Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Automotive 16 Valve vs 8 Valve

  1. Jan 13, 2013 #1
    I want to know exactly why 16V engines produce more HP?
    Please explain in detail.
    What is the exact reason?
    Why usually 8 Valve engines produce more torque lower down the rev range?
  2. jcsd
  3. Jan 14, 2013 #2

    Ranger Mike

    User Avatar
    Science Advisor
    Gold Member

  4. Jan 19, 2013 #3
    Look at the LSx series engine from GM. Two valves per cylinder and they make good power. 400 HPs from 5.7 liters.
  5. Jan 19, 2013 #4

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    I thinnk it's a practical matter - manufacturability.

    The flow area through which the engine "breathes" would be the circumference of the valve, not its area, times valve lift.

    flow area of valve = pi X diameter X height
    cylinder head real estate occupied by valve = pi X (diameter/2)^2

    Make it simple - look at one 2" valve vs two 1" valves, all having 1/2 " lift..

    The two inch valve requires pi square inches of cylinder head real estate, and provides pi square inches of flow area.

    The smaller valves provide the same flow area in half the cylinder head real estate.

    So, when valve flow area becomes the limit on breathing, which would be at high RPM, switch to more and smaller valves . That way you can fit more flow area into available real estate.

    Sound logical?
    Last edited: Jan 19, 2013
  6. Jan 19, 2013 #5
    So what?

    The reason for 2 valves per cylinder creating better low down torque, is partially inlet geometry. Typically the valve is off to the side, so when the cylinder fills swirl is generated, allowing for a better mixture and combustion. At high rpm tumble is the dominant flow in cylinder.

    Variable valve systems with 4 valves, now shut off 1 inlet at low rpm to induce swirl in cylinder.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook