![]() |
![]() |
#1 |
Senior Member
Join Date: Dec 2005
Location: Humble, Texas
Posts: 262
|
Distrbutor?
Can anyone explain to me the purpose of the Vaccume Advance on a distb? and exactly what it does for the engine?
|
![]() |
![]() |
![]() |
#2 |
Registered User
Join Date: Oct 2006
Location: maple ridge, b.c., canada
Posts: 190
|
Re: Distrbutor?
At part throttle, your engine is more efficient when the timing is slightly advanced. Your centrifugal weights are just starting to open and adding vacuum advance, makes the engine burn the fuel better thus increasing mpg's.
|
![]() |
![]() |
![]() |
#3 |
Senior Member
![]() Join Date: Jul 2006
Location: Leander, Texas
Posts: 850
|
Re: Distrbutor?
It is also a way to not have a bunch of innitial timing in the motor at idle. Like mentioned above, as soon as you start giving it gas the vacuum drops because the motor is under a load. Once that happens the vacuum advance module starts to give your distributor more timing to get all that weight moving. MOST vacuum advance distributors have an adjustable module to make it give more or less timing. They usually take an allen wrench to adjust it. Check out the pick below.
|
![]() |
![]() |
![]() |
#4 |
Semi-Senior Member
Join Date: Feb 2003
Location: Washington, MO
Posts: 390
|
Re: Distrbutor?
In addition to what they already said, the vacuum and centrifugal advance are to ADVANCE the timing when RPM's raise.
To get the best performance and fuel economy, you need to get the most timing advance WITHOUT causing spark knock (pinging). With a SBC engine, total advance (base+centrifugal+vacuum) it's about 40 degrees BTDC (before top dead center) and 2500-3000 rpm. Not sure about the RPM spec. Too much base advance will make it impossible for the starter to start the engine.
__________________
'68 50th Anniversery LWB Custom Fleetside, '77 305 v-8, turbo 350, factory speed alert (still works), '71 drivetrain w/front discs. Some call it ugly yellow, others call it Ochre '83 Jeep CJ-7, <80,000 miles, original owner '04 Chevy Suburban, 4x4, 2500, 6.0 ltr, Predator Diablo programmer '95 GMC K1500 Extended cab |
![]() |
![]() |
![]() |
#5 |
Account Suspended
Join Date: Sep 2005
Location: Monroe, WA
Posts: 3,815
|
Re: Distrbutor?
I'll give yet another spin
![]() Setting vacuum advance for a particular application is both a science and a bit of an art ![]() Last edited by Billla; 01-05-2007 at 02:45 PM. |
![]() |
![]() |
![]() |
#6 |
Account Suspended
Join Date: Sep 2005
Location: Monroe, WA
Posts: 3,815
|
Re: Distrbutor?
|
![]() |
![]() |
![]() |
#7 | |
Semi-Senior Member
Join Date: Feb 2003
Location: Washington, MO
Posts: 390
|
Re: Distrbutor?
Quote:
You definately have aced me on your specs. I was quoting from what I THOUGHT I remembered, don't get to play with mechanical type advances much anymore. Good post. You get rep points for that one!!!!
__________________
'68 50th Anniversery LWB Custom Fleetside, '77 305 v-8, turbo 350, factory speed alert (still works), '71 drivetrain w/front discs. Some call it ugly yellow, others call it Ochre '83 Jeep CJ-7, <80,000 miles, original owner '04 Chevy Suburban, 4x4, 2500, 6.0 ltr, Predator Diablo programmer '95 GMC K1500 Extended cab Last edited by 68speedalert; 01-05-2007 at 03:28 PM. |
|
![]() |
![]() |
![]() |
#8 |
Senior Member
![]() Join Date: Jul 2006
Location: Leander, Texas
Posts: 850
|
Re: Distrbutor?
I run a full mechanical advance on my SBC. I sometimes wish I had both mechanical and vacuum again.
The port that the vacuum advance hose is supposed to be hooked up to is the port that does not see vacuum until after part throttle is achieved. If you have it hooked up wrong you'll be adding timing in through the distributor at idle. |
![]() |
![]() |
![]() |
#9 |
Semi-Senior Member
Join Date: Feb 2003
Location: Washington, MO
Posts: 390
|
Re: Distrbutor?
What's wrong with that? Many engines (all makes and models) had that from the factory?
__________________
'68 50th Anniversery LWB Custom Fleetside, '77 305 v-8, turbo 350, factory speed alert (still works), '71 drivetrain w/front discs. Some call it ugly yellow, others call it Ochre '83 Jeep CJ-7, <80,000 miles, original owner '04 Chevy Suburban, 4x4, 2500, 6.0 ltr, Predator Diablo programmer '95 GMC K1500 Extended cab |
![]() |
![]() |
![]() |
#10 | |
Senior Member
![]() Join Date: Jul 2006
Location: Leander, Texas
Posts: 850
|
Re: Distrbutor?
Quote:
![]() |
|
![]() |
![]() |
![]() |
#11 | |
Account Suspended
Join Date: Sep 2005
Location: Monroe, WA
Posts: 3,815
|
Re: Distrbutor?
Quote:
![]() Hooking the vacuum advance to the manifold vacuum isn't a problem; it just occasionally leads to an uneven idle depending on the cam. Some high-perfomance engines from the factory had manifold vacuum to provide advance at idle to smooth it out. |
|
![]() |
![]() |
![]() |
#12 | |
Account Suspended
Join Date: Sep 2005
Location: Monroe, WA
Posts: 3,815
|
Re: Distrbutor?
Quote:
![]() |
|
![]() |
![]() |
![]() |
#13 | |
Senior Member
![]() Join Date: Jul 2006
Location: Leander, Texas
Posts: 850
|
Re: Distrbutor?
Quote:
|
|
![]() |
![]() |
![]() |
#14 |
Account Suspended
Join Date: Sep 2005
Location: Monroe, WA
Posts: 3,815
|
Re: Distrbutor?
|
![]() |
![]() |
![]() |
#15 |
Senior Member
![]() Join Date: Jul 2006
Location: Leander, Texas
Posts: 850
|
Re: Distrbutor?
|
![]() |
![]() |
![]() |
Bookmarks |
Thread Tools | |
Display Modes | |
|
|