Proper Vacuum Reading for 350 w/ Cam - 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 03-26-2005, 07:30 AM
Registered User
 
Last photo:
Join Date: Jan 2005
Location: Vancouver WA
Posts: 7
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Proper Vacuum Reading for 350 w/ Cam

I have just installed a rebuilt 350 in my '76 El Camino. The previous owner had pulled it out of his '70 C10 and put in a ZZ4/700R4 combo. My buddy who goes to church with this guy picked it up and installed it in his Ď75 GMC one-ton crew cab pickup that he used for camping. My buddy is now putting a big block into his truck so he sold me the engine and tranny for $400 (saved me quit a bit of dough). The motor was recently rebuilt before it was yanked the first time and was not used much during the last two years (no papers came with the engine). It sure runs very strong and it has a cam in it. Iím trying to run down the builder, since he goes to church w/ my buddy, and find out what type of cam was installed. I initially set the timing at 12 degrees BTDC but was having problems w/ dieseling after a hot shutdown. Yesterday I reset the timing to 8 degree BTDC, added an insulated carburetor gasket and checked the vacuum. It runs a steady 15 inches at idle. My manuals say it should be running about 20 inches with a stock cam. What is a good reading for a motor w/ a mild cam?
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 03-26-2005, 08:13 AM
NXS's Avatar
NXS NXS is offline
wind & fire = guides to power
 
Last photo:
Join Date: Nov 2004
Location: Oklahoma
Posts: 1,534
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
If it "runs on" ad 12 BTDC either the idle is too high, there are vacuum leaks or the plugs are too hot.(or it's not really at 12*).

15" is ok if it's steady, probably around a 270(+/-5*) adv duration cam.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 03-26-2005, 08:19 AM
bracketeer's Avatar
489 Lemans
 

Last journal entry: Street Legal
Last photo:
Join Date: Dec 2004
Location: Courtenay, BC, CehNehDeh
Age: 55
Posts: 2,139
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
vacuum

I had a Comp XE268H cam with Edel heads and could only pull 9 in of vacuum. Ran good though. Don't fret over vacuum. It's used to set the carb. Idle mixture is set by vacuum or rpm. Power valve on low vacuum cars have to be changed.

Last edited by bracketeer; 03-26-2005 at 08:50 AM.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 03-26-2005, 08:58 AM
spinn's Avatar
More dogs than bones
 

Last journal entry: This makes a huge difference
Last photo:
Join Date: Oct 2004
Location: midwest
Posts: 2,212
Wiki Edits: 0

Thanks: 0
Thanked 67 Times in 65 Posts
i would have to diagree with you. in my expireience the less vacuum it makes, the worse it idles, and usually have to make it idle higher. 12 is good, 15 is fine, and ya 20 is like a stock engine.


hey ghetto didnt your xe268 make 15"?

Last edited by spinn; 03-26-2005 at 01:10 PM.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 11-28-2009, 05:03 AM
Registered User
 
Join Date: Jun 2007
Location: pickering
Posts: 243
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
vacumwith a mid cam

I've got a sbc with a XE268h and pull 16 inches of vaccum @ idle rpm timing is set at 16 initial total 36 she runs like a charm.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 11-28-2009, 05:44 AM
sqzbox's Avatar
My pipes are my music
 
Last photo:
Join Date: Sep 2009
Location: indiana
Age: 64
Posts: 2,938
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
ANOTHER THING THAT WILL CAUSE RUN-ON IS LOW OCTANE GAS IN A HIGH COMPRESSION ENGINE. I bought a 71 javelin new and had a problem with run-on and after burning a couple of valves, discovered it had a 70 engine in it.
10:1 compression doesn't like reg. gas. If that's what your useing, you need to switch now before any damage occures. It might take a couple tanks to straighten out the problem. Also, 1970 engines didn't come with hardened valve seats and if you have pre 70 heads, the UN-leaded gas ain't helping either. Might want to ask the previous owner what gas he used in it and any additives he might have put in it.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 11-28-2009, 07:37 AM
Registered User
 
Last photo:
Join Date: Mar 2007
Location: montreal quebec canada
Posts: 162
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Bracketeer, what rpms are you getting 9 lbs at?? Gotta be careful here as any lower vaccum reading, and power brakes could be a problem.. Even with a vaccum can, you might only get one or 2 more pumps on the binders with power brakes..
I have a REAL stock old 2bbl Rochester 350ci 145 hp engine that I get 22lbs from.. Can't get no more stock than that, eh?? Try and set up your unit with a good reading vaccum guage getting the highest steady HGs at the lowest idle you can deliver without stalling. You'll know the "sweet spot" by ear and sometimes smell..
T.
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
Port or Full time vacuum cool rockin daddy Engine 129 10-05-2010 03:00 PM
vacuum advance help batman09 Engine 14 09-09-2004 09:42 PM
Proper vacuum line hookups 66Caprice Engine 2 07-18-2004 09:52 AM
IGNITION and CAM TIMING sum87mustang Engine 3 07-11-2003 07:52 PM
Cam Help black66 Engine 3 05-12-2003 06:15 PM


All times are GMT -6. The time now is 11:28 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.