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Old Sep 26, 2013 | 11:45 AM
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I have then 4.8 ls-1 in my 51 Chevy truck, can someone tell me what the function is of the (vac port ?) that is located on the intake manifold passenger side about halfway the manifold? It is on the passenger side near the top of the manifold ,looks to be vac ? maybe. what goes there and where does it terminate?
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Old Sep 26, 2013 | 12:53 PM
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Pic? Is it real small? Half way down the length and half way down the height? I think that is the port that I un-capped and used to run my vacuum HVAC controls. Mine was capped off from the factory but I just broke off the tip when I was looking for something to run my controls. If you don't need it you can probably cap it off, I don't think it serves any engine/performance specific purpose on the vehicle it originally came out of.
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Old Sep 26, 2013 | 07:29 PM
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looking at the rear of the manifold on 2004 model 5.3 and all I see if the vacuum connection for the power brake.
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Old Oct 1, 2013 | 03:09 PM
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Originally Posted by Ken Reid
looking at the rear of the manifold on 2004 model 5.3 and all I see if the vacuum connection for the power brake.
not on the rear, on the side passenger side about 1/2 way the manifold towards the top.
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Old Oct 1, 2013 | 06:28 PM
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ok. I found it. it has a nipple on it for a vacuum hose, but it is sealed from the factory with a little break away tab on the end of the nipple.

the engine is a 2004. so whatever that vacuum source supplies wasn't used with this engine/truck.
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Old Oct 2, 2013 | 08:01 AM
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Is your 4.8 out of a van? Vans use that port for the HVAC controls, where as trucks have the little tab on the end since the HVAC is controlled by electric motors. You can just cap it off.
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Old Oct 2, 2013 | 10:23 AM
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I used that port for my vacuum modulator , in my ly6-turbo 350 68c10
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