This is something I never fully understood when it comes to HP vs Torque. I understand 100% what torque is all about. But horsepower I don't fully understand. Like if you have two motors with identical torque. But the horsepower is a lot different. How would they behave differently?
Horsepower is torque (work) over time. If you apply 1 foot pound of torque for one minute, vs 2 minutes, the torque is always the same, but the work is doubled. Transmissions/gearing effectively multiply or divide the torque and each can be exploited to different ends. You need to read up on theory of HP, Torque, "work over time" and how they intersect. Think of torque as strength and HP as stamina. An athlete might be very powerful in strength, but lack endurance, another might not have as mush strength, but have a great deal of endurance. Exploiting both in different ways, yield varied results, but both individuals posses both strength and endurance. The highest performing athlete will have a best mix of both.
Torque is a measure of rotational force. Power is how much of that you can do in a given time. In other words, the ability to do work per unit of time.
A few thoughts: Sustained top speed takes horsepower / Accelerating to that top speed takes torque. The heavier the vehicle, the more torque (work) you need to get it moving / A lightweight sport-bike does what it does better with more horsepower while a heavier Harley needs more torque for ride-ability. Or - Horsepower is how fast you hit the wall / Torque is how far you take the wall with you.
Buicks have lots of torque, - so they put a lot of force down on the pavement, - technically the more torque you've got the faster you'll get going, particularly if the torque comes in at a slow engine speed which a Buick does best. Where it dies is at the top end of the curve; - this is where horsepower takes over. You need the horsepower to sustain the torque, like a runner with long legs, good and quick at the start, but the faster those legs have to move over distance, the more unsustainable it becomes to maintain that power. A stock Buick Big Block has over 510 lbs-ft of torque and close to 370 horsepower. It will apply a ton of power at low RPM onto the pavement and get moving fast or twist the driveline out doing it. If you know what you are doing and happen to get the engine into the max RPM where torque is at max and the HP is close to max, then you have a formidable 1/4 mile car. This is what your stall RPM in the torque converter should be at so the engine quickly revs to that speed and starts the pull at max power. (This is also why BBB was good on a "Switch pitch" TH, it allowed the engine to spool up and get into a better power band and hold it there, Buicks die on revs at max HP) There are more than enough people on this forum who can tell you that, I'm not one of them. Now the Chevy small block can have some wicked horsepower, but it's limited on torque, - now a good stall and gear ratio becomes paramount if you want to get performance out of it. My experience was that you could do wonders with a dead stock Buick BB in good tune against a mildly hopped up SBC, which was what most of my friends all had back in the day. And that was exclusively because of torque, the Buick would come in hard at 2800 RPM, the Chevy wouldn't budge under 3500. The Buick would die off at 4200, and the Chevy would hold up to 5500 unless modified. Nasty things would begin to happen to the Buick at over 4500, whereas the Chevy is fine to valve float, which happens at around 6000. Another example of horsepower vs. torque is an aero engine; - ever wondered why it is you never see Merlin or Packard engines out of a P-51 in a car? These things had stupid horsepower, about 15-1600 if memory serves me right, but they had no torque. You need a lot of horsepower to whip a prop around, but you need torque to get away from a stop light unless you have that prop which then converts horsepower to a form of torque by switching the pitch in the prop and working against the air. A neat example of this is a Pratt and Whitney PT-6 turboprop; - I once saw a demonstration of this, do not try this at home. Before the engine starts up, grab the prop and hold it. The pilot then starts up the turbine, and spools it up to take off speed, - you're still hanging on to the prop and it can be done with one hand. This engine has no torque, but it has something like 10,000 shaft horsepower. (It also has an indirect coupling between the turbine and the prop, which is what allows this experiment to work) The caveat here is once you let go of the prop, get out of the way, you won't catch it without getting chopped to bits. but because the engine is all horsepower and has no torque, you can get away with it. (Just please, don't go to your nearest airport and hang on to the prop on the nearest Cessna or ATR-42, - it will not end well, they have direct drive gearboxes and enough torque to make mincemeat of you) Another example of high torque and horsepower is an electric motor. At rest you can turn it either direction, apply power and the torque comes on full as does the horsepower. Depending on voltage, amperage and all that, an electric motor can be totally unforgiving, it's power band is right there and the only thing that destroys it is heat, where chemistry takes over. This is why Teslas are stupidly quick; - the power is instantaneous as soon as the foot feed is pressed, and since it's a rheostat, you floor it, it goes to max output instantly, whereas an ICE takes time to spool up. The obvious disadvantage is how much capacity this can take; - which obviously limits functionality over time. Sorry for the long winded explanation, hope it makes sense.
Horsepower = torque x (engine RPM/5252) The above equation is why you see horsepower and torque curves always intersecting at 5252 RPM. Two motors with identical max torque but different horsepower values means the max torque in each motor occurs at a different RPM. 4x4s and diesel trucks that pull a lot of weight tend to have higher torque numbers at lower RPM so they can get moving from a dead stop. Fullsize Buicks are heavy cars that require low RPM peak torque numbers to make them driveable at street friendly speeds. This also helps makes them red light tire shredders
From my teen years, the Buick was always the Torque monster! The Chebbies are always the HP peeps. Majority of the time the Buick won! I know that's basic, but those of us know owning a torque monster Buick is the most fun! just my $.02 worth
If you have two motors with the same torque but different HP from 0 RPMto 5252 RPM with the same load they would accelerate in RPM nearly identically. After the 5252RPM the higher HP motor will have the ability to continue to accelerate in RPM with load over the low HP motor.
Torque allows you to run more friendly gear ratios Hp needs deeper gears to he able to take advantage of it. Torque is where it's at for street cars.
and that folks is why the Buick is out front it doesn't care about weight, it leaps out and waits for those Chebbys to catch up with their hp but then the next light comes or the 1/4 mile ends then it is over.
"The Buick would die off at 4200, and the Chevy would hold up to 5500 unless modified. Nasty things would begin to happen to the Buick at over 4500, whereas the Chevy is fine to valve float, which happens at around 6000." Something wrong with a 455 if it "dies off" at 4200. And "nasty things" over 4500?? Any stock 400-455 will pull strong to 5K. Maybe you are thinking nailhead, Marc.....?.
These characteristics also explain why, when GM (and others) dropped compression ratios and burdened engines with smog tunes and equipment, they still drove ok. I had a ‘78 Coupe deVille with a 180? hp 425, but the torque moved it on down the road well. (It made 325lb/ft at 2000 rpm). People who don’t understand write crappy ‘American cars sucked’ articles, centered around the fact that often these mid ‘70s and later cars, especially the big ones, struggled to make 200 hp, but then get surprised if they actually drive one and realize they just move well, almost silently, with no need to wind the (imaginary) tach past 2500. (Compared to most 4 cylinders, my El Camino’s 305 is torquey; making 240 at around 4000. Very few 150hp four cylinders could get away with only three gears and 2.41 rears in a 3500 pound car). Patrick
That's exactly why the 65-66 GS was great at beating other cars in stoplight races which were usually 1-2 blocks long. In stock form at the dragstrip they were easily beaten due to their limited HP. On the street in short races the torque was a winner
