engine = air pump. Air being pulled in is slow at lower rpms. Velocity is the speed of something moveing, in this case air. Volume is the amout of something required to full a area. This case the intake/cylender. Cfm is the volume of air moveing. For positive preassure to be created, the volume of air in has to be greater then the volume being used. For the motor to rev faster the velocity has to be greater then the air being consumed. If a motor use's 200 cfm but 250 cfm is being forced in then there would be positive preassure. Air would be waiting to enter. If a motor needs 200 cfm and 200 cfm is there but the speed at which it flows is only = to the speed the motor is useing it then the rpms will not raise. For the motor to increase in rpm more air has to be there each time the cycle is completed. Let me try to give a example.
Lets say a motor needs 400 cfm at 6k rpm. THe TB will give 600 cfm at 6k rpm. At 1500 rpm the motor might need 90 cfm. We know the TB can offer a full 400 cfm. When you go WOT the motor bogs and slows why?
Volocity, see even though there is sufficent volume, the air is moveing to slow for the pump to pull it in. Each time the motor takes a breath air has to fill the void created. If it fills it faster then the motor needs it then it will spin faster due to more air/fuel charge. If it does not fill the void fast enough (low volocity) then the motor will starve on the next cycle. This cause's the rpm to fall, stay the same, or rise very slow. Its the same reason the motor will stop revving at 6k rpm, when it hits the 400cfm that can be flowed no more air is there.
A engine will rev till it blows it can get enough volume and volocity. It's nature is to consume every once of air it can get. It's why the motor stops reving at part throttle when you go down the road at 60. It has the volocity to fill the void, but not the volume to increase it.
Volume is the amount of air needed. Volocity is the rate of movement. Both are needed always. At higher rpm Volocity is naturale due to the air stream already moveing, so Volume becomes the limiting factor. At low speed the Volume is there, but the volocity is lacking. That is the delemia that has been plauging High performace N/A motors for decades. Turbos fix all
As far as filling a bucket. Only so much volume can come out of the hose, you increase the velocity, you added a restriction to the flow. You limited the volume with the same restriction. Odds are it was a different water mark, or the valve was opened a bit more in one test vs another. The way you did it was not a rw test, to many variables. Any factor, could add subtract 2 seconds. A small crimp in the hose you didnt see would add to it.
In fact you proved why velocity and volume are so imporant in your own test. The water got to the bucket from the nossle faster, but it was less of it. The stream got thinner, but moved faster. In the case of a motor that is ok, because it needs alot less at lower rpm, but to accelerate it has to get there shit loads faster. Hope this helps. Mark
