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Those Complete Power Boosting & Drivetrain Mods..
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By EvoStu
#49004
This is brilliant. This is from the http://www.uk-mkivs.net golf forum.
Someone asked me for a definitive explanation of this and this is it.

It long winded but it's worth it.

Posted by Pottsy from the MKIV forum.

Introduction

I've written this article to explain the differences between measuring BHP (power) and torque, and illustrate the effects of power and torque when comparing petrol and diesel engines.

I'll try and start with the very basics, and build up the technical stuff until you get lost! Don't worry, I'll be using crates of apples soon...

In order to simplify a complicated subject, I've made quite a few broad assumptions, many of which are not entirely true to life, but have been ignored for simplicity.

Background

To most, power dictates how fast a car will go, and torque is something to do with "pulling ability". Well from now on, open your mind and forget what you thought! Torque is in fact the easy bit, power is the stuff of physicians...

What is torque?

Well forget power for the time being. Gasses and stuff are exploded in your engine, and they make a very high pressure above your piston. This pushes the piston down, which then pushes your car along the road. Simple! The amount of push, is torque.

So, double the push (torque) and you accelerate twice as fast!

So, lets look at how much torque a theoretical engine makes at different revs:
Image

Ah! This engine has 250 ft lb torque from 1000 rpm to 4000 rpm. So lets imagine we open it up in third gear, starting at 1000 rpm. We feel a constant push in the back right up to 4000 rpm. That because the amount of torque = amount of acceleration.

Gearboxes

Well it had to get tricky at some stage! Let's do the same as before but in fourth gear. How much acceleration do you feel compared to third? Less. In fact you know you get most acceleration in first gear and least acceleration in sixth. Why??

Well, the engine turns fast and the wheels turn slow. So we have to reduce the speed of the wheels by a gearbox. If you reduce the speed of the wheels to half that of the engine, the torque at the wheels is doubled!

Bit tricky to understand - but you can imagine it. Imagine we attached your engine to a special gearbox, so that when the engine was going at 2000 rpm, the output shaft of the gearbox was turning so slow you could see it turn. Attach a mole grip to that slow turning shaft. Are you going to stop it? No way. In fact could you ever grip it hard enough with any device to stop it? No. That's because the turning force (torque) is very high. Now imagine your engine also at 2000 rpm, but this time connected to another special gearbox with the output shaft turning at a trillion rpm. So fast you think the world is going to end. Now grab the shaft and you could slow it down. There's not much torque there now!

So back to the car. In first gear, the wheels are turning slowly, so there's lots of torque. Great until the engine can rev no more - so we have to select second gear. Now there's less torque at the wheels, and so less acceleration. And so on up the gears. Here it is, visually:

Image

See, loads of go in first, and less as we go up the gears. At some point, the force in our wheels is equal to the wind resistance force, and we can't go any faster. In this graph, it's at about 135 mph. So torque is related to top speed as well as acceleration! Let's use torque forever more!!

So why do we not measure cars by torque alone?

You may have noticed that the car above is a diesel. Lots of torque but only 4000 rpm available. So what, you may say. Well imagine you're having a race against your mate in an identical car, except it's got less torque but the ability to rev to 6000 rpm (i.e. a petrol car).

You both start off in first gear, and you race ahead (you've more torque at the wheels than him).
Then you run out of revs at 4000 and have to change gear into second. Now you've got less torque at the wheels as he continues to race up to 6000 rpm, still in first gear.
But then he has to change gear into second and now has less torque than you and you catch up.
But now you run out of revs and have to change gear, and watch him scream up to 6000 again.
And so on.
Lets look at a picture of the amount of torque (thrust) at the wheels as the two of you drag race:

Image

You are in the purple car (nice choice!) See how after 2.5 seconds, you have to change gear and he (in the blue) has more thrust than you do in second gear.

Damn! Pretty obvious that you need torque and revs! Both are important. The two cars above in fact in a drag race are equally matched. So with torque and revs alone how do we easily compare cars?

The diesel car above has crates of 60 apples. But just 2 crates of them. The petrol car has smaller crates of 40 apples. But it has 3 crates. Yes we want large crates and lots of them!! So we multiply the number of apples in a crate, by the number of crates. Easy. Both cars have 120 apples, and so both are even.

