Chicago Auto ShowCHICAGO – Mercedes-Benz’s AMG high-performance tuner division makes ultra-powerful vehicles capable of going fast. In some cases, approaching 200 mph (322 km/h) fast.

It is a big reason their exclusive customers pay impressive prices for AMG’s wares.

But in 1987, mass-producing German auto makers, such as BMW AG, Mercedes and Volkswagen AG, entered into a voluntary agreement with the German government to limit the top speed of even their most powerful models to 155 mph (249 km/h).

This “gentleman’s agreement” was conjured up to offset a “social and political environment in Europe,” that was beginning to target automobiles as an environmental liability, says a BMW insider. If all cars pollute, fast, powerful cars must be particularly unsavory, the logic presumed.

Seeking not to rouse an increasingly vocal environmental lobby, the German auto makers agreed no vehicle would be permitted to exceed 155 mph – despite ever more powerful engines with the capability to generate considerably higher velocities.

BMW believes the ’88 750iL, with a 5L DOHC V-12, was the first vehicle to employ the 155-mph speed governor.

But wide-ranging fuel-economy and emissions legislation adopted in the last two decades effectively has calmed concerns about the environmental impact of automobiles.

Mercedes CLS 55 AMG

That change in sentiment, along with the fact that 500-hp V-8 and V-10 powerplants now are almost commonplace, means buyers of ultra-high-performance vehicles are paying big money to modify their beasts’ electronic reins.

Every volume vehicle leaving German auto makers’ factories capable of exceeding 155 mph still has engine-management software limiting top speed.

But after taking delivery of these invariably expensive high-performance models, a staggering number of owners drive directly into the service bay and pay to have the speed-limiting software modified to permit speeds that in some cases approach 200 mph (322 km/h).

The BMW source confirms that European customers buying the new M5 and M6 models from the auto maker’s in-house tuning division, “have the option of turning off the (speed) limiter.”

He says these vehicles, with 500-hp V-10s, are capable of reaching 186 mph (300 km/h), and many buyers, particularly those using sections of the German Autobahn that have no speed limits, insist on the ability to go faster than 155 mph.

A charge of about €2,500 ($3,000) includes an upgrade to tires rated for such speeds. And the customer must attend a BMW driver-training school.

But BMW will not remove vehicles’ speed governors in the U.S.

Archrival Mercedes’ AMG high-performance division has for some time permitted European customers to have speed-limiting software modified for some models.

And beginning late last summer, Mercedes inaugurated its clandestine-sounding “030” order code for AMG customers in the U.S.

The 030 option – part of a seemingly innocuous “performance package” – allows buyers of the SLK 55 AMG, SL 55 AMG and CLS 55 AMG to circumvent the 155-mph speed-limiting software.

But code 030 buys more than speed-governor rollback, says Rob Allan, AMG product manager for North America.

The not-inconsequential 030 option price, which runs from $6,900 for the SLK 55 AMG to about $14,000 for the SL 55 AMG, includes substantial chassis and tire upgrades to make it safe to more than double the highest legal speed in the land.

Allan says the number of customers opting for 030 has been remarkable.

Through Dec. 15 (about four months of the option’s availability), 600 customers returned to Mercedes dealers for the 030 option, which raises the top speed of the SLK 55 AMG and CLS 55 AMG to 176 mph (283 km/h) and makes 186 mph (300 km/h) a possibility for the SL 55 AMG.

That number represents a significant portion of sales for those three models, and total AMG sales in the U.S. last year were less than 10,000 units for 12 models.

Mercedes does not ask buyers to sign any waivers or other legal papers. But Allan says 176 mph or 186 mph is “equally illegal” in the U.S. as the standard governed speed of 155 mph.

Electronic speed governors are largely irrelevant for the majority of U.S.-made vehicles, which typically are not engineered for the high speeds possible in Germany.

But for most high-powered domestic models, there is no speed-restriction software in their engine-management systems. Chevrolet press material, for example, says the Corvette Z06, with its 505-hp 7L V-8, is capable of 198 mph (319 km/h) “as measured on Germany’s Autobahn.”