Haulin_in_Dixie

OOps, I think you miss that I have a six speed. That would be your forth....

Barry Smith

I've always heard you could gear a 5 hp Briggs to pull a house trailer?

Hannibal

You can! But with only 5hp you'll be moving at less than walking speed! Through gear reduction you can "make" the torque but you can't "make" the hp. You'd need over 300hp to move it 60mph on flat ground. The ISBe HO could do it.

Haulin_in_Dixie

It does not make the torque either, that is why it needs the gearing to convert it. Gearing for torque has no place in the discussion. The torque that the engine produces is the torque that it produces. That times the rpm, devided by 5252 is the horsepower. Horsepower, torque and rpm are related mathamatically. I think the term is inversley proportional.

As I said before, the engine makes a certain amount of torque at a specified rpm, the horsepower is calculated from there. Cut the rpm at the same torque and the horsepower goes down, raise it and the horsepower goes up.

On an engine such as our cummins that keeps the torque curve flat for most of the rpm range and you have a 325 hp engine 2700 or 2800, cut the rpm range down to 2500 and you have the same torque but less horsepower. Hence the 12v engine doing the same work as the 24v, but the 24v is rated at a higher horsepower.

Jeez, can't you see that, my engine is 275 horsepower at 660 torque at 2500 rpm, the new 600 engine is what, 325 horsepower at 600 torque? But at a higher rpm. I flat blow their doors off with a load. I have less horsepower (the mathamatical computation) but more power (torque) pulling a hill with a load. High torque makes a pulling machine, high rpm horspower makes a hot rod. Always been this way, otherwise I am sure the engineers would have a 500 cat turning 3600 instead of 1400. My 275 horsepower engine would be 339 at 2700 rpm.

KATOOM

Haulin_in_Dixie, save your breath, or your typing fingers. This is a no win situation. You can lead a horse to water but you cant make em drink.

Haulin_in_Dixie

You are right....

Hannibal

HID, My truck uses gear reduction no matter what gear I'm in. It multiplies torque 4.1-1 at the rear axle even when the tranny is in direct. It's all about gear reduction. The only thing constant from flywheel to rear wheel minus frictional losses is horsepower. Torque can be multiplied many times. Horsepower is constant. That's why is doesn't make much difference what gear you use on the dyno.
Gear reduction is no different than rope and block rigging. A 2:1 rig will lift twice and much at half the speed. A 4:1 rig will lift 4 times as much at 1/4 the speed. The 5hp Briggs can be geared to "make" enough torque to move the house trailer. The engine doesn't make the necessary torque. Gear reduction does. My truck's 460ft/lbs wouldn't move my trailer up a grade. But my transmission and rear end ratios multiply that torque to the point it will. Even in direct I'm putting 1886ft/lbs of torque to the rear axle. That gets me up the hill. That torque applied at a high enough rpm (horsepower) is what allows me to run up the grade at a reasonable speed.
Then again, if you two can't see that... Go ahead and remain ignorant and believe torque moves you without rpm.

KATOOM

You need to run in direct 4th or 5th, depending on your tranny to get accurate results for "to the ground" or your getting numbers from gear reduction.

Hannibal

So you're saying the rear end isn't gear reduction? 2.73-556:1 is all the same to you? The dyno is reading the rate of acceleration of the drum compared to engine rpm. Yes you get a more accurate reading in direct drive but for the most part the dyno doesn't care what gear you're in.

KATOOM

When was the last time you saw someone post their dyno results IN 1st GEAR? When you dyno from the wheels you are after the least amount of gear reduction and that is whatever your direct gear is. Even at this you are getting LESS than if your engine was hooked direct to the dyno because of the power it takes to turn the tranny and the differential and the size of your tires.

Haulin_in_Dixie

First, thanks, appreciate that, I'm ignorant.

