i have heard different things from different people(maybe it's just a matter of preference), but is there any kind of reasoning to where you connect your vacuum advance? some people go manifold, some ported. does one work better than the other? makes the engine run better? my mote and my truck are both connected to the manifold vacuum port on the backside of the carb baseplate, the one kind of in the middle. this means i'm getting advance at idle as well as all through my rpm range. with ported, i'm only getting base timming until the rpm comes up. i guess i'm just curious to see what other people think.
proper vacuum connection for your hei vacuum advance
- Thread starter monte85
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Well, the difference is that ported only comes into effect when the throttle is opened since it is above the throttle blades. This is why it is usually used for vacuum advance.
i understand the difference between ported and manifold. i was wondering if there was a performance benefit or something to connecting it one way or the other. i guess what i want to know is why one person will tell you one thing and the next person you talk to will tell you something else.
Well, it is because it does not come into effect when the throttle is closed. This way, it does not over-advance at idle, but still gets a signal during part-throttle cruise, which is it's intended time of operation. This is mainly to improve fuel economy at steady-state speeds when you are getting far less than optimal cylinder filling due to a mostly-closed throttle plate. Hooking it up to manifold vacuum can over-advance the ignition and make it kick back at the starter in extreme examples. This is why the OEM's always connected it to ported vacuum. You can even adjust the amount of advance the can gives you if you get one of the adjustable cans from Crane or MSD.
I just recently went from ported vacuum to manifold vacuum last year after reading this article in HP Pontiac magazine and noticed a big difference.
http://www.highperformancepontiac.com/t ... index.html
But like it said in the article that every ones tuning scenarios are different. And this test was on a 455 which is what i have. By the way you said
"my mote and my truck are both connected to the manifold vacuum port on the backside of the carb baseplate, the one kind of in the middle"
This sound like to me that you have it hooked up to the wrong port. this port is usually for the brake booster. I am not sure what carb you have though. Just my opinion but i was running ported vacuum for my distibutor for 15 years until last year, and i'm not going back! :wink:
http://www.highperformancepontiac.com/t ... index.html
But like it said in the article that every ones tuning scenarios are different. And this test was on a 455 which is what i have. By the way you said
"my mote and my truck are both connected to the manifold vacuum port on the backside of the carb baseplate, the one kind of in the middle"
This sound like to me that you have it hooked up to the wrong port. this port is usually for the brake booster. I am not sure what carb you have though. Just my opinion but i was running ported vacuum for my distibutor for 15 years until last year, and i'm not going back! :wink:
actually my carbs both have one of the little tube shaped ports which are just off-center but located next to the booster fitting. these are both the larger sized q-jets(either 795 or 800 cfm). maybe others don't have these ports. all the carbs i have got 'em. also i misspelled "monte". i feel so ashamed for that. 🙁
oh yes there is an extra port on the back of the qaudrajet,you are correct. on a edelbrock there is just the brake booster port on the back and the extra ports are on the front which is where i used to hook up my vacuum advance. you should try it! just block off that port on the carb and go straight into the manifold somewhere.
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