Fans of sports car racing generally have better access to behind-the-scenes action in the paddock than in other racing series. Just try getting a peek at what’s going on in an F1 garage–or even in NASCAR outside of the carefully curated viewing areas–and you’ll understand. Big-time sports car racing has its secrets and crowd control, but generally the rabble are …
The Showroom Stock era of production-based sports car racing is becoming a legitimate force in the historic scene. Cars like this Porsche 944 Turbo competed professionally in IMSA’s Firestone Firehawk series, or the SCCA’s Playboy Series, and were minimally prepared. They would typically be allowed minor upgrades like shocks and springs, safety gear, radios, brake pads and little else. They were far closer to street cars than today’s GT4 or TCR machinery, and independent teams could and would build their own examples to compete professionally.
Not much analysis here aside from the fact that velocity stacks are awesome. A bundle of four dual-throat downdraft Webers on top of a big V8 means the intake noise is going to be every bit as satisfying as the exhaust note.
Race cars are all about efficiency in packaging. You want them to be as light as possible, and when you do need to add weight, you want to add it at the most advantageous spots.
Case in point: The alternator on this single-seat sports racer is not driven from the engine, but rather from an output shaft off the back of the transaxle. This allows it to be mounted lower in the chassis and keeps one more parasitic drag off the engine.
Of course, it’s still not free electricity. The engine still drives the alternator, just through the driveline rather than directly. This also has the added benefit of being able to easily spin the alternator slower–meaning less parasitic drag–than driving it directly from the crankshaft.
This R32 Nissan GT-R looks like a heavily production-based car at first glance, but even a quick look under the skin shows an insane level of mechanical wizardry afoot.
Much of the unibody still exists, but the rear suspension appears to be mounted on a custom tubular subframe. This allows the use of a full articulated upper and lower A-arm suspension, with horizontally mounted shocks and springs being actuated through rocker arms. The rockers appear to have a ratio of pretty close to 1:1, meaning suspension travel translates directly into shock travel. The full-length Penske shocks would seem to confirm a near 1:1 motion ratio.
In the front, there’s even more cool packaging. The front suspension also appears to be mounted to custom tubular subframes, although here they appear to be more integrated into the original unibody as well. Front shocks are also horizontally mounted and actuated through rocker arms, but here they’re located between the upper and lower A-arms. It’s a clever packaging decision that keeps the mass lower in the chassis.
Maybe the most fascinating detail on this Nissan, however, is the method for roll couple on the front suspension. Instead of a traditional anti-roll bar, the left- and right-front suspensions are connected through a Watt’s linkage that’s activated by rocker arms at each front corner. The rocker arms appear to have various mounting holes available, allowing the crew to easily change the rocker ratio.
The pivot point for the Watt’s linkage also provides its adjustability. The Watt’s crank pivots on a blade-style anti-roll-bar end link that will provide different rates of deflection based on the blade’s angle relative to the force being put into it. Lots of flex or deflection at the pivot point equals less roll couple, and reducing the deflection equals more roll couple. The cable leading to the blade’s base gives the driver a way to adjust the relevant angle of the blade from the cockpit on the fly.
In addition to roll couple, this arrangement would also provide some “third spring” action. A third spring is a common feature in cars with lots of aero downforce. When both sides of a suspension are subjected to similar compression forces–as they would be on fast straights when experiencing a lot of aero downforce–the job of the third spring is to resist that compression to maintain ride height on straights. In this case, when both corners are compressed at once, the forces bind against each other, and only the non-rigid mounting point will provide resistance. It’s an undamped third spring–unless there’s a damper we just couldn’t locate–but the individual corner dampers still provide damping for the entire system, so it’s not like the blade will be oscillating uncontrollably.
The Kremer K3 is one of the greatest GT racers of all time. The slope-nosed 911 variant dominated GT racing in the early 1980s by turning over 20 psi of boost into glorious Porsche flat-six noises.
But a quick peek under the skin shows just how close to production these cars were. While there was an extensive roll cage, and it looks like there’s some additional non-factory structure in the rear, up front you have a regular 911 strut suspension with the upper mounting points looking like they’re in a location remarkably close to stock. Some camber plates provide for a more aggressive alignment, but the K3 is a testament to the capability of the platform as much as the Kremer brothers’ engineering abilities.
If you like the combination front anti-roll bar/third spring on that GT-R, here’s the idea taken to its most insane conclusion. The rear suspension on this Acura ARX-05–the car that won the 2022 Rolex 24 At Daytona, in fact–uses a functionally similar system, but it decouples the anti-roll bar and spring functions.
The third spring lever, which actuates the third spring that’s riding in a cartridge via a pulling motion, is also a rocker that couples the roll on each side of the suspension through a blade. The blade rides in a carrier mounted in pillow-block bearings, allowing the base of the blade to articulate as the suspensions move together.
That silver donut wrapped around the drive axle is one of the keys to the IMSA BoP program. It’s a rotational force sensor that measures torque in real time to let teams and rules makers know just how much thrust the cars are producing. Think of it as a tiny dyno that can send you on a trip to the principal’s office if the readings come back a bit too high.
The ARX-05’s front suspension is just as interesting as the rear. Borrowing technology from the Honda back catalog, the ARX-05 uses torsion bar springs, just like a 1985 CRX. The torsion bar endcaps are those two black, horn-looking dealies.
Actually, what’s notable about the interior part of the front suspension on the ARX-05 is that it’s a fairly conventional layout. Rocker arms actuate vertically mounted shocks, and end links coming off those same rocker arms actuate the fairly conventional anti-roll bars to couple roll from side to side.
What the picture doesn’t really do justice, however, is just how tiny everything is. Even the largest fasteners were probably 6mm threads, and many appeared to be custom machined to the exact length they needed to be and not a millimeter longer. Why carry the extra weight of a 25mm-long bolt when all you need is a 22mm-long bolt, right?
