Timing SBC by vacuum - 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 01-15-2003, 09:48 AM
Dave E Shank's Avatar
Member
 
Join Date: Apr 2002
Location: Fishers, Indiana
Age: 70
Posts: 676
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post Timing SBC by vacuum

I have a 350 SBC showing a number of symptoms of having timing too much retarted. It has a non OEM cam but I do not know it's specifications. I wanted to check optimum timing by checking vacuum. What is exact proceedure? Should you have vacuum line going to distributor disconnected and plugged? Anything else I should know before trying this method. Last time I put vacuum gauge on intake manifold, needle just fluctuated all over gauge making it tough getting exact reading?? Any suggestions appreciated THANKS DAVE

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 01-15-2003, 10:58 AM
aka Duke of URL
 
Last wiki edit: Finding vacuum leaks Last photo:
Join Date: Oct 2001
Location: Rockville, MD
Posts: 4,821
Wiki Edits: 1

Thanks: 0
Thanked 0 Times in 0 Posts
Arrow

-Go here- for diagnosing vacuum gauge readings. This may give you some insight on what is wrong with the engine.

To set initial timing with a gauge, you merely unplug the ported vacuum advance, plug the vacuum source and find correct initial timing wihen you come to the highest vacuum reading. The engine has to be in fairly good condition to go about it this way.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 01-15-2003, 02:26 PM
dmorris1200's Avatar
doesn't play well with others
 
Last photo:
Join Date: Feb 2002
Location: Maine
Age: 49
Posts: 1,834
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

This is a direct quote from an old post by Jim Weeks on vacuum timing.
[quote]The reason this came up in conversation to begin with is that one hot rodder had an engine that could not be identified thus you could not even look up the timing specs. Another hot rodder had an engine with a slipped vibration damper, and slack in the timing chain so you know before you start your marks are going to be off. A timing light is almost useless in both of these situations.

Here is the procedure as explained to me.

l. Adjust your carburatur settings and then bring the car to an idle.

2. Advance the distributor until you get the highest vacuum.

3. Back up the distributor until you get one less unit. (Example is your highest reading is 14 you back it up to 13 and lock your distributor down.

OK I took this advise and applied it to a 1965 Plymouth 273 that I completely rebuilt a few years ago, so the engine was in good shape. The factory spec with a timing light is 10 degrees before top dead center, and that is what I had it set at. I hooked up the vacuum gauge, rotated the distributor and the best vacuum I got was 20. I then backed it up to read 19 and locked the distributor down. I ran the car thru a series of tests and the car started faster, idled smoother, excelerated faster, and ran a little cooler than it ever had before. I re-cheched the timing with a light and it read 14 degrees before top dead center.

I wish some of the rest of you would try this technique and report your results good or bad. I was sceptacle about this myself in the begining.
<hr></blockquote>

This is a copy of the results from my car as I tested it after Jim's post.
[quote]OK so I finally got a few minutes together to try the vacuum test. I found that I reached max vacuum at approx. 23 degrees advance. I backed off one degree and was at 18 deg. advance. Dropped another deg. vacuum and was around 11 deg. advance. So with my engine it took me about 2 degrees vacuum drop to get to an acceptable advance. I still feel safer with my light but it is an interesting test. I suppose in a pinch I could use this information to get an engine running and set it with a two degree vac. drop to be safe until a light was available. It's better than nothing. Just wonder how a radical long duration cam or a burnt valve would affect the test. I saw BowTie's results, hope others try also. Maybe we can get info on a stock engine and a real radical one too. Thanks for the test. <hr></blockquote>
Jim originaly quoted a one inch vacuum drop for setting timing but I actually found that almost a two inch drop in vacuum put me where I run her. I would also check out the vacuum link Kultulz gave to ensure you don't have some other problem going on.
__________________
BUILT FORD TOUGH
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 11:19 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.