Do you talk power or drive torque?

H

HDi fun

TC ModFather
Points
637
Location
Buckinghamshire UK
Car
Passat 2.0 TDi
What's your take on this;-

'We all talk power but we all drive torque.'

The two are inextricably linked, and different engine configurations (fuel type, air delivery etc.) give massively different numbers for each.

In which camp do you sit?
 
I personally talk both. Having a V8 (when it works) I have oodles of BHP and torque. I often find it difficult getting it through to some people having power coming out of your ears is all good and well but if you have little torque to go with it the engine will struggle to pull the weght of the vehicle.
 
I'm still trying to fully understand it all :s

Am I correct in saying torque is what pins you to the seat when you accelerate? (very technical :p )
 
Here is me being controversial or trying to.

Torque is a measure of bhp and RPM. If you have a 400bhp tractor which only revs to 2500rpm it will be much slower than a 400bhp Car with a 6000rpm redline.... Discuss and ponder. let battle commence etc....
 
BHP is a derivitive of torque and revs. You can't have one without the other.

It is torque that shoves you in the seat when you accelerate. Torque is twisting force. So more torque is more twist which means more acceleration.

It's the lack of revving ability that makes diesels feel breathless as revs rise hence the constant gear changing.
 
BHP is like PMPO wheras Torque is like RMS! Both describe loudness but 1 is a better measure of the effect of loudness. BHP and Torque both measure power but Torque is the better description of the effect of power :???:
 
Horsepower = Torque x rpm / 5252.

if an engine if in good running order HP, not bhp but the engine actual hp and torque lines should cross at 5252rpm ( must be in bhp and foot pounds or watts and newton meters not a combination of ether otherwise it wont work)

another thing a lot of cars now especially continental are expressed as PS (PferdeStarke the german version of horsepower ) however they are quite often expressed as having the same bhp there is a slight difference

1 PS = 1.014 BHP
 
That's an interesting point PG, proving that BHP is a function of torque and revs. I've taken the numbers from my car last time on the dyno and plugged in 331 (lbft) at 2500 rpm. That suggests that at 2500rpm my engine's dishing out about 157bhp. I'll do some more arithmetic and see what the torque figure is at 4300rpm (where power is recorded at 192bhp).

Kind of shows where diesel strengths and weaknesses are.
 
using it the other way then
Torque = Horsepower x 5252 / rpm

192 x 5252 / 4300 =
234 lbft

going to have a look myself next time the laptps connected to the car to find out my own reading it gives me a engine torque reading but nthing about power
 
PG, your numbers sit with the dyno plot very closely. It shows that torque falls off quite steeply as revs rise with my (diesel) car. And it drives as such. Loads of torque in the midrange - so much so that you can accidentally get some wheelspin in third or even fourth gear on a slippery road.

A large capacity petrol engine with good turocharging and supercharging might be the best on all fronts. ie. A flat torque graph. Imagine having 300 lbft from idle and all the way up to 7000rpm. with 300bhp at 7000rpm.

Anyone said 'Honda'?
 
well at least i know now it works came across it last year in a mag but a never had any figures to work with

yeah hondas are torque shy its all up high. really after the vtec kicks in. nice revving fun but a pain when you have to drop it all the time to pass
 
Most Japanese fours are that way. I had a Primera 2.0 which is a 16v twin cam effort and that revved to about 7600 before the red. Great fun, but basically lifeless below 5000rpm.
 
yeah civic was the same gutless under 5000 but without it having vtec meant there wasnt that much difference under closer to the 7100 red

just taken some figs from the laptop from a run i did this afternoon on the way to pick up the wife

171 bhp at 6200rpm and a pitifull 170 ftlb at 3100 that wasnt running full throttle as road was very wet. spec boost was registering at 1620 mbar and actual 1670 mbar (taken from reading in second gear as wagon turned off plenty of room to take to red line )

think i might try again when the roads dry up so can use full throttle
 
The Honda VTEC engines are a delight. I'd like to try Honda's current 3.5 V6 VTEC unit. I know the Legend is an old man's car (suit me fine, then) but with nearly 300bhp it's gotta go quite pleasantly!!

I've driven several dozen cars in the last twenty years, some for short periods, some for years and I always find Hondas to be well executed. They even manage to make the most modest 1.4 Jazz or Civic feel lively. That is down to superb engineering and production quality control.

