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Old 02-11-2017, 02:47 PM
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rang-a-stang rang-a-stang is offline
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Ported or manifold vacuum to the Dizzy?

Now that I am through smog, I am trying to wake my 401 up. A buddy of mine (Chevy guy) said I should hook manifold vacuum to my Dizzy and plug the hole for the ported vacuum until next smog check. My static timing is at 10 degrees.

What do you guys think? Is it better to leave it ported or should i hook it to manifold?
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Old 02-11-2017, 02:52 PM
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Manifold all way...but some will disagree.
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Old 02-11-2017, 03:57 PM
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I tried both. I could never get rid of a really nasty off-idle bog when I had it on ported vacuum.

No issues on manifold vacuum with the stock setup.
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Old 02-11-2017, 04:48 PM
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Give it what it wants. It ought not make much difference to throttle response because the only difference between the vacuum signal is when the throttle is at idle and just off idle.

If it responds well now, leave it alone. It not, then experiment.

What it definately will do is reduce the combustion heat going into the block and head as well as out the exhaust at idle.
Looking at the '79 diagram, there's CTO that switches the distributor over to manifold vacuum when the water temperature gets over a certain temperature (220 F on '85).
A possible downside of running on manifold all the time is fouling the spark plug at idle. So if you do it, after some time check your plugs and see if there's a bunch of carbon on them.

Another thing you can do is experiment with shifting the whole curve by setting the initial at the maximum specified. If it pings, back it off. If it only pings part throttle, back off the vacuum using the adjuster.
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Old 02-11-2017, 07:38 PM
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ZackN920 ZackN920 is offline
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I gotta read up on some of this stuff! It'd be nice to wake my 360 more. Got better ignition, rebuilt carb, dual snorkel air housing, less restricted exhaust but don't notice anything extra with any of it...well except for the carb. It ran like crap before I pulled it apart. PO of my jeep also ripped off the air pump.

Ported... is that at the carb? On my wag the diagram show's it connected to some thingamajig (with another line on it) on the intake manifold. And the unregulated manifold vac port had way too much vacuum to connect the distributor. It'd be advanced all the time!
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Old 02-12-2017, 10:36 AM
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copy all, everyone! Thanks for the input. I also have the off idle stumble, when warm. I haven't driven it with 10 degrees timing yet because while I was adjusting the timing i added a motor flush to my oil and will be pulling my oil pan and replacing the rear main seal.

So I guess I will do my rear main, take it for a spin (with ported, as factor) with 10* and see how it does. then I will change over to Manifold and see how it does.

Yeah ZackN920, if you google "Ported Vacuum" there is a lot of info out there on it. The way I understand it, its a vacuum signal taken just above the butterfly valve in the carb so it's "delayed" a bit. The port signal comes off the carb, goes to the coolant temp switch on the front, top, passenger side of my engine (I believe its the bottom nipple of the the 3 nipple switch). middle nipple is the Dizzy, and the top nipple is Manifold vacuum. SO it runs on manifold vacuum until a certain temp is achieved, then it switches over to ported vacuum. I can tell when my truck warms up because it gets the off idle stumble, and generally feels like it is driving through water. I am not sure if it is the change in the vacuum signal to the dizzy or the EGR system turning on. One thing a time I guess....
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  #7  
Old 02-12-2017, 11:12 AM
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probably egr...do you have a delay valve on EGR hose?
Did you install a restriction washer before installing EGR valve(if it was universal/new one)?

Only difference with ported/manifold on distributor is no vacuum advance @ idle.
It'll have full vacuum advance @ idle on manifold.
Throttle response is much improved IMHO.
Ported vacuum is an emissions band aid for EPA regs to reduce emissions @ idle.
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Old 02-12-2017, 01:18 PM
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I used to think ported vacuum came along with emissions controls of the late 60s because thats when you find a lot of GM engines in particular getting idle stop solenoids etc. However, its not true. It was used before that and is also frequently the better choice on hot rodded engines.

Some examples are mentioned in this archived wide-band tuning thread in posts #19 and 20 as they straignten out you know who (post 17). Also for a really good and detailed explanation of the choice between ported vs. non-ported advance starting at post 10 second paragraph & more in post 13.
You'll have to scroll down the page to get to the posts, but its worth it.

And any of you guys that don't have the timing at idle at the factory setting should do that first. It most certainly will be slow responding as well wasting energy to be firing the spark plug any later the recommended initial. Do that first, then adjust idle mix. Repeat if needed.

One last note newbies. The 'A' on AMC/Jeep timing covers is 'Advance' not 'after'. So those marks are degrees Before top dead center.
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Old 02-12-2017, 02:32 PM
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Quote:
Originally Posted by nograin
And any of you guys that don't have the timing at idle at the factory setting should do that first.

That's not always true. The Buick motors in Jeeps are supposed to be timed to 0*. They run MUCH better around 10-12. Factory specs aren't always the best.
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  #10  
Old 02-12-2017, 03:05 PM
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No arguement from me on that it could run better with more. I was responding to the two guys above who were fiddling with 360s with base timing less advanced than spec.

