manifold or ported
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From: midwest
manifold or ported
i still cant decide if i like manifold or ported vacuum advance better on my engines. if i run ported i seem to have a rough idle but more topend. if i change to manifold the idle smoothes and i lose some topend but gain bottom end. i was told if i set the timing at 10 degrees and plug the vac advance into manifold vac and it jumps to 20 degrees at idle then it should be plugged to ported vac cuz it would have to much initial advance. how are they hooked to from the factory on a 78' 460?
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In 78 with all the emissions crap it would have been timed/ ported vacuum.
I like it with full manifold vacuum, as you mentioned it makes the low end feel stronger, I didn't feel a loss in the top end though.
If your emissions equipment is non functional then go with what you want, if it is functional, then I'd keep it on the timed/ported port.
With full vacuum to the vac advance, It doesn't matter if your running 20 degreeBTDC at idle, the second you put a load on the enigne (using full vacuum) the vacuum drops, in turn the timing retards quickly. The timed port on the other hand would increase or advance your timing further which isn't always ideal with high initial.
I like it with full manifold vacuum, as you mentioned it makes the low end feel stronger, I didn't feel a loss in the top end though.
If your emissions equipment is non functional then go with what you want, if it is functional, then I'd keep it on the timed/ported port.
With full vacuum to the vac advance, It doesn't matter if your running 20 degreeBTDC at idle, the second you put a load on the enigne (using full vacuum) the vacuum drops, in turn the timing retards quickly. The timed port on the other hand would increase or advance your timing further which isn't always ideal with high initial.
Last edited by jwtaylor; Dec 14, 2004 at 12:46 PM.
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From: Orlando
Was just reading this post on another forum
Check out the 385 (429/460) forum at http://www.network54.com/Hide/Forum/85220
its easier than me retyping what was said.
Mike
its easier than me retyping what was said.
Mike
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mshumack
I disagree with one thing in that link, timed port does increase the timing as you accelerate. Say your at idle, using timed port, you have no vacuum to that port or the vac advance, say you set it at 8BTDC, the second you accelerate the timing begins to advance along with the rpm because the vacuum is getting stronger. Where full vacuum, it stays the same until its under a load and the vacuum drops, which means it takes out timing (retards) and decreases the chance of predetenation....thats how my reacts.
Whether one or the other is better in all cases....thats a huge debate and application specific. All I know, is if a person has functioning emissions equipment and smog tests then the timed port should be used.
I disagree with one thing in that link, timed port does increase the timing as you accelerate. Say your at idle, using timed port, you have no vacuum to that port or the vac advance, say you set it at 8BTDC, the second you accelerate the timing begins to advance along with the rpm because the vacuum is getting stronger. Where full vacuum, it stays the same until its under a load and the vacuum drops, which means it takes out timing (retards) and decreases the chance of predetenation....thats how my reacts.
Whether one or the other is better in all cases....thats a huge debate and application specific. All I know, is if a person has functioning emissions equipment and smog tests then the timed port should be used.
Last edited by jwtaylor; Dec 14, 2004 at 12:52 PM.
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From: Orlando
I think the 385 thread agreed with what you said -
the Ported vacuum source increases with rpm and the manifold vacuum source decreases with rpm.
Which is best is still up to the individual engine/vehicle combo.
I also agree with you regarding if you have emissions leave it on Ported.
However, for non-emission, street performance vehicles - it looks like manifold vacuum may have advantages.
mike
Which is best is still up to the individual engine/vehicle combo.
I also agree with you regarding if you have emissions leave it on Ported.
However, for non-emission, street performance vehicles - it looks like manifold vacuum may have advantages.
mike
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