My Nissan didn't have the benefit of variable valve timing so power was nowhere near that of a Honda unit but it still revved its little head off. There were times when it felt truly dire, the A/C used to sap power severely (but it was the freeze-you-rigid-when-it's-30-degrees-outside type of A/C, not the Vauxhall slightly-cool-breeze type of A/C) and the auto transmission seemed to get caught out between 3/4 and o/d on uphill roads.
 
yeah shes also due an oil change as thats getting near 6k since it was last done normally use super but unfortunately shell was out of it the other day ( and nowhere else does it other than tescos and ive had problem with supermarket fuel in the past) so it was run on roughly 60% normal 40% super. hopefully itll dry up over the week so can have a good go at it see if i can get the 180 outo it

originally thought i was getting the wrong figs from the engine as it was showing up as 231 bhp reason was vagcom registrars torque as Nm but when its logged into excel it shows up as ftlb, but its still in Nm so had to work out how to change it between
 
Tesco petrol (and diesel) is questionable. I've used it occasionally but seems to turn a smooth and swift car into a rough one.

But then, I dislike Tesco anyway. Fresh meat from Tesco? No f.....' way, not for me or mine.

Poultry? Again, not keen - and I don't buy the stuff - haven't done so since 1998.

Why would I run my car on fuel from a company whose food I refuse to buy/eat/feed to my children?

It's time Tesco started to wind in its corporate neck and start giving US a choice of products beyond those which it can wield it's corporate might against British farmers and growers.

So there's no way I'm going to use Tesco's petrol. diesel or rocket fuel until tnat company starts to play fair.
 
pgarner said:
171 bhp at 6200rpm and a pitifull 170 ftlb at 3100 that wasnt running full throttle as road was very wet. spec boost was registering at 1620 mbar and actual 1670 mbar (taken from reading in second gear as wagon turned off plenty of room to take to red line )

think i might try again when the roads dry up so can use full throttle
Click to expand...

ok tried again. shes been running on super for a couple of weeks now so should be running near enough pure 97-98 ron, what ever V-power is optimax was 97Ron


between 4640 Rpm and 5800 Rpm torque sits around 165 ftlb peaking at 179 ftlb at 5280

power was up to 184.6 bhp at 5680 rpm

so up 9 ftlb and 13 bhp
am happy with that. time to update the profile ;)

i cant comment on lower than 4500 rpm as only took figures from 1 run from 1st through to 4th gear. so only have the figs for below 4.5k rpm for 1st gear where the traction control was on. also had to remove some figs from 2nd gear where traction control intervened. i didnt bother to take boost reading so i had a better sample rate for the torque
 
Last edited:
this is what torque and power is to me

Torque takes care of acceleration but as it drops of quite eirly its no good for top speed

Power takes care of top speed but as it takes a while to build up its no good for acceleration

that means you need one to help the other, you use the torque to get your accelration but when that runs out power takes over to get your top speed

everyone follow that ?
 
Basically the torque starts to lessen above its peak rev point. It's when the torque curve starts to drop steeply that max power is achieved. Top speed is also a function of gearing. Over geared cars often reach their top speeds in one gear down from the (overdriven) top gear. Quite often this was the case in early 1980's BL cars. Fourth was just about capable of 100mph if you could stand the racket (and the wait to get there). 5th, by contrast was only good for about 90 and gave glacial acceleration.

The industry has grown up now and you usually get 5 or 6 useable gears. I still favour modern automatics over manuals but there's still a lot of slushy 3.5 speed autos out there.
 
ok i cleared up a lot of the data recorded from vagcom. basically the ones where ive changed gear and allowed the revs to drop and at the end of the run originally i just organised the the revs into ascending order through access them transferred it back to excel. this was made a lot easier as the time stamps were in ascending in the original CSV file. deleted the ones where the revs started to drop then exported to excel sorted revs into ascending before plotting the graph

if you look at the orange line (5280 rpm) and the line before hand (5160 rpm) the lines cross around about this area. remember that a perfectly running engine should cross at 5252. thus showing that torque and horsepower are related. the only thing is the sample rate varied through out the run if you look at the revs that are marked up some times the revs climb in 40's at other times its 120. in other places when the car was accelerating and sample revs were matched over several gear they were averaged out

image003.jpg


i hope that this shows that power and torque are connected. you cant have one without the other it only depends on how the engine produce each one
 
i found the formula in a issue of car magazine last august but like you i didnt know where they got the 5252 from so i had a quick look on google for it and how stuff works turned up this


http://www.howstuffworks.com/question622.htm


its worked out from 1 hp = 550 ftlb per second over the number of radians in a seconds

its easier to read it yourself than me trying to explain it
 
All graphs should cross at that point - its just a mathmatical thing. A 60bhp car and 1000bhp will always cross over at 5252 rpm.
 
