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Old 27-11-2008   #61
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Re: Panda 100hp Performance

Quote Originally Posted by John R Smith View Post
So the mystery remains - not so much that the power outputs are different - but that Fiat specify them as identical.
No they don't.....HP has already confirmed this in post #23....
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Old 27-11-2008   #62
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Re: Panda 100hp Performance

Well, I don't think we will quibble over 1bhp, particularly when the Panda is quoted there as having very slightly less power and torque. Which we know cannot be the case. And anyone who could detect 1bhp difference on the road, let alone against the watch, would be a better man than I am, Gunga Din.

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Old 27-11-2008   #63
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Re: Panda 100hp Performance

You're the one saying 'Fiat specify them as identical'.....Which they clearly don't....

But as I indicated earlier in the thread....You cannot work backwards from a 0-60 time to get an output of an engine....

The Panda and the 500 have almost identical set-ups, yet the Panda is a second quicker to 60....This doesn't mean it has 10hp more and Fiat are keeping it a secret....
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Old 27-11-2008   #64
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Cool Re: Panda 100hp Performance

Difference in performance between the two cars on the road could also be down to the weight difference ..is there a substantial difference in the weight of the two cars..
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Old 27-11-2008   #65
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Re: Panda 100hp Performance

Look. Anyone who has ever done any serious engine tuning and performance testing knows that a one second difference on a 0-60 time is a huge amount. You don't get it by playing around polishing your spark plugs or putting a silly little filter on your oil-breather pipe. You don't get it by minor changes to gearing or kerb weight, and you certainly can't tell anything much from the seat of your pants or the car speedo either. You need solid experimantal data.

If you compare the figures from the Italian Panda test to the Autocar road test of the 1.4 500 you will see not just very large difference in the 0-60 times but also in the 0-400 meters and particularly in the 0-80m/h and 0-130kph times (almost identical road speeds). The Panda is near enough two seconds faster to 80, a very large amount considering that it probably has a larger frontal area and a worse Cd. Air and rolling resistance really starts to count over 60 m/h. The Panda was also tested at a much higher ambient temperature than the 500, which would actually reduce its power output to a measurable degree. As far as weight is concerned, the data from Fiat indicates that the Panda 100hp is actually heavier than the 500 1.4, which would make it slower, not faster.

And yes, you can work backwards from 0-60 times to a power output. Not in terms of absolutes, but in terms of difference. There are several simple formulae for this, which just use a simple constant using weight, power and elapsed time. Surprisingly, they turn out very accurate results, because up to 60 m/h Cd and frontal area have only just started to have much effect.

So all you Panda 100hp owners can bask in the knowledge that you have a very brisk little car which punches well above its weight.

John
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Last edited by John R Smith; 27-11-2008 at 12:07.
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Old 27-11-2008   #66
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Re: Panda 100hp Performance

You have been told with evidence the power and torque curves are different.
You have been told the two cars feel different with different power deliveries.
Live with it.
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Old 27-11-2008   #67
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Re: Panda 100hp Performance

HP, my dear chap, I don't have a problem with it. I am just such an anorak (having spent years tuning engines for a living back in the '80s) that I find the issue absolutely intriguing, that's all. Back in the day, the first thing I ever did when I got hold of my next car / motorcycle was to take the engine to bits, gas-flow the head, put on bigger carbs, new cams, etc etc. It's just the way I am. If something doesn't add up, I want to know why. Often I am quite prepared to spend hundreds of pounds and hours of work finding out why. I would quite agree that all this is totally irrelevant to most sane people But I love it.

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Old 27-11-2008   #68
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Re: Panda 100hp Performance

Quote Originally Posted by John R Smith View Post
So all you Panda 100hp owners can bask in the knowledge that you have a very brisk little car which punches well above its weight.
We already know that....
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Old 27-11-2008   #69
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Re: Panda 100hp Performance

By the way, and just as an aside, it is not at all unknown for manufacturers' power figures to be wide of the mark. The Japanese, in particular, seem to be masters of this. The Mitsi Evo VI GSR was one example, and a recent one is the mighty Nissan GTR where the quoted bhp is probably about 100hp adrift of the true figure. I leave it to you to examine the figures and decide in which direction. As to why this should be, your guess is as good as mine.

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Old 27-11-2008   #70
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Re: Panda 100hp Performance

Been following this thread with interest as have just had my 100HP on the RR at the most recent Red Dot day with standard setup producing 106.7 bhp at 6400 rpm increasing to 109.4 at 5800 with the GSR induction kit fitted. Being largely ignorant of the interplay between torque and horsepower p'haps someone could enlighten me as to the role torque plays in producing a sprint time such as 0-60 ? Some or none at all ?
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Old 27-11-2008   #71
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Re: Panda 100hp Performance

Quote Originally Posted by airlog View Post
Being largely ignorant of the interplay between torque and horsepower p'haps someone could enlighten me as to the role torque plays in producing a sprint time such as 0-60 ? Some or none at all ?
It's not simple ... but you weren't expecting it to be, right?

