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#129661 - 8th Dec 2005 2:05pm the great power debate
scoop Offline
Wiki Addict

Registered: 18th Nov 2004
Posts: 7238
Loc: Leuchars
What do we think peeps. What makes a car faster,power or torque?

Here we have 2 examples (not real life)

1.1100KG hatchback with 150BHP@6000RPM 131Ft/LBS torque

2.1100KG hatchback with 136BHP@5200RPM 137FT/LBS torque


What would win 0-60?
What would reach a higher top speed?
What would win 1/4 mile?
What would win round a racetrack?

Ur views please
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#129662 - 8th Dec 2005 2:30pm Re: the great power debate
StuyMac Offline

Wiki Master

Registered: 24th Nov 2003
Posts: 12002
Loc: Wirralshire
Power - bhp gives top speed, and Torque gives acceleration.

Due to the closness of the 2 examples above, there are many varying factors, tyres, driver, aerodynamics of the car etc etc etc

Have a read of this article, maybe it will help clear it up a little more smile

Measures of engine performance such as torque and horsepower are relatively simple, yet are often badly misunderstood by the public. Some of this misunderstanding is due to automobile advertising, some to people having just enough knowledge to be dangerous, and some to the continuing death-spiral of science education in America. I'll begin by explaining power vs. horsepower, then torque and how it is related to power. Finally I'll give examples of why knowing something about these concepts is important when comparing automobile engines.

First, let’s note that horsepower is a unit of measurement for power, in the scientific sense of the term, just as the foot is a unit of measurement for length. Horsepower measures the same thing that the watt does--the power that a device can create or consume. Just as the wattage of a light bulb tells you how much power it will use, the horsepower specification for an engine tells you how much power the engine can produce.

Power is measured in many other units besides horsepower, depending on location and application. Watts (W) and kilowatts (kW) are in common use worldwide. Less common measures include British thermal units per hour (Btu/hr) and foot-pound force per minute (ft-lbf/min). Since any or all of these could be valid performance measures, technically it's more correct to talk about an engine's power than its horsepower. However, in practice most people in the United States use the two words synonymously.

Standard mechanical horsepower is defined as about 33,000 ft-lbf/min, or 745.7 watts. However, there are many different official and unofficial definitions of horsepower. Some of these definitions refer to different ways of measuring power for a specific application. For example:

“Brake horsepower” generally means that the power was measured on a type of dynamometer called a “prony brake" (sometimes incorrectly called a “pony brake”--prony refers to the inventor, Gaspard de Prony)
“Drawbar horsepower,” used in railroad applications
“Air horsepower,” used in fan calculations.
Some types of horsepower define power at different magnitudes. Listing them in terms of relationship to the standard horsepower, we see:

Definition Watts ft-lbf/min
Horsepower (also called “standard” or “mechanical”) 745.7 33,000
Boiler horsepower 9,809.5 434,107
Electric horsepower 746 33,013.3
Metric horsepower 735.499 32,548.6
Water horsepower 746.043 33,015.2

How did we end up with the “horse” in horsepower? The term was coined by James Watt (1736-1819), the British inventor best known for his improved steam engines, who used the term to relate steam engine performance to that of horses. At the time horses were the primary energy source for applications ranging from pumping water from mines and turning grinding mill wheels to pulling carts and loads. Although sources differ on exactly how Watt arrived at the number, it’s generally thought that in 1782, he noted how quickly a brewery horse could turn a mill wheel of a certain radius, estimated the amount of force the horse needed to exert to turn the wheel, did the math, and came up with a value of 32,400 ft-lbf/min, later rounded to 33,000 ft-lbf/min. Comparing the power output of a steam engine to an equivalent number of horses was an easy way for prospective engine purchasers to compare power ratings, so the term stuck.

What type of horse was a brewery horse? In England at the time a work horse most likely would have been one of the three British "heavy breeds" – the Suffolk punch, the shire horse, and the Clydesdale. The Clydesdale is said to have originated in the latter 1700s, perhaps too late to be a common work horse at the time Watt was doing his horsepower calculations. So it seems likely the horse in question was either a Suffolk punch or a shire horse.

Now let’s talk torque. Torque is turning force, which for automotive applications is most often measured in either foot-pounds (ft-lbf) or Newton-meters (N-m). Sometimes these are written as lbf-ft or m-N, a convention some use to differentiate torque from work, since they involve the same units . . . but I digress.

