Vacuum Advance Canister question - Page 2 - Hot Rod Forum : Hotrodders Bulletin Board -- Hot Rod Forum

Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
lost password?   |   register now

LinkBack Thread Tools
  #16 (permalink)  
Old 04-16-2008, 10:39 AM
Jmark's Avatar
Last photo:
Join Date: Sep 2003
Location: phoenix
Age: 64
Posts: 5,033
Wiki Edits: 0

Thanks: 124
Thanked 103 Times in 83 Posts
Stokey, I'll give you credit for your patience! LOL

I think some are just razzin ya on the vacuum can. I've called it that for years. For me, "vacuum can for the dist" and "vacuum advance" are the same.

Back to your original question.
There are many many STOCK advances out there that begin moving at different amounts of vacuum AND pull different amounts too.

The aftermarket advances do NOT let you set when it begins to move, but only let you adjust HOW MUCH it moves, by turning the stop screw that is inside the advance port. You can LIMIT the amount of travel, but NOT when it operates.

If you are using an aftermarket adjustable vacuum advance, the easiest way to determine WHEN it begins to pull is to "T" in a vacuum guage between the advance and you. I usually have the advance laying on the bench and "T" in a guage and then suck on the hose and watch the advance for first movement and note the amount of vacuum needed to get that first budge. Atleast then you have a good starting point. You can do the same thing with a timing light and the engine idling. Just "T" into the hose and suck on it till the timing mark begins to move.
You can also continue to suck on it to see what the total advance on the unit is set at. (using the timing light.)
Mine was set to max when I got it. I did not need to add another 15 degrees!!! I adjusted it down so it only adds 5 degrees at max pull. For me, it is borderline pinging but getting by ok.


Reply With Quote Quick reply to this message
Sponsored Links
  #17 (permalink)  
Old 04-16-2008, 10:45 AM
Registered User
Join Date: Nov 2004
Location: California
Age: 70
Posts: 839
Wiki Edits: 0

Thanks: 31
Thanked 26 Times in 23 Posts
For whatever it's worth, I've go along with Bogie on this. (I usually do anyway.) I think you have a torque converter problem. The converter is just too tight for that cam. I think (if memory serves) that comp says an XE268 is all you can use with a stock converter. So, I've gotta imagine a cam with the timing you've got is gonna demand a lot of idle speed (you're at 1300 now?) and when you drop it into gear, several things happen. A -- The converter places a load on the motor, reducing the idle (and the manifold vacuum) B -- The reduced idle is also pulling down the mechanical advance C -- The reduced advance (mech and vac) contribute to slowing the motor further. This is a viscious cycle that, hopefully, will reach a point of equilibrium, and the system will stabilize. But, in your case that isn't happening. What is happening is that the engine dies. You could tweak the mechanical advance to try to make its cut-in speed a little higher, or change cannisters to make the vacuum demand for full vacuum advance a little lower, but I think that fundamentally, you should be looking at a 2500 or so stall speed for your converter.
Reply With Quote Quick reply to this message
  #18 (permalink)  
Old 04-16-2008, 11:04 AM
Registered User
Join Date: Jun 2007
Location: NY
Posts: 46
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I totally understand that the converter is wreaking havoc. Heck Comp recommends a 2800 stall for this application.

However at the time I dont have the funds to go out and buy a new converter for this 700r4 and in the mean time I'm just looking get the advance curve a little more squared off.

J Mark - Do you think I should skip the after market adjustable advance.

I've looked over this link that was provided earlier in the thread.

Do you think vacuum advance vc1852 AR22 would be a good choice for me?
Reply With Quote Quick reply to this message
  #19 (permalink)  
Old 04-16-2008, 11:51 AM
AmericanPackMule's Avatar
Registered User

Last journal entry: Adolessent J.R.
Last photo:
Join Date: Feb 2004
Location: Los Angeles, Calif
Age: 74
Posts: 151
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Adjustable Vac. Adv.

I Hope that works for you... But, The Cam Duration, Plays a big part on Vac. @ Idle. & Through the power curv.
Reply With Quote Quick reply to this message
  #20 (permalink)  
Old 04-16-2008, 12:46 PM
Last photo:
Join Date: Nov 2004
Location: Lakeland FL
Age: 68
Posts: 4,110
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 4 Posts
to add to Jmarks info a bit.... here's a graph for how this particular (accell) vac unit works/adjusts....the rate of change only changes in that narrow near vertical line and the actual Hg is only at that Hg range for about one heartbeat...

yes, with a 284 cam if the rpms are less than 1200 there is no advance added possible using manifold vacuum due to very low low Hg so you are at the base 12*....and with no timing the motor makes next to no TQ and it will stall and die due to the convertor drag

the 284 cam needs 18*+ base to make decent TQ and about 1,000 idle speed for decent Hg....confirm that your dist only has 20* centrifugal and set the base to 16- 18*.... and don't use the vacuum advance at all..... or hook it to a ported timed source so timing is added when the Hg is high

click on the 284 chart on this link for idle Hg characteristics on your cam

the principal function for vacuum advance is added hwy mpg...not...performance tuning a big cam

old bogie. you have a link to all of Lars articles....his personal website that I used has gone off the I don't have them anymore
Attached Thumbnails
Click image for larger version

Name:	vac settings.jpg
Views:	156
Size:	81.5 KB
ID:	29317  

Last edited by red65mustang; 04-16-2008 at 12:52 PM.
Reply With Quote Quick reply to this message
  #21 (permalink)  
Old 04-16-2008, 01:12 PM
Last photo:
Join Date: Nov 2004
Location: Lakeland FL
Age: 68
Posts: 4,110
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 4 Posts
here's one of Lar's articles on how to set up your timing...incuding vac advance....

he's calling for 18b*'s+20c*'s+16v*'s=54TT (max practical possible)

my .02
18+20+12=50 is plenty....depending on the curve and car wt and gears

but anything from 46 to 54 is normal depending on the car

and here's a excellent article from Barry Grant's Demon Carb tech section for how cam duration changes base timing and dist set up....

once you have swapped the convertor for more slip...about 21-24* base wiill make the motor launch so hard your neck will get sore!....obviously you need to have the dist re-worked for less cent to stay at about 38* max WOT...
(and with that much actual base timing you can probably have a 800rpms idle)

Last edited by red65mustang; 04-16-2008 at 01:30 PM.
Reply With Quote Quick reply to this message
  #22 (permalink)  
Old 04-16-2008, 01:34 PM
Registered User
Last photo:
Join Date: Jul 2007
Location: norcal
Age: 61
Posts: 762
Wiki Edits: 0

Thanks: 1
Thanked 2 Times in 2 Posts
hey red, lars hangs out in CFOT, when i run across him i'll update this post with a link. meanwhile here's another cool link:

ibfun is a cool websight...
Reply With Quote Quick reply to this message
  #23 (permalink)  
Old 04-16-2008, 02:54 PM
Last photo:
Join Date: Nov 2004
Location: Lakeland FL
Age: 68
Posts: 4,110
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 4 Posts
thanks techron....

looks like most if not all of the articles are on that link...

(they sure can save a bunch of typing on these threads)
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Please select your insurance company (Optional)


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools

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

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Vacuum advance source-ported vs non ported JUSTINH Engine 49 09-19-2013 07:52 AM
Distributor Tuning and Theory - Part 1 Rick WI Engine 35 04-26-2011 12:38 AM
detonation 71 chevy c-10 Engine 33 04-29-2010 12:20 PM
Ported Vacuum 72Orange Engine 18 08-07-2006 08:56 PM
mechanical advance settings?? Lthompson Electrical 10 02-10-2005 03:19 PM

All times are GMT -6. The time now is 12:37 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999 - 2012. All Rights Reserved.