Always a bit more than I have now! But I'm just as happy in a 1100cc Minor as long as it's only local pottering.
When I had a 2 litre Legacy I was always thinking, if only it was a 3 litre. I've now got a 245bhp Spec B, it felt lightning fast at first but now I keep wishing it had a turbo. I suppose you just get used to whatever you are driving, but where does it end?
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but where does it end?
In a ditch, usually...... :-)
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LOL, let's hope not, they're very deep round my way!
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Enough to make any car I own feel eager. Not bothered about 0-60 or in gear times. Just how the car feels - does it want to go? Obviously its use has to be taken in to account, so this "feel" would depend on the wether it will go ok when laden.
To illustrate this point heres my actual situation:-
I have two cars - 45bhp and 850Kgs and the other 180bhp and 1660kgs. The lower powered car "feels" nippy and eager, the more powerful, heavier car doesnt - but its faster any way you want to measure it.
I try a car - does it "feel" fast enough? Yes? Then it is. Not very scientific I know but there you go.
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245 bhp sound plenty :-)
Turbos arent all they're cracked up to be.
When I got my first turbo car I was distinctly under whelmed with the performance. The car seemed very flat untill 2100 rpm then it'd pick up. It was a Rover 620 turbo with a tad under 200Bhp. I had to learn how to drive it properly and try to visualise what the turbo was doing (I later fitted a boost gauge). I found out that turbo cars need a level of commitment by keeping the right foot down and therefore the turbo spinning. If you come on and off the throttle then it does power output no good at all and make the car feel flat. All this leads me to say that 200BHp headline figures are okay but can you access the 200Bhp easily without driving like a looney?
I've dropped down to an auto car with 180 bhp and more weight these days and I dont miss the performance as the novelty of a 200bhp turbo wore off (as well as the tyres LOL)
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Torque is needed not power. My VW turbo diesel estate is only 100hp but can maintain speed on hills no problem. SWMBO little Getz is 95hp and is a gutless wonder in comparison. The car that is.
Edited by Glaikit Wee Scunner {P} on 23/10/2007 at 14:01
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Some one mentioned Hardknot Pass earlier.
I went flying up that in my Alfa 1.6 with 'only' 120 hp, but it could happily rev up to 7000 rpm and you would not need to get out of second gear.
I would not relish the same road in the Mondeo TDCi 130 as the gears and revs are all wrong. Once past 3500 rpm there is not much power left so you would have to change up into third which would then be far to high a gear for the corners.
You need the right car for the job. And a 1.6 Grand Scenic is not for Devon.
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I can't fathom what the fuss is all about regarding whether you use metric or imperial units in normal life. I admit that when I'm doing a deal with a car salesman I want to get my pound of flesh. But if I'm on a congested street and I can see that I've got a few millimetres clearance either side of my car I just inch forward, safe in the knowledge that a miss is as good as a mile. Sometimes when I get to the end of a 10 km race I feel so fit that I go the extra mile and complete a half marathon. When presented with the choice of buying either a litre of milk or two pints I know that in reality it's a case of six of one and half a dozen of the other.
The people I feel sorry for are those brought up purely on metric dimensions. What a restricted vocabulary they must have. No wonder most continentals talk in such a stilted way.
--
L\'escargot.
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Sorry
Edited by OldSock on 23/10/2007 at 17:01
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"The people I feel sorry for are those brought up purely on metric"
Same here. It must be a real pain having to order your beer in multiples of 568ml.
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Ok, I accept that Nm/tonne isn't nonsense because pound force and pound mass aren't the same - my excuse is that I learnt (or not in this case) all this longer ago than most of you.
A question, in case my memory is failing again, doesn't torque at the tyres depend on the gearing, unlike power?
A diesel giving 99bhp/230Nm in a 1250kg car geared at 27.8mph/1000rpm may give a 22% improvement in Nm/tonne over a 134bhp/188Nm petrol of the same capacity and weight geared at 21.7mph/1000 but the torque at the wheels in top gear is actually 5% worse, although gearing of 1st gears are similar.
The power-to-weight ratio of the diesel remains 26% worse whatever gear or gearing is used.
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Ruperts Trooper,
I just wish you'd explain this to all the motoring journalists who think that engine output torque is the be all and end all of acceleration.
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L\'escargot.
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R-T, it's quite difficult marrying up the physics with the 'feel' of a car's performance.
Torque, without reference to rpm, is a somewhat meaningless measure, as it is power which actually causes vehicle acceleration - and power is simply (torque) x (rotational speed).
