Torque Vs Horsepower | 8 Minute Read

Torque, Horsepower…. and Engine Response

Start this discussion around the bar, braai (barbecue), tea trolley or at the car club covering the explanation of horsepower and torque and everyone is an expert. In(s)ane comments such as  “Horsepower can drive your car into a wall but torque determines how far you go through it”  attempt a cynical, jocular reasoning but just confuse the issue. Explanations will continue to abound however, from the very basic to the inevitable boffin who will detail a mathematical ‘clarification’….but seldom do these really create understanding.. .The role that torque plays in engine related car chat is either misunderstood, completely overplayed…or both.

The surprising thing is that most of us know what is meant by the expressions ‘a torquey engine’ or ‘the engine has grunt’ (euphemism for torque)…these simply express the fact that a driver feels good response between the action of the right foot and the G-force in his/her back. This interestingly also tends to be associated with low/mid speed engine response more so than that at high rpm. (We will get back to the important word response in a ‘mo’). Where the system fails, however, is deciding how torque relates to horsepower in an easily understandable way. That is because the whole thing is currently confused to a point of insanity…to the extent that car scribes who should know better, talk more readily about the massive Nm of torque in a particular vehicle, than referring to the all-important horsepower. They do so of course because most engines these days are turbocharged and as a consequence have massive torque numbers which need to be channelled into the conversation…somehow… even though they are technically irrelevant.

Torque in the real scheme of things does nothing… it is purely a measurement tool from which we can arrive at Horsepower or work.

 We have all heard of the difference between ‘talkers’ and ‘doers’…. In this case, ’Torque’ is the talker….’Horsepower’ is the doer. ….

 Doing’ stuff and by that I mean actually getting the job done, like moving a vehicle, is the exclusive preserve of Horsepower… alone…. torque is a stationary measurement.

 Ask the following question of anyone talking about torque….when does torque become horsepower or horsepower become torque?… or better still, what functions do the two perform?…or as they say so often in politics…what is the separation of ‘powers’ ?… and there will be silence, incoherent babble or a propellerhead will start that discussion on how you use a formula to calculate horsepower.

Let me put forth an explanation which has at least some attachment to daily life:

Most of us folk have had the call from our better-halves asking to open that bottle of jam… the difficulty in opening those lids often defying the laws of physics. You arrive at the spot and attempt to open the offending lid with bare hands. After a few attempts of eyeball popping, wrist-wringing, muscle tearing effort applied to the jar…..nothing happens…. all you have really done is applied a large amount of torque, hands slipping (wheelspin) .…and achieved exactly nothing.  This calls for reinforcements and in our house, it is the twenty-year-old ‘Tricky Dicky’, a flat piece of tacky rubber designed specifically to increase grip so that the lid gives way before our joints explode. You try again and after a superhuman grunt…eventually, the lid cracks open…you have now achieved something… work has been done…movement…and here is the key to this conundrum….

Torque resulting in radial movement… and caused by applying that torque = Horsepower… that’s it.

Don’t make it any more complicated than that and… horsepower is work done… Torque does not do the ‘work thing’ at all…torque needs to be applied repeatedly to generate horsepower or work.

Taking this analogy a step further. Lots of small jars opened quickly is lots of horsepower  (Jam jars per minute, aka rpm), and can be equated to an engine producing good horsepower at high Rpm. Fewer very large jars containing huge amounts of jam, done more slowly and requiring massively more torque to open (jam jars per minute, aka rpm), can be equated to big horsepower at low engine speeds…that’s the simple explanation.

…and here is the good bit…opening lots of small jars quickly can give you exactly the same amount of Jam (horsepower) as opening big jars slowly. This explains why for example, when a diesel truck engine produces 600Bhp at 2000rpm and a tiny petrol racing engine produces 600bhp at 10000 rpm they will both be doing exactly the same amount of WORK. In fact, if you adjust the gearing to suite, that race engine would do the job in place of the engine in the big truck…and sound a lot better in the process.

When we refer to a torquey engine, what we are really saying is that the engine produces relatively good horsepower at low speeds..or as a ‘screamer’,  good horsepower at high engine speed. That is all there is to it…we should technically not be using the word torque at all to describe performance…but it has crept into our vernacular, has a certain connotation attached to it and it has stuck. At the end of the day, that’s OK because it does convey a meaning we all seem to understand in a similar way, despite the fact that it is technically misguided.

