The Suspension Secrets Cayman GT4 goes nose-to-nose with a 991 GT3 RS around Donington Park – but which Porsche will lap faster?
From the beginning, we’ve made our intentions clear with our Cayman GT4. We’ve always wanted to turn it into a GT4 RS beater. We also secretly aimed to make our GT4 capable of hunting down Porsches with the GT3 RS badge. However, we knew this would be far from easy.
Nevertheless, after two years of incremental development and a relentless focus on extracting performance from the GT4 chassis, we found ourselves at a pivotal moment.
With a temptingly empty Donington Park circuit at our disposal, it was finally time to put our modified GT4 head-to-head against a completely stock Porsche 991.1 GT3 RS. A GT3 RS that also happened to be the newest member of our development fleet…
GT4 Platform Gains
When it came to our GT4, it would’ve been easy to chase lap time improvements with a straightforward and hearty increase in engine power. But we like to do things differently at Suspension Secrets.
Granted, our six-speed manual equipped GT4 has been remapped and now produces 484bhp (up from 420hp). That output is not far off a GT4 RS (500hp), 991.1 GT3 RS (500hp) or 991.2 GT3 RS (520hp). However, these Porsches still trump the GT4 when it comes to outright power, rev range and gearing.
To combat such awesome engine performance, we focused on how the GT4 uses its tyres.
We began by maximising the standard suspension. This involved adjusting the ride height, camber and toe angles, and anti-roll bars. In our experience, practically all performance cars run sub-optimal suspension settings out of the box. This ensures the broadest range of driving abilities are catered for, to the detriment of handling precision and response.
After tuning the stock Porsche suspension, it was then time to install new upgrade parts. These bolt-on Suspension Secrets components are designed to increase grip, improve consistency and boost driver confidence while ensuring more even tyre wear.
On that last point, it’s hard to find a stock performance car that doesn’t suffer uneven tyre wear on track due to factory suspension settings designed for road use. This situation introduces soul-destroying understeer at the limit, costs owners money in tyres, and affects lap times.
Reducing GT4 Understeer
Our in-house developed and manufactured front camber plates and rear toe arms allowed us to unlock significantly more camber on the GT4. This dramatically improved how the tyre interacts with the tarmac during hard driving (watch the video here) and massively reduced understeer. That setup alone transformed the GT4, but potential remained locked in the chassis.
Next, stiffer Eibach springs, a lower ride height, and our adjustable bump-steer tie rod ends brought welcome improvements to body control. At this point, the GT4’s stability inspired next-level driver confidence and it really felt like a car capable of punching way above its weight.
From there, we replaced soft rubber in the suspension with solid bushes, ensuring the geometry stayed exactly where it should – even under heavy braking and high cornering loads.
Then came a major leap: tyre optimisation.
By developing our Kinematics Kit with Stage 2 top mounts, we were able to fit 265 front and 325 rear tyres within the standard bodywork, matching the 991 GT3 RS footprint. More contact patch equals more grip, and that means reduced lap times.
Finally, we installed 3-way adjustable Moton coilovers to fine-tune every aspect of chassis behaviour: corner entry, mid-corner balance, exit traction, and pitch control. This is where a chassis truly comes alive, and where small changes can deliver big results.
GT4 vs GT3 RS
Porsche’s 991-series GT3 RS is one of the most capable road-going track cars ever built. High levels of downforce, ultra snappy gearshifts, rear axle steering – this car has it all.
But how does a lighter, mid-engined GT4 platform optimised for handling performance compare? In the hands of GT racer and driver coach Chris Dymond, the answer became clear during our recent visit to Donington Park.
Through the corners, our upgraded GT4 was exceptional. It carried more speed into the apex than the 3RS, held higher minimum speeds, and Chris was able to get back on the throttle earlier. Corner after corner, our GT4 more than had the measure of the GT3 RS.
And yet the battle was not done. Donington Park’s straights allowed the 991 to deploy its greater engine power and reel in the GT4 over and over again.
Verified by VBOX Motorsport’s data logging equipment, it really was neck and neck between these GT Porsches the entire way round Donington Park’s 2.49-mile GP circuit.
Guts and Glory
Before this contest began, we knew the GT4 was down on power. We also knew it lacked the RS’s aerodynamic performance. And let’s not forget it’s running a six-speed manual gearbox compared to the seven-speed PDK in the GT3 RS.
Yet despite all that, the Suspension Secrets GT4 held its own. The ability to brake later, rotate cleanly, maintain stability and deploy power earlier gave our GT4 an edge.
In fact, one of the most interesting takeaways from the test was how the two Porsches felt from behind the wheel. The GT3 RS is undeniably capable, but there’s still a degree of compromise in its stock front-end behaviour and balance on the limit. Racer Chris Dymond (below right) found himself more consciously managing weight transfer, and being cautious on throttle application.
Our modified GT4, by contrast, felt intuitive to Chris: balanced, predictable and confidence-inspiring. That mid-engine layout, combined with a properly optimised suspension package, gives the driver the freedom to push harder. And that translates directly into performance and, ultimately, lap time.
This is exactly what we aimed to achieve with our Cayman GT4 suspension upgrades.
The Results Are In
After clean, back-to-back runs in identical conditions (same day, same session, fresh Michelin Pilot Sport Cup 2 tyres on both cars) the result was almost hard to believe. Just 0.09 seconds separated these Porsches. Effectively identical lap times.
Putting that into perspective, our GT4 has less power, less aerodynamic performance, a manual gearbox with notoriously long gear ratios, and a much lower overall cost – upgrades included. And yet it practically matched one of the most revered track cars ever built.
This performance validates each and every Suspension Secrets upgrade we have made to the 718 Cayman platform. And we’re not done yet.
Cayman GT4 Upgrades
So, where do we take our GT4 next? The head-to-head reaffirmed the car’s aerodynamic limitations and it’s definitely an area we want to improve.
There’s also the issue of the GT4’s overly long gear ratios, which again presents an opportunity for big lap time improvements once ‘fixed’.
The battle with the GT3 RS was a journey into the unknown – we genuinely had no idea how close these cars would be on track. But what we have demonstrated is that with the right suspension upgrades, it’s absolutely possible to go toe-to-toe with the fastest Porsches of all time using the GT4 platform.
And when our GT4’s aerodynamics and gear ratios are enhanced, this white beauty will be elevated to even greater heights.
We’ll keep you updated on progress.
SHOP suspension upgrades for the Cayman GT4 and 991 GT3 RS.
