I was curious about what aspects of a cam affect the vacumn an engine makes. Is it duration, lift, etc. Does little vacumn mean a wilder cam? I know other things can affect it like the intake/carb combo. My 460 pulls 19hg of vacumn at warm idle with the stock cam, where as my 351W pulls 8.5hg of vacum at idle with what I was told was a stage 2 RV cam. What does the hg stand for anyway?

 

All cam parameters affect vacuum, but a cam with more valve overlap(smaller LSA) will produce less vacuum than a cam with more. The more lift and duration a cam has the more overlap it will generally have, but you can't really put a number on it because the ramp rate also plays a role, a cam with less overall lift and duration could have more overlap than a bigger cam simply because the ramp rate is lower. You can see this by comparing the 0.050" lift, two cams with the same advertised duration may have different 50 thou duration, and the one with higher 50 thou numbers will have more overlap or smaller lobe seperation angle(LSA).

The scale you refer to is in/Hg(inches of mercury), and old imperial scale that is popular for automotive applications.

 

Hg is the chemical symbol for mercury. jd

 

duration is the biggest loss of vac.how much duration are you thinking anything over 300 @.05 would be problem stay in the 280-290 youll be fine

 

The cam I ordered has an advertised duration of 262-intake and 272-exhaust.

 

you'll be fine

 

Throttle opening also affects vaccum. Closed throttle (idle)= high manifold vac., WOT= lower man. vac.


Pete