Quote:
Originally Posted by serialk11r
Then I realized that ITB setups have an extremely small distance from the throttle to the cylinder...and thus a very low volume between the throttle body and the cylinder!
|
This is correct. The amount of work needed to draw a vacuum is proportional to the product of the intake manifold volume multiplied by the vacuum.
Quote:
Originally Posted by serialk11r
Moreover, since you're flowing a smaller net quantity of air through each throttle the throttle plate should be closed more. Then each piston will draw a slightly deeper vacuum during the intake stroke, with less adiabatic free expansion going on at the throttle body.
|
This may well be, but increased vacuum is not good for freeing up mechanical energy. Refer to the below diagram.
This is a representation of the work generated by an ideal gasoline engine with a throttle. The white enclosed area represents the total mechanical work produced by the combustion of gasoline. The grey area represents the pumping work that the engine must perform just so it can run. Essentially, you're wanting to decrease the grey area in this curve.
Lowering vacuum will cause the P(man) value to rise, causing the grey area to become smaller. Conversely, raising vacuum will lower P(man) and cause the grey area to expand.
Quote:
Originally Posted by serialk11r
After the intake valve closes the air pressure after the throttle will start to equalize with the air before the throttle, but since the volume of low pressure air is smaller, the free expansion loss should be lower.
|
May well be. It depends on if the increased vacuum developed offsets the initial air pressure as the intake valve opens.
Quote:
Originally Posted by serialk11r
Of course, getting ITBs solely for this purpose would probably be stupid since I can't imagine the difference being very big, but I wonder if anyone's bothered to document this...
|
Might be worth a shot. I, for one, am certainly not going to try it for this purpose. I'd need 8 throttle bodies!
