Velocity Stacks

[HP2]

Notice how large the grid on that screen is. Screens do allow some airflow through, but the finer the screen, the greater the probability of it becoming an aerodynamic restriction because of the boundary layer of air that will bounce off the individual wires and create a flow over the screen.  This is why the nascar boys use a screen on the radiator opening on their cars. It allows just enough ram air to keep things cool, but pushes the majority of the air around the opening.

[RCCDrew]

How about these?

[RzeroB]

I believe the whole purpose of the screens was not to filter the air, but to prevent FOD (foreign object damage). Their purpose was to prevent a foreign object such as a nut, bolt, tool, bird, whatever, from being drawn into the engine and causing catastrophic engine damage or failure.

[cudabob496]

In the above picture, the screens are recesses a little. I think the stacks by themselves
look best.  If there is a fairly pourous screen down inside them, for foreign objects, I wonder
what the effect on the engine would be, if car is street driven. Will dust and stuff that gets by
screen really hurt the carb/engine??

[RzeroB]

If the car is street driven, will dust and stuff that gets by
screen really hurt the carb/engine??

I would think over the long term it probably would lead to premature piston/cylinder wear by allowing fine particulates to enter the engine. A filtering element would otherwise catch those fine particles, and in theory, extend the engines life by keeping that stuff out of the cylinders. For all out racing engines, long term wear isn't really a concern as they are regularly rebuilt and "freshened" long before any wear issues from using un-filtered air would manifest themselves.

[cudabob496]

I would think over the long term it probably would lead to premature piston/cylinder wear by allowing fine particulates to enter the engine. A filtering element would otherwise catch those fine particles, and in theory, extend the engines life by keeping that stuff out of the cylinders. For all out racing engines, long term wear isn't really a concern as they are regularly rebuilt and "freshened" long before any wear issues from using un-filtered air would manifest themselves.

Ya, my engine is going strong for 15 years, and I have a well oiled K&N that I clean regularly, plus
lots of oil changes, so that's a good point.  I also have fresh oil all the time, because whenever I go out,
I lose about a 1/4 cup of oil, due to rear main seal leak, so I am always topping it off with fresh oil!

[RCCDrew]

When I was a kid, I ran a chevy pickup without an air cleaner. It lasted about a year before it started burning oil.

[cudabob496]

When I was a kid, I ran a chevy pickup without an air cleaner. It lasted about a year before it started burning oil.

Probably depends somewhat on how dirty/dusty the air is.