Originally Posted by supton
Originally Posted by y_p_w
As much as people really don't understand the difference between power and torque, a lot of these engines used in medium-sized industrial vehicles are rather short on power but high on low-rev torque. My 3200 lb WRX can put out a peak of 227 HP. A Caterpillar C7 can apparently put out maybe 350 HP tops, but expected to pull 15,000 or more lbs. But it's a torque monster, so it puts out more power at low revs.
Not sure I follow... ultimately neither engine can do more than 227hp rate of work, or 350hp rate of work. The Cat will presumably live at WOT for days on end, not so sure on the Subie. Ultimately, you can use gearing to increase torque, but hp doesn't change.
Yes, big diesel belts out more torque at low rpm--it has to, in order to make the hp equation work (torque*rpm/5252). But if you take a 350hp gas motor and run it into a 2:1 or 3:1 transmission so as to get the same output shaft speed, you'd have the same hp and the same torque as a 350hp diesel. [Now if that gas motor could live for days at WOT, that is a different question--it's possible, they used to make monster gas motors, after all.]
I'm just saying it's going to take a lot more to get that gas engine to even get started pulling a big load compared to a torque monster. But isn't the whole point to pick a better tool for the job?
I really don't get the hate for electric vehicles. The characteristics of a large electric motor would seem to be ideal for certain applications. Right now of course there's the issue of range, but I've worked college jobs in the shipping industry where we were paying drayage companies to haul container loads relatively short distances to local customers. They were also waiting in lines at rail or container ports with the engine on.
Tesla is claiming 500 miles on a full charge for their tractor and 30 minutes for a charge that will give up to 400 miles. I figure something like that would be adequate (maybe even overkill) for short haul trucking like the example I gave. But then there might be smaller vehicles with lower range just like there are sleeper tractors for long haul vs short haul tractors.
Originally Posted by y_p_w
As much as people really don't understand the difference between power and torque, a lot of these engines used in medium-sized industrial vehicles are rather short on power but high on low-rev torque. My 3200 lb WRX can put out a peak of 227 HP. A Caterpillar C7 can apparently put out maybe 350 HP tops, but expected to pull 15,000 or more lbs. But it's a torque monster, so it puts out more power at low revs.
Not sure I follow... ultimately neither engine can do more than 227hp rate of work, or 350hp rate of work. The Cat will presumably live at WOT for days on end, not so sure on the Subie. Ultimately, you can use gearing to increase torque, but hp doesn't change.
Yes, big diesel belts out more torque at low rpm--it has to, in order to make the hp equation work (torque*rpm/5252). But if you take a 350hp gas motor and run it into a 2:1 or 3:1 transmission so as to get the same output shaft speed, you'd have the same hp and the same torque as a 350hp diesel. [Now if that gas motor could live for days at WOT, that is a different question--it's possible, they used to make monster gas motors, after all.]
I'm just saying it's going to take a lot more to get that gas engine to even get started pulling a big load compared to a torque monster. But isn't the whole point to pick a better tool for the job?
I really don't get the hate for electric vehicles. The characteristics of a large electric motor would seem to be ideal for certain applications. Right now of course there's the issue of range, but I've worked college jobs in the shipping industry where we were paying drayage companies to haul container loads relatively short distances to local customers. They were also waiting in lines at rail or container ports with the engine on.
Tesla is claiming 500 miles on a full charge for their tractor and 30 minutes for a charge that will give up to 400 miles. I figure something like that would be adequate (maybe even overkill) for short haul trucking like the example I gave. But then there might be smaller vehicles with lower range just like there are sleeper tractors for long haul vs short haul tractors.