Email this page to a friend!   Click here to bookmark this site!

TORQUE AND POWER

What does it mean to you?
Horsepower History Lesson

Torque explained
Brake Horsepower explained
Conversions

Torque and Power are fundamental terms that describe aspects of every engine’s characteristics and performance. Most people are familiar with the words and many are comfortable with their understanding of them. It is tempting to simplify the descriptions into easy to remember phrases such as “Torque is Grunt” or “Power is what you buy and Torque is what you ride”, but it is worth spending a few minutes really understanding what it’s all about.

Here at DaiGwy we make no apology for using Horsepower for our Power curves and Pounds-Feet for the Torque curves. (Torque is often referred to in Foot-Pounds.) The reason is simple – over 200 years of engineering history that link us to the very beginning of the industrial revolution.

 

What does it mean to you?

Understanding the characteristics of your engine will help you to ride it to the best of its abilities. The Peak Torque rpm is the point at which the motor is operating at maximum efficiency and gives maximum acceleration. So for quick, smooth overtaking you want the motor to be at or just below this point of the rev range.

Ideally an engine will have a flat Torque profile across the rev range but in practice the Torque profile will generally rise to a peak about 60% to 70% of the way up the rev range. Here the engine is operating most efficiently and economically. Then the Torque declines as the efficiency falls to the engines redline or rev limit. By keeping the revs in the range where the Torque is above 90% of Peak Torque you will have a responsive motor that is working efficiently and economically.

Operating in the rev zone between Peak Torque and Peak Power is where you ideally want to be for maximum engine response and fun. The Torque is high for good acceleration and the Power is climbing rapidly to its peak giving the rider that arm-straightening pull towards the horizon. This is classic sportsbike territory and is where any bike out on the open road can be enjoyed to it’s full potential.

On today’s congested roads it is very important to take care out there. Most modern bikes are now so powerful and with ever increasing speed restrictions it can be difficult to really practice getting the best out of a modern superbike. In recent years we have seen a huge growth in riders taking advantage of race training schools and track days. Here you can really practice getting the most out of your motor in safety and with good advice on riding techniques too.

Look up the figures for your model on our ‘Technical Data’ page and adjust your riding and gear selection to keep the motor in your ‘Sweet Zone’ and you’ll be in for miles of smiles.

DaiGwy models available are listed in the ‘Manufacturers’ pages for you to buy or order as a gift.

BACK TO TOP

Horsepower History Lesson

Back in the 18th century the world was a very different place. Horses were used to perform all kinds of tasks from ploughing fields to pulling stagecoaches. Steam engines had been invented but were not widely used and were rather crude in their design and construction. In 1736 James Watt was born. As a boy he took an interest in the steam coming from the spout of a kettle and began to experiment with simple devices powered by steam. By the age of 33, in 1769, this brilliant Scottish Engineer was ready to revolutionise the world with a new patent “New method of lessening the consumption of steam and fuel in fire engines”. He had solved the problems of early “Fire Engines” that lost steam at the end of each stroke by introducing a condenser to recycle the steam rather than lose it. This, along with other improvements such as double acting pistons that provided power on each stroke, was the giant step needed to make steam engines viable for industrial applications. James Watt also patented five ways to turn the reciprocating motion of a piston into rotary motion to drive looms, lathes, cable-drums and hoists.

The Industrial Revolution had begun.

As in today’s world his contemporaries would probably have said “Nice engine James, What’ll it do? How fast does it go?” and “How can you prove it’s better?”

James Watt set to work devising a way of measuring the amount of Work that his engines could do. The obvious benchmark was the horse, or more specifically the Draft Horse that was the ‘industry standard’ of the time.

Using a hoist, he conducted experiments to determine how quickly a Draft Horse could raise a heavy load. He observed that a load of 550 Pounds (nearly ¼ of a ton) could be raised at a rate of 1 foot per second. That’s 550 foot-pounds per second of work done. Multiply by 60 and that is 33,000 foot-pounds per minute of work or 1 Horsepower (1 HP).

So - Horsepower is a measure of the engines rate of work i.e. how much work in a given time. The higher the horsepower the more work it can do or the faster it can do it.
Simple really.

BACK TO TOP

Torque explained

Torque is commonly used to describe the twisting force required when tightening a nut or bolt to ensure it is not over tightened. Torque is simply the twisting force around a point, described as a force at a distance. In our case the force is one Pound at a distance of one Foot hence the basic Torque unit of 1 Pound-Foot (1 lb.ft.).

