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General VW Discussion This is a place for General VW topics (the company, not your vehicle). General topics about a specific vehicle should be posted in the General TDI Dicussion Forum sections for that vehicle platform. A4, A3 & B4, B5, etc.

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Old March 19th, 2006, 20:20   #1
vwestlife
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Default VW's 2.3L oval-piston diesel

I just came across this on Ti Kan's Audi site... in 1990, VW developed a 2.3-liter 4-cylinder diesel engine with oval pistons (well, actually they're elliptical, not oval):



Comparison to a standard 1.6L diesel block:


The bore was 99.49 mm in the long direction, and 76.5 mm (same as the 1.6L diesel) in the short direction. The crank was the same as the 1.9L diesel. The exact displacement was 2343 cc, with 57 kw (76 HP) and 165 Nm (122 lb-ft) torque. No turbo. The pistons were developed by Mahle, and the engine was used in several VW test cars, but obviously never put into production. It was written about in 1990 in Germany's "Auto Motor und Sport" magazine, if anyone cares to look it up and translate.
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Old March 19th, 2006, 21:25   #2
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Interesting! Wonder what the advantages to this piston shape is?
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Old March 19th, 2006, 21:29   #3
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Quote:
Originally Posted by coachgeo
Interesting! Wonder what the advantages to this piston shape is?
More displacement with less engine length?
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Old March 19th, 2006, 23:15   #4
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Quote:
Originally Posted by whitedog
More displacement with less engine length?
That was the idea, but it was destined to merely be a curiosity, because around that time VW/Audi introduced their first TDI in Europe, and they were already getting a respectable 80 HP out of the intercooled 1.6L IDI TD.

Also, the oval-piston 2.3L diesel did not have the same kind of gains in power over the 1.9L diesel, as the 1.9L had over the 1.6L. For example, the non-turbo 1.9L has 40% more torque than the 1.6L, but the oval 2.3L only has 22% more torque than the 1.9L. I suppose it's like speakers; an oval 4"x10" speaker may have a larger surface area than a 6" round speaker, but a round 6" speaker will have higher power handling and better frequency response than the oval 4"x10" speaker, because the circle is a more efficient shape for turning the voice coil's vibrations into sound.

p.s. 1990-1991 was also when VW was developing the VR6... obviously it became much more of a success than the oval-piston diesel.
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Old March 20th, 2006, 04:59   #5
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It's a cool idea, but I'd be concerned about a non circle piston... and even moreso... a non circle bore.

It's probably not a coincidence that both the oval bore and VR were developing at the same time, since both designs are aiming at the same exact end. More engine in less space.

The VR's revolutionary ideas were based primarily on the offset journals between the 2 banks, and not in changes to the basic, and proven cylinder design, making success a slightly easier task.
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Old March 20th, 2006, 10:12   #6
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Honda played with elliptical pistons in motorcycle engines years and years ago. In their case, the ellipse was the other way, and there were 2 con-rods and doubled-up valves - the engine was an elliptical-piston V4 that was laid out like a V8 but with the adjacent cylinders joined. If anyone's curious, the extremely limited-production NR750 was like this.

It was not a good idea.
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Old March 20th, 2006, 17:37   #7
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Quote:
Originally Posted by coachgeo
Interesting! Wonder what the advantages to this piston shape is?
Looks more like the result of the drivetrain engineering manager trying to prove a point to the chassis department!

Either that or someone in production spilled coffee on the drawings...
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Old March 21st, 2006, 07:58   #8
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Well, aren't the VW 1.6 diesels known for making themselves oval ANYWAY?
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Old March 21st, 2006, 10:39   #9
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Quote:
Originally Posted by GoFaster
Honda played with elliptical pistons in motorcycle engines years and years ago. In their case, the ellipse was the other way, and there were 2 con-rods and doubled-up valves - the engine was an elliptical-piston V4 that was laid out like a V8 but with the adjacent cylinders joined. If anyone's curious, the extremely limited-production NR750 was like this.

It was not a good idea.
I remember reading a motorcycle mag article about that when it came out. Somehow they thought it would give them improved valve flow/performance.
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Old March 22nd, 2006, 16:46   #10
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They raced 2 strokes with the same oval design in the 80's (motorcycles)
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Old July 11th, 2007, 06:16   #11
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Seems like the oval motorcycle engines also featured 6 valves per head!
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Old July 12th, 2007, 08:56   #12
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It seems to me the pressure would be displaced in line with the rod. Piston could be lighter and stronger. Rod bearing wear would also change. The cost and complexity probably not justified.
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Old July 13th, 2007, 22:39   #13
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VW has a habit of developing innovative stuff and either:
- not using it at all
- use it for a couple of years and then revert to a conventional design
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Old July 15th, 2007, 14:06   #14
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IIRC the pistons in my 85 Escort Pony were not round- on purpose-. It was the most trouble free and cheapest car I have owned to date. 200K miles and only normal filter/fluid/plug maintanance and a couple of timing belts- non-interference engines rule-, and one set of front pads.
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Old February 4th, 2010, 14:47   #15
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Many pistons are not made round. They expand and become round as the heat up.
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