I'm struggling to understand what these terms mean

Whats the difference between Horse Power (HP) and BHP, please?

What exactly is torque, please?

Whats the correlation between Torque and Hp / Bhp, please?

Any help would be appreciated, Chris

1 - 20 of 27 Posts

I'm struggling to understand what these terms mean

Whats the difference between Horse Power (HP) and BHP, please?

What exactly is torque, please?

Whats the correlation between Torque and Hp / Bhp, please?

Any help would be appreciated, Chris

1 HP = 550 foot pounds/sec or 33000 ft. lb./min.

Torque is the "twisting force" measured in ft. lb. (or Nm)

It's the same measurement as used in doing up nuts and bolts. 80 ft. lb. is an 80lb load hanging on a 1 ft long spanner, or a 40 lb load hanging on a 2 ft long spanner.

So to get horsepower you take the torque and multiply by the engine speed.Then modify with a constant to get the units right. HP = torque x rpm/5250

BHP = brake horsepower and is really the same but describes how the hp of the engine has been measured (using a "brake" a kind of dynomometer).

Ok with you so farOriginally posted by sgould:

[qb]So to get horsepower you take the torque and multiply by the engine speed.Then modify with a constant to get the units right. HP = torque x rpm/5250 [/qb][/b]

So if an engine upgrade increases the hp but NOT the torque, is the power more available at higher or lower rpm then?

rpm = (hp x 5250) / torque

Is that right?

If so then the rpm must increase if the hp has increased and the torque remained the same. Therefore the extra power is a little further up the rev range............am I getting this?

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If the torque remains constant at higher revs you can increase the engine output by allowing it to rev higher. e.g. Using Wills equation above, if a car has 200lbft of torque at 6000rpm and the limiter is around 6250rpm, then the power output would be 228.6HP. If you then modified the engine/ECU to allow the engine to rev to 7000rpm whilst maintaining the peak torque of 200lbft then peak power would be 266.7HP.Originally posted by Cosmic Blue 9-5:

[qb]Using the equation;

rpm = (hp x 5250) / torque

Is that right? [/qb][/b]

Hope that makes sense. On turbo cars it's easier to improve power output by either increasing peak torque or "widening" the torque band so you have more torque at high revs, this is done by increasing boost pressure and fuel delivery.

Yep that makes sense so is the extra power available only at higher revs then?Originally posted by Jason (Mr Torque-Steer): [qb]Hope that makes sense. [/qb][/b]

Lets say the torque is 340nm and the current hp is 205. The upgrade moves the hp to 225 but torque stays at 340nm. Is the extra 20hp felt through the rev range or only at the top end?

So the engine may have a peak torque of 200 ft lb at 2000 rpm. HP at 2000 rpm will be only 76 hp.

At 5000 rpm the torque may have fallen to 150 ft lb but the HP will be 143 hp.

At 6000 rpm the torque may have fallen still further to 120 ft. The HP will be 137 hp.

In this case the manufacturer says "my engine produces 143 hp and 200 ft lb of torque".

Now along comes a tuner and plays with the engine or electronics. If he limits the torque to protect the gearbox to 200 ft lb. His engine will produce the same 200 ft. lb. at 2000 rpm with the same 76 hp. But using his "magic" he may still have 180 ft lb at 5000 rpm. In which case his engine will be producing 171 hp.

He may still get 160 ft lb at 6000 rpm when his engine will produce 183 hp.

So he has an engine which will be described as having 200 ft lb of torque and 183 hp (+40 hp).

Yes... if the 340Nm (=250 ft lb) is available all across the rev range. Then you will only get more power at higher revs. 225 hp at 4700 rpm instead of 205 at 4300 rpm in this case (rounding figures at bit).Originally posted by Cosmic Blue 9-5:

[qb]Lets say the torque is 340nm and the current hp is 205. The upgrade moves the hp to 225 but torque stays at 340nm. Is the extra 20hp felt through the rev range or only at the top end? [/qb][/b]

Well thats damn sneeky isnt it!Originally posted by sgould:

[qb]Well most manufacturers and tuners quote peak torque and peak horsepower. They won't both happen at the same engine speed.[/qb][/b]

It would make a better bench mark if the power and torque was quoted at particular rpm to make a like for like comparison.

Unfortunately not. Manufacturers would the design engines to maximise the figures at that point and give you no power anywhere else in the rev range.....Everyone would be in the same cars.Originally posted by Cosmic Blue 9-5:

[qb]It would make a better bench mark if the power and torque was quoted at particular rpm to make a like for like comparison. [/qb][/b]

Cheers Sgould!

Thanks for your input guys, especially sgould

Someone pass me the aspirin!!

A 'D' in maths hasn't helped.

A 'D' in maths hasn't helped.

Hmm a film script perhaps....the title......Lord of the ECU'sOriginally posted by sgould:

[qb]Now along comes a tuner and plays with the engine or electronics.... "using his "magic" [/qb][/b]

Some of you refer to torque as

Thanks

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2,277 Posts

lb/ft is indeed what it says(a torque equivilent to) 1 pound of weight at the end of a lever 1 foot from the pivot point, so 1 pound @ 1 foot.

A nm (newton meter) is 100 grammes at 1 meter.

To save you the maths a nm is therefore 0.72 of 1 lb/ft.

Nick.

PS. Hey is that 1000 posts I see. The wife'll know for sure I'm spending too much time on here!

Thanks and welcome to Club Afficionado

1 kW = 1.36 HP

Best to use metric (Nm and kW) - no confusion at all. And it's all decimal

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1,448 Posts

Depends ... 760 Watts = 1 hp ... so 1 kW should =1.32 hp ... unless you metric folks went and muddled up good ol' Mr. Watt's units. *dares not to think*

Dubbya~

Actually, 746watts = 1hp thereore 1.34 hp = 1 KwOriginally posted by Adrian W:

[qb]"1 kW = 1.36 HP" --- Adam

Depends ... 760 Watts = 1 hp ... so 1 kW should =1.32 hp ... unless you metric folks went and muddled up good ol' Mr. Watt's units. *dares not to think*

Dubbya~ [/qb][/b]

Andrew

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