TD Speeds: Yesterday and Today

Hello,

My first car was a Golf 2 GTD with 70 horsepower. Its maximum power output was at 4,500 rpm, and you could realistically rev it up to around 4,600 rpm.
My second car was a 1997 Golf AFN with 81 kW of power, reaching its maximum performance at 4,150 rpm and capable of being revved up to approximately 4,400 rpm.
My current project car is a 2002 Golf with an ASZ engine and 96 kW. Maximum power output at 4,000 RPM, with a usable rev range up to approximately 4,300 RPM.

What is the reason that maximum rotational speeds are constantly decreasing over time?
I don't think it's due to the longer stroke compared to the 1.6-liter engine. The RPMs are still low, even for a 95.5 mm stroke.

Do you have any idea?

Hi,

I actually think that this (also!) has something to do with the increased piston stroke. I believe the increase in engine displacement from 1.6 liters to 1.9 liters was achieved solely by increasing the stroke.
And that's when you get quite rapid piston speeds.
One should really check the maximum. Calculate the piston speed for the 1.6-liter engine and then for the 1.9-liter engine.

By the way, it seems that the next increase in engine displacement, from 1.9 liters to 2.0 liters in the upcoming TDI generation, will this time be achieved through a slightly larger bore. Probably, there isn't much more that can be done with the engine - otherwise, it will soon be shut down at 1,900 RPM - then we'll really be driving trucks...

Michael748 wrote:

What is the reason that the maximum rotational speeds are constantly decreasing over time?

Hi.

Your "meaningful" rev limit is probably quite subjective.

For me, objectively speaking, the actual engine speed at which the fuel injection quantity (along with noise and heat losses) is only sufficient to overcome internal friction is a key factor (see AU). And, as far as I know, it's around 5000 rpm for all TDIs.

If there's a "motor policy" behind it, I suspect the reason is the increasingly higher power output achieved even at "low" engine speeds, which means that the (uneconomical for diesel engines) range above 4000 rpm can be increasingly avoided.

Hello fellow diesel enthusiasts.

I was just thinking: at 4000 RPM, one revolution takes...
Just 0.015 seconds!! Fuel injection and combustion require...
Probably around 45 degrees of crankshaft rotation, which is equal to 1/8 of a revolution. The
results in a time of just under 2 thousandths of a second.
The shorter the time, the more difficult it becomes to achieve completeness.
and to achieve verschandeln combustion!
I think that's why the torque is higher in the upper range.
withdrawn.

Best regards, Chrigu.

@ ulf:

Your objective engine speed is completely irrelevant to me, as it has no practical significance in real-world driving.

Michael748 wrote:

@ ulf:D For me, an objective rev counter speed is completely irrelevant, as it has no practical significance in actual driving.

Sure, I'm not going to push mine to 5000 either.

The torque curve between the rated power point and the final speed limit can, of course, be "modeled" to a certain extent using characteristic curves; however, it is also crucially dependent on the design parameters of the combustion process of the hardware, i.e., the engine.
The latter are generally not as variable as characteristic maps, but instead tend to favor specific speed ranges.

And with VAG diesel engines, the increase in torque around 2000 rpm is growing more rapidly with each generation compared to the peak power output, meaning the engine's "optimally tuned" operating range is becoming narrower.

This may be the reason for the apparent shift of the practical upper speed limit downwards...