I stayed at one of those once too... and used that same line to [jokingly] bust in on my managers meeting to pretned I knew what they were talking about

In your example the man does not have enough weight on the bar to move the vehicle because more force is required. One can argue though that even though he cannot move the bar he is still applying a rotational force, it's just less than 1 rpm because he lacks the strength to move the crankshaft. Between the man and the rear wheels, something is moving, whether it is the breaker bar or his arm or the driveline. It's just not moving enough to actually move the vehicle.

 

Andym, you're taking my sentences out of their context. Rockets have horsepower because it's mathetmatically calculated differently. You can't even measure the kind of horsepower a drag car produces, but they calculated it in yet another way to get an estimation. I'm not a rocket guru, but again...stick to the context we're talking about...horsepower in an automotive engine...horsepower can mean a few different things depending on the context.

We were not just defining horsepower, we were defining horsepower of automobile engines. Horsepower of a rocket is different.

You're missing the exact same concept that Nickfordman was missing earlier. It's not feasible to have 1000 hp and only 100 ft-lbs of torque. Unless you had an engine that spun some crazy RPM. If that 1000 hp engine spun to say 8-9k rpm, it would have in the area of about 1200-1400ish ft-lbs of torque (estimation). That horsepower is calculated based on the torque output and the RPM, so you'd HAVE to have either a lot of torque, or a lot of RPM (or a good amount of both) to make that 1000 horsepower.

The closest thing you'll find I think, is my little RC truck's nitromethane motor. It's a tiny 2 stroke engine that produces 1.3 horsepower, but the torque on it is practically nothing, inch lbs. It's about .15cc's in displacement, but it cranks at about 40-50,000 rpm. See the pattern?

 

You are correct that the man in the example is still applying a rotational force. However, nothing has to actually rotate for the force to exist. Here is another example: The 200-pound man is sitting calmly on the diving board of his swimming pool. The diving board is six feet long so the guy is creating 1,200 foot-pounds of torque. Nothing is actually rotating nor will it ever rotate. The guy could sit there for years creating 1,200 foot-pounds of torque

 

No, they are the same. If you take the formula for horsepower in an automotive engine and work out the math the two formulas work out to HP=(force x distance)/time. If you would like me to post the mathematical proof I will.

So which is it? Is it feasible or is it not feasible? First you say it isn't, then you qualify it with a statement that says it is. I already know the answer, but I want to see you put it in writing.

An engine with a practical operating range of 8-9k rpm will not make more torque than hp. Look at the Hayabusa I mentioned earlier. Hp is 173@9800, torque is 102@7000 as found on the Suzuki web site. Once the peak torque of an engine occurs above 5252 rpm the peak hp will always be higher than peak torque.

I never said anything in disagreement with this. However, if you choose to make 1000 hp with lots of rpm and not much torque you will not accelerate anything without lots of gearing.

And since it makes so little torque how much gear is needed to get it to accelerate? An average RC monster truck has tires roughly 6" tall and runs about 40 mph with a two speed transmission. The overall gearing to run that speed at 40k rpm would be about 18:1 in high gear and probably about 25:1 in low gear. And that's in a vehicle with only about 6.5 lbs/hp compared with a full size truck that has to move 15 lbs/hp or even more that has a total gear ratio of about 10:1 in first gear and 3:1 in high gear. Regear your little truck (with its vastly superior power to weight ratio) to run the same speed as the full size and see how it performs. It'll be a turd because it has no torque. The .17 ft-lbs of torque that your little nitro engine makes couldn't do anything without the 18:1 gearing that turns it into about 3 ft-lbs at only 2200 rpm.

 

Sigma, here's a link to some dyno info. Unfortunately, it appear that Dynojet now views their website as a marketing tool instead of a way to provide information.

 

A hypothetical question with hypothetical engine specs.
Diesel Engine 1 = 300hp with 800ftlbs torque at 1969rpm
Gas Engine 2 = 300hp with 400ftlbs torque at 3939rpm
Each engine mounted in identical cars with constant velocity transmissions so that each engine can be kept at its peak performance point thru all speed ranges.
All weights, friction losses, etc are kept the same.
Will both cars accelerate down the track at the same rate ending in a tie?

 

yes, the differance is one is working harder to get down the track

 

Sorry, but there is no escaping gearing with internal combustion engines. Without gear reduction they have very few practical applications; you could probably count them on one hand. Even ski boats use a transmission, but we can work around that.

If you put an engine with 500 hp and 100 ft-lbs in a boat, it better be a small one. 100 ft-lbs is not much torque, so the force with which the prop could be turned is very limited. However, since there is 500 hp it can turn the prop with that same force at very high speeds. That is perfect for a small boat that needs to go very fast, in this case probably over 100 mph in an 18 ft boat and it will take a long time to get it there. (I was an intern in the Mercruiser lake test department one summer, but it's been a while). If you flip the two to have 100 hp with 500 ft-lbs you could either have a large slow boat with average acceleration, or a small slow boat with excellent acceleration.

 

So high HP and low torque = slow acceleration and (eventual) fast high speed? So top end of maybe 100kts but takes minutes to get there? Unless in this case the boat is an inflatable raft

So in this case you would have a boat that might have a max of 25 kts but get there very quickly, in a matter of seconds?

 

I didn't mean that they were different in that manner, they're different in the respect that there isn't rotational force like a car engine has. We shouldn't even be discussing rockets.

I said it wasn't feasible because an engine of that type is very rare. I have seen one, my RC's motor. Feasible may have been the wrong word to use there. The RC example was the only engine I could think of that could run that type of hp/torque simply because it redlines so high.

Bad estimate, you're right here.

True...

I agree but we were originally trying to keep gearing out of our discussion...to not complicate things...

My RC truck is exactly like you said...40 mph..2 speed...etc etc...

The point of the RC motor...is the same as some of the other examples I gave. It has lots of horsepower and is short on torque. It means that the motor can do a small amount of work but very quickly. Thats a point i've been trying to make for this entire thread.

You can explain the basic concepts of horsepower and torque w/o the use of gearing. One can teach the properties of gear reduction another time. I was doing just fine explaining it by use of examples...just showing what horsepower is.

I've made several examples just like this one.

I'll say it again...high horsepower and low torque = an engine that can do a light amount of work (ie move a light boat, snowmobile, motorcycle..etc) quickly (accelerates quickly).

Just think about it....all heavy boats have big diesels...they can't accelerate worth of crap because those diesels don't have a lot of horsepower, but they have a lot of torque...so they can get a lot of work done but slowly.

I'm tryin' to hang in here but I'm loosing my patience and this thread turned into an absolute mess of information, I don't blame anyone for not understanding this.

 

It will end in a tie, but neither is working any harder than the other.

 

I dont understand why it will be a tie.

 

It will be a tie because of the hypothetical constant velocity transmission. In the real world the low rpm engine would have to shift maybe 10 times to stay in its power band over a qtr mile thereby making it a loser. I asked the question to see if my assumption that since HP is a result of (torque x rpm / 5252) then engines with identical HP should hypothetically (all other things equal) accelerate at the same rate. Just trying to get a grip on this stuff.

 

Actually, the lower rpm engine would only be at a disadvantage if the two were geared the same. If the diesel had a 2.05 gear and the gas a 4.1 they would need the same number of shifts to cover a given distance.

I think we've really got away from the original topic. What causes somethig to accelerate? A force. Torque is a force.

 

We may be off the original topic but your explainations (and Mustang's & Sigma's) have helped me to get some understanding of this torque thing and how HP is calculated using rpms. The highway to understanding is sometimes a narrow twisting trail!?# Thanks for your patience