needforspeed

Fair enough - I think the pull varies quite a lot between 2000-2500rpm.

I've posted before about the weird scenario where rpm sticks at 2000 for several seconds whilst the car continues to accelerate. Some suggested that this was the turbo kicking in a full boost (700700) others that this was the torque converter spooling up.

Wonder if you have noticed this ?

needforspeed

Right here we go .... I have plugged the gear ratios and the torque data into a spreadsheet I found on the web, which calculates the output shaft torque. I had to convert NM to lb/ft and approximate from the graph.

Here are the results:



I think I need some help from someone to interpret this, but I believe the theory is that you should always look to maximise this output shaft torque figure.

So ... crudely the optimum shift points for the 530d should be (approx) as follows ... from 1st to:

2nd @ 4400rpm - output torque drops from 1046-1033 lb/ft
3rd @ 4000rpm - output torque drops from 846-657 lb/ft
4th @ 4000rpm - output torque drops from 525-465 lb/ft
5th @ 4000rpm - output torque drops from 372-369 lb/ft
6th @ 4000rpm - output torque drops from 310-310 lb/ft

This is on the basis that if you hang onto a gear any longer than this you will probably be putting out less torque than would be available in the next gear up.

This sort of suggests to me that D which shifts at 4000rpm is going to be better than DS which shifts at 4600rpm - which is how it feels when driving and that kickdown (which also forces the car to hold on till the redline) is also best avoided.

I believe this also means that due to the gearing the car is trying to lay down 1875 lb/ft of torque when starting with brake torqueing at 2000rpm. This might explain why, when I tried this with DSC off - I just smoked my tyres up to the red-line

znod

From the graph and your tabulation, it looks to me like the calculator is based on the optimal-shift theory I referred to--which says, in short, minimize the RW torque drop when shifting. But I am not sure without additional investigation. I am assuming that shaft torgue is at least close to the same thing as RW torque. Shaft torque might ignore the efficiencies related to the differential and tires. Let me know if you find anything out along these lines. Give me the URL of the site, and I'll check it out. It looks like a good site although I generally prefer to do my own calcs. I'll try the site on my 545i eventually. Also, I'll check out and think about your results as best I can. Also, we are traveling now so my replies will be more sporadic.

znod

My posts hurt my brain too. You yob you.

Ricracing

Hey Znod,

You really need to testdrive one of these new diesels.

I mean, one can not understand the torque without it.

Fly overhere, so we can go for a spin with a 535dA!

red-max

I agree with this - I also feel that DS way over-revs the 530d engine (as if they saved development costs and just used the same gear change profile as the petrol 530i - surely not?).

I'm not sure if it's the best technique, but if I want to burn out of a junction then I push the lever over to DS mode, but once I pull away I slide it back over to D where the up-shifting happens sooner. I also find that easing off the gas to allow the 'box to upshift, then pushing down on the gas pedal (rather gently to avoid kick-down) allows me to "surf" the torque curve better. Just stamping hard on the gas pedal results in far too much noise and unnecessary revs - at least it feels and sounds that way. It would be interesting to time a few runs though.

Next time around I will definitely test-drive a manual 530d - there's no substitute for being in full control, though I have to admit the Steptronic is mostly pretty good, and the auto is generally more relaxing to drive, but not as "involving". There's always a trade-off...

needforspeed

This is EXACTLY how I use my car - DS to pull away then flip back to D, try to avoid kick down and ride the wave of torque.

I agree so much - you would almost think the gearbox was set up for the petrol - but then it obviously isn't given the gear ratios and redline!

oh... for znod the calculator I used is here

http://www.jannettyracing.com/media_...ftpoints97.xls

I tried some others that used HP and some that took tyre size into account - but they were not flexible enough to adapt for 6 speed and a low revving diesel.

I think this is the same principle as your drive wheel torque - just ignoring the 'transmission loss' between driveshaft and wheels. I think this can be ignored as intuitively it seems to me that it should be a constant - or at least linear relative to the revs.

For me, I think the main flaw with the calc I did is that I only mapped rev range with intervals of 400rpm - 100rpm would have been better - but I didn't have a proper dyno reading for torque - just the 'official' data posted by 700700. I also think my conversion may have gone adrift cause the calcs placed the peak HP at 230, but the data I used was for the old model with a peak of 218 (like mine). The calculator interpolates HP for torque at a given rev's and I think something is probably slightly out here due to the simplistic torque data.

If anyone can post a more accurate torque curve I'll try to run the numbers again - with a smaller increment this time.

znod

I'll get there again soon rr. I'll let you know if we end up in your neighborhood.

znod

Thanks for the link. I'll check the calculator out.

znod

Thanks for the link. I'll check the calculator out.