You probably think the ultimate Porsche Cayman is the GT4 RS, the 911 GT3-powered maniac with 493 horsepower that revs to 9,000 rpm and transforms the Cayman into a track beast. But there’s another level of GT4 RS, the Manthey. It sacrifices any on-road comfort the GT4 RS may have had in pursuit of lap times.

Manthey Racing isn’t quite a household name. The German race team, founded in the late 1990s, runs Porsche Motorsport’s GT teams and does so successfully. In 2013, Porsche bought a controlling interest in Manthey, and since 2021 it’s been creating aggressive performance kits for Porsche’s sports cars. They are available through certified Porsche dealers with the sole intention of increasing track capability.
The GT4 RS sets an impressive baseline. Porsche has been intentional about ensuring the Cayman can’t beat the 911—the GT4 RS comes closest. With the gas-powered Cayman reaching the end of the line, Porsche’s GT Department went HAM on the Cayman to create the GT4 RS, even replacing the rear quarter windows with intakes to cram enough air to the 911’s flat-six. Compared to the regular GT4, the RS has a totally new drivetrain, a stiffer body structure, bigger brakes, and heavily revised cooling. It’s essentially an entirely new car.
Manthey leaves the powertrain alone and focuses on making the RS sharper in the corners and more stable under braking. These are all fine-detail changes. The GT4 RS Manthey gets retuned aerodynamics for increased downforce—complete with a bigger wing and carbon blades on the rear wheels—steel braided brake lines, and it ditches Porsche’s Active Suspension Management system for manually adjustable coilovers.
Those chassis and suspension changes take whatever road compliance the GT4 RS had left and shoves it in the trash. The Manthey kit, combined with an aggressive track alignment, makes this a stiff, darty little car. Driving on the road does it a disservice, but there will be buyers who spend $53,946 plus installation—and no, that’s not a typo—to only drive it to coffee shops and brag about the rear wheel aero blades. If that’s you, there’s no need to read further. The Manthey needs to be on track.

That’s why we took the Manthey-equipped car to Lime Rock Park in northwest Connecticut. One of America’s original bullrings, Lime Rock is only 1.5 miles long. A fast, technical track with a wonderful flow, it’s one of those legendary circuits that makes new, overly computer-designed tracks seem irrelevant. For this test, we’re running the IMSA layout. Yes, that bypasses the very fast and fun "Uphill" corner, but it also adds a hard braking zone and a challenging chicane. It transforms Lime Rock into a complete circuit, one that tests every aspect of a car in a lap that’s still about a minute long.
On my installation laps, I’m hard pressed to find any real difference to the base GT4 RS. They sound equally intoxicating, both feel neutral and well balanced, braking is linear and strong, and there’s no obvious changes in how the Manthey drives. And that induction noise, that glorious induction noise that surrounds and invades every part of your brain, is unchanged from the base car. This is as close as you can get to a liter bike for the road. But the stock car sounds exactly the same.

It seems, at first, that the $53,946 package isn’t really worth the expense.

The real changes become apparent when I push. Braking, which has seen modest hardware changes, is a shocking improvement. On Lime Rock’s short but fast front straight, the regular GT4 RS was squirrelly and nervous at a threshold brake. The Manthey kit provides a stronger initial bite and instills more confidence as it slows the car down from 146 mph towards the apex, and with far better stability, likely thanks to the increased downforce. This kit, which appears to make the car more aggressive, also makes it easier to drive.

That’s apparent mid-corner. Like the regular car, the Manthey kit still moves around and is eminently adjustable, but there’s slightly more understeer built in. The stiffer front springs and a shift of balance rearward are the culprits here. It still feels alive mid-corner, but that slight bit of extra stability is the key to a quicker lap.
Lime Rock’s double apex first turn, Big Bend, is an exercise in patience. In the base car, that corner can be a pain. The last GT4 RS I lapped, I found I was dancing between power and lift to get the car to rotate. The Manthey kit gets rid of that dance and replaces it with sheer predictability. I can get back to power sooner and know that the car won’t bite on exit. That slight bit more initial and mid-corner push pays dividends on exit, when the increased steering angle and grip lets the RS shoot out of the corner.

Lime Rock’s faster corners, like West Bend and the Downhill—an especially intimidating right-hander with runoff that leads directly into a barrier—are where the increased downforce and high-speed stability become apparent. I keep entering quicker and watch apex speeds rise as the aero work instills more confidence. I’m sure it’s faster than the regular GT4 RS. There’s one way to find out.

We throw on a set of fresh tires to set a lap time. Over two runs, the Manthey-equipped car runs a lap of 58.47, half a second quicker than the non-Manthey car I drove there a year earlier. Half a second might not sound like much, but remember that Lime Rock is only 1.5 miles long. On longer tracks, like Laguna Seca, Road America, or Spa, that gap would grow. In fact, the GT4 RS ran a 7:09.30 on the Nurburgring, while one with the Manthey kit ran a 7:03.12, a full six seconds quicker.
Now, the question still remains: Is it worth it? I guess it all depends on what you want to accomplish. If you want to just take your GT4 RS on occasional track days to have fun, and aren’t someone who can fall victim to the red mist that overtakes many in the pursuit of lap times, then you don’t need the Manthey Kit. But if you’re the sort of person with a lot of extra money who wants the ultimate factory GT4 RS and every tenth matters, then the Manthey Kit is a no brainer.

If you have no intention of taking your GT4 RS on track but just want to think you look cool, Porsche will sell you the Manthey rear wheel aero disc for $680. Sounds like a bargain.