Secondly, I have no idea what the heck you are talking about. Possibly you do. My ignorance tends to keep me from understanding high tech things like ropes pulleys and things. I am still struggling with why a heavier hammer drives the nail in faster.

Any engine has to be geared to the speed you need to travel. What that has to do with horsepower being related to torque and rpm, I have no idea.

I am done with this thread, enjoy.

Hannibal

"When was the last time you saw someone post their dyno results IN 1st GEAR? "

About the last time I saw some one with a 1:1 rear end ratio...
You'd have too much torque in 1st gear and wouldn't have a gradual rise in wheel/drum rpm. Or you wouldn't have enough traction on the drum. But regardless, 325 hp at 2900 would be read in 1st or sixth if you could eliminate those two obstacles. The difference would be the torque. Torque in 1st gear with a 600 Cummins would be around 13677ft/lbs at the rear axle. Enough to pull the house down or snap a U-joint but not much speed. In 6th gear it'll be reduce by O/D to 1845ft/lbs to the rear axle. Still enought to pull most pickup truck compatable trailers. Oh, how fast can you pull it with that much torque? That would be all that torque X rpm but that's expressed as horsepower and you don't want to hear it...

JamesP

Not sure who's side I will be fighting for but ...

If you take 2 things out of the equation, engine life and existing transmission.

Engine longetivity. Obviously an engine that has to run at 5000rpm isn't going to last as long as an engine running at 2200rpm. All things being equal the less number of engine rotations for a given distance traveled the better in regards to miles to rebuild. I think that is the biggest reason the big rigs run at such low rpm.

Transmission- If a transmission existed that had enough gears to keep an engine at the narrow peak hp band you can totally forget about torque output, wouldn't mean squat. The higher hp engine will always out pull the lower hp engine. It doesn't matter if the lower hp engine has 1000 lbft of torque and the other has 300 lbft. At any given speed the higher hp engine will put more torque to the wheels because of gear reduction.

Is it praticle to have a high hp, high rpm pulling engine that will last maybe 10,000 miles? NO

Does a transmission with 50 gears exist? NO


To make an engine last as long as possible and still have high hp you need 2 things: low rpm and high torque. It's just simple physics. Okay I'm through rambling!

Hannibal

Thank you thank you thank you!!!

1sttruck

I'm late to this and sorry if it's already been covered...

Looking at the offerings in ISB engines from Cummins, typically for medium duty applications, it's kind of surprising to see such low horsepower, but makes sense when you look at how the torque increases. It seems that a given powertrain, tranny, axles, shafts, etc., is limited in how much torque it can transmit. If more 'power' is desired from a given powertrain, such in our trucks, one needs to increase RPM in order to produce more HP. If you want to go fast you need to be able to produce enough torque at a high enough RPM for the vehicle load and gearing. An example that I've owned is a 400cc 2 stroke twin road bike, with pipes, that was low in torque compared to other larger road at the time, like Triumphs, Sportsters, etc., but it produced similar HP over a small, peaky RPM range. It could get you trouble real quick as it would go from nothing to the front wheel coming up while you fought for control, both of the bike and trying to keep your pants clean :^) Everyone else in my battalion that had one wrecked theirs within 6 months.

The bike produced similar HP to some tractors, around 50 hp or so, and if desired you could an even peakier 70 hp out of one, but it would be very difficult to ride on the street. Some magazine editors testing such bikes on a track said that they were unable to ride them. At 50 hp my bike was quick but it wasn't well suited for carrying passengers, as if you found yourself in a lower gear at the bottom of hill it was hard to generate enough revs to increase speed. Friends carrying passengers on their larger, higher torque bikes had no problems in such situations. Consider trying to tow a large load of hay with such a bike, compared to a tractor. Although the bike could be geared to move the load, there wouldn't be enough torque to move the load at higher gear ratios, and it would be very limited in speed.

That's why medium duty trucks have very modest HP ratings for their displacement, and incredible amounts of torque.