What does it mean that an engine puts out 150 lbft of torque at 2500 rpm? If I stand at the end of a 1 foot rod attached to the crankshaft, the rating suggests the engine would stall. Yet I'm sure it would send me into the next county. Is force applied through a wrench more of a moment than continuous rotational torque?

Sixto
83 300SD

Force times perpendicular distance. Having an engine that puts out 150 lb ft at 2500 rpm can be imagined as it reeling in a 150 lb bucket from a well while running at that speed, with the rope winding onto a drum with a radius of 1 foot.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

I'd be lucky to sustain 50 rpm for more than a few seconds. But that's my point - an engine rated at 150 lbft is leaps and bounds more capable than me standing on a foot long bar but both are described as 150 lbft.

Sixto
83 300SD

You're confusing work and torque. Work is force x distance. Torque is the moment of force...force x length of lever. It's confusing because Torque is sometimes measured in lbft, while work is sometimes measured in ftlbs.

Yes, you could stall your motor by standing on a foot long bar. Please don't verify by experiment. The way this is actually measured is by attaching the crankshaft to a turbine where water pressure is applied until the engine stalls. The reason this is counterintuitive is that other stuff...power. Your engine can move that 150 pounds a long way in a fraction of a second. The end of that lever would be moving at almost 2 miles a minute. It would tear your arm off before you could grab on, unless you were also spinning at 2500 rpm.

I follow your words but I can't repeat them in a way that makes sense. Here's another case - an engine rated at 150 lbft at 2500 rpm vs and electric impact wrench than can tighten a lugnut to 150 lbft. Is the reciprocating mass of the engine a factor?

Sixto
83 300SD

An engine has a lot more inertia than a lugnut.
I think horsepower is related here somewhere since an impact wrench won't drive a car at any kind of speed.
Yes it's been a while since I took physics and mechanics...

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Bob Roe
Lehigh Valley PA USA
1973 Olds 88, 1972 MB 280SE, 1978 Datsun 280Z, 1971 Ford T-Bird, 1972 Olds 88, 1983 Nissan Sentra, 1985 Sentra, 1973 230.6, 1990 Acura Integra, 1991 Volvo 940GLE wagon, 1983 300SD, 1984 300SD, 1995 Subaru Legacy L wagon, 2002 Mountaineer, 1991 300TE wagon, 2008 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon, all gone... currently
2007 Honda Odyssey Touring, 2014 E350 4matic

I think it's the rotating mass that's interfering with your mental picture. The engine puts out 150 ft lbs without its speed changing. If you suddenly applied greater load (like dropping a clutch pedal), you would get more torque briefly as the speed fell, but this would be coming from the kinetic energy that was already in the flywheel and crankshaft.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

my dad always said maximum torque was the amount of force it takes to take a leak in the morning when ya got a stifie

I agree with all the statements above.

Ft lb is the same measurement for a torque wrench as it is for a motor. If you weigh 150 and stand on a one foot breaker bar you are making 150 ft lb. of torque by definition. On an engine it all happens quickly over and over but it is still the same basic measure.

Someone said torque applied over a measurement of distance becomes work...that is correct (by scientific definition).

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I know a woman who can really torque my nuts

Sent from an abacus

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TC
Current stable:
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Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

That means you have 71.4 hp at that rpm. (Torque x RPM) / 5252 = Horsepower

While standing on the end of your bar? This is not a pretty picture. Just mentaly or otherwise.

From the look in TBO's face he must know this woman as well

It all is a bit confusing isn't it? Think of trying to drive the car with the impact wrench, the rpms just aren't there. Power is a measure of work over time. An impact has much less power than an engine. Tho an impact can instantaneously do as much work as an engine they are not equal. I could be wrong here, just an opinion.