Does HP matter?

[LD1]

LD,
I think everyone gets your point about torque needing to be sufficient to do the work as you reference.

I had my doubts about that a few pages ago

Horsepower, torque or force, distance and time are all equally important in determining the amount of work done. The amount of work done is not based solely on the sheer force it takes to do the job but includes distance and time.

Horsepower does matter, if any one takes 10 times as long to get the job done because they are underpowered they won't be in business very long. Friction losses can eat up hp, daily overhead costs can eat up profits, getting the job done fast enough is a very real consideration.

Yes HP matters. As does torque. Torque needs to be sufficient enough to get the job done, and HP needs to be sufficient enough to do it in a timely manner.

[EE_Bota]

I have no numbers to add to this discussion, nor do I have any new groundbreaking scientific explanation, as I am but a lowly musician and numbers make my head hurt. I will, however add a little anecdote from high school, demonstrating the effects of horsepower without sufficient torque.

A bunch of kids were hanging out after school in the student parking lot. They were all checking out each other's cars, each bragging his up over the others. One kid, who was parked on the grass, decided to show off his awesome machine. He started it up, floored the go pedal, set the brake put it in gear and proceeded to do a burn out (in the grass?). As he let off the brakes to move, the car made it's way to the pavement. As soon as the rear tires hit the pavement, the resulting friction and added load killed the engine. Seems his engine just didn't have the torque to do the work when the rubber hit the road. Poor kid never lived it down!

True story.

Joe

This is completely unrelated, but your story gave a visual image that is easy to see. Here is something I witnessed:

I was going down an on ramp onto Hwy 64. There was a jeep in front of me doing the same. It had snowed, and the road was very icy. In my Subaru, I am moving an appropriate speed down the ramp, but the jeep in front is "cutting up" and deliberately goosing his Jeep to make it go sideways...like when they are "drifting." I'm about the freak-out seeing all this and I immediately try to slow to a stop because I can PLAINLY see that there is a bridge crossing the highway at the bottom of the ramp and the road under the bridge is coal black and dry as a cob. That jeep hit that clear spot sideways and started rolling at the same rate had been sliding. And two lanes of oncoming traffic had to slam on brakes to make sure they could stop in time. I'm sweating bullets watching him, and the oncoming traffic, and the guys coming down the ramp towards me. Amazingly, the jeep was the only one to actually get any damage and no one else collided.

[MF1433V]

This is completely unrelated, but your story gave a visual image that is easy to see. Here is something I witnessed:

I was going down an on ramp onto Hwy 64. There was a jeep in front of me doing the same. It had snowed, and the road was very icy. In my Subaru, I am moving an appropriate speed down the ramp, but the jeep in front is "cutting up" and deliberately goosing his Jeep to make it go sideways...like when they are "drifting." I'm about the freak-out seeing all this and I immediately try to slow to a stop because I can PLAINLY see that there is a bridge crossing the highway at the bottom of the ramp and the road under the bridge is coal black and dry as a cob. That jeep hit that clear spot sideways and started rolling at the same rate had been sliding. And two lanes of oncoming traffic had to slam on brakes to make sure they could stop in time. I'm sweating bullets watching him, and the oncoming traffic, and the guys coming down the ramp towards me. Amazingly, the jeep was the only one to actually get any damage and no one else collided.

Sounds like an expensive and probably very scary lesson for that Jeeper to learn. I am like you when I see someone acting a fool in snow I back way off!

[MF1433V]

So can I safely say we have consensus on the OP's question that both are capable of putting the same torque to the ground, but the higher HP engine will be able to put the max torque to the ground or the PTO at a lower RPM without bogging the engine? That's probably what he is concerned with??

[EE_Bota]

So can I safely say we have consensus on the OP's question that both are capable of putting the same torque to the ground, but the higher HP engine will be able to put the max torque to the ground or the PTO at a lower RPM without bogging the engine? That's probably what he is concerned with??

Honestly, I can't say. I let the tractors stated PTO HP speak for the ability of the PTO. I think the two engines mentioned are close enough that my ultimate decision would likely be made based on something other than the engine differences. For example, if both tractors are hydrostatic drive, if you tip the swash plate only a tiny bit, the speed will be incredible slow, and the torque to the gears will be limited not by the engine, but by the pressure relief device in the HST.

[LD1]

So can I safely say we have consensus on the OP's question that both are capable of putting the same torque to the ground, but the higher HP engine will be able to put the max torque to the ground or the PTO at a lower RPM without bogging the engine? That's probably what he is concerned with??

I would simply say that both tractors are able to put the same amount of torque to the ground, but the higher HP one will can do it quicker and with less lugging. That dont necessairly mean at a lower RPM.

A good example of HP would be for those of you who drive your tractors on the road and tow things. We tow wood in the trailers behind the tractors. Up some decient grades in road gear. IT only requires so much torque for the given weight to crest over the hill. But the more HP you have under the hood, the faster you can crest it. I can maintain speed with my 34hp tractor. But if I were to pull the engine and drop in a 15HP motor, I would likely have to down shift a gear of two (to increase the torque at the rear wheels that the smaller motor lacks), and this will be a slower treck up the hill, but it would still do it.

[MF1433V]

Points taken. I would have to admit that the bulk of my experience with boosting HP has been in supercharging. In forced induction via roots based chargers the increased HP of the blower ALWAYs also increases torque at a lower RPM. It is a very linear torque curve and a lot of fun.

[LD1]

Since HP is a mathametical calculation using torque AND rpm, if you boost the HP at a given RPM, the torque increases as well.

I guess it could be said that you actually increased torque (since that is what they CAN measure) and as a result, it also increased your HP.

The only way to increase "peak" HP and NOT increase the torque is to gain the HP by increasing the RPM. Since HP is a function of torque (force) and speed (rpm in this case) to gain HP, you can either increase the force (torque) OR increase the speed. But you dont necessairly have to do both.

[MF1433V]

Well here is a dyno that is part of the basis of the opinions I have gathered over the years. This one is based on speed and not RMP but the car hits just under 60 mph in 2nd gear at redline.

You will see that at about that time it is making peak torque and stays linear even as HP increases. In addition there is a point where HP increases and Torque actually decreases. This is in a 1.4L Mazda engine.

[arrow]

Well here is a dyno that is part of the basis of the opinions I have gathered over the years. This one is based on speed and not RMP but the car hits just under 60 mph in 2nd gear at redline.

You will see that at about that time it is making peak torque and stays linear even as HP increases. In addition there is a point where HP increases and Torque actually decreases. This is in a 1.4L Mazda engine.

Torque limit or peak on an engine will always come first. Power can still increase in a small window because the torque drop off is small (as seen on your dyno chart) and not enuf to effect increasing rpm so overall hp can increase at this point. The torque eventually drops off and so much so that it countermands any gains seen with increasing rpm and that's when you see power start to drop.