But let’s get back to that all-important word ‘response’.  As car buffs we all like to know the horsepower (Ok Ok… & torque) of things and yes that number gives us an idea of how well a given machine will go but absolutely does not let us know how it will feel when driving it. In my early days as an engineer, I was fortunate enough to get to understand this and able to work on engine response issues. It stemmed from an experience in the very late 60’s driving a 1600 Ford Capri against a 1600 Opel Manta, it is a very basic example but explains the issues that can affect the feel of an engine.

1. 1600 Opel Manta

1600 CIH Opel Manta

2. 1600 Ford Capri

1600 Kent Ford Capri

In a flat out, full bore thrash from a standing start, the Opel would match the Ford in acceleration and be slightly quicker on maximum speed…but here is the kicker… when driving the two cars ‘normally’, it did not feel like that at all, the Ford felt more alive and more responsive to messages sent from that right foot.   Two simple modifications carried out on the Opel could change its character dramatically. By removing a fair amount of weight from the flywheel and fitting a carburettor with a mechanically operated secondary barrel, the difference was night and day and response (almost) matched that of the Ford.

Going a little deeper, the comparison looked like this…and I know it’s a bit ‘geekish’ but bear with me because it does clarify the point.

1.The mass of the Opel’s Piston + Conrod + crankshaft + flywheel + Clutch was around 25% heavier than the Ford…and that because the Opel engine represented the smallest capacity* in the ‘Cam In Head’ Opel engine range. (That engine would eventually be enlarged to a 2.4 Litre). The 1600 Ford Kent represented the maximum production engine size for that design and therefore did not carry any ‘deadweight’ in internal mechanicals for a larger capacity derivative. Naturally to ‘wind up’ the extra weight there would be an effect on response.

  * (there was a 1500cc engine in the CIH range but that was truly a bit of a dog and did not did not last long)

  1. The inlet/exhaust manifolds and valve sizes were optimised for the 1900 version of the Opel engine and when used on the 1600, whilst max power was good, optimum transient gas velocity (accelerating the mixture) was mildly compromised. Ford optimised the equivalent packaging for their 1600.
  2. The carburettor on the Opel was a Solex dual choke, running vacuum operated secondary barrel opening. This made the onset of secondary barrel power progressive, rather than immediate as on the mechanically connected Weber equipped Ford.
  3. The Opel ran a 3.67 final drive, the Ford a 3.9 with the same tyre size and very similar vehicle weights.

If we add to these the less significant response-sapping issues such as larger bearing journal sizes, all these factors explain the difference in engine feel  and throttle response between these two cars…and here is the rub. If you asked the average tech guy what the difference between the cars was, the answer you got was that the Ford had more torque….but did it?   No it did not….the real torque Figures for the respective 1970 models :

Ford Capri 92 ft Lbs torque @ 3600

Opel Manta  95 ft lbs torque @ 3800

These were effectively the same I would say, as were the torque curves

The lesson we learn here is that the issue of engine response is a characteristic less obvious in the Torque vs Horsepower argument /conundrum …. but is probably the most effective message being sent to the driver in the everyday use of a car and, surprisingly, often has little to do with quoted ultimate horsepower or torque…. But quite a lot to do with what point in the rpm scale you press the loud pedal…. and in turbocharged applications, just how sophisticated the spool-up of the turbo.

So what is the very worst and best engine response I have felt in a road car? For the purpose of this tale, the accolade goes to two cars, both achieving the worst and best… with the same 302 V8 engine.

The 1969 Z28 Camaro and the 1973 Firenza Can Am

The 302 Brothers

3. Camaro

1969 Z28 Camaro          

4. 1973 Firenza Can Am

1973 Firenza Can Am

Prod the accelerator hard on either of these machines at around 2500 rpm and your thoughts move to an urgent need to remove the elastic bands which are restricting the message to the carb. Not much happens, there is the faint gurgle from the intake and fair forward shove but not great at all. Let’s assume you did this exercise in 2nd gear but now repeat the manoeuvre at 4500 rpm…. All hell then breaks loose…. and one can safely say that engine response is not just good, but spectacular. However…read any road test of either machine and scribes complain of a lack of torque ….that, of course, is rubbish. The 302 Chevy generates plenty of torque, it just happens to rise fairly quickly from a low initial base and peaks at 4200 rpm, giving the engine excellent horsepower at that point…but less torque lower down results in relatively little horsepower at 2500 rpm.

