What'll she do, mister? - Rolling Road results

[robin]

Just forget you ever heard about torque - it's very important to engine and gearbox designers, but irrelevant to drivers of cars; all you care about is power output of engine at whatever RPM you are driving at.

Kilowatts out => Kilowatts of kinetic energy + hot molecules (friction losses in transmission, tyres, air).

Cheers,
Robin

[campbell]

So how come a diesel putting out 150bhp of power *feels* like it is hauling you along with the acceleration of a car with 200? All these TDIs in the world whose key number seems to be Nm rather than bhp ... ???

[scratches head]

[MacK]

I've always understood torque to be the 'power' that gets you going, and that works at low revs, till the BHP takes over.

Torque matters for things like towing and off-roading etc, but not for fast stuff like racing etc. F1 cars have big BHP but comparitivly low torque. Tractors (used by farmers) or HGV's have high torque but comparitivly low BHP.

[robin]

Nope, forget torque. Keep forgetting it. Have you forgotten it yet?

Torque and power are one and the same thing. Torque = power * rpm/5252 (assuming you're using BHP and lbft).

It's all down to how much power your engine produces and whether or not the gearbox is correctly configured to utilise that power.

A windmill has 1000's of Nm of Torque but revs at 1 rpm, so not much power.

A diesel is a faster windmill with a better gearbox

Cheers,
Robin

[campbell]

Hm. This is going to keep me awake at nights now

Anyway, I'm off to drive my car the long way round to the takeaway. Cos I can. And I like it very much

Campbell

PS - it's fun having a reason to post and read SELOC too !!

[thinfourth]

i think we are going to enter the nasty world of torque curves, gear ratios etc and driveablilty and all those other factors that make a car feel quick when it ain't

And please can we avoid the turbo lag saga

[campbell]

What, do you think I should get a Terbo fitted as well?!

[thinfourth]

No turbo diesels with their huge torque and bugger all horse power

the landrover has comedy turbo lag to go with comedy handling, brakes, steering, tyres etc

[campbell]

good work fellas
do you notice any difference in performance driving it?

Paul,

Realised I probably never addressed your question!

And also realised, Robin hasn't had a shottie to test his handiwork yet either...must rectify that soon

Yes, the RR numbers game was to provide some objective evidence of what we have done, but the proof of the pudding is in what Lawrence called "seat of pants Dyno", IIRC!

The car drives just like it always did around town, and up through the gears in "economy mode". No loss of performance (let's not call it torque after Robin's science expose!), but when it gets above 3500 it just feels so much more eager.

Very smooth delivery and power build-up, lovely engine note, all the way to 7k rpm if you need it. 2nd gear is banzai, 3rd gear is the perfect blend for fun factor beanz or overtaking. Using the extra revs in 4th would definitely be license-limiting so I haven't been there...will save that for KH!

My prediction is an extra 10-15mph under the bridge, which for me is shedloads. And I remember Dave Minter telling me that the Lotus 135 stock conversion was worth a couple of seconds off the 0-100 time, so that's surely a few carlengths at any rate

It has certainly injected a new lease of life, or at least interest, into a car which at nearly 8 years old has now been owned by me almost 4 times longer than any other car before it!!! And I like the subtlety of it all.

Howzat?! Fancy one instead of your TT conversion?!

Campbell

[campbell]

I found these...some of us might find them useful...they really do just amplify what Robin has said using various other analogies to help, but they are nicely written so enjoy...

http://vettenet.org/torquehp.html

http://www.largiader.com/articles/torque.html

http://www.allpar.com/eek/hp-vs-torque.html

And I really must try to follow through this bit of homework from that last article:

"Not all cars should be shifted at the redline for maximum performance. But it's true for many cars. You can determine optimal shift points by graphing horsepower vs. velocity or transmission torque vs. RPM. Engine torque alone will not determine shift points."


Told you it would all keep me awake...

[campbell]

And I particularly liked this article (my emphasis):


Torque versus Power

In the simplest terms, torque is the twisting force the engine applies to the crankshaft and then on to the transmission.

Power, by contrast, is measured as the torque times the rotational speed. In imperial measures, one horsepower is equal to 550 foot-pounds (of torque) per second. Two engines can produce the same power but have very different torque ratings for the following simple reason:

One horsepower can be produced by moving one pound 550 feet OR by moving 550 pounds one foot, provided that either function is achieved in one second.

The difference comes in the fact that the high-torque engine will be rotating slower than the low-torque engine at the same power output but it will be twisting the crankshaft a lot more vigorously.

In theory, different gear ratios - most commonly four or five in cars' gearboxes - should mask different torque characteristics by altering engine speed to suit but the reality is that engines which produce high torque figures at low revolutions respond much more readily in give and take driving.

The practical advantages come in the form of reduced gear changing, lower engine revs and wear and, invariably, lower fuel consumption in all conditions other than constant speed driving.

For Mr Average, torque is therefore more important than horsepower, unless you spend your life racing around at high revs

[ends]


Now who on earth would do something like that I wonder...




I still don't feel I can explain any of this in pub-conversation stylee yet, and I tried with my bruv tonight (!) but I am working on it.

[thinfourth]

I think without actually reading any of those links and ignoring robin who is correct it can be put as the following

A torquey engine is about low down grunt which is why the turbo diesels feel powerful

This is where the confusion comes in

[GregR]

torque, my favourite from my 6th year physics days, represented by the symbol 'tau'. Its all about rotational force.

Do as Robin says, ignore the torque!