Engine output figures are always quoted at full throttle operation, whereas little real-world operation (hopefully) takes place under these conditions. The torque and power outputs at part-throttle operation are hardly ever mentioned - yet it is these which largely determine the 'feel' of a vehicle.
As you say, gearing also plays a vital rôle in exploiting how the engine's power characteristics are applied at the driving wheels. I can't be certain, but I'd imagine that the transfer efficiency from flywheel to driven wheel differs with respect to power and (gear-adjusted) torque.
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I went from a chipped Golf GTi Turbo (mk4) with approx 180BHP to an older Boxster 2.5 (204BHP). The Golf felt faster in mid-range in-gear acceleration but the Porsche is faster if you use 5000-6500 RPM. Which is a lot of fun BTW. I was thinking about this power question the other day, as 200BHP doesn't sound like that much by today's standards, and on a motorway, many fairly mundane cars like diesel Mondeos can match or even better the Boxsters performance (up to a point), but not so on the twisty stuff - I certainly don''t need any more power for country lanes. So I'd say that 200 is plenty as long as the chassis can put it all down nicely.
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>>Torque, without reference to rpm
Yes, that's right - as RT says, you also need to consider the gear ratio.
However!, the peak power figure is only obtained at one point in the rev range. If you look at a superimposed torque and power plot (ironically, this works much better using imperial units!), the torque curve is always much flatter.
Some power centric types will say that;
acceleration=power/(mass*speed)
and then go on to justify that you don't need to consider the gear ratio when using power to estimate vehicle performance.
But, they're wrong!
The formula above is correct, but, you have to work out the engine speed - for which you need the gear ratios - and then use the engine power at the correct engine speed. You can't just always plug the maximum power in to that formula.
Going a little further, there are a coulple of seemingly inconsistent facts;
If you use a CVT, you get the best acceleration by keeping the engine speed set for maximum power
If you have a manual gearbox, if you stay in any particular gear, the maximum acceleration is obtained at the engine speed for maximum torque!
Number_Cruncher
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"If you have a manual gearbox, if you stay in any particular gear, the maximum acceleration is obtained at the engine speed for maximum torque!"
I have a nagging thought that what makes acceleration is not power, but the rate of change of power, and if you differentiate the power curve that gives you an idea of the available acceleration. I also suspect that if you differentiate power you will get torque, and hence torque is analgous to acceleration. Never manged to get the equations to prove it though.... This is probably why subjectively diesels are faster mid range - the torque is higher so the power curve is steeper, and hence they accelerate faster. Time to sharpen my pencil perhaps.....
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RichardW
Is it illogical? It must be Citroen....
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>>I have a nagging thought that what makes acceleration is not power, but the rate of change of power
In the simplest sense, taking the engine's torque, and multiplying by the overall gear ratio and dividing by the rolling radius gives the tractive effort - the force pushing the vehicle forward. As, according to Newton's Second Law, F=ma, the acceleration is directly proportional to the force, which in turn is directly proportional to the torque.
As for the applying calculus between the two curves, I think it can be done, but you'll end up with some odd terms involving engine speed. Is your pencil sharp yet?
For example, at the engine speed for maximum torque, you know the torque curve has no gradient, and so, you can work out what the gradient of the power curve will be at that engine speed - as you also know the engine speed and the torque at this point, you also know the power.
Repeating this trick at the engine's maximum power speed, but in reverse, you can work out the torque and the gradient of the torque curve. So, using the 4 pieces of info typically quoted, you can actually put a few more points and gradients on the curve, sufficient to either sketch the curves, or use a curve fitting routine to obtain an estimate of the whole characterisitic. This method doesn't work well with engines which have switchable intake systems, their torque curves are too "bumpy"
A long time a go, I made a spreadsheet available that used this method - GordonM was kind enough to host it and provide a link from this forum.
Number_Cruncher
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"doesn't torque at the tyres depend on the gearing"
Indeed, but I assume that is largely normalised by the similar overall gearing (relative to the usable powerband of the engine) of most passenger cars. Diesels are usually geared a bit higher because they have more lower-down torque (and run out of puff sooner) but the speed range you are likely to get in each gear should be comparable, as will the torque at the wheels when pulling away in first.
Whether they feel similar is a different matter, of course!
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All getting very technical here. Rather than "power" and "torque" and wotsits per kilowatt etc , I think the word we are searching for is "poke".