I'm curious, how is the factory distributor vacuum arranged on the Buick v-8?
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Old 02-12-2017, 11:20 PM
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I've found running with both hdc and spark CTOs without the nonlinear valve works best. At least with my msd dist, 6a and edelbrock 1406.

Here's a diagram



This way dist gets manifold when cold under 160 degrees, ported during normal operation temp, and manifold again if engine is really hot over 220.


I've found that wiring the grey/white (10 sec) reverse delay so it effects both manifold sources to the 2 CTOs results in slightly smoother operation.
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Old 02-13-2017, 05:24 AM
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Quote:
Originally Posted by babywag
probably egr...do you have a delay valve on EGR hose?
Did you install a restriction washer before installing EGR valve(if it was universal/new one)?


Man! More conversation started here than I thought there would be! I thought this was going to be an easy one!

I don't have a delay on my EGR hose. It literally goes, vacuum source (carb nipple E) to CTO, to EGR. That's how the 79 manual had it for the 49 state set up. I swapped the factory EGR when I swapped intake manifolds. I cleaned it and verified its operation before I installed it. I am not sure what a restriction washer is...
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Old 02-13-2017, 08:56 AM
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The universal replacement EGR valves come with diff size restriction washers.
If one isn't installed it dumps too much and you get hesitation.

A delay valve slows the rush of EGR if getting hesitation try adding a delay valve.
It just slows the vacuum to egr, and helps.
I had to add one to my '90...
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Old 02-13-2017, 11:43 AM
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those are cheap and easy to find at Autozone/Oreilly/Napa, right?
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Old 02-13-2017, 01:40 PM
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NAPA probably, not sure about other stores.
Anytime I need something that isn't the "norm" lookup an show them part# for vehicle, I go to NAPA and the guy is always willing to look through the books and find me exactly what I need.

YMMV
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Old 02-14-2017, 06:11 PM
WrenchMonkey WrenchMonkey is offline
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Quote:
Originally Posted by babywag
NAPA probably, not sure about other stores.
Anytime I need something that isn't the "norm" lookup an show them part# for vehicle, I go to NAPA and the guy is always willing to look through the books and find me exactly what I need.

YMMV

Yep, everywhere else I go they only want to look up my specific vehicle, napa will work with you to try to find something that "may" work from another vehicle. For example Mini have some funky threaded t35 or bigger disc retaining bolt, the guy and I tried for at least half an hour to find something similar (in this case it was literally unique to mini's) and I've been successful a few times.
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Old 02-14-2017, 08:19 PM
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Rang, Don't panic it. Yours might be fine, especially if it is the correct replacement. Tony's talking about some universal replacements. Also, realize there are multiple ways EGR was done over the years.

For example, In '84 EGR systems used a dump valve whereas '85 systems do not. Also when I was checking my EGR valves for operation, they didn't seem to work under vacuum. Turns out that's because early ones just worked off of ported vacuum (except California models that get a special backpressure valve.) But by '84 they are all 'positive back pressure' types that have a double diaphgram. So by then the back pressure valve was built into the valve for all 50 states. The upper diaphragm doesn't hold vacuum until the lower one seals it. The lower one is exhaust driven. Go figure. Wouldn't surprise me if there were more changes in later years.
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Old 02-14-2017, 10:54 PM
440sixpack 440sixpack is offline
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Manifold vacuum.

This article is the best on the subject anywhere. it applies to all makes of engines so ignore the fact it's from a vette forum.


http://www.corvette-restoration.com/.../Timing101.pdf
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Old 02-15-2017, 10:36 AM
twmattox twmattox is offline
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I did mine like kansasboy001 below. However, I started looking into it and ended up adding the non-linear valve back in because it is supposed to blend ported and manifold vacuum and that is supposed to help get rid of an off idle stumble.

Honestly, I have tried manifold and ported and notice zero difference in my rig. I just ended up going back to "stock" without the AIR injection stuff. When I change intakes and add my 4v carb I will most likely look manifold; just to eliminate the miles of vacuum hose under there.

Quote:
Originally Posted by kansasboy001
I've found running with both hdc and spark CTOs without the nonlinear valve works best. At least with my msd dist, 6a and edelbrock 1406.

Here's a diagram



This way dist gets manifold when cold under 160 degrees, ported during normal operation temp, and manifold again if engine is really hot over 220.


I've found that wiring the grey/white (10 sec) reverse delay so it effects both manifold sources to the 2 CTOs results in slightly smoother operation.
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Old 02-15-2017, 11:58 AM
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Quote:
Manifold vacuum.

This article is the best on the subject anywhere. it applies to all makes of engines so ignore the fact it's from a vette forum.

Actually it does apply to a specific set of characteristics as described, which is a pretty high performance engine.
There's different ways to accomplish the same, but our engines are low compression and have little overlap at idle. Also, at least the later years, the initial timing is set at 10 or 12 degrees BTDC. That's a far cry from 0 or 2 degrees after TDC.

It's also wrong to state that AIR is the only reason for retarding the timing to help emissions. (see link in my earlier post). That's a GM centric point of view :LOL: However it is true that retarding initial was often used to reduce pollutants at a slight expense of efficiency. The bottom line is to give the engine what it wants or works best. Compression and cam play a big role.
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