Here's an explanation I saw ages ago that I thought I'd save away as it explains it excellently imho....



Q. Is it power or torque that defines acceleration and top speed?

A. Yes.

That's usually the full depth of explanation folks are given……

In reality (switch on memory now) it is the torque that reaches the drivewheels that dictates both acceleration AND max speed. This figure is comprised of engine torque and gearing. That's it. Simple. Nothing more.

Higher engine torque = higher torque at the wheels = higher acceleration.

Lower gearing = higher torque at the wheels = higher acceleration.

Remember that TORQUE is the only engine output a driver feels. Power is a kind of esoteric measure that is simply calculated from Torque and Engine Speed. If we are talking “BHP” and “lbs.ft” then the equation is:-

Power= (Torque x rpm)/5252

So that's you then……thanks for listening.

But wait a minute. If Torque is all that matters, why is power always considered so important?

Because (re-engage your memory banks again) “power dictates how much advantage you can make of gearing”……which is where it all gets a little bit complex…and folks start switching off…but come back…it's not that difficult!

I've seen a few analogies before, but the best one I've thought of now is YOU. Well, you on a bike actually – we can all relate to that (yeah?).

Torque is what your legs generate. As stated above ~ If you press harder on the pedals you'll accelerate harder…..simple! You use the gears on your bike to multiply the torque your legs generate. In 1st gear the bike wheel may only rotate once for every 5 times you spin the pedals. In this gear you can zip up a hill (or accelerate really quickly), ‘cos this gearing has the effect of multiplying your leg power by 5.

If you maintain a steady force on the pedals, the bike accelerates at a steady rate. The torque you are generating stays constant, but the faster you spin your legs the more power you muster. Eventually you discover that you run out of “RPM” – your coordination goes, and you can't really get any force into your leg strokes. This is like your engine going upto and beyond its' peak power point.

Higher gears allow you to move along quickly whilst your legs go round at a comfortable pace. Nice one. Try to pull away from a standstill in the same gear however and (without enormous multiplication of your leg strength) it'll take you significantly longer to get up to speed.

Lets invent two characters:-. Arnie and Splinter. These guys epitomise two extremes of engine genre. Arnie has whopping leg muscles…thighs thicker than Tara-Palmer-Tomkinson. He is however a little clumsy and uncoordinated, so whilst he can REALLY “pump dem pedals”, he can only manage slow rotations. Anything else is too much for his feeble mind and coordination. (whisper…he's the turbodiesel).

Splinter conversely has spindly “twiggy legs” - He can barely stand up from his seat when his cup of Horlicks is full to the brim. Splinter however has been surgically enhanced with “VAJ” (variable-ankle-jeometry) that endows him with an uncanny ability to “spin da cog”. Although he can only manage a feeble push, he can maintain the coordination needed to rotate the pedals at…oh god knows how many rpm…it's so fast I can't count. You'd really need to see this guy. (whisper again….he's the VTEC)

We line them up on the drag strip and Whooaa! Arnie storms into the lead, his rear tyre barely able to contain the thrust created by those burly legs. But…oh dear….his coordination is going, and he's quickly forced to change up into second, then third…and look at this! Splinter is staging a comeback, still in first with his legs flailing like ….a flaily thing. Whilst Arnie is producing major leg thrust, he's currently using 3rd gear, which only doubles the torque his legs generate before it reaches the rear wheel. Splinter is still in first, so his weedy leg strength continues to be subject to 5-times multiplication…and he's reeling Arnie in!

It's a similar story when they are up to maximum speed. By enormous coincidence they appear to have an identical flat-out pace. Arnie is pumping his top gear firmly and steadily ~ wind resistance and friction conspire against him – he can go no faster. Splinter is right up there with him, but he's still in 3rd - legs whizzing round.

If we assume they have the same drag coefficient & weight etc, they are both producing the same POWER at this point. Arnie via high leg torque and low rpm, Splinter via low leg torque and high rpm. Their two power outputs are equal, and each calculation is valid.

It's exactly the same story when you look at the torque arriving at the rear wheel of the bike ~ Arnie is making high leg torque, but it's being blunted by the high gearing he has to use. Splinter uses low gearing to maintain the multiplication of his leg muscles and provide an identical torque at the rear wheel.

Back to the world of cars. You should now be able to understand why TDI's are often quoted as having “massive in-gear thrust”, whilst it's acknowledged that they suck fat ones when it comes to both “0-60” and top speed. Most TDI's barely get to 60 in third (let alone second), so in addition to requiring an extra gear change over most petrol models, they pass “the magic 60” in 3rd ~ which is by definition higher geared than 2nd, so the prodigious torque is multiplied to a lesser extent before it get's the chance to arrive at the drivewheel and “do the business”.