in theory yes it works. And HDI, your 406, i doubt it will have a red line as high as 5252rpm but when i used your the details you gave you admitted it was very close to what your dyno showed.

im sure that if someone posted up figures from a tractor then they would work out the same

when you brake down most things do do with cars it just comes down to maths. sometimes very complex maths that most of us would never understand
 
the reason that the graphs should cross is at this point 1 hp = 1 ftlb. i had a quick look but cant see anyhing over than how they have worked this out from what James watt worked out.

what i did find out is the formula given before ( [torque (ftlb) x rpm] / 5252 ) but with the full figures not rounded is used by dyno to work out the horsepower. which does make sense as your turning the wheels on the dyno and torque is the turning force

if i get a chance this afternoon al have another go at searching for info on it
 
OK - so 1bhp = 1 ftlb at 5252rpm. Bear in mind that ftlb is rotational force (torque) and bhp is power (rate at which work is done).

So an engine that produces 100bhp at 5252rpm will develop 100lb/ft at 5252 rpm.

I think something has been lost in translation here. Eg. an engine that develops 100bhp at 2626rpm (half of 5252) will need to develop 200lbft at 2626rpm.

This has no bearing on what it will deliver at 5252, or whether the curves will meet at that point.
 
Typically HP is measured at the engine and Torque is measured at the rear wheel. 1000HP does no good if you cant get it to the rear wheels. The true measurement would be torque/weight but who does that?
 
Question? My laptop was stolen along with my software and cables. I have an old laptop with some older versions of software on it but no cable. I bought a cable on E-bay that doesn't work. Any one know where I can get a real working cable to link obd11 to my laptop at a decent price?
Thanks
 
Torque is generally also measured at the flywheel (if measured at the drive wheels then xmission losses are added to give a flywheel figure).

Measuring a true flywheel figure would mean taking the engine out of the car.

Which is a lot of mucking about for a quick dyno run.

Cheers,

Rgds,

P.
 
kevin usb cable may not have been setup correctly by windows this is the info i was sent when i got my cable of ebay



If you have problems getting this cable to work then it is normally due to
the ports being incorrectly set within windows.

Please check the following:


1, Install the driver supplied.

2, Insert the usb end of the cable into you PC.

3, go to 'Device manager' (via the start menu, right click on my computer,
select properties, select hardware & then device Manager)

4, Select view, devices by type.

5, Go to ports and check the USB serial port is set to Com 1,2,3 or 4. If
not then select properties/port settings/advanced and select com 1,2,3 or
4.

6, Insert the cable to your car.

7, Install and run the Vag-Com software.

8, within Vag-Com select options and change the com port to match the one
selected above. Click test and then save.

9, Finally select auto scan and choose your chassis type.

Also please make sure your cars ignition is on!


Tony
www.mediasave.co.uk
 
Stumbled on this one this morning.
5252 number is not the spot at which engine should cross its torque and horse power. It is an constant for simplier math. If you wanna see relation between HP and torque in Newtonmeters that constant is 7024.
Those numbers are derivated from fact that moment is twisting force - or turning force to an axle. So somewhere along we use radians. :lol:

In my opinion ideal engine in real world would have constant torque until it reaches max horse power and after that point the torque is decreasing while max power remains the same.
For egsample, I would be happy to see dyno sheet on my car that produce torque of about 360 Nm from 2000 rpm to 3300 rpm where the power rise up to 170 Hp and after thet point torque decrease but power remains at 170 HP untill 4300 RPM. At that point torque would be about 278 Nm.
Think that should produce linear pool trough revs. That is not maxed out. Manny mapper and street racers use as much torque in revs where ever is possible because it decreases ceconds, but for civil use i guess above scenario is quite good even for road and trafic.
Ideally torque should be constant like in electric cars but here we enter some major phisyc obstacles with our internal combustion engines.


P.S. This post is also major test for my english and I have improvised a lot. Hope something understandable is written after all. :lol:
 
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