Intake Manifold: The maximum engine size in the Trans-Am series from 1966 through 1972 was 5000cc. To fit this requirement, Chevrolet created the Camaro Z28, which, using a 3 inch crank with the 4 inch bore provided a near-perfect 302 cu.in engine size for the category. Once specialist engine builders such as Traco, Bartz etc got hold of these engines, they worked their magic, and the Chevy teams were at least on a par with those from Ford and Mercury. By early to mid-1967, teams such as Penske were enjoying around 440hp. The Camaro in the early races may not have stopped or handled too well, but it had plenty of boogie in a straight line.
However, not one to go resting on their laurels, GM engineers were constantly looking for ways to squeeze more power out of these motors within the tight confines of the regulations. One of the rules required by the SCCA was that the cars all have a flat hood, and that the motor and all its parts not protrude through the hood. So too, in 1967, the rules also required that while up to four 2-barrel carburettors could be used, not more than one 4-barrel could be used. But with some pressure from the manufacturers, this rule was changed for the 1968 season, from being not more than one 4-barrel, to not more than two 4-barrels.
So in mid-1967, GM engineers began working on a prototype tunnel ram intake manifold, but in which the tunnels ran horizontally, not vertically, and on top of which would be mounted a pair of 4-barrel carbs. A vertical tunnel ram would produce better results, but wouldn’t fit under the hood. So instead they produced a cross ram, whereby a pair of off-set 4-barrel carbs were mounted in an outboard position to keep the entire system very low. Such systems had been used previously by Chrysler in the early 1960s, although the GM intake was much more compact, as engineers also needed to house it within a special plenum into which cold air could be drawn in through the top of the cowl.
The GM cross ram intake is an aluminium two-piece unit with a main mounting plate featuring equal length long tuned runners that create a ram effect of packing in the fuel mixture when using a long duration camshaft on high revving engines. A lid is bolted to the base onto which the carbs are fitted. The cross ram was designed specifically for this small 5 litre engine, and its ability to rev.
In August 1967, back-to-back tests were undertaken pitting a Chevy Trans-Am engine fitted firstly with a single 4-barrel, then the new cross ram. The single 4-barrel engine used an 800cfm Holley, which was the typical set-up in 1967, and produced 441.5hp @7400rpm. The cross ram intake was then fitted, using a pair of 600cfm Holleys, and it produced 467hp @7400rpm. The cross ram netted an impressive 25hp gain. That was a massive increase for a 5 litre engine, and particularly in a championship where all the various makes produced roughly around the same amount of power. By the end of 1969, the cross ram equipped Traco built Chevys in the Penske Camaros were punching out close to 500hp.
Two 600cfm carbs sound way too much for a small 5 litre engine, but in fact after several tests using different carb sizes and carb types, this was the combination that produced the best result.
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