Gear Ratios: Calculation & Optimization

Hi everyone,

Inspired by the discussion about the "long" 5th gear, here's a question:

According to the "documentation" for the Ibiza 6K (not the strange new model, which by the way is called 6L; I checked the VIN number once at a dealership ), the 90 hp version had a gearbox with a gear ratio of 0.717 on the 5th gear, while the 110 hp version has 0.744 (see below). It's exactly the same as in the Golf 3 and the 1Z and AFN engines. The axle ratio is always the same, and the other gears are proportionally adjusted accordingly (so they are longer on the 90 hp model).

Does anyone have any idea what the exact purpose is of combining a more powerful engine with a shorter gearbox? Is it just for acceleration, or are there other reasons? Because, especially after what Diesel Goette wrote in another thread, it seems that the 110 (I'm assuming he has that one, otherwise the swap wouldn't make sense) runs very well with the different gearing.

And, another thing:

The ASV differs from the AFN, among other things, in that it reaches its peak power of 81 kW at 4000 rpm, whereas the AFN only achieves this at 4150 rpm, similar to the 90 hp engine. Doesn't this eliminate any justification for this gear ratio?

Or is this simply a piece of misinformation from Seat, and do the current 110 models also have a different gear ratio? That would contradict the fact that my car fits Ulf's Excel calculator quite well, which is based on the AFN transmission, which according to that Seat document corresponds to the one for the ASV. If I remember, I will check the GKB; then we can probably look into it .

Data regarding Ibiza TDI transmissions: http://media.seat.com/en/Barcelonannr01/aleman/caracteristicas/ibiza3.jpg

Best regards,

Jan.

Hi Jan,

In my wife's vehicle registration document, the ALH engine is listed with a rated speed of 3,750 rpm.
Considering that, the "longer" translation of the 90hp Ibiza makes sense again – it then revs slightly above its rated RPM at each respective top speed, just like the 110hp version (if my calculations are correct).

Hi Ulf,

Okay... I didn't know about the 3750 either. In the file I mentioned earlier, it also said 4000 (probably from the predecessor), but it also listed the 110 model with 4150, while in reality, the ASV was already installed at that time, which has a Pmax of 4000.

Otherwise, you're right about the RPMs... at maximum speed, the ASV typically reaches around 4300 RPM, assuming there are no hills or headwinds assisting it.

What then arises as a new question for me }: Why haven't they changed the gear ratios for ALH/ASV compared to 1Z/AFN, even though the engine speeds at which maximum power is achieved have decreased...?

Riddle upon riddle.

Best regards,

Jan likes low RPMs.

Quote:

But then a new question arises for me: Why didn't they change the gear ratios for ALH/ASV compared to 1Z/AFN, even though the engine speeds at which maximum power is achieved have decreased...?

Hi Jan,

The ASV engine only rotates at 150 rpm less than the AFN engine, but the ALH engine rotates at a full 250 rpm less than the 1Z engine.
Perhaps the "threshold" for a gear change lies somewhere in between, around 200?

Hi there,
'This directly affects me, as I drive an Alh with a DQY transmission. Have I already received the .707 version? It would be annoying to have to buy it again now, or is this another variant, since you're talking about the .717 here...? (Maybe a typo?)'
When I compared my old A4 (110 hp) to my in-laws' older A4, the latter definitely reached its top speed at a lower RPM. *[I'm very confused, it's late, and I can't explain my sentence structure.]*

greetings
I'm sorry, I can't translate that word because it doesn't seem to be a real word in any language I know. It might be a typo or a made-up word. Could you please double-check the spelling?

"At least with the Ibiza, the 5th gear in the ALH 0.717 engine is indeed a 0.717 ratio, so that's not a typo. In my opinion, there's no gearbox with a 0.707 ratio; only the one with 0.717 exists. Therefore, the gear set for the 5th gear that Diesel Goette uses is likely the same one you already have, because you have the longer-geared 90 hp engine."

For the Ibiza (older model, 6K), the gear ratios are shown in the JPG file I mentioned earlier. I don't know the gear ratios for the Golf and similar models, but there are probably tables available online that provide this information.

"@Ulf: It doesn't seem to be the case right now... they didn't change anything between the 1Z and the ALH either, if I understood correctly. So, despite the difference of 250 [units], they have the same transmission. Similarly, the ASV and AFN engines have the same gear ratios despite a difference of 150 [units] in their maximum power RPM. Or am I mistaken about the 1Z vs. ALH?"

Best regards,

Jan.

The 90 horsepower TDI Golf Mk3 came with two different transmissions: the ASD with a final drive ratio of 0.717 and the CTN with a final drive ratio of 0.756 in 5th gear. I'm not sure which transmission was paired with each specific engine.

Jan6K wrote:

@Ulf: It doesn't seem to be the case right now... they didn't change anything between the 1Z and the ALH either, if I understood correctly, so despite the difference of 250, they have the same transmission. Similarly, the ASV and AFN have the same gear ratios despite the difference of 150 in the maximum power RPM. Or am I mistaken about the 1Z vs. ALH?

Hi Jan,

I'm not familiar with the transmission options for the older 1Z Ibiza. Therefore, I assumed that it had the same gear ratios as the 1Z Golf (and that only the ALH engine received the longer transmission due to its lower rated RPM).

The 1Z engine has a slightly shorter gear ratio compared to the AFN. As a result, both engines reach their respective maximum speeds while operating slightly above their rated RPM.

Okay, great, then I can forget about that for the exam (by the way, I double-checked, 707 was a mistake, I also found 717...).
nonsense, no further translation needed...
Then I can look forward to having an acceleration rate of up to 200 (units), but no more than that.

greetings
eltipo (disappointed and eyeing a new car *GGG*)

Hi Eltipo,

guck dir mal in dem Seat-PDF, das ich da gepostet hatte (Thread "Wunschgetriebe") die Daten beim 100 PS PD TDI an. Von der Achsuebersetzung und der Gangzahl entspricht es genau dem Getrieben von ALH und ASV, aber es hat einen 5. Price: €0.70.

So, you're not completely without hope then... these parts might at least offer a small improvement, assuming they can be installed.

Best regards,

Jan.