Senior Member
Jun 8, 2016
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The Evergreen State
That's how gearing and torque multiplication generate acceleration force from a given amount of torque and rpm, which is what horsepower really is.

It's highly likely I can answer this better than anyone here, without resorting to the internet but just from 50 years of gearheading.

Horsepower come from the crankshaft, direct, nothing else.

Horsepower is speed, if you have the torque to get there.

"Torque" comes from many factors, including gearing, torque multipliers.

Say if you were to put an overdrive on an old truck because it's too slow out on the road, at a 2:1 ratio, you would double your speed (theoretically) but your hill climbing power would absolutely suck. That hill climbing power is torque, the force that gets things moving, or keeps it moving.

This old guy was real proud of his Dodge Diesel 1st Gen that would pull a trailer load up this incredibly steep Carnahan hill from a standing start and hit 60 by the top of the hill. That's torque, from a diesel, different torque in fact, more grunt, diesels have twice the compression ratio of gas engines = more efficient. A gas pickup would have a tough time hitting 30 by the top of this hill, any gas pickup, regardless of avertized HP/torque ratings. 500ftlbs of advertized gas engine torque is might be worth 300ftlbs of Diesel torque.

Gas engines are better at the horsepower thing, high revs, up to 20,000 rpm.

Redline on a Cummins diesel is like 3200rpm. It's all torque.

What is Horsepower, the power of a horse? And like a these racing engines with 600hp, on the street... can you imagine a carriage needing 600 horses? Silly people.

The inherent torque of an engine has everything to do with its design, and here is where gas engines help to solve this HP/vs Torque conundrum.

The bore to stroke ratio.

The bore, cylinder size, say 4", an average size piston, if the crankshaft stroke - hence stroker cranks with longer throw, longer lever - was equally 4", we would call that a square engine, or oversquare if the bore is bigger than the stroke (common) or undersquare if the bore is smaller than the stroke (rare in modern engines).

When you have a 4" piston with a 3" stroke, you get some pretty decent engine RPM and decent torque.

When you have a 3" piston with a 4" stroke, a lot of torque, very little RPM.

When you have a 4" piston with a 2" stroke, crazy high revs and very little torque.

The longer stroke generates more torque, but will shake itself to piece if you rev it high. A perfect example would be the Harley V Twin, all grunt, long stroke, vs a modern bike like a Suzuki GSXR, high rpm, no vibration.

They'll both get you there, but in a different way.

We could go on about this for a couple days probably.

Here's what the internet does have to say, you can see the torque here, the tires are already going 60 but the car hasn't taken off yet ;[]

Screen Shot 2023-03-19 at 5.17.36 AM.png

Short stroke

And low RPM, Also, we haven't touched on 2 strokes yet so this takes care of both ;[]

That is an insane video.

On a more personal note, my '95 Subaru 2.2l has amazing "low end torque", the ability to hold 60mph at only 2700rpm - it's a stick so RPM/speed are locked, no torque converter slippage - so highway cruising under 3000 RPM, to me, fabulous, for a wagon.

And you just breathe on the pedal at 2700 on a hill and it sails past 3700 pulling like scalded dog, sweet spot up to about 4100, just sings, and the HP figures for this engine are dismal on paper. USA customers really complained about how slow the 2.2 was so Subaru had to unveil the nightmare of head gasket leaks that was the 2.5, just to satisfy a speed craving, a visible one as people on the roads here are lawless as he¬¬, insane. Taking wife to dentist other day, flying along at 80 on a 60 just because everybody else is but still getting passed like standing still. A year or two ago the speed on the same road was more like 70 and if you did that you were fine, you didn't get passed.
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