Vacuum advance not needed? - 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 04-03-2013, 06:36 PM
Registered User
 
Last photo:
Join Date: Feb 2011
Location: Jennings, Florida
Posts: 31
Wiki Edits: 0

Thanks: 2
Thanked 0 Times in 0 Posts
Vacuum advance not needed?

I have been restoring my 84 C 10 and installed a GM 350 HO crate engine. The spec sheet from GM states not to use the vacuum advance on distributor but to keep it plugged at all times. I'm just wondering if any of you experts would comment on this. Seems strange to me. Engine has small hyd roller cam. Thanks.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 04-03-2013, 06:58 PM
vinniekq2's Avatar
Registered User
 
Join Date: Jun 2012
Location: BC,Canada
Age: 56
Posts: 7,453
Wiki Edits: 0

Thanks: 292
Thanked 709 Times in 684 Posts
try it and see if mileage changes?
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 04-03-2013, 07:46 PM
Custom10's Avatar
my KARMA ran over my DOGMA
 

Last journal entry: SS
Last photo:
Join Date: May 2009
Location: Saskatchewan, Canada
Age: 49
Posts: 1,095
Wiki Edits: 0

Thanks: 14
Thanked 24 Times in 22 Posts
The GM instructions do this in part to cover their butts, less advance means less chance of detonation/pre ignition due to over advancing and thus fewer warranty issues.

Learn the advance curves of you distributor, how much mechanical advance does it add, how much vacuum adv does it add. There are hundreds of threads on this. Set them up to suit the engine/truck

For the most part it is advantageous to run vac advance as it can help improve part throttle effiecencies (fuel milage as vinnie states), clean up idle characteristics etc. some motors can benefit others not so much.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 04-04-2013, 05:12 PM
Registered User
 
Last photo:
Join Date: Feb 2011
Location: Jennings, Florida
Posts: 31
Wiki Edits: 0

Thanks: 2
Thanked 0 Times in 0 Posts
Vacuum advance not needed?

Thanks Custom for reply and Vinnie. I'll hook it up and tune accordingly. I just thought it was might strange.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 04-04-2013, 10:32 PM
Custom10's Avatar
my KARMA ran over my DOGMA
 

Last journal entry: SS
Last photo:
Join Date: May 2009
Location: Saskatchewan, Canada
Age: 49
Posts: 1,095
Wiki Edits: 0

Thanks: 14
Thanked 24 Times in 22 Posts
I might strange indeed, makes one wonder.

If you do get the vac can hooked up you can measure its total added advance using a timing light. Trick at idle is to get full extent of the canister rod to pull full advance and not start the mechanical advance addition via rpm increase. Also if the engine vac is less than 14 at idle you may need a vacuum pump, most vacuum cans dont pin out until around 12-13 " hg

The point is if you have mech adv and vac advance at idle you cant always count on mech advance being steady one way or the other at lower rpms, making the vac adv determination tricky so just try and keep mechanical adv out of the equation.

Otherwise the skip my morning coffee method is to spin the RPM to 4000+ and take a BTDC timing reading without and with the vacuum advance applied, a vacuum pump is good plan here.

All this needs is a good vacuum gage, dial back light or marked balancer to 60 BTDC and someone to hold the brake
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 04-05-2013, 04:42 AM
Member
 
Last photo:
Join Date: Dec 2004
Location: San Antonio, Texas
Age: 50
Posts: 4,021
Wiki Edits: 0

Thanks: 0
Thanked 23 Times in 23 Posts
read this.

http://www.corvette-restoration.com/.../Timing101.pdf
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 04-05-2013, 08:24 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,571
Wiki Edits: 0

Thanks: 3
Thanked 337 Times in 334 Posts
The reason they don't want the vac advance used is because it is a generic tune and will need specific dialing in to match your motor and car-truck . Plus they have no control over what fuel you will fill the tank with.

Its up to you to dial it in. May want to replace with a fully tunable vac adv.

Some allow up to 20+deg at high vacuum basicly for EGR equiped engines.
Too much for a non egr engine... limit it to a max of 12-15deg at highest vacuum.
The rate has to be found by drive testing.
The mechanical cent advance set up is pretty generic too. Can also benefit from fine tuning too.
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


Similar Threads
Thread Thread Starter Forum Replies Last Post
No vacuum advance needed? cullencombs Engine 16 01-07-2012 09:22 PM
Opinions on ported of full vacuum for vacuum advance ? y2k600f4 Engine 15 10-07-2011 09:38 PM
Timing... vacuum or no vacuum advance? 454ChevelleMalibu Engine 18 04-25-2010 09:37 PM
ok to use same vacuum line for vacuum advance and tranny vacuum modulator? brian400ex Engine 4 02-19-2003 02:25 PM
computer advance or vacuum advance?? 1984camaroZ28 Engine 1 10-12-2002 02:57 PM


All times are GMT -6. The time now is 05:49 AM.


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.