DOHC vs SOHC: what the camshaft count actually changes

SOHC engines have one camshaft per cylinder head. DOHC engines have two. That single change cascades into different valve counts, different airflow, different power curves, and different rebuild costs.

Most new cars sold in 2026 are DOHC. The exceptions are budget commuter engines, some pushrod V8s (which aren’t overhead cam at all), and a handful of motorcycle engines. Here’s what the difference actually changes when you’re driving the car or wrenching on it.

What the camshaft does

The camshaft opens and closes the intake and exhaust valves in time with the pistons. Lobes machined into the shaft push the valves down through followers, rockers, or bucket tappets. A timing belt or chain keeps the cam spinning in sync with the crankshaft.

Each cylinder head sits on top of a cylinder bank. A straight-four engine has one head. A V6 or V8 has two. So a DOHC V6 has four camshafts total, not two.

SOHC layout

One camshaft per head. That single shaft runs both the intake valves and the exhaust valves, usually through rocker arms.

Most SOHC engines run two valves per cylinder (one intake, one exhaust) or three (two intake, one exhaust). A few SOHC designs squeeze four valves per cylinder, including Honda’s older J-series V6, but those need clever rocker geometry and are unusual.

SOHC strengths: fewer moving parts, cheaper to manufacture, lighter cylinder head, lower belt or chain replacement cost, more compact. SOHC engines tend to make their torque lower in the rev range, which suits trucks and economy cars.

SOHC weaknesses: harder to flow air at high RPM because of the valve count and geometry, lower peak horsepower per liter, less room for variable valve timing on both intake and exhaust independently.

DOHC layout

Two camshafts per head: one runs the intake valves, the other runs the exhaust valves. Four valves per cylinder is the standard arrangement (two intake, two exhaust), though some performance engines run five.

DOHC strengths: better breathing, higher RPM ceiling, more horsepower per liter, independent control of intake and exhaust cam timing (Toyota VVT-i, Honda i-VTEC, BMW Double VANOS, etc.). A naturally aspirated 2.0L DOHC four typically makes 180 to 200 hp; a 2.0L SOHC four typically makes 130 to 150.

DOHC weaknesses: more parts to fail or service, heavier head, wider engine (a problem in V-engines fitting into tight engine bays), more expensive timing service.

Side-by-side comparison

Fuel economy

A DOHC engine isn’t automatically more efficient. It can spin higher and make more peak power, but at cruise it’s the same physics: air in, fuel in, exhaust out. The smaller cars get better mileage either way.

Where DOHC wins on efficiency is in being able to run aggressive variable valve timing on both intake and exhaust, plus features like cylinder deactivation and Atkinson cycle (common in hybrids). Almost every modern hybrid is DOHC for this reason.

Maintenance

Timing belts and chains last roughly the same on both layouts. The difference is what’s behind the front cover. A DOHC head has twice as many cam sprockets, more tensioners and guides, and often a balance shaft setup. Replacing a timing belt on a DOHC V6 (think Honda 3.5L) costs $900 to $1,400 at a shop. On a comparable SOHC engine, it’s $500 to $800.

Valve adjustments on solid-lifter DOHC engines (some Hondas, older Toyotas) involve more shims to measure and swap. Hydraulic lifter engines (most modern DOHC) need no adjustment.

Which one’s better

For performance, fuel economy in hybrids, and modern emissions compliance: DOHC, which is why it’s now standard.

For cost, simplicity, and rebuild-friendliness: SOHC, which is why you still see it in budget compacts and some commercial engines.

If you’re buying a car, the layout is decided for you by the engine you pick. The thing to know is that a DOHC engine making 200 hp from 2.0L is doing more work than a SOHC engine making 140 hp from 2.0L. That work has a cost at rebuild time.