Can someone explain to me how port velocity affects torque?
I understand that low port velocity leads to low torque, but I'm not sure why that would be. The same volume of air-fuel is filling the same size cylinder, so why does it matter if it sucks it through 3/4 in^2 or 2 in^2?
Same volume is not filling thats why the valves have overlap that is to say the piston starts to go back up before the valve closes. If the port velocity is low less will fill the cyl if the port velocity is just right as the valve closes it will still push in and fill it is possible to get more then 100% filling. Remember that it just asmoshpreic presure pushing the air in and theres no time at speed.
Read up on pontiac and mopars ram air for more help
44
My limited understanding: Air has inertia. When the valve is closed, slow moving air simply "stops" Faster air "packs" against the valve (localized pressure) to allow better cylinder filling.
ReverendDexter wrote: Can someone explain to me how port velocity affects torque? I understand that low port velocity leads to low torque, but I'm not sure why that would be. The same volume of air-fuel is filling the same size cylinder, so why does it matter if it sucks it through 3/4 in^2 or 2 in^2?
It's not the same volume of air-fuel, that's why.
More velocity means the airflow is less wont to slow down/reverse direction at the end of the intake stroke when piston speed is low or actually rising. Therefore, more cylinder filling, more cylinder pressure, more torque, more happy driver.
Sizing the port so the velocity vs. restriction tradeoff is in the right powerband is where the fun is at.
44Dwarf wrote: Same volume is not filling thats why the valves have overlap that is to say the piston starts to go back up before the valve closes. If the port velocity is low less will fill the cyl if the port velocity is just right as the valve closes it will still push in and fill it is possible to get more then 100% filling. Remember that it just asmoshpreic presure pushing the air in and theres no time at speed.
That's why positive displacement forced induction rules!
as for port size, when one piston is having trouble sucking air through a small hole, that piston is putting a parasitic drawon the piston that IS firing at that moment. also, high port velocity lessens the mal-effect of exhaust gasses rushing back into the intake manifold when the valve opens sayyy 20 degrees before tdc. while on the topic of valves, depending on ones's combination of port size and valve closing, dependent upon ur cam, volumetric efficiency can go down. i took engine blueprinting :)
You'll need to log in to post.
