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As you go faster at higher RPMs, do you get more vacuum from the manifold, or less?

My understanding is that you have a little vacuum at idle and the strength of the vacuum increases as you go faster. Am I correct?

Thanks!
 

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I remember the vacuum-assisted wipers on my old Rambler a few years back. If you accelerated hard, the wipers slowed way down, almost stopping. If you let off of the gas (especially like when you come up to a red light), the engine vacuum went way up and the wipers hauled a**. So I guess it's more related to accel and decel rates as opposed to what speed you are going.

Now with your supercharger, the vacuum is totally different, right? Aren't you under pressure most of the time, especially when you accel? I hope somebody weighs in on this that knows for sure - I always wanted to understand this better.
 

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I remember the vacuum-assisted wipers on my old Rambler a few years back. If you accelerated hard, the wipers slowed way down, almost stopping. If you let off of the gas (especially like when you come up to a red light), the engine vacuum went way up and the wipers hauled a**. So I guess it's more related to accel and decel rates as opposed to what speed you are going.

Now with your supercharger, the vacuum is totally different, right? Aren't you under pressure most of the time, especially when you accel? I hope somebody weighs in on this that knows for sure - I always wanted to understand this better.
 

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Vacuum

Best answer is not necessarily. Vacuum at idle is typically high. Open the throttle and vacuum goes down. At high RPM you can get more vacuum by closing the throttle than with it open.
Going back the pump analogy the engine is essentially an air pump. When it is pumping more air through, the intake pressure approaches atmospheric pressure. Therefore little vacuum. With the throttle closed or near closed the pump doesn't work so well, but the intake pressure is way below atmospheric pressure hence you have more vacuum.
 
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