View Full Version : Long runner/ short runner system?
08-28-2003, 06:32 PM
I don't really understand how this works. I am assuming that in long runner the air has to travel we'll say 12 inches to the engine. And in the short runner it has to travel 6 inches to get to the engine, thus doubling your intake. Is that right? I am not an engineer in anyway but why would it engage at 6000 rpm when red line is 7200 rpm? Wouldn't it be better to enable this system sooner for longer use? Like say 5000 or maybe 5500 rpms?
08-28-2003, 07:40 PM
The longer the runner, the farther the air travels before it enters the engine. Long runners produce greater low end (lower RPM) torque. Typically trucks have long runners for good low-end torque and throttle response. Short runners are better for torque at high RPM. It is an acoustical phenomenon. Max torque is achieved when the wavelength of the incoming air charge (tuned by the length of the runner) matches the intake valve frequency maximizing the amount of air delivered to the Zetec. The ideal runner configuration would be infinitely variable to produce the correct air-charge wavelength for every possible RPM. However, a two-stage long runner/short runner system is rather effective (Way to go SVT). The switching point is set to maximize the area under the torque curve. Bellow 6000 RPM the long runner configuration makes more torque. Beyond 6000 RPM the short runner configuration creates more torque.
Sorry for the long response. I am a car nerd.:spinem:
08-28-2003, 07:43 PM
Thats cool at least I understand.
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