Here's a simple way to visualize torque: Imagine holding a 1-pound weight straight out, with your arm parallel to the ground. My arm measures about two feet from shoulder to wrist. If I hold a 1-pound weight straight out, the torque my shoulder experiences is roughly 2 foot-pounds (2 feet times 1 pound). If I were to hold a 10 pound weight in my hand, then the torque on my shoulder would be roughly 20 foot-pounds (2 feet times 10 pounds).

Now think of this turning force applied to a wheel, such as if a lever was attached to the center of an automobile wheel. The more force you apply on that lever, the more torque you apply to the wheel, the more readily the wheel turns, and the faster the car starts moving. See where I’m going with this? Torque is a measure of the ability of an engine to do work. It's a component of, but not the same as, the (horse) power of the engine, which is the rate at which work can be done. In an automotive engine, power and torque are related by a simple equation that considers torque, engine speed (in revolutions per minute), and a conversion factor:



In this equation, torque is expressed in terms of ft-lbf, the engine speed is given in revolutions per minute, and 5252 is a conversion constant. An engine's horsepower, then, isn't constant, but rather varies with its speed. The numbers you see quoted in brochures and so on indicate peak horsepower. Such figures can be misleading, as we shall now see.

Let’s say we're trying to decide between Engine A and Engine B for a high-performance car. Here's a chart showing the peak power and torque for each engine:

Power, hp Torque, ft-lbf
Engine A 224 300

Engine B 247 210

At first glance, Engine B looks like the better choice – it has 23 more peak horsepower! However, now let's look at a graph of the power curves of these two engines, showing their power as a function of engine speed.



Notice that although Engine B has more peak horsepower, Engine A has more power at speeds up to 5500 rpm. What's more, it has significantly more power in the 1500-4000 rpm range (highlighted area), the range of engine speeds in which you'd typically operate a car.

Now let's look at the torque curves of the two engines:



We see that Engine A puts out much greater torque, especially over the typical engine speed range, indicating that under normal conditions Engine A will give you much more “oomph” than Engine B. Peak numbers are nice to brag about but often don't mean much, since few people operate their engines at peak conditions (which would generally be full throttle) in a typical day.

I'm oversimplifying things with this example, as many other factors come into play when selecting an engine, such as fuel efficiency, emissions, weight, cost, etc. Depending on circumstances, a performance enthusiast or racer might opt for Engine B, especially if she can mate it with transmission gearing that will take advantage of the power available at high engine speeds. But how many of us are shopping for that kind of performance when we head down to the dealership for the ritual shakedown known as buying a new car?
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#129663 - 8th Dec 2005 2:33pm Re: the great power debate
StuyMac Offline

Wiki Master

Registered: 24th Nov 2003
Posts: 12002
Loc: Wirralshire
But in answer to your question, Power - bhp, makes your car go faster.

Torque is how much force is developed making that power.
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#129664 - 8th Dec 2005 3:06pm Re: the great power debate
Cali_16v Offline
Wiki Guide

Registered: 17th May 2004
Posts: 6261
Loc: Birkenhead
Are those figures taken from the vauxhall redtop engine and the later ecotec engine cos they produce that sort of power.
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#129665 - 8th Dec 2005 3:17pm Re: the great power debate
scoop Offline
Wiki Addict

Registered: 18th Nov 2004
Posts: 7238
Loc: Leuchars
I dont think so daz.Thats an awful lot of torque there,also ive never seen a torque graph that curved. That helps stuy but doesnt really answer the question

Assuming both cars are identical,ie/ 3 door white escorts with no additional weight and the same wheels,tires and driver

What would win in races,0-60s,1/4 miles etc.I believe it will be the one with more BHP, the torque is only 6 less and the power over 12 more BHP.Yes u have to stir the gears to use all that power but thats the idea

Quote from stuys essay

"a performance enthusiast or racer might opt for Engine B" Thats me
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#129666 - 8th Dec 2005 3:26pm Re: the great power debate
StuyMac Offline

Wiki Master

Registered: 24th Nov 2003
Posts: 12002
Loc: Wirralshire
Well, have a look at this thread wink

.....torque v power.
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#129667 - 8th Dec 2005 3:28pm Re: the great power debate
scoop Offline
Wiki Addict

Registered: 18th Nov 2004
Posts: 7238
Loc: Leuchars
So the all power no torque jap beast wins the all torque no power bavarian beast. Or is the NSXR mega powerful and shud be ashamed of the fact it was nearly beaten?
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#129668 - 8th Dec 2005 3:34pm Re: the great power debate
StuyMac Offline

Wiki Master

Registered: 24th Nov 2003
Posts: 12002
Loc: Wirralshire
I would hardly call 0.2 of a sec beaten - pipped maybe.

