Normal vacumm for Poly 318

[vanrj1]

My Vacuum is running about 12hg in my poly 318 with a 264/450 cam. I think normal stock runs 17hg or so correct?
Would 12hg be right for this more aggressive cam? initial Timing is 12° with "ready run" distributor using vac advance but can use mechanical if desired. Any input appreciated.

It also has power brakes in case that matters and also was in park not in gear.

Thais is a fresh build (500 miles on it) that runs great, just not sure if Vacuum is desirable?

 

[Meep-Meep]

If the overlap on that cam is larger than stock (as I think it might be by a little bit) then the vacuum will be lower than what you would see with a bone stock cam. You might not have an overlap spec but rather a lobe separation angle somewhere on the cam card. Stock may be in the 115 deg LS range while a mild perf cam can be 110 or 112.

- - - Updated - - -

And to answer your question, normal vacuum for any engine will be in the 15-18" Hg range.

 

[vanrj1]

If the overlap on that cam is larger than stock (as I think it might be by a little bit) then the vacuum will be lower than what you would see with a bone stock cam. You might not have an overlap spec but rather a lobe separation angle somewhere on the cam card. Stock may be in the 115 deg LS range while a mild perf cam can be 110 or 112.

- - - Updated - - -


And to answer your question, normal vacuum for any engine will be in the 15-18" Hg range.

Ok, Thanks for the info

 

[Moparsmitty]

I wouldn't be too concerned about a 12hg vacuum reading if the reading is steady and the engine is otherwise running fine . Like Meep says, the more overlap or LSA a cam has the lower your vacuum reading will be. That low of a vacuum may by a little iffy as far as your power brake booster is concerned. I've seen some work with as little as 10hg and others not work well at 15hg. You might have to use a vacuum booster.

 

[Meep-Meep]

Me personally I don't have a problem with 12" on my Belvedere but something to consider if your brakes don't work well.

 

[vanrj1]

I wouldn't be too concerned about a 12hg vacuum reading if the reading is steady and the engine is otherwise running fine . Like Meep says, the more overlap or LSA a cam has the lower your vacuum reading will be. That low of a vacuum may by a little iffy as far as your power brake booster is concerned. I've seen some work with as little as 10hg and others not work well at 15hg. You might have to use a vacuum booster.

Me personally I don't have a problem with 12" on my Belvedere but something to consider if your brakes don't work well.

Thanks for the reply's.... I was thinking of getting rid of the brake booster anyway, they seem to work as manual as it is.