Low vacuum at idle. Solutions?

lucky 1985

Apprentice
May 5, 2016
63
14
8
1985 Conquista, 383 mild cam, Sniper FI, BTO 700r4. Getting closer to being streetable. Working on issues as they arise.

This week it's the brakes. The vacuum level was too low to operate the power booster. At fast idle (cold start) the gauge read about 15 inches, which seems to be enough for the booster. At normal idle the gauge read 8-10 inches and the booster seemed not to be operating.

I installed a vac tank like this https://www.jegs.com/i/JEGS/555/63010/10002/-1.

I have it plumbed from the vacuum source to the check valve on this tank, then from the tank's brass fitting to the check valve on the booster. Now the vacuum level at normal idle is about 15 inches. Which is what I want.

Hope this helps somebody in the same situation.
 
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CdnCutlass

Greasemonkey
Jan 14, 2010
155
12
18
Halifax, Nova Scotia
I just went through this earlier this year, I am only pulling 10-11inches of vacuum at idle and ended up getting an electric vacuum pump in addition to a vacuum tank I had installed a few years ago.
 
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64nailhead

Goat Herder
Dec 1, 2014
5,659
1
12,059
113
Upstate NY
Mild cam? The 250 at .050 mild or 215 at .050 mild?

I solved my vacuum starvation issue, did you see that?
I’m curious of the cam specs as well. I’m guessing mid to upper 220’s intake duration with a a little but more on exhaust on a 108-110 ICL in a 383.

I’ve messed with vacuum cans and had success in your range of vacuum. But at 12-13 or less they lose some effectiveness.

Glad it has worked out well for you. Very budget friendly solution.
 
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