The magical 1.9

Hello everyone,

Let's talk about an unusual topic, perhaps something quite relevant to practical applications .

Why do our (small) TDIs have a 1.9-liter engine displacement?

"Typically, the industry standard is 1.8 or 2.0... and Volkswagen is also moving in that direction with its new 16V TDIs, specifically towards 2.0."

Is there a reason behind this?

I have a theory... Could it be that they initially based the design on the existing gasoline engines and simply used a slightly larger displacement to at least partially compensate for the lack of power (of the naturally aspirated diesel)?

The first diesel passenger cars, in my opinion, had a 1.6-liter engine from VW. At that time, 1.5-liter gasoline engines were common. Later, there was a 1.6-liter engine for gasoline engines, and a 1.7-liter engine for diesels. Then there was also the 1.9-liter engine, which matched the 1.8-liter gasoline engines. And in the Polo 86c, there was a 1.4-liter diesel (48 hp) whose engine block was very similar to that of the 1.3-liter gasoline engine (and whose crankshaft is often used to increase the displacement of gasoline engines). Is there any truth to the theory?

Or is it simply the maximum that the VP37 is capable of? Because Renault's electric diesel engines are very similar to those of VW... and also have a 1.9-liter displacement.

Does anyone know anything about this, or is it just a field of pure speculation?

Best regards,

Jan.

Hi,

Actually, 1.9 versions aren't that unusual.
1.8 was mainly produced by Ford, while 2.0 was used by Opel (although they previously had a 1.7 engine, which is also an unusual size).

By the way, the first Volkswagen diesel engine was a 1.5-liter.
They had essentially 'dieselized' the 1.5-liter gasoline engine.
But soon, the 1.6-liter engine became the dominant choice.

I don't know why VW specifically chose 1.9.
But it's true that the 1.9-liter engine is based on the 1.6-liter engine, isn't it?
To my knowledge, in the 1.6-liter engine, the increase in displacement was almost entirely achieved by increasing the stroke. That's why the 1.9-liter engine also has a very long stroke (resulting in good torque). That's about all there is to it.
And the new 2.0-16V engine receives an even larger bore diameter to accommodate the extra 0.1 liters of displacement. Then that block is probably finished.

The bore spacing is the same for all VW 4-cylinder engines (correct me if I'm wrong). This is due to manufacturing reasons (the same production line is used for different engines).

Regarding the TDI engine, I heard back then that VW was trying to determine that, within a 4-cylinder diesel engine (likely under VW's specific conditions), a displacement of 1.9 liters represents the optimum (whatever that may mean).

The smallest possible engine displacement has previously always been 0.4 liters per cylinder for diesel engines. However, Smart has surpassed this with 0.266 liters per cylinder. This was long considered unachievable. That's why the 3L Lupo also has a 3-cylinder engine with a displacement of 1.2 liters.

I hope I've contributed something, even with my limited knowledge.

Hi,
The four-cylinder TDI engines are part of the 827 engine family, which has indeed maintained the same cylinder spacing since 1972. The maximum... The engine displacement, originally 1.5 liters, was increased to 2 liters through various modifications.
They simply didn't grasp the idea in Wolfsburg of making a significant change, of switching to a wider spacing. The changeover is not easy because, when machining the block, all cylinders are processed simultaneously, which requires specially adapted machine tools that are not flexible in terms of cylinder spacing.
Because the bore diameter was initially maximized, very long-stroke engines were ultimately developed. However, this wasn't a problem for diesel engines, but it negatively affected the smoothness of operation in gasoline engines due to their higher RPMs.
2 liters applies to gasoline engines. The diesel engine likely had thicker walls to increase stability, which would have resulted in a slightly smaller bore.
Christian

Hi,

The smallest possible engine displacement has previously always been 0.4 liters per cylinder for diesel engines. However, Smart has surpassed this with 0.266 liters per cylinder. This was long considered unachievable. That's why the 3L Lupo also has a 3-cylinder engine with a displacement of 1.2 liters.


But isn't it true that there was a 1.3-liter diesel engine available in older Polo models? With 4 cylinders, as far as I know?
That would have been only 0.325 liters per cylinder.
But VW is certainly also building engines that they themselves consider impossible...

