1969 CAMARO "SUPER SCOOP"
RPO ZL2 - SPECIAL DUCTED HOOD: RACE-BRED TECHNOLOGY
by Wayne D. Guinn
by Wayne D. Guinn
An insider's look at the development of the Cowl Induction hood by the author of
"Camaro - Untold Secrets"
"Camaro - Untold Secrets"
The hood dubbed "Super Scoop" by Chevrolet was designed specifically to be a functional piece of high-performance equipment. The intention was to increase overall horsepower by delivering cold fresh air to the induction system. Not only did it effectively accomplish its primary objective, but its stylistic beauty greatly contributed to the mark resulting in the classic appearance of the 1969 Camaro equipped with the "Cowl Induction" hood. THE COLD AIR THEORY
The principle of utilizing cold air induction was nothing new at Chevrolet. It was used in racing as far back as 1963 on the Chevrolet Z11 stock cars running on the NASCAR circuit and again with the "Plenum Air Intake" released as a special service option for the race-oriented 1968 Z/28s. Rather than using a raised hood panel like the 1969 RPO ZL2 option, the first two designs drafted cold air from the base of the windshield under the hood via a special air cleaner and duct, much like the NASCAR racers of today.
Chevy engineer Doug Roe, who worked with Product Promotions chief Vince Piggins, found a dramatic performance gain by taking the cool dense air at the high pressure area near the base of the windshield. Ducting pressurized fresh cold air from this area to the carburetor creates a more dense fuel charge with increased volumetric efficiency resulting in more horsepower An approximate 1% horsepower increase is gained for every 11 degree drop in temperature providing the mixture is adjusted accordingly. That means if your engine has a gross horsepower rating of 350, a drop of 43 degrees would net you an additional horsepower increase of 4%, equal to 14 hp, for a total of 364 hp. These gains are typical, since under hood temperatures in normal conditions are relatively hot, and under racing conditional even hotter. Therefore, given the temperature differential of under hood and outside the hood along with pressurized unrestricted air flow, it is not unreasonable to expect this type of power gain at the upper levels of engine performance.
The reverse drafting method used on the special ZL2 hood was chosen over forward facing scoops which create greater pressures and increased ram effect but have problems associated with air turbulence at the carburetor air horn. Turbulence causes uneven pressures within the metering bodies and upsets correct air/fuel ratio and delivery. Correcting this type of system is involved and not worth the insignificant power increase the additional pressure affords.
Larry Shinoda, of Chevrolet's design group, began development of the hood system approximately May 1967. That primary aim of the system was to give advantage to the TRANS-AM competing Camaro Z/28s. Although the hood was fully developed and ready much earlier, the concept reached the production level for the 1969 model year.
The delay can be indirectly attributed to the SPORTS CAR CLUB of AMERICA (SCCA). Chevrolet held back the special hood production until it could be homologated into the SCCA TRANS-AM events. It wasn't until the 1969 racing season that the SCCA loosened up and allowed hood scoops, stipulating that they must be of "modest" design and in no way interfere with driver vision.
The 1969 SCCA recognition forms filed by Chevrolet included the RPO ZL2 single four barrel "steel hood" in order to satisfy the minimum production number of 1,000 units necessary to utilize these parts in the racing series. Chevrolet then qualified the rare counter part fiberglass 2x4 hood as optional heavy-duty equipment for use in the series. It was strictly a matter of economics that led Chevrolet to produce and homologate the steel hood even though it was their intention to use the fiberglass hood in the racing series.
As you can see, the folks at Chevrolet were masters at SCCA rule bending and/or interpretation -especially when it came to economics and gaining advantage in competition. Consequently, an extremely LIMITED production of fiberglass hoods were sold in stark contrast to the unlimited production run of 1969 RPO ZL2 "Special Ducted Hoods", which sold an amazing 10,026 units due to their overwhelming popularity. There is no doubt that the TRANS-AM race car's appearance with the hood had an impact on the buyer.
The fiberglass hood was costly to produce. If the SCCA were to hold Chevrolet to the 1,000-unit minimum production number and sales for the fiberglass hood were realistically targeted at a mere 100 units, the expense of production would be justification alone nor to produce the fiberglass hood. However since the steel counterpart was inexpensive to produce (relative to the fiberglass unit) the steel units would be easier to justify cost-wise as a Regular Production Option (RPO) with a sales potential of well over 1000 units. Because the steel hood and the fiberglass were of the same basic design and function, it would be easy to homologate the steel hood on the recognition form, and then offer the fiberglass hood as a "heavy-duty" service option allowing Chevrolet to produce only as many fiberglass hoods as they determined there was a need for.
FUNCTIONAL DESIGN
The RPO ZL2 system works by drafting air through the special ducted hood from an opening near the base of the windshield. The rear facing air intake is well-shrouded in an effort to smooth out excessive turbulence. An air valve is placed at the opening which is controlled by an electric solenoid and activated by a switch on the throttle arm. The valve opens when the throttle is approximately 90% depressed. With the valve open, cold air is directed though the hood's raised plenum chamber to a special air filter that seals to the hood and delivers the cold air to the carburetor.
WHY AN AIR VALVE?
The air valve was specified fur use on the production RPO ZL2 option for the sake of better overall drivability. Taking into account the diversity of climatic conditions and their effects on the system, it was determined that the system should function only when called on. If the system remains open in extreme cold weather, icing of the carburetor could occur. The valve also affords longer air filter service life. The cowl induction hood was and still is one of the most popular options offered for the first generation Camaro. The combination of its aggressive good looks and ability to lend additional power without engine alterations is truly amazing. Best of all is the sen sation derived by pressing your foot down, hearing the flap open with a unique roar of air rushing in and the whining gearbox in concert with that free-flowing tune of extra horsepower!
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source: www.camaro-untoldsecrets.com
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