Horsepower vs. Torque

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MagicMtnDan

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The 2010-model F-150 Raptor with the 5.4-liter engine produces 320hp and 390 lb-ft of torque. The 6.2-liter engine will produce 411hp and 434 lb-ft of torque according to published info.

There have been some lengthy threads about 5.4 vs. 6.2 but let's talk about HP vs. Torque while we wait to see the actual performance of both of these motors in the Raptor (on the street).

Nearly every truck and car review you read tells you the vehicle's horsepower and torque ratings -- but they don't usually explain what the terms mean or why they're important to you as a driver. And when you do see an explanation, it's often in tech language that still doesn't make sense on a level that most of us understand. So here goes -- a basic explanation of horsepower and torque, in everyday English. No tech experience required.

Horsepower, abbreviated hp, and torque are two separate measurements that help reveal the capabilities of your truck or car's engine. Don't worry too much about how they are measured or exactly what the abbreviations you see with them mean. Just look at the numbers and the specs for revolutions per minute (RPM).

How Horsepower and Torque Differ

• Horsepower is responsible for moving the vehicle along and gives it the ability to cruise on the highway and accelerate in normal conditions.

• Torque is the force that helps the vehicle start moving from a stop and pulls it up steep hills. Torque steps in again to provide power when you're hauling items or towing something behind the vehicle.

Published Horsepower and Torque Specs

• Automakers state peak hp and peak torque at specific revolutions per minute -- rpm, the numbers you see on a tachometer.

• HP and torque both drop off before and after their peaks.

How Do You Use Your Truck?
When you look at pickup truck specs, think about how you drive. If the majority of your driving is in-town and at 60 to 70 mph on the highway, your vehicle's engine is spending most of its time in the 1800-2500 rpm range. An engine that produces its peak horsepower or torque at 5500-6000 rpm might not be the best choice (unless it's the only choice for the vehicle you're considering) because that's not your typical rpm range.

Choosing Horsepower and Torque
• Higher torque ratings are more important than high horsepower ratings if you pull a trailer, haul heavy loads or drive on roads with long, steep grades.

• If you like to see how fast you can get from stoplight to stoplight -- or if you do a lot of other quick acceleration driving -- horsepower is more important.
Keep in mind that horsepower and torque don't necessarily peak at the same rpm. They can differ by a small to wide range. Reviews don't always include the peak rpm for horsepower ratings, but they're available in factory specifications.

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MagicMtnDan

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Most street cars are relatively heavy, sometimes carrying as much as 12-14 pounds/hp. To overcome a heavyweight's inertia-the property of a body by which it tends to resist a change in its state of rest or motion-requires lots of initial leverage. And if nothing else, torque is leverage.

All this seems to argue in favor of building for low-rpm performance. Many builders call this "building for torque" or "assembling a torque monster." But in the final analysis, it's really a matter of semantics. Whatever the term, the goal is maximizing engine output in the rpm range where the engine spends most of its time-whether it's because of inherent design limitations, or because of intended use, or a combination of these factors. Even with low-rpm setups, the engine that makes the most torque at equivalent rpm points will make more power-and should be faster.

Area Under The Curve

Notice we said "the rpm range where the engine spends most of its time." Merely considering peak numbers is misleading. In almost every case, it is better to look at the average area under the power curve rather than simply at peak numbers, because a broader, flatter curve generally delivers superior performance to a peaky curve. As SuperFlow's Harold Bettes puts it, "Some engines [that] have a power curve that looks like a tabletop [instead of] a mountain range in profile are pure pleasures to drive." Comp Cams' Scooter Brothers adds, "If it's a Comp Eliminator, Pro Stock, or Winston Cup car, maybe peak power is the answer," because these engines operate in a relatively narrow rpm band. "But for the dual-purpose car, torque must be flat for an extended period of time."