Hi,

Yep, that's correct about the 1.3-liter diesel with a 4-cylinder engine. However, it was essentially a diesel version of a gasoline engine, and it was apparently prone to breaking down. In the later 86c-model Polos (i.e., those before the 6N), there was also a 1.4-liter diesel engine, also with 4 cylinders.

Therefore, they had already exceeded the 400 cm³ limit early on... although all of those were naturally aspirated diesel engines.

Best regards,

Jan.

Jan6K wrote:

Hi, Yep, that's correct about the 1.3-liter diesel with a 4-cylinder engine. However, it was essentially a diesel version of a gasoline engine, and it was apparently prone to breaking down. In the later 86c-model Polos (i.e., those before the 6N), there was also a 1.4-liter diesel engine, also with 4 cylinders. Therefore, they had already exceeded the 400 cm³ limit early on... although all of those were naturally aspirated diesel engines. Best regards, Jan

... and this 1.3-liter diesel engine belonged to the 801 series, not the 827 series!!!!

The 827 initially had a "mere" 76.5mm bore and even had water passages between the cylinders for a 1500cc engine. A 375cc cylinder size was considered ideal at the time. In 1975, the 827 lost its water passages between the cylinders, was bored out to 79.5mm, and became a 1600cc engine (the GTI could now appear!!). In 1981, the engine was modified again and bored out to 81mm. The 1800 engine was born. For the 2.0L engine, the engine was bored out to 83mm. This reduced the cylinder spacing to 3mm, and the engine block had to be reinforced with special alloys. The 1.9 diesel engine block is a modified 827 block, raised by 1.5 cm to accommodate the longer stroke (despite the 79.5 mm bore).
The engine wasn't replaced with a new one because it was a compact and reliable motor. Furthermore, this design saved a significant amount of money. Considering that other manufacturers introduced four completely new engine series during that time, one can imagine what that meant. By the way, the five-cylinder engine is an engine that has been extended by one cylinder.
This engine is quite unique: it was even sold to Chrysler in the USA (in 1979, as a 1700cc version with a 79.5mm bore and extended stroke)!!! A few years ago, Chrysler (DC) sold this engine to Rover, and it was then used in the new Mini! This is the great-grandfather of the current engine in the new Mini (it's been across the Atlantic and back).
By the way, the ancestor of the 827 engine is a discontinued 2L Mercedes engine, which was first used in the first post-war Audi in 1968. It is a copy.
An unconfirmed rumor suggests that the engine is a diploma thesis written by a mechanical engineering student, which was even graded poorly... only to become the most successful engine in Europe.

Here's an addition regarding item 827: The engine block was modified by increasing its height to improve running smoothness through the use of longer connecting rods.
The hub itself was also included with the old block. There was something similar briefly in the Audi 80, but it wasn't very popular due to its loud noise.
I, however, do not believe in the "Diplom-Arbeit" (likely referring to a specific design or concept). The intermediate shaft seems to me to be too much like a crippled remnant of a lower camshaft. That is, the engine would be a half-hearted development of an old design. That would explain the bad grade...
With the five-cylinder engine, they also removed them.
Christian

Hi Bertil and Christians,

That's an interesting story; I didn't know all the details. If there are more of those... I find things like that extremely fascinating!

What about the new 1.4-liter diesel engine with 3 cylinders? Is it an 827 engine with one cylinder removed, or something completely different? The hub diameter is 95.5, the same as the 1.9 version, and the bore is only one millimeter smaller (78.5).

Following the Polo 6N DIY guide, the small 1.3L, 1.4L, and 1.6L engines from the Polo, which I believe belong to the 801 series (or perhaps a completely different series, but they fit in the older Polos, where only the 801 engines fit, not the 827 engines), have a bore of 76.5mm, which is very close to the original 827 engine bore... or is it simply that the cylinder spacing is smaller? Or is this also a derivative of the 827?

Best regards,

Jan.

