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Discussion Starter · #1 ·
Morning all,

ive just done my first lab experiment at uni which was a fueling test for a vauxhUL 2.2L ecotech on part and full throttle. Sorry not my fault, they dont have RB's :)

any ho getting to the point, I have got my head around BSFC, BMEP and the merits of diesels but I am still struggling to get my head around the following:

Why does peak power occur at higher rpm than peak torque

If someone can provide a good link to a website that would be great.

I know this isnt a skyline question but I am sure im not the only person who wants to know :)

cheers
 

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Power = torque x rpm (or even 'torques per second'); torque is a turning force caused by the piston pushing down on the crank which turns this downwards force into a turning force.

As the rpm increases, it happens more, so there's more power. Sadly, as the rpm increases the efficiency decreases hence less torque. But, as it happens more often, power continues to rise. Up until a point where even though you're getting more 'torques per second', the lack of torque means power starts to decrease.

It's a common misconception to think that torque and power are separate.

Anyway, I'm sure these two links will explain it better than I can right now: :D

Clicky Part 1

Clicky Part 2
 

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As above, but

HP = (rpm x torque)/5252

5252 (rpm) is also usually where you will seen torque & horsepower cross on a dyno chart.
 

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If your familiar with power = force x distance moved per unit time then its easy to visualise what torque and power mean to each other.

Torque is a measure of rotational force and rpm can be thought of as a rotational distance moved per unit time (per minute).

Think of a man turning a massive water wheel (perfect with no friction) by hand. He can be pushing it really hard with the brake on and it wont move. Ie he's exerting a force on it (torque) but its not generating any power. Now remove the brake and let it move, he exerts the same force but now we get power. Torque is a static (force) concept whilst power involves movement. In an engine the man is replaced by pistons and the wheel by the crank but its much the same concept.
 

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As above, but

HP = (rpm x torque)/5252

5252 (rpm) is also usually where you will seen torque & horsepower cross on a dyno chart.
Okay, I should've said power = torque x rpm x K (where K is a constant). As it's a constant it can be ignored to conceptualise. :D
 

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Discussion Starter · #6 ·
Wicked. Thank you very much, you all explained it very well i.e. in idiot speak so my head doesnt hurt to much.

The 2 articles are very good as well so I actually get it now.

ps if I don't get a 1st on this i'm blaming you lot :p
 

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...ps if I don't get a 1st on this i'm blaming you lot :p
Fair enough, but we'll claim 10% of your earnings when you start work for the first year if you do get a 1st! :D
 

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In this equation, what unit is torque measured at?
Nm or pound foot??
lbft.

i assume your asking to relate to the crossing point on a graph at 5252, in which it must be in bhp (power) and ftlb (torgue)

kev

whilst we're here could someone explain the difference between hp and bhp please.

???
 

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whilst we're here could someone explain the difference between hp and bhp please.???
hp is horsepower, but bhp is brake horsepower, which is horsepower measured at the engine... horsepower by itself does not make reference to where it is measured from.
Awhp, or rwhp is horsepower referenced power at the wheels, which has losses such as drivetrain etc to make it lower than bhp figures
 

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bhp isn't necessarily at the engine (flywheel) it can be at the wheels, or the hubs etc.; it's a way of measuring hp, using a brake essentially (against the dyno rollers).

See the 'Dyno Operation' bit of this article (I do like AutoSpeed): http://autospeed.com/A_107757/cms/article.html
 

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ok ru' so bhp is just hp measured by means of creating load then holding that load with a 'brake'. so a bit like 'returning load' or 'resistance'.

i assume the chassis dyno that we see at our tuning shop uses the eddy current method?

thanks mate.

i really like the idea of a 'physics' or 'maths' disscusion area on the board.

kev
 

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Torque the the rotational force produced, and Power is the amount of energy (KW) produced.

Alot of people don't like high rpm low torque engines... just rev is higher like its _designed_ for, no problems.

EDIT: and it occurs at higher RPM because of the measurements used, and the scales used. Remember the UNITS are different.
 
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