Honda’s single-overhead-cam engine just might be more revolutionary than you think. In 1984, Honda Motor Company launched NCE (New Concept Engine), a program that resulted in the modern-day single-cam D-series engine and ultimately led to such technology as VTEC and 100-horsepower-per-liter-capable rotating assemblies. And when Honda released the first of its D-series lineup alongside its third-generation Civic, it did so to the beat of its own drum. The absence of a second cam allowed for more space and a unique rocker arm assembly. Because of this, and unlike other automakers’ twin-cam engines, Honda’s later SOHC D series was among the first to feature four-valve, pent-roof combustion chambers and centrally located spark plugs that together allowed for greater combustion efficiency and more power.
In a way, Honda’s early single-cam engines have gotten short-changed. Once the B16A was introduced, 16 valves, mid-9.0:1 compression ratios, and advanced combustion chamber designs weren’t good enough. Even the later (and remarkably efficient) D16Z6, D16Y8, and F22B1 VTEC engines pale in comparison to the amount of aftermarket support available for their twin-cam counterparts. Except for the fact that they’ve got but a single cam, Honda’s SOHC engines aren’t all that different from their DOHC alternatives, though. Both feature overhead-cam valvetrains and rocker arm assemblies. In fact, all things being equal, a single-overhead-cam engine will produce more torque than a twin-cam one. Fewer parts, which results in less valvetrain inertia, translates into more usable energy. Of course, all things are never equal, and the ability to adjust intake and exhaust valve phasing independent of one another without having to install a new cam to do so is what makes DOHC engines so hard to beat.
The SOHC situation is nowhere near as bleak as it may appear, though. Take the Accord’s non-VTEC F22A1, for example. Famed Honda engine builder Bisi Ezerioha relied on this particular cylinder head for years, helping push his naturally aspirated, F-series-powered Honda Insight into nine-second territory. According to Ezerioha, the F22A1 isn’t just cost-effective with a more simplified valvetrain, it features one of the best port configurations of any Honda, including twin-cam engines. The single-cam package allows for a more ideal valve angle that’s more difficult to achieve once an extra cam’s in the way. Ezerioha’s F series wasn’t the first to set single-cam history, though. Before the F22A1, he broke all motor ground with the non-VTEC D series. JG Engine Dynamics did the same with similar engines, only turbocharged. Andrew Yang’s and later James West’s JG-backed CRXs both broke the 10-second barrier at a time when such feats were considered best left for B-series and H-series mills. Perhaps more notorious than all of these was “Killing Time,” longtime Honda builder Jason Whitfield’s infamous, NuFormz-backed, turbocharged CRX. Regarded in the mid-1990s as “the world’s fastest 1.5L,” Whitfield’s CRX pumped out impressive power and handily secured twin-cam-like timeslips.
Honda’s modern-day single-overhead-cam engine’s lineage can be traced back to the early-1980s when the company began developing its third-generation Civic. The technology helped usher in the Honda cylinder head as we know it—one of the industry’s most efficient and no doubt one of many factors responsible for making Honda engines as beloved and as powerful as they are. Save the SOHC!
|D-Series Breakdown (8-valve, 12-valve, and “earth-lover” versions excluded)|
|D15B1: non-VTEC, 1,493cc, 16-valve, 70hp|
|D15B2: non-VTEC, 1,493cc, 16-valve, 92hp|
|D15B7: non-VTEC, 1,493cc, 16-valve, 102hp|
|D16A6: non-VTEC, 1,590cc, 16-valve, 108hp|
|D16Z6: VTEC, 1,590cc, 16-valve, 125hp|
|D16Y7: non-VTEC, 1,593cc, 16-valve, 106hp|
|D16Y8: VTEC, 1,590cc, 16-valve, 127hp|
|F-Series Breakdown (“earth-lover” versions excluded)|
|F22A1: non-VTEC, 2,156cc, 16-valve, 125hp|
|F22A4: non-VTEC, 2,156cc, 16-valve, 130hp|
|F22A6: non-VTEC, 2,156cc, 16-valve, 140hp|
|F22B1: VTEC, 2,156cc, 16-valve, 145hp|
|F22B2: non-VTEC, 2,156cc, 16-valve, 130hp|
|F23A1: VTEC, 2,254cc, 16-valve, 150hp|
|F23A5: non-VTEC, 2,254cc, 16-valve, 135hp|
|F23A7: VTEC, 2,254cc, 16-valve, 150hp|