Can you see that we also need to multiply torque by revs ('cos we want lots of both of them too), in exactly the same way to see how much go we have in total? Well guess what:

Apples in a crate x number of crates = Total number of apples.
Torque x revs = Power! Yep, power is the same as number of apples!!

So power tells us, overall, how well the car is going to go. Yippee! Don't try to understand it too much, just remember how I got here and it all makes sense. More power = better performance. But that's by no means the end of the story, and it was based on theoretical cars...

Torque curves

Well, my imaginary diesel (above) had a flat torque curve. So that's equal thrust all through the rev range. In reality a diesel has a low peak torque, which gradually declines as you rev higher:

Image

A petrol car has a torque curve that peaks about 2/3 of the way up the rev range, but it has torque figures that are less all the way along the curve:

Image

This makes sense with what we feel when we drive the cars. The diesel seems to really accelerate well at low revs, then it fades out a bit and then we have to change gear at only 4000 rpm. The petrol car seems to increase in acceleration as we climb up the rev range (though it does fade a bit higher up), and we can keep going all the way to 6000.

So what's the problem? I now know I want power! Well, the problem is this. We only look at peak power. So that's normally right up at the top of the rev range, where we have both lots of revs and still a fair amount of torque. This tells us very little about what happens in the rest of the rev range, where we spend 99% of our time driving.

I think the best way to show what differences there are, is by doing an experiment.

Take one car.

Change nothing except the engines.

Engines are:

Diesel, 190 BHP, with a flat torque curve at 250 ft lb
Petrol, 190 BHP, typical petrol torque curve (193 ft lb at 4500 rpm)
Diesel, (tuning box style) 183 BHP, but with a big torque peak of 291 ft lb at 1900 rpm

Do some performance runs! (Luckily, I have the software to do this for me...)

Image
Image

Drag race: First past the post is the flat torque diesel, with the petrol very close. The peaky torque curve car suffers a bit. Note how the petrol is first to 100, but the diesel is first to do the standing quarter. See how gearboxes muddle the situation horribly?

In-gear acceleration (i.e. overtaking). At low revs, the peaky diesel makes use of the peak. But at high revs the flat torque diesel makes better use of its higher torque figures. In all cases the poor old petrol, that did so well in the drag races, is suffering badly. In fact unrealistically so. Why's this? Well these figures are correct if we did the experiment as I've done it. But in reality manufacturers have to put different gearboxes in diesel cars, simply because the rev ranges of the engines are different.

So if the petrol car changes from second to third gear at 60 mph (at 6000 rpm) then the diesel does too (but at 4000 rpm). To do this the diesel gearbox isn't reducing the wheel speed as much, so the diesel car has less torque than it would have had, if it had had the petrol engine gearbox in! Oh no!!

So we'd better pop in the proper gearboxes and see what happens:

Image

See how the thrust is now very similar between the petrol and flat torque diesel cars?

Now lets do the full analysis, complete with the peaky tuning box style diesel (less power, more torque):

Image
Image

See how there's not much in it? Drag racing times are very similar. In-gear acceleration times are similar at high revs, with the diesel getting the edge at low revs (high gear). The tuning box diesel, with it's high peak torque figure, is slower in a drag race but does a pretty good job at higher speed when the revs are near its torque peak.

Conclusion
Peak power figure is a very good way to compare performance. Both 190 BHP petrol and diesel cars are an even match. This may explain why people have been using power to compare cars for years and years...
In-gear acceleration times are affected enormously by gearbox type. Comparison can only be made if the gearbox and final drive are identical (which they never are).
A 250 ft lb diesel with a flat torque curve goes better than a 291 ft lb diesel with a peaky curve, in most situations.

EvoStu.
Last edited by EvoStu on Sun Jun 15, 2003 6:22 pm, edited 1 time in total.
User avatar
By Plantie
#49014
What a fantastic thread Stu!

Well spotted!

:D
User avatar
By R-type
#49021
nice 1 stu, thats brill
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By Tommo
#49022
I have learned something today, cheers Stu :D
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By johnny74
#49035
what can i say dude


NIIIIIIIIIIIIIIIIIICE!!!!!! :D
User avatar
By EvoStu
#50240
I thought it needed sharing. 8)

Cool eh?

