I tried this topic in the appearance forum a few days ago and didn't get any response, so I figured you guys would probably know.

I am curious about how cowl induction hoods work. Are they just like ram air scoops that feed outside air right into the air intake? If so wouldn't a ram air hood be better for performance than a cowl induction hood since they give higher pressure at high speeds?

Are there pros and cons to the two?

 

Here's what I can tell you, being an ex-drag racer, for what it's worth:

A cowl induction hood, like the Chevelle or Corvette types, works by taking advantage of the (slightly) higher pressure area found at the base of the windshield on most vehicles. In reality, most of the gains come from the colder (more dense) air found outside the engine compartment, rather than any "ramming" effect. This air also tends to be relatively calm and straight-flowing. The cold air, if the scoop is sealed well, and the carburetor is jetted properly to compensate, can make a very noticeable difference, sometimes as much as 25hp, although the avg. person would probably get more like 10-12hp. On the other hand, the "ram air" hoods and scoops for the most part don't work well. There are some exceptions..., but mostly they are better for appearance than anything else. Over the top of the hood exists a layer, several inches tall, of mostly dead air, when the car is in motion. The ram air hoods/scoops mostly get this air, which is often heated by the ambient heat of the engine compartment. Not what you want. In certain other cases this air, though not dead, is turbulent enough to cause buffeting in the carb venturis, or bowl vent problems. A forward-facing scoop, to be effective, must be tall enough to get over the boundary layer, & large enough to supply the engine airflow needs. This causes sightline problems for the street. The old snorkel & "Grump Lump" scoops have gone by the wayside, for the most part (the "Lump worked for Bill Jenkins, but he went to a great deal of effort to control & straighten the airflow, which most others didn't). The NACA scoops are only effective when speeds exceed what most cars are capable of.

Incidentally, for any Chevelle fans out there....the "Power Dome" hood beats the c**p out of the vaunted "Cowl Induction" hood for effectiveness, if ducted correctly. I know, I know, it's not a Ford....

Ending my lecture now, Mike

 

Thanks for the information.

I wondered how a rear facing scoop could improve air intake, but it makes sense now. I know that a lot of scoops are decorative and do nothing. I like the look, but if you find out its just for looks its rather disapointing.

 

Many of the bigger Ford trucks used the rear facing scoops. It seems that Ford was on the right track as far back as 58, long before Chebby started using that idea.

Michelle