on 2/4/04 10:11 PM, tom at [EMAIL PROTECTED] wrote: > I got the latest issue of Chevelle World with the article about installing a > cowl induction setup through a hole in the firewall (Rudisill's cowl plenum > system). I also noticed that John Bedenbender's 66 Elky > http://www.midwestchevelles.com/past_shows/mw2002/66elky.htm had a similar > cowl plenum arrangement through the firewall (pretty cool). Some articles > about cowl induction on the web said that the cowl induction intake should > be 1" or more above the hood line since air flow at the hood line was low. > If this is the case, could there be an air flow problem with intake through > the firewall, which I assume gets its air through the cowl grate which is > below the hood level? > > Tom Tomlinson > '71 Malibu > '66 El Camino > > Tom, Somewhere in the article I'm sure I mentioned the fact that a high pressure area exists at the base of the windshield. Smokey Yunick may not have been the first to figure it out, but he sure put that theory to practical application, and if you peek under the hood of any NASCAR racer you'll find that essentially the same system is still put to use. The pressure differential at the base of the windshield is also the same reason that Chevrolet configured the '69 Camaro and '70-2 Chevelle Cowl Induction packages like they did.
The cowl plenum system that Rudisell is offering duplicates the over-the-counter package that Chevrolet offered during the late Sixties, to help improve on- and off-track performance of serious Chevy competitors. I've seen them installed on Camaros, Chevelles, Novas, and even full-size Chevys. The discussion of airflow over the surface of the hood is a bit out of context for a true "cowl induction" setup, because the high pressure at the base of the windshield is quite adequate enough to yield a "force air" effect. The notion that the intake location should be at least an inch above the hood's surface applies most directly to a forward facing "scoop," and placing one in that location (at least an inch above the hood's surface) increases its effectiveness substantially. An even better solution for a forward facing scoop is to locate it at the leading edge of the hood, much like the Olds 442 setups of the early Seventies. The rearward facing scoop on the second-generation Trans Ams, however, were minimally functional at best... and purely cosmetic at worst. The location, elevation, and direction of the "scoop" all conspired to reduce its effectiveness considerably. They did "shake" whenever the engine was throttled, however, and DID LOOK pretty cool. I also question the effectiveness of the Mopar and Ford "Shaker" scoops of the same era. At the very least, they did allow a cooler, denser charge of air into the engine, although it had to be sucked in rather than forced in by using nature's physics to accomplish the job. My '69 L89 convertible has been finished since last June, and the cowl plenum setup is a definite attention-getter at all the shows and cruises I've taken it to, not to mention the unique wail that emanates from the firewall opening every time the secondaries are called into action. It may not be for everybody, but for me it was the perfect complement to my '69 SS! Those of you who watch HorsePower TV will get a quick peek at it in a week or two... Chuck