Also consider, the NSX is the race suspension, lightweight, "special" model.

The BMW is a lardy, executive, oil burning, tank eek
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#129669 - 8th Dec 2005 3:47pm Re: the great power debate
scoop Offline
Wiki Addict

Registered: 18th Nov 2004
Posts: 7238
Loc: Leuchars
Well said BMW is faster than these (amongst others)


Ford Focus RS - 1.32.2

Lotus Esprit V8 - 1.32.5

Audi TT V6 - 1.32.7

MG ZT - 1.33

Noble - 1.33.1

Mercedes SL 55 AMG - 1.33.2

Volkswagen Golf R32 - 1.33.2

Cadillac CTS-V - 1.33.3

Holden Monaro - 1.33.9

Ford Focus ST - 1.34.9

Volvo S60R - 1.35.0

Ferrari 575 - 1.35.2

Alfa 147 GTA - 1.35.6

but slower than these(amongst others)

Subaru Impreza STI - 1.30.1

Aston Martin DB7 GT - 1.30.4

Vauxhall Monaro VXR - 1.30.16

Audi S4 - 1.30.9

Porsche 911 turbo - 1.31.0

Vauxhall VX 220 turbo - 1.31.3

So its still really confusing

I reckon u shud write in stuy,ask them if they'll entertain you and let the stig take ur car roud,i reckon itll do quiet well
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#129670 - 8th Dec 2005 3:49pm Re: the great power debate
StuyMac Offline

Wiki Master

Registered: 24th Nov 2003
Posts: 12002
Loc: Wirralshire
.....the BMW does have 560Nm of torque though wink

Its quite hard to explain the difference between power and torque, so the best is prolly an example.

Take a Vtec Honda and Skoda Fabia VRS - the Diesel.

Honda 160bhp, but no torque, and the Fabia 150bhp but loads of torque.

The Fabia will pin you in the seat more than the Honda, and maybe give a more urgent feel to the car, where as the Honda wont give the same Force you to the back of the seat feel, but the speedo will still climb nicely once the revs start getting up.

Ideally a good match of power and Torque is ideal wink
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#129671 - 8th Dec 2005 4:04pm Re: the great power debate
dikky5 Offline
Wise One

Registered: 11th Jul 2004
Posts: 869
Loc: Pensby
torque is brilliant. bm has 226 pounds o torque ish an 171ish bhp. big flat 6 means power is all ova the range n throttle response is gr8 (aint it chewy). whereas drivin vtec (notoriously high bhp 4 engine size) powered 1.6 honda civic type s was poo tother week. type s has 110bhp yet lack o torque meant u had 2 b scewin it 2 even move. i say by big or go turbo
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#129672 - 8th Dec 2005 5:40pm Re: the great power debate
Sanchez Offline

Wiki Veteran

Registered: 17th Dec 2003
Posts: 8019
Loc: my house
nah, go yap, my 1.8 pulled like stink in any gear, honda s vetec rules, its a shame that every one gets jealious of it and refers to turbos, can t other car manufacturas invent some thing new ????? ( like honda did)
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#129673 - 9th Dec 2005 8:52am Re: the great power debate
StuyMac Offline

Wiki Master

Registered: 24th Nov 2003
Posts: 12002
Loc: Wirralshire
Quote:
Originally posted by sanchez:
can t other car manufacturas invent some thing new ????? ( like honda did)
Nissan where using variable valve timing on their original Skylines in the 60's eek

Honda have just perfected it to suit their needs, as they require their engines to rev due to the lack of torque.
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#129674 - 9th Dec 2005 12:42pm Re: the great power debate
scoop Offline
Wiki Addict

Registered: 18th Nov 2004
Posts: 7238
Loc: Leuchars
It is beacause they rev that they have the lack of torque,everything is set-up for high revs on the VTECs. Remember Torque=(Max power/Peak power RPM) x 5250

A 150BHP car that peaks BHP before 5250 will have more torque than power.a 150BHP car that peaks after 5250 will have less torque than power
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