The Little Engine That Can

By Robert Bowen
Nov 24, 2008 | Volkswagen | Posted in Drivetrain | From the Feb. 2006 issue | Never miss an article

While lots of hotrod VW Rabbits and Golfs are powered by naturally aspirated engines, many of Volkswagen’s current offerings rely on turbocharging.

These force-fed, 1.8T-spec engines can now be found in many cars carrying the VW and Audi badges, including the popular Golf, GTI and TT models. Like the German manufacturer’s earlier engines, it isn’t hard to make more power from the 1.8T, provided the proper recipe is followed.

Earning Its Cred

When Volkswagen released the five-valve, inline four-cylinder 1.8T engine in 1997, enthusiasts gave it a lukewarm reception. The engine just didn’t get much respect outside of diehard VW geeks.

There were two reasons for this. The first was the engine’s initial application, the heavy and unloved-by-enthusiasts Audi A4. The second was its unimpressive 150 horsepower rating.

VW and Audi deemed the engine fit enough to drop into the Golf, Jetta and TT for the 2000 model year. The VW products initially got the 150-horsepower version, while the Audi TT made 180. Increases in output were around the corner, as the TT could also be had with an optional 225-horsepower version of the 1.8T starting in 2001. Likewise, the Golfs and Jettas started to get the 180-horsepower engine in 2002.

VW actually produced two different versions of the 150-horsepower engine, one for the New Beetle and another for the Golf and Jetta. The New Beetle version is choked by a smaller turbocharger, smaller intercooler, smaller injectors and a smaller exhaust system.

The 150-horsepower engine found in the standard-issue Golf and Jetta, in contrast, shares the turbocharger, injectors and exhaust systems with the 180-horsepower setups. So if you’re thinking this means that the only difference between these two powerplants is the engine management system, you’d be right.

The ECUs found in the 150-horsepower Golf engines limit boost to 0.6 bar, while the 180-horsepower mills are allowed to produce 0.8 bar. There are some minor differences in compression ratio, exhaust and turbocharger specs between the years, but for the most part the 150-horsepower Golf/Jetta engines can all be made to run like the 180-horsepower versions with nothing more involved than a modified ECU.

The 225-horsepower engine found in the Audi TT is a different beast altogether. While the block and head are pretty much standard 1.8T parts, they received two big intercoolers, larger injectors, stronger pistons and beefier rods in addition to different engine management software.

No matter what their origin, however, all 1.8T engines have similar five-valve heads. The first versions used a separate idler shaft to drive the oil pump; after 2000, the 1.8T moved to a crankshaft-mounted oil pump and dropped the idler shaft. Note that although these engines resemble VW’s earlier four-cylinder versions, the shape of the oil drain ports rules out bolting the 1.8T’s head on the older engines.

Stage 1: Basic Tuning

According to Kris Valdez, resident VW expert at Dynamic Racing Solutions and all-around tuning wiz, the 1.8T responds very well to ECU modifications—with two exceptions, which we’ll hit in a minute.

“The 150-horsepower version will usually go right up to 190 at the crank with just a chip and larger exhaust, and the 180-horsepower versions will see a proportionally smaller increase to about the same level, since they are already at a higher state of tune,” Kris says of the Golf and Jetta engines.

According to Kris, the New Beetle engine is one exception to the previous statement—the small turbo, intercooler and injectors keep it from being safely pushed beyond stock power levels. Likewise, the 225-horsepower Audi TT engine is also difficult to improve, as its high state of tune from the factory is hard to beat.

Kris says that most of the widely available chips are very good. “All of the chip makers offer stages of tune, and we really haven’t seen a bad one as long as it is matched to the modifications on the engine.”

On the subject of exhausts, he is adamant: “The larger, the better on a turbo car. On a high-boost engine, we’ve seen as much as 20 horsepower from going to a three-inch exhaust,” he explains. “In fact, if you’re running lots of boost, your money is best spent on a large exhaust.” The only disadvantage to a sewer-pipe-like system is that as the exhaust gets larger, it also gets noisier.

Interestingly, Kris says that the stock VW airbox is very good and should not pose a restriction at reasonable power levels. In fact, some aftermarket turbo kit manufacturers even recommend reinstalling the stock airbox if it has been removed. “As long as you use a good filter, the stock airbox is not really a restriction,” he says.

The stock intercooler is not especially restrictive, but it is small and quickly heat soaks. An engine with a stock intercooler can pull big numbers on the dyno, but its performance will not be consistent. “If you want to drive the car fast, as opposed to doing dyno pulls, you want a larger front-mount intercooler,” Kris says.

Stage 2: More Advanced

The next step up the tuning ladder is a larger turbocharger and bigger injectors. According to Kris, the stock K03 turbo should be good to around 250 horsepower at the crank, or 190 or so at the wheels. “The stock TT turbo is good for a bit more power,” he says, “but for the price there are better turbo upgrades out there. The GT35/GT40 kits are very good for the money and should take you all the way to the limits of the stock bottom end—say 300 horsepower or so.”

Unfortunately, the stock turbo runs out of room at about the same time the stock injectors do. “They aren’t much good above 210 horsepower,” Kris says of the stock squirters. Larger injectors and a matching chip will allow the engine to run right up to the 300 horsepower level, after which the factory ECU becomes the limiting factor.

“Without custom programming, we haven’t seen more than 250 horsepower at the wheels with the stock ECU,” Kris says. Custom programming of the stock ECU is available, but expensive. “With our high-horsepower cars, we go to an aftermarket stand-alone ECU because it is cheaper and more flexible than a reprogrammed factory ECU. Anything more exotic than a packaged turbo upgrade kit needs a lot of custom tuning to get the most from the engine.”

Stage 3: Bottom End Mods

If 300 horsepower isn’t enough to scratch your 1.8T itch, Kris and the guys at DRS have another couple of tricks up their sleeves—namely two ways to stretch the engine’s displacement and beef up the lower end at the same time.

The easy way to build a stout 1.8T is to use custom forged pistons and rods with the stock crank. “Our 1.9-liter upgrade uses JE Pistons with an off-the-shelf 9.0:1 compression ratio for high boost—up to 30 psi,” he explains. “To get the most from this, you want a larger turbo and tubular exhaust manifold.” At this level of tune, the engine likes bigger cams and head work on the intake side, too.

If up to 400 horsepower won’t do, Kris and company can swap a specially machined 2.0-liter crank into the 1.8T block and build a 2.0T monster motor. This combination has made a proven 500 horsepower at the crank on the DRS dyno, and the setup is good enough to haul a heavy A4 down the drag strip in the 12-second range. While it’s not for everyone, the 2.0 liter proves that the little 1.8T really has more potential than many non-VW enthusiasts will admit.

The Rest of the Drivetrain

With well-planned mods, your 1.8T engine could be cranking out more than twice the horsepower that VW intended it to have.

According to Kris, the stock clutch is the weak point in the drivetrain. “You will certainly need a new clutch after a turbo upgrade,” he says. With a stronger clutch, the factory transmission holds up well, although transmission life is linked more to driving style than engine output.

“These transmissions aren’t as bad as the old VW five-speeds that broke all the time. The Audi gearboxes are stronger, but the VW boxes are pretty good.”

While enthusiasts haven’t yet had 30 years to figure out all of the nuances of the 1.8T engine, many tips and tricks have already been discovered. As with other turbocharged cars, making big power from a 1.8T is in many cases simply a matter of making—and controlling—more boost.

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