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Originally Posted by frank.g
All SD's built for production (the ones with an "X" in their VIN) were after the emission change over date, so all have the later emission system. Some intake manifolds were originally manufactured for the earlier system, and they were re-tapped and stamped with the later part number. Occasionally, you can see the double stamp on some of these manifolds.
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Cool thx. Reason for my Q here:
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The next time you see a '73 Pontiac model like Steve Schappaugh's SD-455 Trans Am, check under the hood and take a close look at the emissions control system. Many fail to realize that two separate systems were used that year. Although each had the same basic components and functioned similarly, the early system fell victim to the EPA's watchful eye. Continue on as we discuss the first and second types and explore why changes occurred. Read more: http://www.highperformancepontiac.co...ntrol_systems/
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