A Mercedes-Benz 190SL Built for the Track

Story and Photography by John Webber

On the small-bore grid, it’s the only Mercedes-Benz, parked in a long line of MGs, Porsches, Triumphs, Healeys, Minis, Morgans and more. In fact, after more than a decade of racing this 190SL, owner Doug Radix has never seen another on the track.

Doug says he wanted to race something different and distinctive—something that drew a lot of attention. He got that and more, as the old Benz proved to be pretty competitive and as dependable as an anvil, especially in endurance races. Since 1998, he has filled two logbooks and is working on a third, flinging this unlikely warrior around road courses from Road America to Sebring.

Doug, who lives in Oconomowoc (try saying that after Happy Hour), Wisconsin, knew that four-cylinder Mercedes-Benzes were not prized for their speed and agility. But he didn’t care; he had reliability in mind. “I’ll never be the fastest car on the track,” he says, “but I’ll be around at the end of the race.”

Doug has always been a gearhead—beginning with snowmobiles as a kid and later moving up to cars. When he was 15, he started sweeping floors in a body shop, learning his trade from the ground up. Countless wreck repairs and rebuilds later, he’s still in the business. Today, his auto body enterprise handles collision repairs and restoration of vintage cars and motorcycles, along with repairs on the occasional race car that gets bent at Road America, just a short rollback ride away.

He started driving at vintage track events in the late 1980s when a customer asked him to maintain and help exercise his fleet of high-performance Ford racers—including a couple of GT-40s, Cobras and GT350s. After a taste of high-speed action, Doug came down with the fever and decided to build a racer of his own, although he wanted one a bit slower than a Cobra and cheaper to maintain. 

That’s when he remembered the street-driven 190SL he had restored a few years earlier. While he was rebuilding that Mercedes, he came to admire the car’s styling and the way it was put together. “It was built like a tank—overbuilt, really,” he explains.

Back From the Dead

So in 1992, when he saw an advertisement for a 190SL parts car, he jumped on it. “I think I paid $500,” he recalls. “It had an engine and transmission, but the interior was stripped-out and the body was rusty and dented—so bad, the sheet metal was just about gone.”

Thinking that this hulk might make an interesting race car, Doug also started accumulating piles of 190SL parts. “Back then, you could get a tranny for $100 and rear ends for $250 or so,” he explains. “It was easy to accumulate mechanical parts for that car.”

Putting those pieces to good use proved more difficult. For the next seven years, Doug slowly brought the Benz back to life, wrenching and fabricating in his home garage. His day job remained running his business.

This was not an easy rebuild. Those who build production-class racers from the likes of MG, Triumph and Porsche have volumes of instructions to guide them, along with other racers’ experience. Doug found no manuals or support groups for building a Mercedes 190SL. So he drew from his own experience, an SVRA rule book, and every racer’s helper—trial and error. “I pretty much winged that part of it,” he recalls. “I was thinking, ‘Hopefully it’s got enough power and speed.’” 

Doug started by stripping the derelict to its bones. Then he replaced bent and rusty sheet metal, renewed and strengthened mechanical parts, and reduced weight. Once he got the sheet metal in shape, he turned to safety upgrades, which included a stout cage featuring a vintage-style hoop topside and a network of braces inside. “It’s plenty stiff,” he says. Next, he added a 12-gallon fuel cell, a Holley electric fuel pump and a 5-pound fire system, along with a long list of other upgrades.

In the engine compartment, he wanted an understressed, long-lasting powerplant. “I’ve never liked to work on cars at the track,” he says. So he rebuilt and balanced the engine using stock, lightened connecting rods and Arias pistons, which raised the compression ratio to around 10:1. He ported the head, performed a competition valve job, and installed a stock Mercedes cam that drives the factory valvetrain. 

A pair of Weber 45 DCOE carburetors handles the fuel delivery, and to help the engine breathe, Doug replaced the restrictive factory exhaust manifold with a handcrafted, free-flowing exhaust header. An oversized aluminum radiator paired with a Fluidyne oil cooler keeps fluid temperatures in check. 

To help get the power to the wheels, he lightened the flywheel and mounted a racing clutch. From the clutch rearward, the drivetrain remained stock, including the four-speed transmission, driveshaft and open rear end.

Doug completely rewired the car and installed an impressive array of gauges. For a hotter spark, he installed a modified VW distributor and MSD ignition system. 

As you would expect, the bodywork, paint and graphics look like they were done by a guy who owns a body shop. The small curved windscreen and half-tonneau cover add to the vintage look. From the custom tow hooks on either end to the braided hoses and fabricated catch tanks under the aluminum hood, the work is both functional and tidy.

