distrib question: vacuum vs mech advance - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- 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
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 08-20-2003, 08:54 AM
Member
 
Join Date: Oct 2002
Location: KATY , TX
Posts: 76
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
distrib question: vacuum vs mech advance

Stupid question of the day:
What role does the vacuum advance play when your distrib has weights on it to advance it?

I found a crack in my vacuum line. Dont know how long its been there. How can I tell if my vacuum advance is even working? Can I use my timing light to watch it advance with and without the vacuum hooked up?

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 08-20-2003, 09:38 AM
BOBCRMAN@aol.com's Avatar
Member
 
Last photo:
Join Date: May 2002
Location: Holly, michigan
Posts: 8,117
Wiki Edits: 0

Thanks: 25
Thanked 266 Times in 249 Posts
check in the knowledge base for specifics, but, vac advance makes your engine more responsive and drive able at part throttle operation, also helps gas milage
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 08-20-2003, 09:51 AM
Frisco's Avatar
Glad To Be Here
 
Last photo:
Join Date: Nov 2002
Location: Canton, North Carolina
Age: 72
Posts: 2,244
Wiki Edits: 0

Thanks: 0
Thanked 8 Times in 8 Posts
Re: distrib question: vacuum vs mech advance

Quote:
Originally posted by JUSTINH
Stupid question of the day:
What role does the vacuum advance play when your distrib has weights on it to advance it?

I found a crack in my vacuum line. Dont know how long its been there. How can I tell if my vacuum advance is even working? Can I use my timing light to watch it advance with and without the vacuum hooked up?
Bob answered what the vacuum advance does. Yes, you can use your timing light to watch the advance with and without the vacuum hooked up.

Just remember that the total advance you see when the vacuum advance is hooked up and the RPM of the engine is up around 2000-3000 will NOT be what you will have under load (driving) conditions. The vacuum will not be there under load and the vacuum advance will not be working at that point. I mention this because when I was just learning I had set my Total advance to 36 degrees (with the vacuum advance disconnected and plugged) and thought I'd check it with the vacuum hooked up. I about freaked. Advance was upwards of almost 50 degrees. I forgot that the vacuum drops off and that figure will not be there under load.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 08-20-2003, 10:35 AM
Vetter
 
Join Date: May 2003
Location: New Jersey
Age: 28
Posts: 192
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Frisco, then why is there the vacuum advance? How exactly does it help with gas mileage if, when under load and at high RPMs with little vacuum, it gives away? Can you explain this?

Thanks!

78SilverShark
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 08-20-2003, 11:21 AM
johnsongrass1's Avatar
Race it, Don't rice it!
 
Last photo:
Join Date: Jul 2002
Location: Columbia, Mo
Age: 37
Posts: 4,080
Wiki Edits: 0

Thanks: 0
Thanked 10 Times in 10 Posts
Advance is there to increase power without detonation problems. When under cruise or really light throttle the air flow through the carb will generate vacuum that pulls on the canister, advancing timing for better fuel efficiency. When you step into the throttle, the vacuum will decrease in the dist. due to the sudden momentary loss of vacuum in the carb, this will retard timing and prevent detonation under loads, saving the engine. You must have a way to increase timing when there isn't a vacuum signal to the canister under load to allow earlier spark timing to compensate for rising engine RPM and increase drivability. That's where the mechanical advance will come into play. Seems alot people seem to get confused as to which timing measure is the primary advance mechanism, the vacuum advance. The mechanical advance is there to help support the vacuum at times where vacuum isn't available. The trick is with Mechanical timing can only be read at idle because there will be no vacuum to tell the vacuum advance what to do. Unless you hook the canister up to full timed vacuum port, but then you would be defeating the purpose of the timing retard feature under higher loads, which would allow less use of mechanical timing. I hope this explains well enough.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

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:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

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



All times are GMT -6. The time now is 11:29 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.