When the pregnancy announcement went out, I could almost hear my friends mocking me in a sing-song chorus: “Pablo’s gonna get a minivan!” I started to panic.

I’ve only owned sports cars and sedans, and our two older children have been comfortably hauled in an E36 M3. But with a rear bench only 50 inches wide, and each child seat more than 20 inches wide, something with third row seating would become an agonizing necessity.

If today’s child seats weren’t so huge I could easily fit five baby butts in the M3’s back seat. Too bad we’re not in the ’70s anymore. It’s a tough world for daddy car enthusiasts today.

Then I had a revelation: Sunshine Kids. Not only do they manufacture high-end child seats, they’ve got the narrowest ones available specifically for my goal—fitting three wide. At only 17 inches wide, Sunshine’s top-of-the line XTSL convertible seat has gotten great reviews, and feature a steel frame and forward- and rear-facing configurations that can safely accommodate kids ranging from a 5-pound newborn to the 80-pound Twinkie lover.

I was set, and after my wife gave me the green light with a “yeah, yeah” along with a roll of the eyes (a “yes” in my book), I found this ’03 Mercedes-Benz S600 with an AMG aero package. Hey, the car is safe, which is most important. It’s also got a twin-turbocharged 5.5-liter V12 pumping out 493 hp and 590 lb-ft of torque, but that’s beside the point. I learned it can easily be bumped to 650 hp. See where I’m heading with this one?

The S600’s performance in stock form is intoxicating. With a mid-12-second quarter-mile at around 114 mph, it feels some 2,000 pounds less when you punch it (maybe not so much while turning). It’s a textbook sleeper with a cabin so quiet you can hear your child’s tummy rumble.

But I’m not very interested in stock Mercedes—not in my garage. That’s where Renntech comes in. Renntech’s founder, Hartmut Feyhl, has 12 years at AMG under his belt, even overseeing the iconic AMG Hammer project built in the ’80s. Numerous Mercedes dealerships across the country sell Renntech goodies because the company’s products don’t void factory warranties.

We upgraded this S600 with Renntech’s Stage 3 package. Rated at a monstrous 650 hp and nearly 800 lb-ft of earth-moving torque, it starts with a recalibration to the engine and transmission ECUs so that it not only makes more power but unlocks the torque limiter on the tranny, bringing it to current AMG 65 specs (it’s the same transmission). The package is also complemented with Renntech’s carbon-fiber intake kit and carbon engine covers, as well as an intercooler upgrade featuring a larger pump and twice the stock intercooling capacity for cooler intake air temps.

For aesthetic touches, the car sports Renntech’s Monolite 9x19 wheels wrapped with General Tire’s new ultra-high performance GMAX AS-03 tires (245/40 front, 275/35 rear). The package provides awesome performance in all four seasons, including light snow, and we didn’t even realize this combination would also be good for a 15-pound weight savings per corner. Coupled with the sporty yet elegant CL-style black grille from 55 Tech Motors, the wheels and tires truly transform the look of this S-Class.

While Mercedes are known to be safe tanks, you’re still at the mercy of a tire puncture and the dangers behind it. To lessen this possibility we installed TyreShield’s tire puncture protection system in all four tires. And yet again we got a performance gain because this allowed us to remove the spare wheel and jack for even more trunk space. Coupled with the wheels and tires, the weight savings total 118 pounds.

After unleashing all that torque with the TCU software update, Renntech’s limited-slip differential was a much-needed upgrade. This unit uses OS Giken internals to power both wheels instead of one, which we’ll test separately in a future Proven installment.

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