mechanical or vacuum advance? - Team Camaro Tech
Tech 2000 Our previous General Forum
Replies ONLY - no new topics.

LinkBack Thread Tools Display Modes
post #1 of 3 (permalink) Old Jul 2nd, 00, 07:51 AM
Posts: n/a

Can anyone tell me if there is a disadvantage to running a distributor that does not have vacuum advance, such as the Mallory Comp 9000, on a street driven 67? This is my daily driver with a stock 327. Is the lack of a vacuum advance hurting my gas mileage? Will the car be more driveable at low speed in traffic if I used a distributor with a vacuum advance? This distributor seems to work very well with the throttle wide open. I guess my question is, why do some distributors have vacuum advance while others don't?
Sponsored Links
post #2 of 3 (permalink) Old Jul 2nd, 00, 08:39 AM
Senior Tech
Join Date: Sep 1999
Location: Idaho
Posts: 219

Vacuum advance was used mainly for fuel economy. Yes, using a mechanical advance will hurt fuel economy, but mechanical is much more adjustable for street use.
As far as a daily driver, it's a toss up as to which is better. An engine with performance mods would benefit from mechanical over vacuum.

67 Camaro LS6 454/TH400/12bolt 3.73
1989 TransAm 5.7L WS6 W/all the options
cardude is offline  
post #3 of 3 (permalink) Old Jul 2nd, 00, 07:44 PM
David Pozzi
davidpozzi's Avatar
Join Date: Nov 1999
Location: Central California, USA
Posts: 10,064

Your engine needs more advance under part throttle but the mechanical advance can't provide it. You can get by with mech only advance if you have an agressive advance curve and jet the engine lean in cruse mode.

If not, it will load up when cruzing and when you punch the throttle it will smoke a bit and then "clean out".

When crusing along the plugs will run cooler because of the retarded spark. This will form deposits on the plugs. When you punch it the plugs will warm up and burn off the deposits, or most of them.

With todays fuels maybe it's not such a problem anymore.

I had mine a little off and when driving on the freeway for about a hundred miles. I pulled in for gas and my engine almost quit! I revved it up and it belched smoke.

I re did the advance and leaned out the primary jetting and it worked very well. I could cruze all night and when I punched the throttle it accelerated cleanly.
The problem with running a vaccum advance is that the stock ones have too many degrees of advance to work with a re worked mechanical advance.
They tend to ping just off idle. Once the vaccum drops and the vaccum advance moves to retard, it stops pinging.
In this instance you need a vaccum advance can that retards sooner under fairly high vaccum and does not have too many degrees of advance. (stiff spring, limited travel)
The L88 Corvette distributor uses a good one.
I think it's about 12 degrees advance.

Check my web page for suspension info:
David's Homepage
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer

[This message has been edited by davidpozzi (edited 07-02-2000).]
davidpozzi is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user 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.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may not 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

For the best viewing experience please update your browser to Google Chrome