EvoStu.
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By bad boy
#51294
Nice explanation :P . My colleagues think I'm a complete anorak though ! :oops:
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By Tarzi
#90445
This was cool. I learned something new... 8)
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By The Rabbi
#94891
ive just had a look at this and this is quite fantastic!.. now to get my new civic to over 200lb/ft!!
User avatar
By Trung
#98224
Can someone provide me the torque figures and HP at the wheels of a standard CTR?
User avatar
By sonnyredline
#215099
And here's another version (albeit with less detail and dealing with the basics!) :wink:


The term horsepower was invented by the engineer James Watt. Watt lived from 1736 to 1819 and is most famous for his work on improving the performance of steam engines. We are also reminded of him every day when we talk about 60-watt light bulbs.

The story goes that Watt was working with ponies lifting coal at a coal mine, and he wanted a way to talk about the power available from one of these animals. He found that, on average, a mine pony could do 22,000 foot-pounds of work in a minute. He then increased that number by 50 percent and pegged the measurement of horsepower at 33,000 foot-pounds of work in one minute. It is that arbitrary unit of measure that has made its way down through the centuries and now appears on your car, your lawn mower, your chain saw and even in some cases your vacuum cleaner!

What horsepower means is this: In Watt's judgement, one horse can do 33,000 foot-pounds of work every minute. So, imagine a horse raising coal out of a coal mine as shown above. A horse exerting 1 horsepower can raise 330 pounds of coal 100 feet in a minute, or 33 pounds of coal 1,000 feet in one minute, or 1,000 pounds 33 feet in one minute. You can make up whatever combination of feet and pounds you like. As long as the product is 33,000 foot-pounds in one minute, you have a horsepower.

You can probably imagine that you would not want to load 33,000 pounds of coal in the bucket and ask the horse to move it 1 foot in a minute because the horse couldn't budge that big a load. You can probably also imagine that you would not want to put 1 pound of coal in the bucket and ask the horse to run 33,000 feet in one minute, since that translates into 375 miles per hour and horses can't run that fast.

Horsepower can be converted into other units as well.
For example:

1 horsepower is equivalent to 746 watts. So if you took a 1-horsepower horse and put it on a treadmill, it could operate a generator producing a continuous 746 watts.

1 horsepower (over the course of an hour) is equivalent to 2,545 BTU (British thermal units). If you took that 746 watts and ran it through an electric heater for an hour, it would produce 2,545 BTU (where a BTU is the amount of energy needed to raise the temperature of 1 pound of water 1 degree F).
One BTU is equal to 1,055 joules, or 252 gram-calories or 0.252 food Calories. Presumably, a horse producing 1 horsepower would burn 641 Calories in one hour if it were 100-percent efficient.


Measuring Horsepower

If you want to know the horsepower of an engine, you hook the engine up to a dynamometer. A dynamometer places a load on the engine and measures the amount of power that the engine can produce against the load.

Torque

Imagine that you have a big socket wrench with a 2-foot-long handle on it, and you apply 50 pounds of force to that 2-foot handle. What you are doing is applying a torque, or turning force, of 100 pound-feet (50 pounds to a 2-foot-long handle) to the bolt. You could get the same 100 pound-feet of torque by applying 1 pound of force to the end of a 100-foot handle or 100 pounds of force to a 1-foot handle.
Similarly, if you attach a shaft to an engine, the engine can apply torque to the shaft. A dynamometer measures this torque. You can easily convert torque to horsepower by multiplying torque by rpm/5,252.

You can get an idea of how a dynamometer works in the following way: Imagine that you turn on a car engine, put it in neutral and floor it. The engine would run so fast it would explode. That's no good, so on a dynamometer you apply a load to the floored engine and measure the load the engine can handle at different engine speeds. You might hook an engine to a dynamometer, floor it and use the dynamometer to apply enough of a load to the engine to keep it at, say, 7,000 rpm. You record how much load the engine can handle. Then you apply additional load to knock the engine speed down to 6,500 rpm and record the load there. Then you apply additional load to get it down to 6,000 rpm, and so on. You can do the same thing starting down at 500 or 1,000 rpm and working your way up. What dynamometers actually measure is torque (in pound-feet), and to convert torque to horsepower you simply multiply torque by rpm/5,252.

