The Mercedes-Benz R129 SL Class is German engineering at its finest, remnant of an era where Mercedes was undisputed in regard to build quality. This page is just a collection of my thoughts on this fine automobile.

M120 V12
6.0 Liter Displacement
4 Valves Per Cylinder
Double Overhead Cams
Liquid Torque

5 Speed Driver Adaptive Transmission
Curb Weight - 4,445 lbs
Fuel Capacity - 21.1 US Gallons

Some Photos:

Photo Update:

I absolutely adore the V12 motor, and the rush it provides when top down, exposed to the symphony of pistons, valves, and camshafts peaking their crescendo in the upper echelon of the power band. The requirement is simple. Provide it with quality gasoline and oil, and the M120 will gladly return a couple hundred thousand miles of longevity. What I have come to learn is that this is an automobile that needs to be driven hard frequently. Driving it softly is a waste, in my humble opinion; why purchase a "Bahn-Stormer" and feather-foot it? What I have also learned is that not only is this motor underrated from the factory by a bit over five percent, as several dyno tests have indicated, but that there is also quite a bit of hidden potential locked away within it. For instance, the exhaust manifolds are tiny to accommodate the cramped space, consequentially inhibiting free flow. There are four cumbersome and restrictive catalysts, leading to a bulky muffler in back. Not bad considering the lack of room underneath, but a set of long tube headers and uncorked exhaust would do this motor wonders. Another area for improvement is the intake. The R129 has a dual ram air setup, which is great, yet hindered by absolutely puny air inlets. Opening these up would yield some noticeable gains.  Additionally, the factory map is shockingly conservative, as software tuning alone yields nearly thirty dyno proven horsepower to the crank; for a naturally aspirated car, this is stunning. However, although the potential is certainly there, it costs a bit to amp up the M120, even with basic performance upgrades.

For simple gains that won’t put a big dent in the wallet, a set of high flow filters and Royal Purple 5W-30 will free up a few ponies. K&N advertises up to a 5% gain and Royal Purple advertises up to a dyno proven 3% gain. An 8% gain from such simple upgrades is comically optimistic for a car that comes fairly well engineered, but with a combination of the two, my car does feel more responsive. At an absolute best, I feel I could have picked up a 3% gain from both, which bumps the already underrated output to a little over 400 bhp and 430 ft-lbs of torque. The motor itself I left entirely stock. While a nitrous kit could make things very naughty, repair bills could easily exceed the value of the car when experimenting to such a degree.

Maintenance costs have constricted my modification budget, so I am withholding further performance upgrade spending. The maintenance is not for the faint of heart, mind you, and while the motor itself is quite durable, little things do add up. Still, a couple percent for $200 is not a bad deal.

The SL600 is not designed for off-the-line performance. It is a very heavy car with a good portion of weight up front, and due to the fat power band, traction is consistently an issue. With the OEM 225's in back on a wet road, the ESP light was vibrantly flashing until 80 mph! The 275's do a far better job at reigning in the power, but still spin coming out of a tight corner or on an aggressive sprint from standstill. 0-60 is fairly decent, with tests ranging from 5.1-5.9 seconds, depending on conditions, rear rubber, and whether or not the driver power braked. However, where the 600 shines is 60-120+ mph. The power band is fluid, not letting off even as you dip into the triple digits, getting up there without fuss. Most high-powered Mercedes-Benz vehicles are engineered for autobahn-style driving. So while an R129 is certainly not the best choice to take to an Auto-X, it is a solid selection to weave through highway traffic waiting for that open stretch of smooth road to let the motor breathe.

Now, the gears are there, so use them! Since peak torque is made at 3800 rpms, downshifting manually to stay in the midrange makes a dramatic difference in acceleration. Cruising at 50 mph, downshift into 2nd, and liberally apply throttle for some fun. On the highway, I downshift into 3rd and the V12 just opens up. Or, one can just leave it in 4th for high speed endurance, as 5th gear exists for fuel economy. Since the M120 is designed for mid-range and top-end performance, it is built for highway fun.

Performance wise, it depends on the comparison. On the motorway, an R129 SL600 can easily stick with a Ferrari 348. It has the ability to outrun a C5 Corvette and even a standard Porsche 996 convertible on a straightaway (I have proven both correct, although everything changes in the corners, assuming equal drivers). I am just naming a few of the top contenders within the same production years. Compared to most cars in the current price range, the safety, value, and highway capability of the R129 is tough to surpass. Cruising on the highway and observing traffic, the R129 is ready to outrun the majority. It is a car built for comfortable, solid, spirited driving.

Videos of the R129 SL600:

Acceleration 0-200KPH
All credit to ilko01 on YouTube.

Highway Power (Great Sound)
All credit to eaegnet on YouTube.

600SL 4SP v. E46 M3 SMG
All credit to Shaq 89 on YouTube.

Hope you enjoyed my page, and drive safe!