Camshaft count is the quiet spec that shapes an engine’s character. Vietnam’s underbones split into SOHC and DOHC camps, and the manufacturers name their layouts (retrieved 23 September 2026).
Who uses what (verified)
DOHC: Honda’s CBR150R page lists a DOHC four-valve liquid-cooled engine - the most sophisticated valvetrain in the class. SOHC: Yamaha lists single-overhead-cam engines for the Sirius RC 110 and the Exciter 155 VVA (the Exciter with four valves under that single cam). Honda’s Wave/Blade/RSX/Future/Cub/CT/Winner pages publish valve counts without cam-layout claims - those cells stay empty in our model database, as no claim should be invented.
What the difference means
A camshaft pushes the valves that breathe the engine. SOHC uses one cam per cylinder, operating valves often via rockers - simpler, cheaper, compact, and entirely sufficient at underbone power levels. DOHC uses two cams, allowing better valve angle, direct actuation and high-rpm breathing - which is why the CBR150R safely spins out 12.6 kW at 9,000 rpm, the highest specific output in this comparison.
Does it matter to you?
As a rider: DOHC buys top-end performance and costs complexity at service time. As an owner: SOHC underbones are the cheaper long-term proposition - fewer components, simpler clearances. Our valve-clearance guide covers the maintenance both layouts share. For 99 percent of Vietnamese riding, the SOHC 155 of the Exciter - with its VVA variable timing - delivers more usable performance than the layout debate suggests. Rental classes here (Wave and Sirius, 150,000 VND/day) are simple SOHC machines; contact us to confirm current availability.