Firstly start off torque needs to be 75% of that at maximum rated revs, not of absolute maximum torque. Secondly, the gearbox is almost irrelevant here unless a torque converter automatic is utilised because the start-off torque has a direct relation to the stalling behaviour of an engine with a manual box. An engine with a high start-off torque will start typically with little or no revs from a standstill whereas a low start-off torque will necessitate significant revving to get going.
I noticed in looking over
Again, how many times do I have to illustrate that a torque curve should be read from the high rev side down to make any sense. The diesel car will always have a torque curve that rises from high revs towards the point of maximum torque at lower revs. A petrol engine would also have a similar curve if it were not for inlet manifolds and cams [both adjustable on the best engines] to enhance the curve at lower revs so as not to have a very low torque at low revs. A consequence of this tuning is a torque curve that is flatter [and even may have two peaks] so as to enhance low end torque. The need for this is because the engine would otherwise and naturally peak at high revs with a steadily declining torque which would relate to very poor low end performance.
I am not amazed at all by the ignorance of so many people who think they know it all.
You cannot over rev a diesel engine which is not pushed [as in going downhill] because the governor [whether mechanical or increasingly electronic] prevents it.
Maximum torque will be produced at 1100erpm in your example. Possibly only 80% of maximum torque will be available at maximum power, although this would not be a typical modern example. More typical would be a 11litre engine which was rated at 2200erpm which produced an extra 10% of power at 2000 and only fell back to its rated horsepower again at 1800erpm. Maximum torque would indeed be at around 1100erpm and would be about 40 to 50% higher than at rated top speed. Such a positive engine characteristic is only posible by dint of the very steep torque rise as revs drop from maximum. As you know, the engine power is not measured by a dynamometer but the torque is, and it is this, in combination with engine revs which is used to compute the power at any point. An heavy hauling engine such as this would need at least 110% start up torque, calculated as explained previously, to start the load off without drama.
In a 250 cc naturally aspirated gasoline
Yes but notwithstanding the engine, lets assume 60hp, and the gearbox, the extremely low start off torque produced by such an engine would never start a 2 ton towed load off from standstill. By contrast, my
67hp landrover will happily start a 5 ton load and tow it around up hill and down dale from one day to the next. This perfectly illustrates why a gearbox will just not compensate for lack of torque in practice.huw