Torque and Power numbers

[Hadders]

Hi All,

Last time I asked a basic mechanical question (about the Golf gearboxes) I got really helpful answers.

Now I am trying to understand torque and power. The reason is that I have a 95 Ibiza GTI and the intended upgrade would be to the 77TDI if it is ‘powerful’ enough, using the word loosely. I would test drive it of course, and if I was not satisfied, I would probably find the extra brass and go to the 103. Right now, I am trying to deduce how the 77 would compare to the Ibiza, from the numbers. A reason for that is that I doubt that I could test drive to a really demanding situation, such as my favourite hills coming south on the F3, after Palmdale and after crossing the Brooklyn Bridge.

The Ibiza does 85Kw at 5400 rpm and 166Nm at 3200 rpm.
https://www.mynrma.com.au/cps/rde/xc...car_review.htm

I basically understand the concept of the torque peak. Fortunately 3200 rpm corresponds to about 115Kph in top gear. If the Ibiza is at that speed when it reaches the bottom of those hills, then it has no trouble maintaining that speed up those hills. I give it more juice as the hill gets steeper and keep to 3200 rpm and I don’t have to drop to 4th unless I’m slowed by traffic.

Query how much power the engine is producing at such times.

FIRST QUESTION: Is it always 85 x 3200/5400 = 50.4 Kw or does the power output vary with the steepness of the hill that the car is climbing at 3200rpm? (You’d think: more juice = more power, but who knows?)

(I found a formula Kw = (Nm x RPM) divided by 9549 which gives 55.6 Kw so maybe the Ibiza specs are slightly off maybe one set of numbers is for wheels and the other for the engine – just letting you know that I’m trying hard with this.)

The figures for the 77TDI are 77Kw at 4400 rpm and 250 Nm at 1500 – 2500 rpm. So I read the 77 as having its maximum torque over a range of 1000 revs.

Now I imagine that I hit the bottom of the same hill at the same speed as the Ibiza, but driving the 77. I want to be in the max torque range, maybe close to the middle, but lets keep it simple. At least one gear of each type of gearbox would have to do that for me ie 115 kph at between 1500 and 2500 revs. Maybe three gears of the 7 speed DSG would handle 115 kph somewhere in that range?

Now while the Ibiza produced 166Nm max, the 77 offers 250 Nm. Maintaining speed up that hill should be easy, even though the 77 has stacked on 300kgs over the Ibiza.

SECOND QUESTION: Is that a reasonable conclusion?

THIRD QUESTION: Does the extra torque, though lower power, that the 77 has over the Ibiza, indicate that the 77 would also compare favourably on other important occasions; eg getting quickly from 80 kph to 100 kph for a swift overtake?

Many thanks for any comments

Martin Hadley

[Greg Roles]

To answer your underlying question, diesels excel at hill climbs and holding gears, and in gear acceleration, all due to the tremendous torque figure. With the wider rev range of a petrol car, and thus less gear changes, the Seat will still probably be quicker 0-100, but not by much.

I'd suggest a test drive will answer all your questions and reckon you'll love it with the empahsis you have asked of it.

[gregozedobe]

You have indeed done some homework, good to see

As Cogdoc says, it's time for a test drive. I suggest you drive both diesels and a 118TSI as well (just to show where modern petrol engines are these days). If you can't afford one, don't let the salesperson trick you into driving a GTI (quite a few people have ended up buying one even though they weren't intending to). Manual vs DSG can also make a big difference to the driving experience.

It is worth remembering the differences in weight and gearing, so 5th gear in your Seat may be doing similar revs in 4th in a Golf. Also diesels tend to have higher gear ratios than petrols due to their limited rev range.

Even though they make good torque at low revs, I always feel more comfortable having at least 2,000rpm on a (car) diesel engine when asking it do serious work (accelerate hard, go up a steep hill), as I don't think it is good for them to lug too hard at low revs. TDI's feel best if you "surf the wave of torque" rather than rev them out like you would a petrol engine.

Enjoy your test drives

[gldgti]

quite right on all counts here.

being an old hand at the F3 myself, i know where your coming from - but in my position its like this - my 16 year old mk3 turbo diesel does 2900rpm at 115km/h. the brooklyn hill is nothing at all, i can accelerate in 5th gear up that hill without any probs, not more than 3/4 throttle to get to very illegal speeds. at full throttle, my clutch gives out

the mooney ck bridge hill is a steepy but even so the diesel just eats it. no probs accelerating up there in top gear. if i get slowed to 90km/h (2300rpm, ish) i can still acelerate up to 115km/h no probs, all the while babying the clutch.

i dont know how much power or torque its making, but I would guess that i could make (without clutch slip) slightly more power than a 77kw TDI, and slightly less torque. peak torque in the mk3 is between about 2500-3500.

HTH.

[Hadders]

I'm very grateful to all who responded.

Noting Gregozedobe's reference to gear ratios.....

At the risk of digressing, it was ratios that led me to the land of Ibiza.

In '95 I was fantasising about a new Golf but was a bit short of the brass. A solid 2.0 litre engine appealed after years of peddling an old fashioned 1.3 (in a heavy Lada body no less) up and down the hills of the eastern suburbs.

The chaps at Rushcutters Bay also gave me an Ibiza brochure as well. I'd never heard of SEAT. When I had the brochures at home side by side, i noticed that the gear ratios were the same to two decimal places and the penny dropped - THESE TWO CARS HAVE THE SAME ENGINE.

With the Ibiza 3 grand cheaper, I got very interested. There was another selling point which I only found out later from Matthew the wise Pom at Campbelltown - yes it is the same engine, gearbox etc but the Spanish took out a lot of weight to make the Ibiza lighter than the Golf. It's smaller too, but it was plenty big enough for me and the scuba gear.

The relevance of this for the current discussion is that Mk 3 Golf owners with the 2.0 litre engine can understand that I have the same, though pulling a lighter body at just over 1000 kgs.

Copyuz,

Martin Hadley