During the development we ran both a standard inlet manifold (with no EGR provisions) and the manifold on your engine. On the dyno, the EGR-style manifold actually made slightly more horsepower. The ports on the floor of the plenum are deadheaded at the block-off plate beside the carburetor. Any fuel that builds up in the ports is drawn back into the airstream without any consequence.
The ZZ3 engine was always intended to be a dual-purpose engine. It had to produce at least 300 hp in Emission trim, and make as much horsepower as the previous ZZ2 GM crate engine. Luckily, we were able to meet both bogies and the rest is history. The ZZZ-ZZ4 engine is the best-selling OE crate engine of all time. CHP
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