Vacuum Presure questions
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,841
Likes: 0
From: Inver Grove Minnesota
Vacuum Presure questions
I have a 350 with a Holley systemax 2 kit on is and a Holley 750 double pumper. I'm getting about 11 pounds of vac at and idle. Does this sound low, or should I be fine? When I give it throttle it will drop a little then rise up. As shown in this video: http://24.118.233.41/vacgauge.mov What do you guys run for vac at idle and then about 2000 rpms?
Last edited by JustinD; Jun 9, 2006 at 05:10 PM.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
First off it is vaccum not boost. Boost is positive pressure. 11 inches is not bad. I run at about 8 to 9 with a pretty radical cam. If your cam is mild you should be at around 14 to 16 inches depending on the condition of the engine. 
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
First off it is vaccum not boost. Boost is positive pressure. 11 inches is not bad. I run at about 8 to 9 with a pretty radical cam. If your cam is mild you should be at around 14 to 16 inches depending on the condition of the engine.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Where is your initial timing and are you running a vaccum advance. If you are are you running it to a ported or manifold vacuum. My vacuum went from 8.5 to 11 with my old cam and running a vacuum can to manifold vacuum. It was much more responsive. I was running 14 initial with another 12 degrees of vacuum for a toatl of 26 at idle with vacuum advance hooked up. It idled much cleaner and with better vacuum. My old cam was 248 @ .050 with a .525 lift. in a 350.
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,841
Likes: 0
From: Inver Grove Minnesota
What is a vac can, just is like a backup device(stores the vacuum)? My vac advance is on the one that kicks in when you open the throttle. i am having problems with the car hesitating when you add throttle.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
He is talking about the vac diapram on dist.He likes his hooked up to full vac not ported like you have yours.How light are your cent. adv, springs---are they letting the weights come out at 1200rpm?In his the advance is full until you hit the gas and then it backs off.
Last edited by ...Roger...; Jun 9, 2006 at 10:46 PM.
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