A few years ago, when I was still trying to get SHARK Quarterly magazine going, Greg Fadler helped me out with a few articles. Greg did a nice technical piece on the L88 hood. Im extracting the text portion for you. He went on to do some technical discussion of how to measure the total effects but, maybe, the straight text is more practical for this posting.... During the late sixties, all of Detroit was running at a fever pitch in the quest for horsepower. One of the most aggressive performance programs of the time was Chevrolets Corvette equipped with Regular Production Option (RPO) L-88. This engine option, if ordered, demanded several other options including heavy duty brakes, suspension, transmission and cool/ram air hood. The L-88 option was available from 1967 to 1969. Its cousin, the all-aluminum ZL-1 was available only in 1969 as an extension of the L-88 option. These special Corvettes employed all of the best technology that GM had at its disposal. One of the more effective performance parts on these cars was the specially-designed hood. Because the hood picked up air from the base of the windshield, it achieved the combined benefits of bringing higher pressure ram air and cooler outside air to the engine. I refer to it by the short form name “cool/ram”. Hoods could also be purchased through the dealer parts system, but these hoods in themselves were not the only parts needed to achieve the free flow option. To achieve the full free flow effect the correct manifold/carburetor setup was also required. There is often some confusion in this respect since both Camaros and Corvettes could be fitted with the L-88 style hood as an aftermarket piece and, to make matters worse, it was sometimes referenced (internally and by Camaro collectors) as the ZL-2 hood. However, this was not an official RPO code. For Corvette, only the L-88 package delivered from the factory on an L-88 engine was fully prepped to provide the cool/ram effect. The RPO L-88 hood also evolved over the three year run. In 1967 Chevrolet started with the existing big block hood. Holes were cut in the inner hood panel to allow high pressure cool air from the base of the windshield to enter an (added) air box. The base of the standard air cleaner sealed against the bottom of the air box, which also contained the requisite filter. Outwardly the 1967 L-88 hood looked like any other big block car. For 1968 and 1969, the L-88 Corvettes received a unique hood. It was several inches taller than the regular production big block hood, again to allow for cold air entry at the base of the windshield. Like its 1967 sibling, the 68-69 hood held the air cleaner in an air box that sealed against the base of the standard air cleaner. It should be noted that pulling air from the base of the windshield is important for several reasons. First, outside air is generally cooler than under hood air. Underhood air temperatures of 140 to 160 degrees are not unrealistic. Second, the ram air effect also provides a slight increase in horsepower. Most vehicles generate their best source of high pressure air at the base of the windshield; that’s why virtually every HVAC (heater/ventilation/air conditioning) system gets its air from this area. Third, the air at the base of the windshield is cleaner than air taken from closer to the ground; a dirty air filter is horsepower lost for no good reason.
Posted on: Mon, 31 Mar 2014 09:05:58 +0000
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