lolQuote:
Originally Posted by LOVEMYRANGIE
Would, but they might say ``who?'' :D
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lolQuote:
Originally Posted by LOVEMYRANGIE
Would, but they might say ``who?'' :D
Certainly, but my money is on the torque and power being tuned to take a dive to encourage the drivers to use higher gears. Thus saving fuel.Quote:
Originally Posted by isuzurover
If we can get an aftermarket tunable commonrail ECU for less than new vehicle prices then it's something that's easily fixed. I'd expect most commonrail diesels to keep making more and more power until about 3500-4000rpm given the chance.
I would say that most of the "industrial" motors you are looking at would last a lot longer than anything in a car. I would definitely say that this is the case because of RPM. Engine wear is accelerated at the square of rpm. So if you could fit an overdrive and bought some longer ratios from Ashcroft, you could potentially have a car that would not rev over 2500rpm and last forever. Your car may not be very nice to drive though, as it would now become more like a truck. I mean that it is now geared for torque then more so power. Your best option would be to find something that is controlled via an ECU.. At least this way you would have some hope of changing the rpm limit... However, this now presents another issue of weight and compatibility of bell housings. This could be your second biggest hurdle... The major issue that I think that you will face is emissions. Some of the younger stuff should be okay i.e. EURO 5 etc... I just don’t know how you would go taking a motor that is meant for mobile plant use and then putting it in a production car...
Are these quoted engine data on an engine dyno or real world figures at the road wheels on a vehicle dyno?
Am I correct that we should be looking for max torque to be developed at final drive for desired highway speed? i.e. 100 KPH
Everything automotive is quoted flywheel. Max torque at 100km/h is the best for drivability, most factory diesels hit this.Quote:
Originally Posted by Lotz-A-Landies
Not sure I agree with this except as a very rough rule of thumb.Quote:
Originally Posted by Dougal
As a rule of thumb, you would want maximum torque at the speed you normally drive at, in the gear that you normally drive in. But this assumes that there is sufficient power available at that engine speed, which is not necessarily the case. For driveability, it is probably more important to have a wide spread of torque, in other words, not a sharp peak. This often means peak torque at quite low rpm, at which rpm there would be insufficient power to drive the vehicle at 100kph. (remember, power is torque x rpm, and power required goes up roughly as the square of the speed). A rather extreme example would be the 2.25 diesel, which produces maximum power at 1750rpm. if geared to do this rpm in top at 100kph (it is nearer 3000 at 100kph), you would never reach 100! Not in top, anyway, maybe third.
My view is that the key torque consideration for driveability, at least with a manual box, is the torque available at normal clutch engagement rpm. This figure is rarely if ever quoted, and you have to guess at how good it is from where the peak is, unless you have the complete curve.
John
After reading that, I'm not sure what you mean.Quote:
Originally Posted by JDNSW
There's nothing remotely close to the old 2.25 diesel on the market at the moment so it's an example we can safely ignore.
All modern diesels are geared to be right in their max torque (which is usually flat over a good range) at 100km/h cruising. They have more than enough torque and power at this speed to do the job. If a diesel has a peak it's usually 1800-2000rpm. Often these days it's flat over a range centred about that (like constant torque from 1500-2500rpm). The advantage of electronic control, get the most from the engine while respecting the drivelines torque limits.
It only takes about 30hp to cruise a landrover at 100km/h. 30hp at 2000rpm is only 105Nm, I can't think of any current diesel vehicle putting out less than 200Nm.
If you want a good rule of thumb for clutch engagement torque, go for displacement in litres x about 60 for a diesel.
I was not suggesting any figure for clutch engagement torque, merely commenting that this figure is more important for driveability than the position in the rpm/top gear speed range of the peak torque.Quote:
Originally Posted by Dougal
John
When has automotive technology gone back to old designs or theories (excluding a brief flirtation that japanese had with revised IDI designs). Current designs are optimised using FEM/CFD. Modern diesels have much higher outputs and much better fuel efficiency than old designs - easily an order of magnitude.Quote:
Originally Posted by JDNSW
Every healthy 2.25D I have driven can hold 100km/h on a flat road while loaded.
With the disco 300 tdi the peak torque is around 1800 rpm and peak power at 4250 rpm. If you drive it at 1800 rpm it feels like it is being lugged along. The motor is better to drive between 2-3000 rpm.
With the specs in mind I am trying to improve my understanding of how torque and power relate to a vehicles driveability and if i could understand this then maybe a performance curve of a motor would mean more than a couple of nice lines.
my analogy came out like this. Torque is the ability to maintain the status quo. Power is the ability to move away from the status quo. Both are bound by vehicle weight. In the case of the disco 300 tdi, when driving at peak torque ie 1800 rpm and you try to accelerate not much actually happens though you will be able to maintain your speed going up inclines without having to accelerate. At 1800 rpm the power being generated is insufficient to overcome the weight of the vehicle. And this explains why the car is much livelier (yeah I know it is a 300 tdi) from 2000 rpm upwards. Both power and torque (which I’ve learnt are mathematically related) useability in the real world are constrained by the mass which they are acting against.
So I gather torque and power figures are one dimensional, power to weight ratios add a second dimension, all of which in turn can be used to shed some light on the third dimension of how a motor will actually perform lugging the chassis and body around.
If this is kind of how these things hang together then there would be some benchmarks for what is considered acceptable torque nm per kg and same with power to weight ratios???
It sure would make it easier for people like me who have no experience/knowledge in interpreting performance curves if they also graphed nm/kg and kw/kg then it would be easy to use accepted benchmarks for these and see at a glance a good indication of real world performance.
(apologies to those reading this for whom this is second nature and are fast falling off to sleep and off their chairs!)