For an engine, the Torque is a measure the force the pistons are exerting to turn the crank and the point of maximum Torque is where the engine can produce the most turning force and is therefore operating at maximum efficiency. This is the important point to remember since engines are very complex machines where many parts and systems contribute to the overall efficiency. We will examine some of these in the ‘Engine Tuning’ page.

To complete the picture it is important to understand the relationship between Torque and Power and this is done by looking at the work done by the engine.

Work is equal to the force applied multiplied by the distance travelled. In equation form

Work = Force x Distance

For our basic Torque unit, if the Force is 1 Pound on a crank (radius) of 1 Foot then in one revolution of the crank the force moves a distance (circumference) of 6.2832 feet. So the Work done = 1 x 6.2832 = 6.2832 ft.lb. of work. (Note: Units for work are ft.lb.)

Earlier we saw 1 Horsepower equals 33,000 lf.ft. per minute so to produce 1 HP our crank will need to rotate 5252 times. (That’s 33,000 divided by 6.2832.). So 1 ft.lb. of work at 5252 rpm = 33,000 ft.lb. of total work = 1 Horsepower.

From this we derive the equation for Horsepower calculation

   
(Torque x RPM)
Horsepower
=
---------------------
   
5252

From this equation we can see that Torque will always be higher than Horsepower below 5252 rpm, then Horsepower will be higher. Torque will equal Horsepower at 5252 rpm.

BACK TO TOP

Brake Horsepower explained

Engine Torque is measured using a dynamometer, often referred to as a ‘Dyno’
Typically measurements are taken in one of two places, at the crank or at the back wheel.

At the crank, ‘Loading’ Dynamometers use a friction brake to act against the Torque produced by the engine. By measuring the forces at the friction brake an accurate measure of the torque is determined. As we have seen above it is then a simple calculation to produce a ‘Brake Horsepower’ figure. These types are generally used by manufacturers and race teams to set up bikes for optimal performance in the racing rev range under ‘steady state’ conditions.

Measurements taken directly from the crank are always higher and provide the best indication of the torque being produced by the motor across the rev range. For this reason manufacturers develop engines using this figure to determine the best set up for the engine to produce the Torque and Power characteristics they are seeking. The result is usually a ‘claimed’ horsepower figure in the marketing literature produced.
Where this is technically accurate is can be very misleading.

The problem comes down to Mechanical Efficiency, sometimes referred to as ‘Drive Chain Losses’. From the crank to the back wheel a large number of things need to happen and all along they cause a loss of power.
The oil needs to be pumped to lubricate the engine and gearbox.
Coolant also needs to be pumped to cool the engine.
The alternator needs to be driven to provide electrical power.
The gearbox needs to be driven as does the final drive to the back wheel.
All through the drive chain heat is generated compounding the losses further.
The result is a lower figure measured at the back wheel. However, this is really the ‘true’ figure of the useable power produced by the bike.

To measure the rear wheel horsepower is relatively simple using a ‘Rolling Road’ Dyno. Recent years have seen an explosion of these in performance tuners and many dealer workshops. The motorcycle is strapped down with the rear wheel resting on two rollers of the rolling road. The motor is started and 'ridden' by the tester through the gears until top gear is reached. The Dyno run commences usually at about 3,000rpm accelerating hard up to the red line or rev limiter.

‘Rolling Road’ Dynos measure the acceleration of the rollers from a low speed to a high speed in a given time. The mass of the rollers is known so the acceleration is directly related to the rear wheel Torque that is turning the roller and therefore the Brake Horsepower of the engine. The resulting graphs show a Power curve and Torque curve record of the engine’s performance.

It is these curves we use at DaiGwy to produce our unique ‘Engine Art’ range for each motorcycle model.

To find the DaiGwy model for your bike go to the ‘Manufacturers’ page.

BACK TO TOP

Conversions

Power and Torque figures are sometimes quoted in units other than bhp and ft.lb.

Here are a few conversion factors you may find useful.

Power
1 BHP = 0.7457 kW = 550 lb.ft/s = 76.04 kg.m/s= 2,545 BTU/hr
1 kW = 1.341 HP
1 PS = 0.9863 bhp = 75 kgm/s

Torque
1 ft.lb. = 0.138 kg.m
1 kg.m = 7.233 lb.ft. = 9.8 N.m
1 N.m = 0.102 kg.m = 0.738 lb.ft.

Fax / Post / On-Line ordering – go to the Manufacturers pages, make your selection and off you go!

BACK TO TOP

 

HOME | TORQUE & POWER | TUNING | TECHNICAL DATA | VISIT US
DAIGWY VMAX | A BIT OF FUN | SHOPPING CART | CONTACT US
LINKS | NEWS | EMAIL A FRIEND

site © iResolutions.co.uk 2003