If you plot the horsepower versus the rpm values for the engine, what you end up with is a horsepower curve for the engine.
What a graph like this points out is that any engine has a peak horsepower -- an rpm value at which the power available from the engine is at its maximum. An engine also has a peak torque at a specific rpm. You will often see this expressed in a brochure or a review in a magazine as "320 HP @ 6500 rpm, 290 lb-ft torque @ 5000 rpm". When people say an engine has "lots of low-end torque," what they mean is that the peak torque occurs at a fairly low rpm value, like 2,000 or 3,000 rpm.

Another thing you can see from a car's horsepower curve is the place where the engine has maximum power. When you are trying to accelerate quickly, you want to try to keep the engine close to its maximum horsepower point on the curve. That is why you often downshift to accelerate -- by downshifting, you increase engine rpm, which typically moves you closer to the peak horsepower point on the curve. If you want to "launch" your car from a traffic light, you would typically rev the engine to get the engine right at its peak horsepower rpm and then release the clutch to dump maximum power to the tyres.


How do you convert engine torque to horsepower?

Have you ever looked at the specs of an engine in a magazine and seen something like "this engine makes 300 pound-feet of torque at 4,000 RPM," and wondered how much power that was? How much horsepower are we talking about here? You can calculate how many foot-pounds of horsepower this engine produces using a common equation:

(Torque x Engine speed) / 5,252 = Horsepower
The engine that makes 300 pound-feet of torque at 4,000 RPM produces [(300 x 4,000) / 5,252] 228 horsepower at 4,000 RPM. But where does the number 5,252 come from?

To get from pound-feet of torque to horsepower, you need to go through a few conversions. The number 5,252 is the result of lumping several different conversion factors together into one number.

First, 1 horsepower is defined as 550 foot-pounds per second. The units of torque are pound-feet. So to get from torque to horsepower, you need the "per second" term. You get that by multiplying the torque by the engine speed.

But engine speed is normally referred to in revolutions per minute (RPM). Since we want a "per second," we need to convert RPMs to "something per second." The seconds are easy -- we just divide by 60 to get from minutes to seconds. Now what we need is a dimensionless unit for revolutions: a radian. A radian is actually a ratio of the length of an arc divided by the length of a radius, so the units of length cancel out and you're left with a dimensionless measure.

You can think of a revolution as a measurement of an angle. One revolution is 360 degrees of a circle. Since the circumference of a circle is (2 x pi x radius), there are 2-pi radians in a revolution. To convert revolutions per minute to radians per second, you multiply RPM by (2-pi/60), which equals 0.10472 radians per second. This gives us the "per second" we need to calculate horsepower.

Let's put this all together. We need to get to horsepower, which is 550 foot-pounds per second, using torque (pound-feet) and engine speed (RPM). If we divide the 550 foot-pounds by the 0.10472 radians per second (engine speed), we get 550/0.10472, which equals 5,252.

So if you multiply torque (in pound-feet) by engine speed (in RPM) and divide the product by 5,252, RPM is converted to "radians per second" and you can get from torque to horsepower -- from "pound-feet" to "foot-pounds per second."
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By mr cyanide
#343948
Very nice indeed, learnt a bit more my fionsea thinks im sad now though :roll: , is there anyway of getting the CTR up to about 220-240 ft lbs of torque without using forced induction??
#1619537
Wow what a great thread, it really puts it all into perspective and makes it simple for anyone to understand. Been trying to explain this to me Fiancé for a long long time, going just print this out instead :wink:

Dave
#2693137
good thread, maybe someone cleverer than me can use this to show how a Rotrex and jrsc compare.

it's always been my opinion that the Rotrex compliments the k20 and the jackson is kinda working against it.

the simple way i have always thought of it is......

Torque = size of an explosion
RPM = how many explosions happen in a minute
horsepower = the total damage done by these explosions.

good info, cheers

Long time ago I had and Ep3 for 220k kilometers in[…]