peaks, then falls, is the point at which the power output after the gear change is equal to the power output before the gear change.
No ifs or buts. It's fact. It doesn't matter if the car is powered by petrol, diesel, or the salvaged red wine that welshbeef has spilled down the sofa.
Oh and when you change gear the revs don't drop by a set rpm, they drop by a ratio/percentage (the ratio of the ratios if you will). So if they drop from 3000 to 2500, they would drop from 6000 to 5000.
335d said:
There are official BMW graphs of the 30d engine on page 2 of this document
http://www.matlawrence.com/images/bmw/powerkit.pdf
This suggests that peak power happens at 4000rpm. The graph only goes up to 4500rpm, but by extrapolating you can see that holding on to 5000rpm would not be sensible with a close ratio box. Shifting up at 4500rpm appears to make sense.
If gear changes are 4500rpn them according to the chart, torque had been in the slide for a while and it's 500 above peak power. If the drop is 1000 rpm then it's dropping to 500 below peak power. In essence, the auto box is keeping peak power in the middle of the used rev range (and if we want to talk area under the curve, it's maximising the area under the power curve over a 1000 Rev range.http://www.matlawrence.com/images/bmw/powerkit.pdf
This suggests that peak power happens at 4000rpm. The graph only goes up to 4500rpm, but by extrapolating you can see that holding on to 5000rpm would not be sensible with a close ratio box. Shifting up at 4500rpm appears to make sense.
I imagine when not in sport it does the same but under the torque curve.
blank said:
This is an amusing thread. There is clearly a lot of misunderstanding of power, torque and acceleration.
'Riding the torque' and changing up so that you hit peak torque in the next gear is not how to maximise acceleration.
The ideal point to change up for maximum acceleration, assuming the power rises, peaks, then falls, is the point at which the power output after the gear change is equal to the power output before the gear change.
No ifs or buts. It's fact. It doesn't matter if the car is powered by petrol, diesel, or the salvaged red wine that welshbeef has spilled down the sofa.
Oh and when you change gear the revs don't drop by a set rpm, they drop by a ratio/percentage (the ratio of the ratios if you will). So if they drop from 3000 to 2500, they would drop from 6000 to 5000.
Don't disagree, but this ignores the affect of gearing, in the higher gear, given the same power, acceleration will be commensurately lower. Therefore there is some merit in going slightly beyond the point at which power will be equal, there is also the affect of the marginal slowing of the vehicle (and therefore of resultant engine speed ) at the point of change.'Riding the torque' and changing up so that you hit peak torque in the next gear is not how to maximise acceleration.
The ideal point to change up for maximum acceleration, assuming the power rises, peaks, then falls, is the point at which the power output after the gear change is equal to the power output before the gear change.
No ifs or buts. It's fact. It doesn't matter if the car is powered by petrol, diesel, or the salvaged red wine that welshbeef has spilled down the sofa.
Oh and when you change gear the revs don't drop by a set rpm, they drop by a ratio/percentage (the ratio of the ratios if you will). So if they drop from 3000 to 2500, they would drop from 6000 to 5000.
It would be worth seeing some cascade curves...
Dave
Edited by DVandrews on Sunday 14th December 11:34
drmark said:
Just back from a party and old advice rings true. Never argue with a fool. I tried but failed.
Over and out.
Are you going to come back in now or are you hovering as the argument you put forward has been taken apart by multiple other forum posters. Over and out.
Silence speaks volumes - as you were
. Welshbeef said:
drmark said:
Just back from a party and old advice rings true. Never argue with a fool. I tried but failed.
Over and out.
Are you going to come back in now or are you hovering as the argument you put forward has been taken apart by multiple other forum posters. Over and out.
Silence speaks volumes - as you were
. When BMW set up the launch control to give maximum acceleration what gear change point do you think they chose?
Wills2 said:
Welshbeef said:
drmark said:
Just back from a party and old advice rings true. Never argue with a fool. I tried but failed.
Over and out.
Are you going to come back in now or are you hovering as the argument you put forward has been taken apart by multiple other forum posters. Over and out.
Silence speaks volumes - as you were
. When BMW set up the launch control to give maximum acceleration what gear change point do you think they chose?
I can assure you all performance tests and racing wouldn't be changing up as you indicate - heck when I was driven by a racing driver he was going at least 500 rpm Uni the red on every gear even hanging it in at such high revs none of this changing up early stuff instead ensuring he has the highest % of max power all of the time.
Wills2 said:
Welshbeef said:
drmark said:
Just back from a party and old advice rings true. Never argue with a fool. I tried but failed.
Over and out.
Are you going to come back in now or are you hovering as the argument you put forward has been taken apart by multiple other forum posters. Over and out.
Silence speaks volumes - as you were
. When BMW set up the launch control to give maximum acceleration what gear change point do you think they chose?
From the BMW chart, it looks like they chose a change point 500rpm above max power.
Jon1967x said:
Wills2 said:
Welshbeef said:
drmark said:
Just back from a party and old advice rings true. Never argue with a fool. I tried but failed.
Over and out.
Are you going to come back in now or are you hovering as the argument you put forward has been taken apart by multiple other forum posters. Over and out.
Silence speaks volumes - as you were
. When BMW set up the launch control to give maximum acceleration what gear change point do you think they chose?
From the BMW chart, it looks like they chose a change point 500rpm above max power.
Welshbeef said:
Drnark do we take the silence to = tail between legs admitting you were wrong .
I bow to your superior ignorance. You win. . 
Edited to add: but there is another reason the OP's car changes up at 4500. The redline on my (2011) car is 4750, not 5250, with hatching starting at 4500 . Is his different?
Edited by drmark on Monday 15th December 20:28
blank said:
From what I can see on the BMW website the 330d produces peak power at 4,000rpm. Which makes changing up at 4,500 sound about right.
I know but Welsbeef thinks bashing into the redline is always best (it is for some cars) and won't listen to anyone who suggests the OP's car is an exception. In most gears (3rd and beyond) on the 8 speeder a change down equates to around a 500 rev drop that high up (at least in mine) so I agree with you - and BMW.
Here is the sort of calculator BMW use to decide on optimal shift points - bit more complex than wringing its neck.
http://vlsicad.ucsd.edu/~sharma/Potpourri/perf_est...
Edited by drmark on Monday 15th December 20:51
blank said:
From what I can see on the BMW website the 330d produces peak power at 4,000rpm. Which makes changing up at 4,500 sound about right.
But apparently the diesel "experts" think it's best to bounce them off the red line and go way beyond peak power? My personal experience would suggest such antics are a total waste of time but I guess that has me agreeing with Drmark (and he's now completely discredited, at least according to Welshy).Gassing Station | BMW General | Top of Page | What's New | My Stuff