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