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some hook it to a timed port...you only get vacuum under heavy accel...some hook it to manifold vac, i think this helps with pinging when under heavy accel...i personally dont use it at all...ps, on a holley, ported vac is in the metering block on the pass side...
 

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Silver Can to FULL MANIFOLD VACUUM source on Carb! This will allow your engine to idle smoother, increase gas mileage, and reduce engine temperatures.
 

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true, but your timing dumps out when you nail it...(vacuum drops harshly initally during wot...)jmo...i have hooked it up to manifold vacuum on some apps, but thats why i listed three ways of doing it...i guess it really depends on your setup...really have to test all of your options...
 

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kustomwerker, this is why there is no reason to use ported vacuum. Timing advance drops off when vacuum dumps from mid-heavy throttle in both setups. So you might as well have your engine idle smooth, run at a higher timing advance under light throttle, and idle at a higher timing advance to reduce engine temperature and gas usage. There is no advantage to using ported vacuum.
Full Vacuum Advantage : Reduced Engine Temperatures, Smoother idle, increased mileage from idle advance
Ported Advantages : None
 

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Is this a failry mild engine or a race motor? the advance is there for a reason. With out it you set your curve with the springs on the centrifigual weights.
If you run a fairly stock set up hook it to venturi vaccume(has vacc when throttle opens) this will advance the timming when you get on it and let it idle as well. If you are totaly unsure about all of this buy a chiltons for any small block car. Youll want 8 to 12 at idle and 30 somthing when at full advance(takes some tuning to find optimum). the advance cannister will be stamped or the instructions will tell you what it has for degrees of timming built in.Then you get to play with springs till you hit the curve right. Nothing beats a Dyno for this. Go to the MSD site and read the insructions. Being an MSD MVP dealer...there is alot of info there for you.
good luck and don't get discouraged when you get it right it will be alot better than a stock hei.
 

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JohnZ's writeup in that thread is excellent
 
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