PDA

View Full Version : torque vs power



DAN THE MAN
03-11-2006, 09:14 PM
just a scenario

2 cars, same gearing, weight, everything. EXCEPT

one has 250bhp and 150LB FT

one has 150bhp and 250LB FT

which would win in a stright drag??

flat road say...

leavingeasy
03-11-2006, 10:08 PM
Well i reckon the first one is an R500 evo and the second is an Audi 2.5 TDi.

Dead heat then.

In a straight drag I reckon power would win over torque. But cant prove it.

Tony
03-11-2006, 10:50 PM
Ultimately power will win when taking the engine to the redline. However, do not dismiss torque in day to day driving. When my wife still had her 330d you would be amazed how hard I had to drive the M3 just to keep up......... and she wasn't ragging it :whistle:

T

Pooky
04-11-2006, 08:13 AM
Power = torque x revs so it all depends on what part of the rev range the torque is generated.

Andrew
04-11-2006, 09:03 AM
This is always a tough one to prove. But around a track, my old Fabia vRS [160 WHP and 300W lb/ft + 1215kg with no driver] was tagging along with caged 200hp Clio Cups and 260hp Mini Cooper S's. In a 1/4 drag on the same day [hot engine/tyres] i did a 6.6 0-60 and 15 second 1/4 mile. I needed 3 gears to 60mph and 4 to 1/4 at just over 90mph. Relative to it's power it was boxing above it's weight.

Steven
04-11-2006, 02:32 PM
Torque gives flexibility, power gives outright speed.

E.g. Integar Type-R. You have to drive it hard to get the excellent performance, if you don't, it's actually not a quick car at all.

DAN THE MAN
05-11-2006, 09:20 AM
well true but ANY car not driven HARD is not a quick car( ok veyrons excluded :D )

and revs would come into it ill agree

Must be a certain pint where is more needed than the other

MACCA F1 has more power to weight then a VEYRON but the veyron will kill it due to its phenominal torque (plus it aint short of power either)

Hmm..u cant have one without the other <_<

DanST
05-11-2006, 02:23 PM
power or bhp is a calculation of torque and revs.

id rather have a happy medium, but then revs are fantastic and utilse gearing so much better... just ask the biker boys.

Tony
05-11-2006, 10:13 PM
Originally posted by DanST@Nov 5 2006, 04:23 PM
I&#39;d rather have a happy medium, but then revs are fantastic and utilse gearing so much better... just ask the biker boys.
True, but if you have decent torque-to-weight then you can use longer gearing to really make use of an &#39;extended&#39; rev range. Look at the latest 500bhp Shelby Mustang. The s/c V8 allows the car to pull 75mph in first and still do a 0-60 in mid 4&#39;s. That&#39;s like trying to pull away in third in most cars :blink:

Race cars (and V-tecs) are tuned to give great power right at the top of the rev range, which is great if you are on a circuit as you will always be ragging the engine close to the redline. For every day driving this is not much use - indeed it was the reason why I got rid of my CRX Vtec many years ago and why I wouldn&#39;t buy a CTR or ITR now (sorry Dan ;) ) as it was great if you were &#39;on one&#39; but tiresome if you just wanted to go into town. For everyday driving you need a bit of both which will usually mean forced induction or larger capacity. It&#39;s why I personally love M engines as they have sufficient torque for daily use, yet retain the top end kick of a vtec type engine for when you want to have fun :thumb:

T

Pistonhead78
06-11-2006, 10:08 AM
id say the one with the torque would pull faster but torque only realy works for a lil bit where as power would kick ass for the last 75% of the race

pete_rallye
06-11-2006, 06:45 PM
Theres a good explanation of power and torque in this months evo. As I can see, power is useful for getting of the line and giving it a good thrashing, but torque really comes into it&#39;s own on big hills, for top speed etc, where it is the torque that really pulls the car along...

Gary Kinghorn
06-11-2006, 06:46 PM
Torque is a rotational force ......

Dave Evans
06-11-2006, 08:01 PM
The one with more power will definitely win.

Hill or flat makes no difference.

As Gary says, torque is the measure of rotational force, ie how hard the gearbox *input* shaft is being twisted. Without also knowing the RPM/gearing (and therefor power) this doesn&#39;t tell you anything about what torque *at the wheels* is achievable, and thats pushes you down the road.

