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Old 12-08-2002, 04:35 PM
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Post Engine Vacuum Help

Need your corporate knowledge here. I have always been told manifold vacuum declines as engine speed increases. Just fired my 406 and tried to adjust the carb with a vacuum gauge. The vacuum increases as engine speed increases. This was measured off the port on the rear of the intake. Adjusting the carb has little or no effect on the vacuum. Might this be somehow connected to the new no-gap Total Seal rings?

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Old 12-08-2002, 04:43 PM
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I've always measured vacuum (when adjusting mixture) directly off the carb on a full vacuum port (below the throttle blades). For instance, on a Holley measure it from the large outlet on the baseplate, or on a Edelbrock from the lower front right port. Also, be sure to drop your idle speed as you gain more vacuum while adjusting mixture.
Good luck!
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Old 12-08-2002, 04:53 PM
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Well I'm not getting into the basics of the combustion engine here cause my fingers would fall off. But to try and explain as easy as I can, vacuum drops from the throttle plates openning not from rpm increases. The cylinders suck in air continuously. The restriction caused by the throttle plates causes a high vacuum in the intake manifold. When you open the throttle plates the vacuum signal drops because of the reduced restriction. The harder you open the throttle, the lower the vacuum drops. But that drop is only temporary, as soon as the engine rpm's increase vacuum increases also. This is because the faster the engines running the greater the amount of air it's sucking in. At higher rpm's even with the throttle plates open there is still enough restriction to cause a vacuum in the intake manifold. I don't know how well I just explained that but I need to hurry and go watch The Supranos in a bit.

[ December 08, 2002: Message edited by: dmorris1200 ]</p>
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