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Discussion Starter #1
Hey guys. Question, should I plug off my vacuum advance or hook it up. I have bbc 4 speed with 600 lift hydraulic roller..low vacuum..rich idle bit when I drive it the plugs look good. I cant tell the difference in performance either way. It does drive well and has lots of power. So performance is not the issue. What's your guys thoughts
 

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I would run it. A properly set up hei is hard to beat. It could help burn that rich off idle mixture with a little more advance.
 

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With low vacuum I would remove it. That way you can run more initial. I never liked having my idle depend on vacuum, I like it to be at the same place all the time.
On my 1978 454 I have it set for 22 initial with 14 mechanical all in by 2600 rpm. My car runs great like this.. Before you try this make sure you have low compression or you will have starting and pinging issues. However these issues can be tuned out by changing the thermostat to 160 and using 93 octane fuel. I presently use 93 octane since it so cheap and swapped the 160 thermostat for a 180.. My car runs like a dream...
 

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Discussion Starter #4
It's almost 10.6:1 compression and I run 110nor 112 racing gas. Vacuum is currently plugged. It doesn't ping or anything like that. I was just curious because if the low manifold vacuum, how much is the engine really benefitting from the vacuum advance being hooked up. And maybe I'm completely bass backwards about it
 

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not very much info to go on??
so
street car = yes
race car = no
.
what does your timing curve look like now ??
.
if you don't see any change,, it may be broke or stuck ??
or on the wrong port ??
full, ported, or venturi - vacuum ??
.
there is no vacuum advance added at WOT..
not seeing any more ""performance"" is normal,
its for a cleaner, better, stronger, cooler idle,, and cruise/mileage..
 

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Discussion Starter #6
With it plugged I'm around 36 to 38 all in. What specs you want jj. Its bbc 408. Around 10.6:1 compression with my aluminum heads. 750 double pump aft. 4 speed and 3.73 rear end
 

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I use a similar set up but daily drive mine. The vacuum advance helps with start and below 3k rpm. After that its all mechanical and controlled by spring rate. I use a MSD box with a Street Fire MSD distributor for rev limit and clean burn. My results yield 0-60 times in the sub 4 seconds at WOT. Cruising around town is easier with the vacuum advance hooked up, however, my vacuum pot had some leaky lines coming off of it due to age. I had to eliminate the vacuum pot from the system to get the best vacuum advance performance, as that leak in vacuum, even though it wasn't directly tied to the distributor, was affecting other power development. I now use an electric vacuum pump to power air con/vent controls.
 
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