As diesels operate using compression ignition they don't require spark plugs. This omission unfortunately makes advancing the spark somewhat difficult ~ the main cause of their high rpm torque defecit. Lack of power (torque at high rpm) alone blunts their maximum velocity potential, but the coup-de-grace is that (with a rev ceiling around 4,500rpm) they have to use higher gearing ~ which again reduces the torque reaching the wheels. These two traditional performance metrics are therefore unreflective of the “real world” performance of a modern TD…it's low-rev torque very noticeable on the road, but fairly irrelevant in the two above circumstances.

A VTEC engine with 140lbs.ft max torque CANNOT punch as hard as a TDI with 200lbs.ft. In a VTEC however you will choose to accelerate with a lower gear than the TD, so the torque it does have is multiplied to a greater extent before it reaches the wheels. A TDI might feel impressive in 4th~ certainly more impressive than a VTEC in 4th, but the VTEC driver would undoubtedly pop it into 3rd (or even 2nd) to make better progress. The TDI has no such option.

Real Life Example – for the average TDI, gearing multiplies engine torque by a factor of approximately 12 in 1st gear, but only 2.5times in 5th gear. A TDI with 200lbs/ft will therefore produce a peak of 500lbs.ft at the drivewheels in 5th.

A VTEC shares pretty similar gearing in 1st, but its' lower top gear multiplies engine torque by a far higher 3.7times(approx) in 5th. Its' 140lbs.ft engine torque peak therefore equates to a peak at the drivewheels of 518lbs.ft in top.

Assuming they are the same weight etc and each car is at peak-torque rpm, you can see that the VTEC will accelerate marginally harder in top than the TDI - despite its apparent torque deficit.

As a rule - lower gearing makes better use of what torque you have available, but leads to unfashionably (and often uncomfortably) high-rev cruising. If you like that – fine. If you don't. what do I care? Your decision ~ there is no “best”.

Just out of interest – lets look at a (current) F1 car example-

Assume 800hp at 18000rpm. Using the equation in the 1st paragraph, we can see that it is only producing 233lbs.ft at this point. Not a lot really….a 1.9TDI VAG unit produces up to 235lbs.ft in el-boggo-standard form.

However…..if we want it to do 210mph, then our mega-revvy F1 engine only needs a top gear pulling 12mph per 1000rpm…..which is barely higher than 2nd gear in most road cars. Hence the “torque multiplier” from the gearing is massive, and you can still spin those fat rear slicks in top gear. Massive power allows vast exploitation of gearing. (I would guess gearing ratio in top is approx 6.5:1….so the engines' 233lbs.ft becomes 1500+ lbs.ft to be shared between the rear wheels).

What if you could extend the rev range further? Okeydokey - let's double it to 36000rpm. With this, the same car could use gearing of only 6mph per 1000rpm (about the same as 1st in a road car) and still manage 210mph. All 800 horses are still required (and produced), although only 116.5 lbs.ft torque is required to create it at this astronomical engine speed. Has the torque arriving at the wheels changed? (No). You can see why F1 engineers love engines that rev.

It aint simple….but then the best things never are. When this all clicks home in your noggin it's as satisfying as your first clean heel&toe downshift, and you'll never look at engines in the same way again.

Knowledge is power as they say. Or should that be “torque x rpm”?

Note1: In an attempt to keep things simple (honest) I ignored the fact that one aspect of your overall gearing comes from the total diameter of the wheel/tyre combination. If you “max da Nova” with 19” rims, then (even using 25 series tyres) the overall diameter will increase. Which raises your overall gearing (and incidentally knocks your speedo calibration out). Does this make it faster then? …..errr….nope.

Note2: Above detail also explains a question that haunted me for years: I could never fathom that I was able to strain on a torque wrench and tighten a front hub nut to approx 160lbs.ft without the wheel spinning, whilst a fwd hot-hatch with 160lbs.ft torque struggled for traction…..despite that figure being shared between both front wheels (????)

I now realise that in 1st gear, 160lbs.ft at the engine becomes approx 2000lbs.ft at the drivewheels due to your gearing. 1000lbs.ft per wheel = I can smell rubber.

I'm off again…..lets call this note 3: It's interesting to compare this with the F1 car example above ~ which achieves 75% of this “torque at the wheels” figure…but in top gear. Now since it weighs less than half of the hot hatch…if it weren't for horrendous aerodynamic drag it would shove you back in your seat in top gear with over 50% MORE force than the hot hatch could in first! Hmmmmmm.

are this with the F1 car example above ~ which achieves 75% of this “torque at the wheels” figure…but in top gear. Now since it weighs less than half of the hot hatch…if it weren't for horrendous aerodynamic drag it would shove you back in your seat in top gear with over 50% MORE force than the hot hatch could in first! Hmmmmmm.


Chris
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Old 01-12-2008   #72
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Re: Panda 100hp Performance

Chris

Thank you for taking the time and the trouble to write the explanation of power and torque above. Anyone who is at all interested in bikes and cars and working with engines could benefit from getting a thorough understanding of these principles.

John
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Old 01-12-2008   #73
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Re: Panda 100hp Performance

John R Smith - nice to hear from another Fiat fanatic down here in civilisation - perhaps one of us could cross the Tamar some time so we could get together and exchange pedantries.
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