Im still having low vacuum issues with a un tuned computer controlled 355 SBC, HSR and a Comp Cams 08-305-8 degreed cam. Basically when the car is at full operating temperature with roughly 600-700rpm idle I am pulling 14" in park and about 10" in drive. The vacuum gauge shows a little fluctuation with about 1-2" of play. My timing is set at 6*. I tried using a leak detection spray thats like a fuel that in theory should cause the car to rev up if a leak is present. I went through the whole can and cant find a leak.


This is what I found online on diagnosing what symptoms cause a gauge to look like. Mine sounds like the 8"-14" one. I took a small video clip of my vacuum gauge with the car in park...then drive and back to park to show how the needle moves. Was hoping someone could look at it and verify if the slight bounce is normal or if it indicates another issue. Thanks

Kris

 

14" in park @ 600-700 RPMs is not really low for a cam that big. The chart above is vacuum readings for a stock engine with a stock cam. The bigger the cam the lower your vacuum will be.

As for the fluctuations.... that's a different story. If everything is tuned properly you shouldn't have much fluctuation in the idle with a fuel injected setup.

I assume the idle is "hunting" up and down as your vacuum readings are fluctuating?

 

http://www.zippyvideos.com/1029113622006156/idle/