For those of you who didn’t live it, exhaust emission regulations were not the only bullets that killed the “muscle car era”. The skyrocketing insurance rates based on engine size and the “oil shortages” of the early seventies contributed just as much, if not more, to the plunge in performance car sales that eventually led to their demise. How many of us here remember waiting in lines for hours to buy the 10 gallon limit of gas every other day (odd even days) to feed our beasts to go cruise or just get to work. Or cringing when the insurance agent wanted your vin number so he could figure out how much more that engine code is going to cost you this year.
Most of us working at the dealers then accept that the Mopar “Performance” car era really ended when the standard engine offered in something like the Road Runner had a single 2bbl carburetor on it, 73-74’ 318? As mentioned, really means nothing today unless you’re a collector.
Those 5mph bumpers did more to detract from the original four-gen Plymouth b-body design than anything else IMO.
Yes compression ratios started dropping around 71’ IIRC (383HP 8.5:1?). For both emission reduction and to be able to use cheaper less refined/lower octane fuel.