Ported or Manifold Advanced
Thread Starter
Racer
Joined: Feb 2013
Posts: 386
Likes: 3
From: Clifton Virginia
Ported or Manifold Advanced
How many of you use ported vacuum advance for the dizzy verses manifold vacuum? I read someone interesting article about using ported vacuum advance is better than using manifold vacuum or it does not make any difference which u use. I've always used manifold vacuum advance since I thought if you had a radical cam and low engine vacuum at idle, it was beneficial also it helps with cooling since timing is advanced. Thoughts anyone?
Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
Its an excellent question.
I have ran my car all 3 ways.
Full vacuum runs the coolest and smoothest.
Ported is stock, and no vacuum at at all is what racers use and you have to tune your curve with exact springs and weights.
I have mine ported right now because it lopes more but I have a clutch so it can handle it.
I think there are some stickies on here all about timing to set you strait on what and how to do it.
I have ran my car all 3 ways.
Full vacuum runs the coolest and smoothest.
Ported is stock, and no vacuum at at all is what racers use and you have to tune your curve with exact springs and weights.
I have mine ported right now because it lopes more but I have a clutch so it can handle it.
I think there are some stickies on here all about timing to set you strait on what and how to do it.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Ported vacuum was designed for emissions control. This was applied to the distributor vacuum can so that there would be NO vacuum on the can at idle. With the timing retarded at idle, the engine runs hotter and burns off excess hydrocarbons. Of course, it also uses more fuel and causes more wear on the engine...but what's all that when you are 'saving the planet'?
If you are seriously "Green", run ported vacuum to the distributor; if you want to improve idle quality, reduce fuel consumption at idle, and give the engine a 'breather', run manifold vacuum...like the engine was initially designed.
P.S. For those who don't understand 'ported' vs. 'manifold' vacuum:
Ported is equivalent to manifold vacuum at all times except at idle. At idle, manifold vacuum is at maximum level; ported vacuum is at ZERO vacuum. But, as soon as the carb throttle plates open just a bit, both sources are at the same vacuum level.
If you are seriously "Green", run ported vacuum to the distributor; if you want to improve idle quality, reduce fuel consumption at idle, and give the engine a 'breather', run manifold vacuum...like the engine was initially designed.
P.S. For those who don't understand 'ported' vs. 'manifold' vacuum:
Ported is equivalent to manifold vacuum at all times except at idle. At idle, manifold vacuum is at maximum level; ported vacuum is at ZERO vacuum. But, as soon as the carb throttle plates open just a bit, both sources are at the same vacuum level.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Ported versus manifold vacuum to the distributor has been addressed in detail be me and two other noted automotive engineers in my papers on timing and vacuum advance. I also have a published paper on the different types of vacuum and their definition and purpose. If you have any questions, please just drop me an e-mail request for the papers.
7T1vette summed it up pretty good, though.
Lars
V8FastCars@msn.com
7T1vette summed it up pretty good, though.
Lars
V8FastCars@msn.com
