Quote:
Originally Posted by xj_man_646
From what I understand, this is not a variable length runner, but when this valve is open, it bypasses the intake runners all together and air goes directly to the cylinder heads.
Maybe I don't understand it correctly, but why not make it the shortest run possible all the time?
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Quote:
Originally Posted by xj_man_646
Everywhere I've read says that when these valves don't work, the engine feels low on power. Maybe there is some sort of fault reaction in the ECU which makes that more noticeable, but I still don't get it. There must be a reason these things aren't found on many other applications outside FCA |
I had a hard time finding a description but it seemed to me that it was an actuator that changed the routing on the intake manifold. Reports also indicated a lack of top end power, not power across the range.
That said, regardless of the actual mechanism, if this is a valve that effectively bypasses the runners or if it's just an actuator that moves the flaps in the runners, it's still acting as a variable length intake manifold.
Manifold design has a big impact on the power production on an engine. In general, long, skinny intake runners increase the air velocity, which helps at low RPMs with getting a lot of air into the motor. However, at high RPMs they become restrictive, you can't get enough air into the motor anymore, the pressure drop is too high for the velocity.
However, if you made it so it breathed better at the high RPMs you'd lose the torque at the low RPM. A manifold with both runner designs that can actuate between them, typically with butterfly valves on a actuating rod, gets the best of both worlds.
So, in short, you don't want the valve stuck open all the time because of....
Quote:
Originally Posted by champ
Dem low speed torques. Dats why.  |
A truck motor will lug around a lot better with long, skinny manifold runs!