The high torque engine has lower power, so we can infer that it is much lower reving than the high power engine (because power = torque x RPM). This means the GEARING required for a given roadspeed will water the torque down to a much lower figure at the wheels than the high power engine and so acceleration will be less.

Basically the "torquey" engine will be slogging along in 4th trying to match the "screamer" which will have the revs to be able to use 3rd or even 2nd at the same roadspeed. Think about how much better your acceleration is when you shift down a gear or two and you get the idea.

If the cars both start from 0 then the torquey car will make a better getaway as its power comes in lower in the revs but it will need to shift early and the power car will stay in 1st longer and quickly catch up. Once the power car is shifting in the upper revs it will walk away.

Dave Evans
06-11-2006, 09:16 PM
Just to fill in the picture for the example given in the first post look at the probable rpm range of each engine:

For simplicity lets initally assume that both engines have power rising steadily through the revs & make max power exactly at redline (not usually true but good enough to make the point).

In this case the power engine would rev to:

(250bhp / 150lbft) * 5252 = 8750 rpm.


And the torquey engine would redline at:

(150bhp / 250lbft) * 5252 = 3150 rpm


So the power engine looks a lot like a Honda S2000, and the torquey engine looks a lot like a marine diesel. Which would you rather drive? In most engines peak torque is normally delivered lower in the rev range than peak power, so the redline for these as real world engines would probably be more like 9000 and 3500. Obviously the power engine would be able to use a much lower gear for a given roadspeed and its torque at the wheels would be far better. Big torque figures may look impressive but they are kinda meaningless without knowing what rpm the torque is delivered at. When you combine those two things you are really talking about power.

Uncle Benz
16-11-2006, 08:55 PM
Just to add a bit to this..........

http://www.mbclub.co.uk/forums/showthread.php?t=500

The technical content here is pretty good.

Dave Evans
21-11-2006, 09:35 PM
Good explaination there

Talking to a friend who wanted a really simple explaination of the difference between Torque and Power expressly *without any maths* I came up with the following so I thought I&#39;d throw it in here;



Image a drag race, but instead of racing cars over a quarter mile two people each have to fill a skip with coal using a shovel (bear with me...)


Torque is like the size of shovel you can lift.

Engine speed (RPM) is how fast you can move that shovel

Power = how fast you can fill the skip (ie the combination of shovel size and speed)


Obviously Power is what matters most because it shows how fast you can fill the skip and win the race.

Its no good being able to lift a huge shovel if you can only move 20 scoops per minute and your competition can move a shovel half the size 60 times per min.

Simply put, Power is the Rate at which you can get Work done. Either fill the skip, or get to the finish line.




People tend to describe an engine as "having good torque", what they really mean is "having a good spread of low end or mid range power", or flexible power delivery. A massive torque figure is meaningless without knowing what RPM its delivered at.

500 ft.lb sounds good, but if its at 1 RPM that less than a tenth of a horsepower. You&#39;d do better replacing the engine with a chain & bicycle pedals :-)

DAN THE MAN
07-12-2006, 06:30 PM
Just re read this and thanks for the posts ;)

Honda i think get their cars acceleration up by fitting lower gears but as a bigger rev range is still able to do normal speeds for each gear but as lower ratio does help with acceleration.

And just to defend- the new honda engines are actually pretty good at lower revs than the old B series out of CRXs and DC2s. Not phenominal but not bad and respond really well to a new aftermarket ecu- givces so much more low torque yet more MPG :blink:

jf_cole
13-12-2006, 03:00 PM
Have had two tuned Vtec cars & know what its like to be lacking in torque.

In a straight line or on open circuits they are wonderful machines, on tight courses or back roads they struggle.

The offset is great MPG and reliability over a higher capacity or forced induction car.

If you match the gearing to suit the high rpm nature you can turn it into a very quick car. My little 1.6 vtec civic saloon had been tuned to 184bhp but i also changed the gearing to keep it within its power band, it always surprised bigger engined cars, but somtimes its lack of torque was a real embarrasment.

GVK
07-01-2007, 11:29 PM
I look forward to going up Kesselchen with 211bhp/197 lb/ft in 1100kg Golf.. :thumb: