International Full Size Jeep Association
Home Forums Reader's Rigs Tech Library Trail Stories FSJ-List
International Full Size Jeep Association  

Go Back   International Full Size Jeep Association > Tire Kickin' > General FSJ Tech

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 01-20-2010, 07:23 PM
scotty1998's Avatar
scotty1998 scotty1998 is offline
Master Mechanic
 
Join Date: Apr 21, 2008
Location: Watkins Glen, NY
Posts: 912
My own two cents on the ported vs. manifold thing

I can't tell you how many posts there are on this issue but there's a long running debate on whether it really matters if you're running your vac advance off of ported vac or straight manifold. As I understand it, vac from the CTO (ported) is blocked off until the engine reaches operating temperature. Once that happens, there is no difference whatsover between manifold or ported but in cold climates, it could take as much as 10 miles of driving before this is so. I suppose that the engine runs a little better when some things are switched off before it's warmed up but why vacuum advance would be included in this from the factory is a mystery.

I have never run well upon starting in cold weather and I've always chalked it up to the choke. It would lag if I hit the accelerator when backing out of my driveway and would sometimes stall. On the flats, performance would be awful... that is, until the beast warmed up.

Tonight, I switched my vac advance to full manifold and it made all the difference in the world. It's like a completely new truck. No stalling and no lagging when cold.

Moral of the story is if there's a poll out there on the subject, there's no doubt which way I'd vote. Someone will have to explain to me why if I'm an AMC emissions engineer, I wouldn't want to advance an engine when cold please because right now, I'm thinking that the idea was just plain stupid.

My two cents...
__________________
1987 Jeep Grand Wagoneer
Stock Everything
AMC 360, 2-BBL Motorcraft



Last edited by scotty1998 : 01-20-2010 at 07:34 PM.
Reply With Quote
  #2  
Old 01-20-2010, 08:24 PM
Jeep Craze's Avatar
Jeep Craze Jeep Craze is offline
Bleedin' Gasoline
 
Join Date: Sep 14, 2001
Location: Kempton,Pennsylvania
Posts: 1,508
actually if your CTO's were working properly you would have full manifold vacuum on cold start up. Then when warm it would switch to ported vacuum, then if the temp got above about 220*f it would switch back to manifold vacuum.

But regardless...I agree....It runs better on Manifold
__________________
91 GW 360/727 Black cherry metallic, maroon interior, 100% restored with some mods.
1985 J20, Chevy 350/700r4/jeep208 3" rough country lift kit
83 CJ8 Scrambler-Wifes Toy MERCEDES TURBO DIESEL /4spd, 4" lift, 35" tires
2014 Polaris RZR 570- PRP Bench Seats. 3 -5 point harness,2" lift kit, roof, windshield
Reply With Quote
  #3  
Old 01-20-2010, 08:39 PM
Mudwolf's Avatar
Mudwolf Mudwolf is offline
Member
 
Join Date: Feb 21, 2009
Location: Midland
Posts: 78
Quote:
Originally Posted by scotty1998

Tonight, I switched my vac advance to full manifold and it made all the difference in the world. It's like a completely new truck. No stalling and no lagging when cold.




Can you post a pic of your setup? Mine does the same pretty much...
__________________
'78 Waggy: 3" lift, 32's, Rebuilt 360, For Sale
'93 YJ7 ('79 front grill conversion) on 38's
'95, '96 and '98 XJ's on 31's.
'01 Wrangler on 32's.
'89 Comanche

"It's all about Jeeps"!!!
Reply With Quote
  #4  
Old 01-20-2010, 08:43 PM
x6xdemonx6x's Avatar
x6xdemonx6x x6xdemonx6x is offline
Gear Head
 
Join Date: Dec 12, 2009
Location: Republic, mo
Posts: 516
if you switch to manifold what else do you have to change if anything?
__________________
FREE 91 grand wagoneer 360 2barrel 4" lift 31" tires rebuilt tranny and tcase dana 44 front and rear
TFI upgrade
Reply With Quote
  #5  
Old 01-21-2010, 06:41 AM
scotty1998's Avatar
scotty1998 scotty1998 is offline
Master Mechanic
 
Join Date: Apr 21, 2008
Location: Watkins Glen, NY
Posts: 912
I'll try to post a pic later when I get home from work but in a nut shell, the stock distributor vac advance setup is hooked directly to the red CTO that sits just to the left of it by an 8" long vac hose. It should be routed that way from the factory.

I merely plugged that CTO port off and routed a new vac hose from the vac advance, into the air pump feed system which runs directly off of manifold vac.

JeepCraze. Can you explain this a little more? I had always thought the CTO opts the manifold vac off until the coolant system allows it to open when warmed up? So, either open or closed. There's actually a diverter in there which opts from either full open, semi open, or completely closed? Perhaps I'm just unclear on what the definition of "ported vacuum" really is. Based on your description, I can now see why the debate, ported or full manifold, for the vac advance because it should work either way. Maybe that's beem my problem all along, the CTO is shot?
__________________
1987 Jeep Grand Wagoneer
Stock Everything
AMC 360, 2-BBL Motorcraft



Last edited by scotty1998 : 01-21-2010 at 06:44 AM.
Reply With Quote
  #6  
Old 01-21-2010, 07:11 AM
L98Waggy's Avatar
L98Waggy L98Waggy is offline
Member (huhuhuh...member)
 
Join Date: Feb 08, 2009
Location: Northeastern Kansas
Posts: 139
My thoughts right away are,if you are using manifold vac. you are basically now running a mech. advance dizzy. As the throttle blades open,the vacum created at the base plate increases and applies vac to the dizzy. It is fully advancing your timing at idle and you could probably do away with the hose and advance your base timing and accomplish the same result. Am I way off base here or does this seem right? Kinda curious.
__________________
God grant me the serenity to accept the impossible trails I cannot crawl,courage to crawl the twisted trails I can and the wisdom to keep tire side down.
Reply With Quote
  #7  
Old 01-21-2010, 07:25 AM
scotty1998's Avatar
scotty1998 scotty1998 is offline
Master Mechanic
 
Join Date: Apr 21, 2008
Location: Watkins Glen, NY
Posts: 912
You know, thinking about this a bit more, are you're saying that the CTO's operate differently depending on which port nipple that an emissions device is connected to? For example, if it's a 3 port CTO, and my vac advance is connected to the wrong port, that might be my problem. If this is the case, how do you know which port goes to which device?
__________________
1987 Jeep Grand Wagoneer
Stock Everything
AMC 360, 2-BBL Motorcraft


Reply With Quote
  #8  
Old 01-21-2010, 07:49 AM
Gambler68's Avatar
Gambler68 Gambler68 is offline
Rabble Rouser
 
Join Date: Feb 29, 2004
Location: Ignacio, Colorado, USA
Posts: 14,081
Interesting...my 360 has been doing the EXACT thing you described..worse in the winter but even during the summer it's a little laggy till fully warmed up. What worries me most is the vac. switch to my part time equipped QT..I have a in dash vac gauge plumped to measure the vac to the SWITCH I am so paranoid about it (part time kits can get screwed up bad if the fork looses vaccum)

I'll have to try replacing the CTO or try straight manifold, either way something should improve. good post lets see some pics please!
__________________
1979 Chero S "Sundog" 1979 Chero S "Hammer"
1968 327 J3000 1978 J10SWB
The Edge... there is no honest way to explain it because the only people who really know where it is are the ones who have gone over.
Hunter S. Thompson .

Reply With Quote
  #9  
Old 01-21-2010, 07:56 AM
scotty1998's Avatar
scotty1998 scotty1998 is offline
Master Mechanic
 
Join Date: Apr 21, 2008
Location: Watkins Glen, NY
Posts: 912
I'll take some pics tonight...

I think at idle, you'd need a little more advance to account for the normally leaner conditions at that time. Same at cruising speed. I guess I was wondering why the CTO would option it off completely when cold. JeepCraze may have explained that one a bit but I'd like more info on the subject.
__________________
1987 Jeep Grand Wagoneer
Stock Everything
AMC 360, 2-BBL Motorcraft


Reply With Quote
  #10  
Old 01-21-2010, 08:00 AM
scotty1998's Avatar
scotty1998 scotty1998 is offline
Master Mechanic
 
Join Date: Apr 21, 2008
Location: Watkins Glen, NY
Posts: 912
I found this statement on the internet which might help to explain the principle L98Waggy. It is interesting...

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.
__________________
1987 Jeep Grand Wagoneer
Stock Everything
AMC 360, 2-BBL Motorcraft



Last edited by scotty1998 : 01-21-2010 at 08:08 AM.
Reply With Quote
  #11  
Old 01-21-2010, 08:17 AM
scotty1998's Avatar
scotty1998 scotty1998 is offline
Master Mechanic
 
Join Date: Apr 21, 2008
Location: Watkins Glen, NY
Posts: 912
Back to X6X's comment. Yeah, why have the non-linear valve or either CTO for that matter when you're running straight manifold for your vac advance?

Couldn't you just plug off the carb port and eliminate the whole mess or am I missing something too?
__________________
1987 Jeep Grand Wagoneer
Stock Everything
AMC 360, 2-BBL Motorcraft


Reply With Quote
  #12  
Old 01-21-2010, 08:44 AM
dbuie dbuie is offline
Grease Monkey
 
Join Date: Jun 29, 2009
Location: Southeast NC
Posts: 398
Here is what I did to mine:

http://tc.wagoneer.net/sblog/images/vac-simple.gif

Runs and idles much better now and allows you to do away with the Red CTO, NLV, and miles of vacuum line.
__________________
1989 GW-Resto Project
My "Labor of Love"
Reply With Quote
  #13  
Old 01-21-2010, 08:52 AM
twmattox twmattox is offline
350 Buick
 
Join Date: Feb 24, 2003
Location: Indiana
Posts: 1,282
Ok, so correct me if I am wrong...but,

-centrifugal advance usually kicks in around 1000rpm and steadily increases with an overall advance of approximately 10*

-the distributor vacuum advance (per factory spec) is supposed to begin around 4" and be fully engaged at around 14"

-manifold vacuum is highest at idle and steadily decreases as throttle is opened (ultimately reaching very low at wide open throttle)

-ported vacuum is approximately 0" at idle and increases steadily and at some point reads the same as manifold vacuum, at which point it begins decreasing steadily just like manifold vacuum

-the Non-Linear Valve (used on our GWs in the mid-'80s onward) blends ported and manifold vacuum at idle so that the spark advance is not "0" but not fully vacuum advanced either

-the CTOs use coolant temperatures to determine what vacuum source the distributor is provided (blended manifold when cold, blended manifold ported when warm, manifold when hot)


So, given all of this, spark curve is a very delicate thing. Ultimately, you are trying to run the most advance you can, without causing pre-ignition. You can alter your vacuum source, the amount of vacuum needed to introduce vacuum advance, the weight of springs on centrifugal advance (allowing earlier/later introduction of centrifugal advance), total centrifugal advance...basically, a lot of variables...
Reply With Quote
  #14  
Old 01-21-2010, 09:16 AM
scotty1998's Avatar
scotty1998 scotty1998 is offline
Master Mechanic
 
Join Date: Apr 21, 2008
Location: Watkins Glen, NY
Posts: 912
TWMattox,
Going back through some of my vac component descriptions. I think you are correct on all accounts. Your last statement is probably the crux of the ongoing debate now that I understand this a bit more and I'm more under the assumption now that either one of my CTO's isn't working right or my plumbing to advance was wrong all along.

Dbuie. For us more simple minded folks, in effect, you're still relying on ported vac for your advance. The difference being that you will get absolutely 0 advance at idle when cold since you won't have the blending of the ported and manifold vac that twmattox speaks of right? If so, wouldn't you definitely have problems with lagging and such when cold?
__________________
1987 Jeep Grand Wagoneer
Stock Everything
AMC 360, 2-BBL Motorcraft



Last edited by scotty1998 : 01-21-2010 at 09:25 AM.
Reply With Quote
  #15  
Old 01-21-2010, 09:28 AM
dbuie dbuie is offline
Grease Monkey
 
Join Date: Jun 29, 2009
Location: Southeast NC
Posts: 398
Quote:
Originally Posted by scotty1998
TWMattox,
Going back through some of my vac component descriptions. I think you are correct on all accounts. Your last statement is probably the crux of the ongoing debate now that I understand this a bit more and I'm more under the assumption now that either one of my CTO's isn't working right or my plumbing to advance was wrong all along.

Dbuie. For us more simple minded folks, it looks like you basically took the NLV out of the equation and the HDC CTO correct? So in effect, you're still relying on ported vac for your advance. The difference being that you will get absolutely 0 advance at idle when cold since you won't have the blending of the ported and manifold vac that twmattox speaks of right? If so, wouldn't you definitely have problems with lagging and such when cold?

No problems at all. No lagging, no stumbles, and accelerates nice and smooth. No pinging either even at full throttle with 87 octane. It dipped down into the teens here about a week ago and she fired right up. Let her idle for about 30 seconds and took off. Not saying that this setup will do the same on another vehicle but on mine it works great. Kudos to the guy who came up with this setup. Besides, these CTO's and NLV's are hard to come by and I just figured that these are two less to worry about.
__________________
1989 GW-Resto Project
My "Labor of Love"

Last edited by dbuie : 01-21-2010 at 09:35 AM.
Reply With Quote
  #16  
Old 01-21-2010, 09:48 AM
scotty1998's Avatar
scotty1998 scotty1998 is offline
Master Mechanic
 
Join Date: Apr 21, 2008
Location: Watkins Glen, NY
Posts: 912
What about NC? Is it a smog nazi state? In NY, I believe that I only quality for what they term a low emissions check. That means that it has to have a catalytic converter and air pump system but it wouldn't need the normal NOx checks at the tailpipe. All of this goes away when the rig hits 25 years old. Soon... soon...
__________________
1987 Jeep Grand Wagoneer
Stock Everything
AMC 360, 2-BBL Motorcraft


Reply With Quote
  #17  
Old 01-21-2010, 09:54 AM
dbuie dbuie is offline
Grease Monkey
 
Join Date: Jun 29, 2009
Location: Southeast NC
Posts: 398
Quote:
Originally Posted by scotty1998
What about NC? Is it a smog nazi state? In NY, I believe that I only quality for what they term a low emissions check. That means that it has to have a catalytic converter and air pump system but it wouldn't need the normal NOx checks at the tailpipe. All of this goes away when the rig hits 25 years old. Soon... soon...

Not where I live. I assume that they would check for a catalytic converter/air pump/hoses/diverter valve but I doubt that where I go they even know about CTO or NLV items. My new T-Stat hosing came with a plug in case you remove the red CTO. So, by keeping my yellow one intact they should have no worries.
__________________
1989 GW-Resto Project
My "Labor of Love"
Reply With Quote
  #18  
Old 01-21-2010, 10:32 AM
twmattox twmattox is offline
350 Buick
 
Join Date: Feb 24, 2003
Location: Indiana
Posts: 1,282
The vac diagram dbuie posted is the way mine is currently plumbed (I keep debating the whole NLV thing).

The thing to understand about the CTOs is that the middle port is always open...however, the other two are not. When cold, the one port is open and when it reaches operating temps, that port closes and the other opens.

So, for mine, I hooked a length of hose to the CTO middle port (this one is always open and should be hooked to the dizzy). Then applied vacuum (sucked on the hose). For mine, the top port was open...so, that got hooked to manifold. Once warm, the bottom port was open...so that got hooked to ported.

Oh, and the delay valve on the manifold line is kind of important. In order for our rigs to fire easily, the ignition module retards the timing a little bit. You don't want your manifold vacuum to advance the timing at the same time the ignition module is retarding it...they just fight each other...

Last edited by twmattox : 01-21-2010 at 10:34 AM.
Reply With Quote
  #19  
Old 01-21-2010, 10:40 AM
scotty1998's Avatar
scotty1998 scotty1998 is offline
Master Mechanic
 
Join Date: Apr 21, 2008
Location: Watkins Glen, NY
Posts: 912
Hmmm. This is all good to know. So, if anything, I should at least plumb the delay valve in line with the dizzy to manifold. Ok.

Thanks for the primer on the CTO too. I'm assuming then that the bottom nipple which is normally plumbed to manifold would be the one that opens up when warm?

I think for giggles tonight, I'm going to rehook everything up but test the CTO's for which one is the constant open port. At least then, that will eliminate one reason for poor cold weather driveability one way or the other.
__________________
1987 Jeep Grand Wagoneer
Stock Everything
AMC 360, 2-BBL Motorcraft



Last edited by scotty1998 : 01-21-2010 at 10:45 AM.
Reply With Quote
  #20  
Old 01-21-2010, 10:50 AM
shackwrrr's Avatar
shackwrrr shackwrrr is offline
FSJ Maniac
 
Join Date: Mar 04, 2006
Location: Lima,Ohio/Piedmont, Ohio
Posts: 3,145
So are you setting the 8* of base timing and then hooking the hose up or are you setting it to something different. I am asking because I have always run ported vac but I have also run around 15* of timing to make it run good. So would I back the timing off so that I get around 15* of timing at idle with the vac hooked up? If I hook it up now It would shoot my idle advance to around 25*

Have you maesured your advance at idle with the vac hooked up to see what it is?
__________________
Jeepless

In to Turbo crap now
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 07:17 AM.


Powered by vBulletin Version 3.5.4
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
corner corner