How Did Honda Squeeze 120 hp Per Liter Out Of The S2000's F20C Four-Cylinder Engine?
Few cars in Honda's lengthy history have attained the same legendary status as the 2001-2009 Honda S2000. The roadster sits alongside the Civic Type R and the Acura NSX as the most desirable and fun-to-drive models ever built by the Japanese automaker. Amazingly, it continues to command a premium price tag on the used market almost 20 years after it was introduced.
A big part of the spell cast by the Honda S2000 when it arrived on American shores was its rambunctious four-cylinder power plant. Tuned within an inch of its life, the high-revving, VTEC-endowed unit managed to squeeze a whopping 120 hp per liter from its tiny 2.0L of displacement, accessible only as one approached its shocking 9,150 rpm fuel cut-off.
Dubbed the '4-wheeled motorcycle' by some enthusiasts, this level of four-cylinder fury had never before been experienced in the United States, and it quickly sparked a dedicated army of S2000 fans who cited Honda's engineering prowess and daring as one of the primary reasons for picking up the two-seat convertible. How did Honda wring so much power from such a modest motor? The answer lies in the attention to detail given to the F20C, the most exciting engine design to ever leave a Honda factory.
Small, But Mighty
Originally, the F20C was intended as an adaptation of the F20B, but the modifications required to transform the passenger car architecture into the fire-breathing, 8,700 rpm redline monster that ended up between the S2000's front fenders were so extensive that almost nothing is shared between the two engines.
The F20C's core was its aluminum block, which featured fiber reinforced metal cylinder liners, a forged steel crankshaft supported by five main bearings, and forged aluminum pistons. The latter had never been installed in a Honda street car, and forged rods worked to maintain strength while helping to keep the weight of the entire rotating assembly as low as possible—crucial when spinning at high rpm.
With a bore and stroke that saw the engine check in at just under 2.0L, Honda focused on keeping the engine proportions modest so that it could be positioned as low down and close to the firewall as possible when balancing out the S2000's weight distribution.
This philosophy included small, but significant choices such as adopting a single valve spring design (borrowed from Honda's racing program), a narrow 25.5 degree angle for the intake and exhaust valves, and moving to distributor-less ignition. Overall, the engine package was similar in its physical dimensions to the simpler, smaller-displacement Civic engine of the same era.
The VTEC system used by the F20C also broke new ground for Honda, making use of a 'co-axial' rocker arm that lowered valvetrain friction, with VTEC switching over to its more aggressive valve lift at 5,850 rpm.
An aluminum intake manifold (featuring 36 mm intake ports and 21 mm exhaust ports) and a 4-3-2 exhaust manifold helped the S2000 breath deeply, an important consideration for a vehicle that made maximum power at 8,300 rpm. The compression ratio was set at 11.0:1 for every market other than Japan, which saw a bump to 11.7:1.
Time For More Torque
Honda continued to refine the F20C, with a major change appearing for the 2004 model year. The previous 'AP1' S2000 was replaced by the face-lifted 'AP2,' which in North America brought with it a 2.2-liter four-cylinder engine labeled the F22C.
What was the reason for the change? With 240 hp on tap (slightly higher in the Japanese market), but only 153 lb-ft of torque, Honda had done its best to ensure reasonably broad access to the modest amounts of twist provided by the F20C, so that around town driving at lower speeds wasn't compromised. Still, there were concerns that the overall drivability of the S2000 was negatively impacted by its relentless focus on high-rev thrills, which led the automaker to reconsider the roadster's personality.
Mechanically, the F22C and the F20C were virtually identical, save for a few key details, most notably the longer 90.7 mm stroke that was responsible for the motor's displacement boost. This 10 percent displacement increase was the foundation for Honda's attempt to satisfy customers who had criticized the S2000's perceived day-to-day sluggishness.
By reconfiguring the F22C's camshafts, Honda now delivered a motor that maintained 240 hp, but at a lower 7,800 rpm, matched with a 10 percent torque boost when cruising from 2,500 rpm onwards (topping out at 162 lb-ft at 6,500 rpm)
The AP2 cars changed the character of the S2000's drivetrain considerably. The redline was now set at 8,000 rpm, compression was moved to 11.1:1, and the less peaky performance made the roadster less frenetic to drive, with VTEC spinning up at 6,000 rpm rather than 5,850 rpm. For 2006, revised SAE horsepower ratings robbed the F22C of three ponies, and tweaks made to the engine management system pushed maximum torque delivery up by 300 rpm,
A Lasting Legacy
The F20C and F22C engines were never used in any other Honda product, living and dying in the decade that saw the S2000 make its mark on the global sports car scene. It left behind a legacy that endures to this day, one that went farther than perhaps any other drivetrain in establishing the expertise of Honda's engineers during that period, and one which is unlikely to ever be repeated in our current turbocharged era.
The Honda S2000's two engines rank among similar screamers produced over the last few decades by Ferrari and Ford as high-revving, track-focused explorations at the very edge of the performance envelope.