[HWYSTR455]

What I've seen time & time again is that aftermarket D port heads need like in the 38 degree range of timing, think that would have made a significant difference.

Since there was a dip/drop in TQ at a lower RPM with the manifolds, bet a Perf RPM intake would have taken care of that. Single planes would probable do better once you get over say 310cfm or so.

As for the SD testing, it was pretty common knowledge OE exhaust systems were restrictive, especially considering the constraints of regulations at the time. One of the top day-one mods were headers & true dual exhaust. Being an F body was considered the main recipient of the SD, it was well known the exhaust was even more restrictive than most, with the bends and crossover muffler.

At least that's some of my thoughts on the topic, in general.


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