Introduction
Early Days
When Volkswagen introduced the Rabbit Diesel in North America in 1977, the diesel drivetrain was revolutionary. Mercedes had sold diesel passenger cars for decades, but the engines they used are heavy, low revving, and low-output for their displacement.
VW based their diesel on an Audi gasoline engine, so the end product was lighter, would rev higher, and made more power per cc than Mercedes diesels. For comparison, in 1977 the Mercedes 240D made 64 HP from 2.4 liters, or 27 HP/liter. The 1.5 liter engine in the ‘77 Rabbit made 49 HP from 1.47 liters, or nearly 33 hp/liter.
And that was before turbocharging came along. In North America, the first turbodiesels were in two VW models: The Jetta, which at that time was essentially a Golf with a trunk added, and the Quantum. Both offered 1.6 liter turbodiesels that made right around 70 HP and 95 lb/ft of torque, a nearly 50% increase over the 1.5 liter normally aspirated (NA) diesel in the Golf.
The addition of the turbo dramatically improved the driving experience, with easier revving, more power, and smoother, quieter operation. And in normal driving, there was little, if any, fuel economy penalty.
When the A2 Golf/Jetta was introduced, the Golf offered only an NA diesel, but the Jetta offered the turbodiesel until 1992. During that time VW introduced the ECOdiesel, which had the same block, but a smaller turbo and different fueling to optimize fuel economy. The ECOdiesel made about 10 HP less than the 1.6 Turbodiesel.
These diesels, both turbo and non-turbo, were all indirect injection (IDI) engines, meaning that fuel was injected into a prechamber where it would start to burn and then spread to the main combustion chamber. IDI diesels had high compression ratios, and the combustion event tended to be both sudden and loud, causing the diesel “rattle” that many associate with these engines. Turbos helped quiet things down, but the engines were still noticeably louder and vibrated more than comparable gasoline engines.
For reasons we can only speculate upon, including emissions regulations, fuel prices, production costs, and consumer preferences, VW took a break from offering turbodiesels from 1993 until 1996. But the best was yet to come…
Enter the TDI
Here’s a quick refresher. TDI stands for Turbodiesel Direct Injection, where a fuel injector sprays fuel directly into the combustion chamber instead of into a prechamber. TDIs are quieter, cleaner, and dramatically more efficient than their IDI predecessors.
In 1989 VW produced its first TDI engine, offered in the Audi 100 in Europe. Some 7 years later, VW offered the 1.9 liter 4 cylinder TDI in North America in the recently refreshed Passat, and a year later in the A3 Jetta. In its early generations (codes 1Z and AHU), this engine made 90 HP and 149 lb/ft of torque. EPA fuel economy figures were in the 40s, with owners regularly seeing 50+ MPG. This engine was also the first drive-by-wire engine VW offered in North America. The TDI was truly revolutionary.
As time passed and new generations of the engine were introduced, the combustion chamber design remained essentially the same, but fueling changed. Early TDIs had a rotary pump like their IDI predecessors, but in the early 2000s VW offered TDIs with unit injection, or Pumpe Düse. And in 2009, VW transitioned to direct injection in all its TDIs.
As technology improved, so did power output from the 4-cylinder TDIs. From 90 HP in the 90s and early 2000s to 100 HP in mid mid-2000s, and 140 HP in 2009. The last 4-cylinder TDIs in North America, offered only in 2015, had 150 HP.
What is the best VW turboDiesel?
Short answer is: hard to say.
- Some appreciate the early turbodiesels for their character, and the huge improvement they offered in power and refinement compared to the NA diesels. But they still didn’t make a lot of power, and they were still somewhat “agricultural” compared to gasoline engines of the era.
- Others say the common rail TDIs are the best in terms of power, refinement, and economy. But, sadly, they are saddled with emissions systems that sap some of that power and economy, and can be difficult to maintain.
The best may be the middle ground: TDI, but early rotary pump engines. These made good power in stock tune, and could easily be modified to make much more power with little sacrifice in economy or driveability. And they are virtually free of emissions hardware compared to newer TDIs.
Take your choice.
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