Natwerk Designs

Why are modern ohv designs making almost as much horsepower as equivalent dohc designs?

In the 90s with a 5.7 liter dohc they made about 350hp and now new 5.7 ohv make that and more for instance.

Public Comments

1. if your talking about GM's LS1 then its because of the technology advances like better airflow, ignition, air/fuel ratio and the drivetrain is much more efficient. if the rotating mass has less vibration and less weight then you will see more power and faster speeds.
2. overhead valve and overhead cam engines still rely on the basics to make power. the more efficiently you get the fuel mixture in, and out the more power you are going to make. the only advantage that an ohc engine has is slightly less friction losses.
3. The number of cams does not necessarily indicate the output of the engine. What is most important is volumetric efficiency... that is, the ability to maximize the amount of fuel and air that enters the combustion chamber, and how quickly the exhaust gases can be purged fron the combustion chamber. Big valves are good. More valves are good. The valve timing is also important. The number of camshafts isn't really important unless the engine has variable valve timing (VVT)that requires the camshaft for the intake valves and the camshaft for the exhaust valves to be controlled independantly. The DOHC with VVT theoretically could be more efficient, but in practice, other considerations such as cylinder head size, weight and complexity take a higher priority. OHV designs are much less complex, have fewer moving parts and save weight so are less expensive. The DOHC benefits are only realized at higher RPMs, so if the engine nevers goes above 5000 RPMs, the OHV designs performs very well.
4. The DOHC or OHC have a higher red-line because the valve train has less reciprocating mass then a typical OHV which gives them an advantage. But when the OHV engines started using valve springs on the valves and on the lifter/push rod that allowed the red line to increase as it counters the reciprocating mass of the the OHV train.