On a SuperFlow dyno, the engine rpm input is from a 60-tooth tach gear counted by a magnetic pickup. The tach signal (rpm) multiplied by the torque (lb-ft) measured by the strain gauge at the absorber and divided by a constant (5,252) calculates the engine's "brake horsepower. "According to David Reher, "We look at the average horsepower within the rpm range we run in; we don't look at the peak number. Anytime you can pick up the average, that's an increase. But you don't want to lose power somewhere else."

"The wider the powerband, the better the acceleration," says turbo wizard Ken Duttweiler. "The best examples are variable-cam engines like the Honda VTEC-they'll pull down to 500 rpm and accelerate to 7,000!" And Norm Brandes at Westech Automotive (of Wisconsin) adds that high-strung, peaky motors "are easier to get out of tune. A carb on a good 'torque' motor sees a much stronger manifold signal, so it's more forgiving. The same holds true with electronic engine management; the computer will be much happier with a broad curve."

Generally the rpm range that is most important is the area between peak torque rpm and peak power rpm. The car should be geared so that you shift 400-500 rpm beyond peak power, and the engine "falls back" to just beyond the peak torque point. Assuming a similar operating range, the engine with the greater area under the power curve between the power and torque rpm peak points makes for the better combination.

On an engine with the most "area under the curve," the torque falls off less rapidly after hitting its peak, so in that sense you are always building for best overall torque, in order to produce the best overall power. This is where Scooter Brothers of Comp Cams gets his axiom, "build for torque, and horsepower will take care of itself," but remember the end goal is always to generate maximum power within your engine's operating rpm range. "There's not one thing that isn't a tradeoff," David Reher points out. "That's the most critical thing in engine-building: deciding where and when to make those tradeoffs." Harold Bettes adds, "It is the package with the greatest area under the power curve that has the advantage. Remember, you cannot have horsepower without torque, but you can have torque without horsepower!" It's called a dump truck.

Source of above info
 

Sgt Williams

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See these are exactly what I miss reading. Outstanding write up. This also brought somethings to light with my truck and the future installation of a turbo on my bike for the 1320 drag. HP to weight Ratio nice info. Don't know how to do Rep points yet but you got some in my book. Thanks Dan..
 

MarkT

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Very good info... thanks Dan!

This reminds me of back around the time I graduated High School... Ford had two "high performance" versions of the Mustang II one year. One with a V-8 engine and one with a Turbo 4 cylinder engine.

I think the V-8 had something like 135 HP while the Turbo 4 had 165 HP or something like that. Quite a bit more power from the Turbo!!! And the Turbo 4 had a lighter curb weight by a few hundred pounds!!!

By the "numbers", the Turbo 4 is the clear winner in a drag race, right? Wrong. I think the higher HP turbo was actually 1 or 2 seconds SLOWER 0 to 60 mph than the heavier, lower powered V-8.

That was a drag race. For everyday driving, the turbo was even worse! You had to rev the snot out of it all the time. While the V-8 had tons (for the day) of torque that was there right off idle and was a pleasure to drive slow or fast.

While this is an extreme (even if real life) example... It all comes down to the "area under the curve".

We already have been told the 6.2 is "drag race" faster than the 5.4. But I hope the "Raptor tune" 6.2 at least matches the great (flat) torque curve of the 5.4 down in the lower rpm ranges... I have my doubts that it will...

It will be interesting when someone does a side-by-side dyno test between a 5.4 and 6.2!
 

SOCOMech

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Awesome Dan, thanks for the write-up! One thing though............. as most already know I'm sure but, for anyone new coming along........the 5.4's 320hp & 390tq rating's are on E85. The actual 87oct. rating for it is 310hp & 365tq.. I realize you got it from another source though.
 

BIRDMAN

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Not for long Greg. Once I take delivery of my 2013, a global announcement will be made that 6.2 is officially > 5.4 . I brought the 5.4>6.2 phrase in to the world, and I can take it out.
 
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