Re: dist vacuum advance- timed port vs. full vacuum
[Re: dem440c]
#981494
04/27/11 03:46 PM
04/27/11 03:46 PM
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Joined: Jan 2003
Posts: 75,043
U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,043
U.S.S.A.
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Quote:
I thought I had this concept down way back when I was a wee lad but recently came across something that puzzled me.
Now, the only way that vacuum advance makes sense to me is if the port is "timed" so that it does not see vacuum signal at idle. Otherwise you have full vacuum advance at idle! Right?
I was working on a car last weekend that had a factory carburetor and only one vacuum port, which was NOT timed. It had full vacuum signal at idle and ramped down from there.
How does this work? Is it really designed to have all that extra advance at idle? Doesn't make sense to me.
Can't explain why it's that way but any GM I ever messed with used full vac at idle .
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Re: dist vacuum advance- timed port vs. full vacuum
[Re: JohnRR]
#981495
04/27/11 03:57 PM
04/27/11 03:57 PM
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Joined: Oct 2007
Posts: 3,894
Oregon
hooziewhatsit
master
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master
Joined: Oct 2007
Posts: 3,894
Oregon
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Allegedly a benefit of using manifold vacuum is to get some advance at idle, rather than running a lot of initial in the distributor. 5* Initial + 15* vac advance at idle = 20* 'initial', versus 20* initial in the distributor, and maybe having issues with kickback on the starter, and/or needing a start retard. As the throttle opens, manifold vacuum gradually goes to zero at WOT. Ported vacuum goes from zero at idle, to full vacuum with the throttle barely cracked, and down to zero at WOT. So both end up with vac advance where you want it (part throttle cruising), and no vac advance at WOT. (well, not completely zero vacuum at WOT, but you know what I mean  ) Any car set up and tuned properly should run just fine with either method. 
If you ever find yourself in a fair fight, your tactics suck.
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Re: dist vacuum advance- timed port vs. full vacuum
[Re: cogen80]
#981497
04/27/11 05:30 PM
04/27/11 05:30 PM
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Joined: Oct 2003
Posts: 3,698
NE Oklahoma
Von
master
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master
Joined: Oct 2003
Posts: 3,698
NE Oklahoma
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Quote:
call FBO. he tells you to run full vac with his dist.
Ya, he tells you alot...most of which is total BS....
72 RR, Pump gas 440, 452s, 3800 lbs, Corked, ET Radials,. 11.33@117.72.
Same car, bone stock 346s, 9.5 comp, baby solid. 12.24@110.
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Re: dist vacuum advance- timed port vs. full vacuum
[Re: hooziewhatsit]
#981498
04/27/11 06:41 PM
04/27/11 06:41 PM
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Joined: Jan 2003
Posts: 338
Montreal Quebec
STROKIE
enthusiast
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enthusiast
Joined: Jan 2003
Posts: 338
Montreal Quebec
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Quote:
Allegedly a benefit of using manifold vacuum is to get some advance at idle, rather than running a lot of initial in the distributor. 5* Initial + 15* vac advance at idle = 20* 'initial', versus 20* initial in the distributor, and maybe having issues with kickback on the starter, and/or needing a start retard.
As the throttle opens, manifold vacuum gradually goes to zero at WOT. Ported vacuum goes from zero at idle, to full vacuum with the throttle barely cracked, and down to zero at WOT. So both end up with vac advance where you want it (part throttle cruising), and no vac advance at WOT.
(well, not completely zero vacuum at WOT, but you know what I mean )
Any car set up and tuned properly should run just fine with either method.
I use manifold vacuum at idle, run better and water temp is lower...
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Re: dist vacuum advance- timed port vs. full vacuum
[Re: Von]
#981500
04/27/11 11:38 PM
04/27/11 11:38 PM
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Joined: Nov 2007
Posts: 5,337
the house on the left.
cogen80
master
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master
Joined: Nov 2007
Posts: 5,337
the house on the left.
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Quote:
Quote:
call FBO. he tells you to run full vac with his dist.
Ya, he tells you alot...most of which is total BS....
i don't have any of his stuff but it seems a lot of guys are happy with his stuff.
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Re: dist vacuum advance- timed port vs. full vacuum
[Re: cogen80]
#981501
04/28/11 12:10 AM
04/28/11 12:10 AM
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Joined: Oct 2003
Posts: 3,698
NE Oklahoma
Von
master
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master
Joined: Oct 2003
Posts: 3,698
NE Oklahoma
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Quote:
Quote:
Quote:
call FBO. he tells you to run full vac with his dist.
Ya, he tells you alot...most of which is total BS....
i don't have any of his stuff but it seems a lot of guys are happy with his stuff.
The best one he has told me on at least 2 differet occasions is that no way will a BB mopar make anymore power with more than 34 degrees of total timing. No way, waste of time, wont do a thing........  
72 RR, Pump gas 440, 452s, 3800 lbs, Corked, ET Radials,. 11.33@117.72.
Same car, bone stock 346s, 9.5 comp, baby solid. 12.24@110.
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Re: dist vacuum advance- timed port vs. full vacuum
[Re: hooziewhatsit]
#981502
04/28/11 01:09 AM
04/28/11 01:09 AM
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Joined: Feb 2003
Posts: 21,318
Manitoba, Canada
DaytonaTurbo
Too Many Posts
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Too Many Posts
Joined: Feb 2003
Posts: 21,318
Manitoba, Canada
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Quote:
Allegedly a benefit of using manifold vacuum is to get some advance at idle, rather than running a lot of initial in the distributor. 5* Initial + 15* vac advance at idle = 20* 'initial', versus 20* initial in the distributor, and maybe having issues with kickback on the starter, and/or needing a start retard.
As the throttle opens, manifold vacuum gradually goes to zero at WOT. Ported vacuum goes from zero at idle, to full vacuum with the throttle barely cracked, and down to zero at WOT. So both end up with vac advance where you want it (part throttle cruising), and no vac advance at WOT.
(well, not completely zero vacuum at WOT, but you know what I mean )
Any car set up and tuned properly should run just fine with either method.
Yes I totally agree. Only place you can get into trouble doing it this was is if you don't make enough vacuum to bring up the timing at idle. Idling or even starting a cammed motor with too little initial timing can be just as troublesome and trying to start it with too much. Either way, the distributor needs to be dialed in for the motor it's on. Too many guys think they can just slap them on and go.
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Re: dist vacuum advance- timed port vs. full vacuum
[Re: Von]
#981503
04/28/11 11:47 AM
04/28/11 11:47 AM
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Joined: Mar 2008
Posts: 5,746
Ontario, Canada
Dodgem
master
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master
Joined: Mar 2008
Posts: 5,746
Ontario, Canada
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Quote:
Quote:
call FBO. he tells you to run full vac with his dist.
Ya, he tells you alot...most of which is total BS....
You are so right!
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