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I almost never go above an indicated 75, often tootle at 50 and I have just discovered I have 278 bhp and a 0 to 62 of 6.7 seconds.
Lumme. Maybe I've overspecced here!
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All getting very technical here.....
Mathematically expressed as:
points = [(poke)^2/(skill)] - (luck)
... in whatever units you prefer :-)
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Gearing tends to be higher in modern cars for economy, my first car was a Renault 16 TS which destroyed it's engine due to a bottom seal going on a wet liner.
I managed to pick up another engine from a 16 TX, which went in without too many problems. Although only about 6bhp more, it totally transformed the car (well, the engine pick-up and straight line performance). Only 2CV's rolled and understeered more.
The TX engine was mated to a five speed box with slightly higher ratios where as the TS had a 4 speed, economy wasn't fantastic but it was much more spritely and felt it too.
Modern cars accelerate faster admittedly but you're aware of it, you don't feel it if that makes sense.
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"95hp and is a gutless wonder"
If you're used to driving a diesel, perhaps you're just not giving it enough revs. Most Japanese built or designed engines that I've used have a split personality - they happily pootle along (sometimes rather feebly) at lower revs, but start getting interesting about half-way round the dial. My old Honda S800 didn't get into its stride until about 5k, but for it, that was half-way!
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The Getz seemed to be reluctant to rev up this particular hill - I was doing about 4000rpm in fourth gear foot to the floor- and would not go faster than 60mph.Did not fancy red lining SWMBO car in third. My old SDI Golf 75hp also was sluggish up the Taddington Bypass(A6).
Passat TDI 100hp goes up at 70 plus in 5th gear.
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How much power do i want?
Sufficient - as the RR salesman used to say.
What is sufficient?
Enough to keep my chosen speed on the motorway without stiring the gearlever or stuffing clog to the floor.
Enough to keep scroat in the L/H turn lane when he wants to jump me at the lights.
Enough to safely see off Eddie, Norbert, and Willi Betz when they are in the way.
How much HP is that? well in a clio its 68 horses, IN a medium car its about 105.
Funny - both are diesels.
------------------------------
< Ex RF, Ex TVM >
Edited by Altea Ego on 24/10/2007 at 14:47
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Sufficient - as the RR salesman used to say.
Wasn't it actually described as 'adequate'?
Whether 'adequate' was 'sufficient' I could never afford to find out :-(
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Whether 'adequate' was 'sufficient' I could never afford to find out :-(
Adequate to move a quite large and heavy car as fast as most of the traffic.
The answer to the question in the thread title is: more, for reasons too obvious to mention.
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>> Sufficient - as the RR salesman used to say.
I think this quote originally applied to the Bentley Mulsanne for which power was described as "adequate"
The power of the Mulsanne turbo R was similarly described as "adequate plus fifty percent"
Personally I like the second option!
Far better to have power available and not need it than need it and not have it.
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I think this quote originally applied to the Bentley Mulsanne
Predated the Mulsanne by decades. RR never gave power figures even when asked, but they did imply that their large and heavy cars went fairly well when required to. And so they did, without drawing attention to themselves or ever feeling dangerous except in poorly maintained examples under heavy braking.
However, no real Rolls-Royce in standard form could take much full-throttle running. Their couple of gallons of SAE30 mineral oil would gradually overheat and the oil pressure would decline steadily until the driver slowed down. I wonder if even these modern ones can take it even with modern oil.
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"IN a medium car its about 105"
My oh my, we are easily pleased, aren't we RF?
I wouldn't get out of bed for less than 200
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I always go for the most powerful diesel option for the car I am buying.
I find this gives effortless mid range power for acceleration, safe overtaking, and hill climbing.
I find 250nm in a Focus adequate.
Hopefully the chav who takes off from the lights will have his accident far enough ahead that I will have plenty of room to stop.
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I guess thats where opinions differ becuase I find 105bhp in a medium size car vastly underpowered. I couldn't put up with it on a day to day basis. It would sap any ounce of pleasure there is from driving well and truely.
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One may fancy lots more power MichaelR, but it certainly isn't true that low powered vehicles are not enjoyable to drive. Indeed the challenge of rowing them along faster than the traffic is quite stimulating.
However I agree with you that we car enthusiasts are brutalists at heart.
:o}
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"Did not fancy red lining SWMBO car in third"
Quite understand. Discretion and valour and all that. How many miles has it done? With modern oils, engines can take a long time to loosen. My Suzuki bike is still pretty tight at 11k...
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