Folks it is not more complicated than that.

So…will we ever get to rid ourselves of the dreaded ‘Torque’ monster? No I don’t think so, it is too embedded in our car culture and as I said, as long as we all have a rough understanding of how the word is used and its intention…all is OK.
Just to drive the point home though…and to point out just how useful it is to rely on horsepower, is the fact that we are able to estimate the horsepower outputs of cars based on ¼ mile times quite easily. In the days of sensible power outputs and with known vehicle weights the correlation between the two was amazingly accurate. Sure, there were differences attributable to front wheel drive, rear engines and gearing but it was sufficiently accurate to prove that max Horsepower can be an equally good measure of work done in a ¼ mile. It remains so today but as I have never calculated the power to weight ratio of a car that runs a ¼ in 12 seconds or under, I am sure there are those that can calculate the necessary… The Point? Knowing the max Torque of an engine in such an exercise is about as useful as knowing how many cups of coffee the driver had before the run.

Just remember, horsepower rules.

Very last word… next time, we will talk about something that needs further discussion and understanding in the power and torque debate… and that is tractive effort . This is because TE provides a more direct mathematical link to torque. It further complicates the discussion because we now have Power, torque, tractive effort and response to digest and I will attempt to put all four into boxes that can not only be understood but how one relates to the other….May the force be with you. P

By | 2018-04-26T10:51:25+00:00 April 26th, 2018|Categories: A Different Corner|Tags: , , |3 Comments

About the Author:

I have been in the motor industry all my life and despite spending 20 odd years with Datsun/Nissan, remain a GM man at heart.

3 Comments

  1. Peet du Plessis April 26, 2018 at 12:12 pm - Reply

    Hallo Mr Clark,

    Have you written the TE article yet?
    I am really an anxious, you have shattered my torque perspective.

    Regards,
    Peet

  2. Eric Booth (Google: EBM Tazio Sportscars) May 8, 2018 at 11:59 am - Reply

    with respect, I dont think you have it quite right. Afraid you cant avoid the maths in scientific discussions even at the braai ! Your example of your magic can opener which seems to change torque into horsepower merely by overcoming friction confirms the confusion. Perhaps that explains why beer cans dont have screw tops.

    However no matter how magic your patented can opener is it is not converting torque to horsepower without the inclusion of the missing link and I am not referring to the tab on the beer can. I am sorry to inform you that all your can opener has done is increase the torque which your scribe’s wrists were not up to unless you introduce the missing value time. It is doing the same as a gearbox which increases the length of the lever as (in the case of your can opener) and hence the torque or twisting force.

    Oh yes you did mention another clever aspect of your torque converter can opener which included a friction pad . Lets avoid friction for now because that subject is really quite bewildering and again the principals are based on unavoidable mathematics which even the boys at Ferrari are still struggling with. You will realise this if you have ever tried to depress the clutch pedal of one of their beauties.Of course the tatooed Itais will say out of the side of the mouth that big engines (torque?) need big clutches which need macho men.

    This leads me to another marketing driven attempt to cloud basic principals of auto design argued for years by the Krauts who perpetuated the theory that earlier 911 were only for skilled drivers because they had the engineering all wrong. Even the dumb yanks reacted to a marketing man { Ralph Nader) on the same subject of swing axles, this time fitted to their gorgeous looking (for yank) equivalent of the Beetle from which herr doctor borrowed the deadly swing axle rear suspension . Nader’s book “Unsafe at any Speed” wasn’t far from the mark and sunk GM’s efforts overnight whilst Porsche and Benz expounded its virtues until a backroom boy later to become Her Doctor with the apt name of Weisach ( wise arse or axle ? -anyway Porsche named their test track after him)….Our Albert is looking bored and querulous.. the term swing axle describes the design of the rear suspension which has a single cv joint at the gearbox end on each drive shaft which results in the contact patch of the tyre varying dramatically under chassis roll conditions thus causing all kinds of problems with unpredictable oversteer which when coupled with a rear engined drivetrain with an inherent high polar moment of inertia, can give rise to sensations of something hard in the mouth if the driver was really trying !

