how come..

[ikeyballz]

I was just wondering, how come all car hoodscoop open up small from the front, to large in the back? it doesnt make any sense @ all?!

if it went from large to small, wouldnt it be 'ram-charging' a bit more? big pressure in the front, high velocity in the neck, high velocity + pressure @ intake manifold?

i have not seen any recent cars w. that design of a hood scoop.
is that just cuz of styling?

[curtis73]

Scoops that are open at the back (called cowl induction) take advantage of the high pressure area at the base of the windshield. There is no "ram charging" of air in any scoop that will help power until about 120 mph.

The forward mounting scoops may or may not collect more air depending on the aerodynamics of the car. In fact, the front 1/3 of many hoods is generating lift, meaning there is an area of low pressure just about the place where the scoop opens up.

For the most part they all work well, none will ram charge, so it boils down to taste and appearance

[Black Lotus]

I read your question a bit differently than the other guy.
In an automotive "duct", you usually want the intake to be quite small in relation to the rest of the duct volume.
It works like this. The intake area is small and thus will have a high velocity. The high velocity air is usually useless for most applications- like radiators, intake systems, etc. Therefore the downstream sectional area of the duct is usually increased gradually to as much as 6 times the area of the intake.
This slows the airflow down- but INCREASES the air pressure.
A good example of this is the WWII P-51 Mustang airplane which is liquid cooled.
A very small intake, large plenum area for the radiator. The air is heated, which adds energy to the system, then squeezed back out the radiator outlet. Voila! More forward thrust than drag.

[dave92cherokee]

Simple answer to your question is most cars you see on the street have regular engines in them with maybe a little modification like a super or turbo charger so they just want the cowl induction hood to allow more cool air to flow into the engine compartment for cooler air intake. For having the scoop turned the other way is ram air induction which is normally used only on high performance engines such as drag cars because they need more air flow into the intake and whatever else air induction system they might have. If you ever see someone with an old mustang or camaro then some of them choose the route of ram air forcing more air into the carbs without having to use a super or turbo charger.

[MagicRat]

Originally Posted by dave92cherokee

If you ever see someone with an old mustang or camaro then some of them choose the route of ram air forcing more air into the carbs without having to use a super or turbo charger.

Just to elaborate, despite the Camaro driver's dreams of ram air supercharging , they are not actually pressurizing the intake tract like a supercharger would. What these cars actually have is just a fancy looking form of cold air intake, as you say.

Any carburetor (such as those on older Camaros and
Mustangs) depends on an air pressure drop over the venturi, so the fuel is drawn from the float bowl into the air stream. Any kind of positive pressure in an air intake will eliminate this effect and the car will not run.

The only way around this is to pressurize the carb in a housing, along with the intake tract.

[Black Lotus]

Originally Posted by MagicRat

Any carburetor (such as those on older Camaros and
Mustangs) depends on an air pressure drop over the venturi, so the fuel is drawn from the float bowl into the air stream. Any kind of positive pressure in an air intake will eliminate this effect and the car will not run.

The only way around this is to pressurize the carb in a housing, along with the intake tract.

Not really.
As far as ram air goes, all you need to do is attach an enclosure over the area that is normally covered by the air cleaner. The fuel bowl vents on a carb are always contained in this area, which pretty much solves the pressure referencing problem. The venturi/ boost venturi would ensure that the fuel would be drawn IN to the carb thanks to Mr. Bernoulli.
On a sensitive engine, the relationship of the sizes of the low speed/high speed air bleeds and the main jets might need looking into also.