Sorting the Benz: Using Whatever Works

After the seemingly endless rebuild, Doug finally got the 190SL on the track, where his education really started. As soon as he started to build up speed, he discovered that the car’s drum brakes were woefully inadequate. “They would get hot, and they just wouldn’t stop,” he recalls. 

The brake upgrade proved to be a major job. Using spindles from a later 280SL roadster allowed him to install larger hubs and rotors. He then fabricated brackets and adapted later calipers for more braking power and better pad selection. To provide for front/rear bias adjustment, he installed an adjustable valve near the driver’s seat. The brakes are operated by a Tilton pedal assembly with dual-circuit reservoirs.

Getting the 190SL to handle required much experimentation, trying different anti-roll bars, shock settings, camber adjustments and springs. In the front, Doug ended up using cut-down springs from a Mustang; the rear set came from a circle track shop. This combination lowers the car about an inch and a half. The shocks are adjustable Carreras that closely resemble the originals.

For many events, Doug used a small alternator from a Kubota tractor. Recently, to provide enough juice for headlights during night enduros, Doug installed a 65-amp unit from a speed shop.

On Track

These days, the 190SL is back on the track after a layoff, but it’s still fully sorted and, as Doug puts it, “as comfortable as an old shoe.” With the number of endurance races he runs, he accumulates a lot of seat time. 

“Every race I go to, I enter the enduros because I want the track time,” he says. “This car has a lot of miles on it.” His records show nearly 50 race weekends plus several high-speed track events.

Despite its hard use, the 190SL has needed little work. Over the years, Doug has refreshed the engine three times—averaging about 57 track hours between rebuilds. Each time, he has fitted new pistons, rings, bearings and valve springs and performed a valve job.

During the Wisconsin winters, he goes over the car from stem to stern, making sure it’s ready for another season. He still marvels at the robust German engineering: “The underside of this car has grease fittings on nearly every moving part.” 

The transmission has proved to be the weakest link. “Second gear is too low to use on the track,” Doug says, “and there’s a big gap between third and fourth.” 

When he first started racing, he shifted a lot between third and fourth, and the synchros failed quickly. So he started experimenting with running most tracks in fourth gear—and actually improved his lap times by driving a better line to avoid scrubbing off speed. “It’s predictable and well balanced,” he says. “I can slide it through the corners, and that makes it fun to drive.”

Since the 190SL doesn’t have a lot of top-end pull, it’s not as competitive on tracks with long straights, like Road America. “Watkins Glen is my favorite track,” Doug says. “The car is competitive there because the sweeping corners allow me to run fourth gear pretty easily. The 356 guys are shifting two or three times in some corners, and I’m leaving it in fourth. I know it sounds weird, but it works for me.”

In SVRA competition, the 190SL competes in Group 1, Vintage F Production Class, where it runs against the other small-bore racers. In its current state of tune, Doug estimates engine output at 145 horsepower, and at 2180 pounds, the Merc outweighs most of its competitors. So Doug doesn’t often find himself in the front row. 

However, no matter where he is in the pack, he enjoys the spirit of vintage competition. “I always find somebody to race with, and I always have fun,” he says.

He also lets the race come to him. The longer the contest, the better. The Merc shines in endurance races, often outlasting faster but more fragile competitors. He has the awards to prove it, winning SVRA’s Mike Stott-UBS Financial Enduro Class Championship five times from 1999 to 2007.

In the Paddock

Other racers, not accustomed to seeing a Mercedes hurtling sideways though the turns, often come around to talk to Doug about his car. “Most have never seen another 190SL on the track,” he says. “So people come up and talk to me all the time. They love the lines of the car.” Of course, Doug always enjoys explaining his handiwork.

Once they figure out what it is, folks compliment him on the car’s wide, low stance, which conveys a taking-care-of-business attitude. Outside and in, this roadster is well appointed in a no-frills way, and the factory color and tasteful body modifications carry the theme. 

Professional touches abound, including the louvers in the hood, the tidy cockpit layout, and the fuel dry-break coupling in the trunk lid. And even during a race weekend, the car looks nearly ready for the show field.

A crowd had gathered around this roadster when we discovered it at an SVRA Sebring Enduro Weekend. By the end of the event, Doug had finished two 90-minute enduros and a sprint race, each session trouble-free. Topping off all that track time, he finished on the podium in all three of his races. 

To him, this old Merc has been well worth all the work, and he thinks it still has plenty of life left. He puts it this way: “I’ll never sell that car. Over the years, I’ve accumulated enough parts, including a body, to build another racer just like this one. I have a 19-year-old daughter who’s always wanted to race. I’d like to put one together for her.”

So if sometime in the future, you spot two 190SLs on a vintage race grid, you can be sure that Doug Radix has built another one. It’s unlikely that anyone else would even try.

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