[Dwight Southerland]

Jeff - The manifold you note for the 1971 Z28 is a Chevrolet produced part to replace the original 594 aluminum intake. The manifold has some slight modifications for throttle linkage bosses and alternator mounting so it could be used on the ZZ3 and ZZ4 crate motors. It's not an apples to apples comparison to the Edelbrock LD340 vs stock cast iron manifold. That's not to say that there are not parts in the tech guides that aren't correct, but it's one thing when the factory proclaims "improved" replacement parts (i.e. Chevy's replacement 401 BB aluminum heads, MoPar's many 559 heads for the Hemi, etc.etc.) and yet a totally different issue when a 50 year old aftermarket part is suddenly made legal that was never proclaimed by the factory as a replacement.