What is the lower limit for the larger model is the upper limit for the smaller model. By the way, the first Passat, which was actually an Audi 80, initially had a 1.3L 827 engine, then one from the 801 series, which was certainly one of the cheaper options. At that time, it still had pushrods instead of tappets. And that's despite the fact that the distributor mounted on the head of the 801 was extremely unsuitable for changing contacts during lengthwise installation.
Christian

Hi,

Okay, I'll try to break this down further.
(or to completely confuse things).

There are other (more exotic) VW-Audi diesel engines that are based on the 827 platform.
If you extended the old 1.6-liter engine by one cylinder, you got the 2.0-liter 5-cylinder engine, which I believe had around 69 horsepower in older Audi 100 models.
Another cylinder added on – and there you have it: the 2.4-liter inline-6 engine from the VW LT van and (very) old Volvos.
If you extend the newer 1.9-liter engine by exactly one cylinder, with the same bore and stroke, you get the 2.4-liter 5-cylinder engine with 82 horsepower, which was briefly available in the Audi 100 C4.
If the bore was then increased from 79.5 to 81 mm, it resulted in the 2.5 TDI engine (1T, AAT, AEL).
Sure, I'm ready. Please provide the text you would like me to translate from German to English.
'Wouldn't that be a rather 'extreme' bore size for the 2.5-liter engine with an 81 mm diameter?'

Jan6K wrote:

Hi Bertil + Christians, That's an interesting story; I didn't know all the details. If there are more of those... I find things like that extremely fascinating!

Boha, you're asking all sorts of things...
Should I write a whole treatise about the 827s? What I just wrote was really just a condensed summary. You can find the beginnings in the book "VW Tuning, Golf, Scirocco, Jetta... this is how you make it faster" by Gert Hack (a completely unknown person in the automotive industry ).

Quote:

What about the new 1.4-liter diesel engine with 3 cylinders? Is it an 827 engine with one cylinder removed, or something completely different? The hub diameter is 95.5, the same as the 1.9 version, and the bore is only one millimeter smaller (78.5). Following the Polo 6N DIY guide, the small 1.3L, 1.4L, and 1.6L engines from the Polo, which I believe belong to the 801 series (or perhaps a completely different series, but they fit in the older Polos, where only the 801 engines fit, not the 827 engines), have a bore of 76.5mm, which is very close to the original 827 engine bore... or is it simply that the cylinder spacing is smaller? Or is this also a derivative of the 827?

I once had a 6N model with 75 horsepower back in 1996, and I'm pretty sure it was a derivative of the 801 engine.
Are the newer engines in the Polo and Lupo actually ALu engines? Are these still 801 engines, or is this a new engine?

Quote:

The intermediate shaft seems to me to be too much like a crippled remnant of a lower camshaft. That is to say, the engine would be a half-hearted development of an old design.

... that's exactly how I see it too. On the other hand, this could be a sign of a "beginner's work" (please don't kill me, mechanical engineers).

I completely forgot about the 827 engine in the Passat and Audi 80. It was installed because the length of the distribution boxes from the 801 model wouldn't fit underneath (the distribution box would then have been located in front of the injection molding machine).
There have been and still are so many exotic variations of the 827 that it would surely overwhelm the forum.

@ Markus H.

The concept of modularity has always been highly valued at Volkswagen. After all, the people at VW weren't that unintelligent. This strategy ensured the use of many identical components, which resulted in favorable prices from the suppliers.

Update on December 13, 2002.

The first V8 engine from Audi was also an engine assembled from two 827cc units.

Hi Bertil,

So, I would be interested in the paper ), but you don't have to go to the trouble of typing it out.

Regarding the newer engines in the Polo, I don't know if they are based on the 801 design (I believe they might have been called something similar in the older Polo EA111), but it's certain that the newer Polo engines with 1.4/100PS and 1.6/125 PS can also fit into the older Polo, which was originally designed for the 801 engine. Therefore, at the very least, the external dimensions should still be correct...

Best regards,

Jan.

Hi,

@Bertil:
I can only agree with Jan!
I would also find such a treatise very interesting.
We could also publish them here on this page, right?
Because otherwise, while you might occasionally find references to '827' on the internet, you'll rarely find detailed information about it (as far as I know).

P.S.:
How did the V6-TDI engine come to be in the Passat and Audi?
Is it that easy to derive?