    Which leads me to… what were we saying… braais are not the best forum for solving engineering problems but vehicle dynamics is almost as interesting as aerodynamics and Sannie’s desmodromic boerewors. No thanks think I have already had enough. Oh yes .. the common gearbox does the same job as your torque converter can opener.. it multiplies torque to suit the load. So this is the cryptic question to differentiate the torquers from the doers as you put it . Vehicle engines are designed to suit the application . trucks with big payloads have accent on torque as with ships engines these are invariably slow turning with huge diameter pistons and long strokes . Therefore this answers the question: what do you need more of to get your 100ton tanker up Sir Lowry’s pass, torque or KW.? of course there are limits to how long your tanker can take to get up the hill so a minimum horsepower is required to get up at a reasonable pace

    Remember without being boring and nerdy.. 1 HP= 33,000 Ft. Lbs (torque) per minute (time)

    Or, as that canny Yorkshireman, that gave his name to the most successful British racing engine responded to a young enthusiast’s question: What makes engines produce more power? Frank hesitated before saying: “Laddy.. The bigger the bang and the more bangs per minute.”
    (The bang for torque and the more RPM to increase the rate of doing the work= increasing power/hp.)

    • Paul May 9, 2018 at 4:54 pm - Reply

      Eric,
      Lets get to the important stuff first and that gorgeous Corvair, with a minor correction. I agree that this was one of the finest styling attempts to come out of the good old US of A but that was in fact the’65 (and later) model which as a consequence of Ralph’s scaremongering had the really good dual A arm rear axle set up. As a follower of these machines there is no question that this was a bunch of headless chickens who screwed up a good car. I did have the pleasure of driving both versions (first the not so gorgeous version) and in comparison to a VW of the time, the old swing axle Corvair was much more well behaved… even in the windy city of Port Elizabeth. The White Monza ’67 Coupe we had at the factory was just an absolute gem and a car that could have made it on its own merits were it not for the silliness of both Ralph and the GM Board.

      Now to the Torque stuff and delighted at your response. When writing this piece I intentionally rattled the Torque cage to engender some interest and generate discussion. You will note that I closed the piece off with the ‘may the force be with you’ bit because the next portion of the discussion will cover tractive effort which is what you allude to when talking about gearing. Naturally the answer to your question on the tanker is simply horsepower. I would assume that moving the tanker would require work to be done and as work = horsepower the issue of how much torque is involved from the engine doing the job is largely irrelevant. As you have pointed out, one could have a massive engine with huge torque turning slowly to do the job…. or an engine a quarter of the size turning four times as fast which would also do the job…work done..The point made is that the torque output of the engines is not the determining factor because by using the right gearing, even a relatively small engine developing the required horsepower can be geared to generate the necessary tractive effort to haul that tanker. I will cover some of this for further discussion in the next article due early next week.

      I have some interesting debate material to put forth, for example…how much torque does it require to power a 100watt lightbulb,…and why do the Australian Supercar administrators only use 14,000 odd BHP (yes fourteen thousand horsepower) model to get parity in the power between the three manufacturers Holden, Ford and Nissan. We also take a given car and fit it with two very different engines..both having the same horsepower. Which will have the faster top speed? and which one will accelerate faster? Some of these will generate lively discussion I am sure for those that are interested…

      Of Ferraris, however, I am clueless but a supporter of a cousin to the marque, that other swing axle machine, the original Fiat 500. Like anything, once one understands the function…countermeasures can be applied. In this case a suitable strap run beneath the sideshaft to prevent tuck-under was mandatory for us press-on drivers. Now this did not improve the handling that much but severe tuck-under would inevitably result in the car falling over.The application of the strap resulted in the lesser alternative which was immediate massive oversteer the instant the device was called to do duty…which offered the possibility of a recovery.

      Thank you again and look forward to further debate after part two. P

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