Diesels are bought for one or both of two reasons. In a heavy-duty truck, it's for stump-pulling torque, and in those trucks or European diesel passenger cars, it's for fuel economy. The U.S. diesel take-rate on heavy-duty trucks is 75% and up at the Detroit 3 makers. On the continent, more than half of the passenger cars are purchased with diesels. Both examples display very conscious decisions of the buyers, according to Gale Banks of Banks Power, aftermarket diesel performance parts specialist and a director of SEMA (Specialty Equipment Market Association).
The history with U.S. trucks is that perhaps 30% of buyers will modify the vehicle in some way, Banks told AEI, leading to a similar possibility with diesel cars sold here.
Many of the changes involve suspension for off-road use or greater cargo-carrying capacity or pickup box modifications for work or camping requirements. But a significant percentage—5% out of the 30%—is for performance, he said.
Banks Power fields a Bosch-sponsored truck racing team and both uses and sells modified Bosch fuel-injection components for racing. However, they are primarily an application of the "race Sunday, sell Monday" approach. Most of the truck performance parts the company sells are for everyday improvement in performance. "Much of my present customer base is towing an RV," Banks said, including motor homes and SUVs.
That translates to installation of cold air intake kits and new intake manifolds, higher performance intercoolers, post-catalyst exhaust systems, and add-on electronic modules.
Another popular retrofit device that goes into trucks, particularly when not an OE option, is an exhaust braking system. For most such vehicles, Banks said, the kit contains a butterfly valve housing for the exhaust system and, if not OE-installed, an electronic brake controller.
However, many General Motors Duramax and Ford 6.0-L V8s have an electronically controlled variable geometry nozzle turbo for which his company markets a control module called "SpeedBrake." It is a plug-and-play installation, and it works by changing the turbo nozzle size for maximum exhaust braking. The module adds downshift and torque converter clutch disengagement with re-engagement if necessary to prevent overheating transmission fluid.
Banks believes the American buyer of a European diesel car is a "gearhead—he knows what diesels are about." Entry of European diesels into the U.S. market gives companies such as his an incentive to expand from diesel trucks to diesel cars. A 2009 Volkswagen Jetta TDI diesel is a Banks showcase vehicle that Bosch has displayed.
The Jetta has a new exhaust and cold air intake kit, which also are usual aftermarket fare for use in gasoline engines, plus a tuner module and dashboard touch-screen PC based on Microsoft's consumer electronics platform. The computer, introduced by Banks at the 2009 SEMA show in Las Vegas, not only permits selecting engine (and in some, transmission) maps but also provides monitoring and diagnostics and even some conventional PC tasks. The powertrain functions are via its connection to the OBD II system and a tuner module. Called the "IQ," it has more than 750,000 possible configurations.
A tuner module, widely marketed for diesel trucks, is installed inline between the Jetta TDI powertrain computer and its harness. It monitors fuel rail pressure and has maps that modify injection timing and pulse, rate of change of acceleration enrichment, and the turbocharger's boost curve. Banks said the company's Jetta tuner also might come with software to manage the automatic transmission shift points curve for greater fuel economy, a feature available in some tuner modules for diesel trucks.
Also available for trucks are lower cost tuners that permit short-term, on-the-fly increases in performance by increasing fuel delivery and raising the boost level above specifications but with an exhaust gas temperature sensor to detune the system if necessary.
Jetta modifications do not affect the launch torque of the 2.0-L TDI—diesels have that in abundance, but in a brief test by AEI (including private-road use), they improved midrange and high-speed performance, although specifications were not available. The diesel felt more like a gasoline engine at speeds up to and exceeding 90 mph (145 km/h).
The North American racing possibilities? Currently, there's only a program with "stock" Jettas, Volkswagen-sponsored, using company supplied and prepared TDIs tuned to European emissions specifications, which deliver 170 hp (127 kW) vs. 140 hp (104 kW) for cars sold to meet 50-state U.S. emissions regulations. The difference is in software, not special parts, according to Clark Campbell, Motorsport Manager, Volkswagen of America.
Banks emphasizes that his aftermarket tuner modules are programmed with performance maps that maintain regulated U.S. emissions levels, and safety overrides that prevent excessive levels for exhaust gas and fluid temperatures, boost pressure and torque converter or transmission clutch slippage.
The Banks Power facility has three engine dynamometers, four sets of all-wheel-drive dynos, and six emissions test benches, plus portable emissions devices that are correlated to them.
California is requiring a biennial smog check of all 1998-on diesel vehicles 8500 lb (3855 kg) and under, starting this January. The program includes exemptions or approvals for aftermarket parts, and the Air Resources Board has listed many parts to date. The shop test procedure includes visual inspections for unapproved parts and idle smoking (plus a snap throttle test for smoke) and an OBD II emissions system check.