Intake vacuum question
Thread Starter
Instructor
Joined: Jun 2004
Posts: 182
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From: Sun Peaks British Columbia
Intake vacuum question
I checked my vacuum yesterday while setting my idle mixture and got a steady needle at 12". Most manuals I've read say you should have 17 to 20 inches of vacuum. Wouldn't a performance cam with a certain amount of valve overlap account for a lower vacuum reading at curb idle.
Thx.
YV
Thx.
YV
Instructor
Joined: Jan 2008
Posts: 208
Likes: 0
From: McDonough GA
Using the ported vacuum below the throttle blades?
Timed vacuum above the blades will always be less and was used for emissions purposes only. Longer duration cams will result in less vacuum as I recall.
Advanced
Joined: May 2009
Posts: 65
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From: La Pine Oregon
Another consideration is Altitude . I don't know yours but here in Central Oregon I'm at
4575 ft. and vacuum is pretty low on my 74 L82. I'm lucky with this cam to get 14
or 15 inches at idle . ( thats pure manifold vacuum with a fitting in manifold )
You also get to run a lot more advance at high areas too.
4575 ft. and vacuum is pretty low on my 74 L82. I'm lucky with this cam to get 14
or 15 inches at idle . ( thats pure manifold vacuum with a fitting in manifold )
You also get to run a lot more advance at high areas too.
Thread Starter
Instructor
Joined: Jun 2004
Posts: 182
Likes: 0
From: Sun Peaks British Columbia
Another consideration is Altitude . I don't know yours but here in Central Oregon I'm at
4575 ft. and vacuum is pretty low on my 74 L82. I'm lucky with this cam to get 14
or 15 inches at idle . ( thats pure manifold vacuum with a fitting in manifold )
You also get to run a lot more advance at high areas too.
4575 ft. and vacuum is pretty low on my 74 L82. I'm lucky with this cam to get 14
or 15 inches at idle . ( thats pure manifold vacuum with a fitting in manifold )
You also get to run a lot more advance at high areas too.
