It wasn't long ago that true sleepers were available from the showroom floor. If none really interested you, building your own was as easy as calling a few aftermarket tuners to turn that sedate daily driver into a fire-breathing powerhouse. Today it seems the sleeper has all but disappeared; fewer and fewer enthusiasts are building them on modern platforms.
Defining a sleeper is difficult. What constitutes a sleeper will vary proportionally to the number of enthusiasts asked. The most general term refers to a car whose pedestrian appearance belies its performance. Performance, however, is also a somewhat subjective term. Do we consider sleeper performance to be based on straight-line ability, handling, braking? Maybe it's a combination of all three.
Manufacturers have moved away from building sleepers for a variety of reasons. From a marketing perspective, they want to advertise just how quick their brand-new machinery is. Vehicles like BMW M cars, Mercedes AMGs, and Audi S and RS lines are all hot-rod versions of more mainstream offerings. They still have the same basic shape of the original platform, but are festooned with more aggressive aerodynamic packages, larger wheels, gloriously detailed brake calipers and large, snarling, chrome exhaust tips that scare small children.
From a technical perspective, those traits-wheels, brakes and shiny orifices-are all necessary to get the desired performance. It's also necessary to consider how much faster they can (or even need to) make a true sleeper. Performance figures from most base European models are enough to send 15-year-old sports cars to run and hide. do you need to build a sleeper version of an E90 335i when it's equipped with over 300 lbft of torque from the factory? It'll already give the previousgeneration M3 a run for its money-and isn't that far behind the current model.
The same can be said for just about every category. The lowest powered S-Class comes with 391 lb-ft of torque and will run to 60 mph in six seconds. The base Volkswagen Rabbit now leaves the factory with 180 lb-ft. That's nearly 40 lb-ft more than the Mk II 16-valve GTI, still considered by many to be the ultimate example of the bloodline. Performance is relative, but at some point you have to try and determine how much is sufficient and at what point sacrifices in usability outweigh performance.
With the continual improvement of factory vehicles, tuners are having a tougher time creating real sleepers. Part of it lies with cars being optimized from the factory. It's becoming increasingly difficult to wring power out of factory setups with simple bolt-on upgrades. At one time, it was easy to add one or two components for a noticeable improvement without the tell-tale outward signs of modification. Engines now require a much broader view for real improvement. You can swap a part here and a part there, but true optimization requires a full tuning package. It's harder to hide extensive modification than one or two key components, making them more obvious to outside observers. More power may come from software tuning, but increasing boost on a forced induction engine too much will work past the limits of the fueling and intercooling systems. Increased boost can soon find the factory exhaust's shortcomings as well. Clearly, a complete solution is the answer.
This idea of holistic tuning can be applied to the entire car. Increasing power and torque requires improvements to suspension and braking systems. a larger turbo or supercharger will show up the vehicle's other systems as inadequate. Larger contact patches will be needed to get that extra power to the ground. A recalibrated suspension will be needed to deal with the added forces of more mechanical grip. Braking capacity will need to be increased to deal with the extra kinetic energy created by greater straight-line speed. Pretty soon, the 'stealthiness' of the modifications has all but disappeared, giving way to larger wheels, lowered ride height and visible add-ons.
Some enthusiasts have found a work-around with a tuning style known as OEM Plus, using factory components from other models or even stock parts sourced from foreign markets that still have a factory appearance. Volkswagen enthusiasts have been swapping K04 turbos and associated fueling components from 225-hp TTs on their 1.8Ts with great success. BMW E36 M3 owners source the more powerful Germanmarket M3 powerplant for big gains. Some even turn to factory performance parts available from the dealership. Outfits like Volkswagen's Driver Gear sell everything from sport springs to exhaust systems, all backed with a factory warranty.
Older vehicles have been fair game for sleeper projects for years. Audi tuners have been swapping later and/ or larger engines almost since the beginning of the brand. VW enthusiasts started swapping 16-valve motors into Mk I cars, then later turned their attention to swapping VR6s into Mk IIs, and more recently 1.8Ts into anything and everything. Even Porsche enthusiasts (who are favored by modular engine designs) have taken to swapping entire engines and electronics from newer vehicles. Sometimes advances made by the factory are the best and easiest solutions.
The future looks even bleaker than the present for sleepers. Manufacturers are becoming ever more diligent about making life harder for tuners. Automotive ECUs are increasingly difficult to access and legal steps are being taken to discourage tuners from tinkering with software. As I write, BMW is fighting tooth and nail to keep tuners out of the new twin-turbo six's ECU. The thought of easy horsepower drove initial sales of the 335i. Most enthusiasts believed 50 or more horsepower would be just an ECU flash away, but sadly that has not been the case. The best software tuners will always find a way to get into new ECUs, but a flash will likely become more expensive and will need to be purchased as a part of a tuning package, not as a standalone upgrade.
Hard parts will always be around, but as stated, they won't supply such a large improvement without software cooperation. But the real downfall of the hardware tuner may end up being environmental laws. CARB certification is difficult and expensive to get and only the most diligent tuners are willing to undergo the process. As more states adopt CARB standards and increase yearly inspections, it will be harder for enthusiasts to modify their vehicles.
All these things may combine to become the ultimate downfall of the sleeper. Most drivers aren't interested in blending in any more. Manufacturers do everything they can to get their cars noticed. Changing views, along with the difficulty in creating a homemade sleeper, may lead to a downturn in projects. Rising fuel costs and environmental concerns may lead to a sudden revelation of: 'we already have more power than we need.' Once power starts declining, the sleepers will rise again.