Vacuum Advance or Not? - CorvetteForum - Chevrolet Corvette Forum Discussion

Notices
C3 Tech/Performance V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette

Vacuum Advance or Not?

Old 06-14-2018, 01:30 AM
  #1  
OldCarBum
CF Senior Member
Thread Starter
 
Member Since: Mar 2016
Location: Napa California
Posts: 1,658
Thanked 265 Times in 222 Posts
Default Vacuum Advance or Not?

I just ordered my new MSD tach drive distributor with the vacuum advance module and it includes a plate to provide the option to remove the module.
MSD also offers the distributor without vacuum advance.
Talking to my local engine builder, he told me it's better to run the vacuum advance on the street as it will increase fuel economy.
I'm building the 496 for my 73 as a hot rod and fuel economy is not something I'm worrying about.
I'm also trying to get rid of as many vacuum lines as possible and wondering if there is any other advantage or disadvantage to removing or keeping the vacuum advance.
What are your thoughts or experiences?
OldCarBum is offline  
Old 06-14-2018, 01:48 AM
  #2  
rcread
CF Senior Member
 
rcread's Avatar
 
Member Since: Aug 2004
Location: Duvall, WA
Posts: 10,426
Thanked 70 Times in 62 Posts
Default

Run vacuum advance, connected to manifold vacuum. Your car will run cooler.
rcread is offline  
The Following User Says Thank You to rcread For This Useful Post:
OldCarBum (06-14-2018)
Old 06-14-2018, 07:29 AM
  #3  
Rescue Rogers
CF Senior Member
Support Corvetteforum!
 
Rescue Rogers's Avatar
 
Member Since: Oct 2015
Location: YUPPY HELL Westford MASS
Posts: 4,141
Thanked 554 Times in 514 Posts
2016 C3 of Year Finalist
Default

I just read alot about this. The others may or may not happen according to Ruggles book but you will have a better idle. He recommends using it for street use
Rescue Rogers is offline  
The Following User Says Thank You to Rescue Rogers For This Useful Post:
OldCarBum (06-14-2018)
Old 06-14-2018, 07:38 AM
  #4  
Tiger Joe
CF Senior Member
 
Member Since: Nov 2016
Posts: 374
Thanked 47 Times in 41 Posts
Default

there is no reason to NOT keep the vacuum advance on a street driven car. they can only benefit you on the street cruising.

I ran an MSD without and switched over to a new distributor with vacuum advance and I can without a doubt say the truck drives better with.
Tiger Joe is offline  
The Following User Says Thank You to Tiger Joe For This Useful Post:
OldCarBum (06-14-2018)
Old 06-14-2018, 08:21 AM
  #5  
stingr69
CF Senior Member
 
stingr69's Avatar
 
Member Since: Mar 2004
Location: Little Rock AR
Posts: 3,889
Thanked 68 Times in 67 Posts
Default

It only needs a vacuum advance if it has a license plate.
stingr69 is offline  
The Following User Says Thank You to stingr69 For This Useful Post:
OldCarBum (06-14-2018)
Old 06-14-2018, 10:22 AM
  #6  
MBrianB
CF Senior Member
 
MBrianB's Avatar
 
Member Since: Jun 2014
Location: Ventura County CA
Posts: 410
Thanked 12 Times in 12 Posts
Default

The instructions for my ZZ502 specifically say to not use vacuum advance.
MBrianB is offline  
The Following User Says Thank You to MBrianB For This Useful Post:
OldCarBum (06-14-2018)
Old 06-14-2018, 10:43 AM
  #7  
zuendler
CF Senior Member
 
zuendler's Avatar
 
Member Since: May 2011
Location: Karlsruhe (Germany)
Posts: 646
Thanks: 0
Thanked 13 Times in 11 Posts
Default

Originally Posted by MBrianB View Post
The instructions for my ZZ502 specifically say to not use vacuum advance.
And I run my ZZ502 with the advance and it works well.
I would like to know what kind of customer complaints GM wantīs to avoid with this statement. Maybe itīs harder to dial it in propperly?
And of course you need the right vacuum advance curve and travel, matching to your other setup.
zuendler is offline  
The Following User Says Thank You to zuendler For This Useful Post:
OldCarBum (06-14-2018)
Old 06-14-2018, 10:45 AM
  #8  
derekderek
CF Senior Member
 
Member Since: Jul 2015
Location: Westville NJ
Posts: 3,435
Thanked 417 Times in 388 Posts
Default

In a boat where you are at 3/4 throttle all the time, vac advance is not necessary. In a car, any car you are at 10 to 25% throttle almost all the time. Gas mileage will suffer terribly without vacuum advance.
derekderek is offline  
The Following User Says Thank You to derekderek For This Useful Post:
OldCarBum (06-14-2018)
Old 06-14-2018, 10:46 AM
  #9  
MBrianB
CF Senior Member
 
MBrianB's Avatar
 
Member Since: Jun 2014
Location: Ventura County CA
Posts: 410
Thanked 12 Times in 12 Posts
Default

Originally Posted by zuendler View Post
And I run my ZZ502 with the advance and it works well.
I would like to know what kind of customer complaints GM wantīs to avoid with this statement. Maybe itīs harder to dial it in propperly?
And of course you need the right vacuum advance curve and travel, matching to your other setup.
Instructions say you will get 32 deg with centrifugal only. That is with the GM dizzy. I have a MSD dizzy so I'm not sure what to do other than block the tube to set the advance at idle.
MBrianB is offline  
Old 06-14-2018, 10:52 AM
  #10  
MBrianB
CF Senior Member
 
MBrianB's Avatar
 
Member Since: Jun 2014
Location: Ventura County CA
Posts: 410
Thanked 12 Times in 12 Posts
Default

No reason other than they say you get enough without vac.
MBrianB is offline  
The Following User Says Thank You to MBrianB For This Useful Post:
OldCarBum (06-14-2018)
Old 06-14-2018, 11:03 AM
  #11  
zuendler
CF Senior Member
 
zuendler's Avatar
 
Member Since: May 2011
Location: Karlsruhe (Germany)
Posts: 646
Thanks: 0
Thanked 13 Times in 11 Posts
Default

I can only recomend: ask Lars.

I have the TI distributor with MSD AL2.
Have full advance of 36°, starting from ~18° at idle.
Vacuum adds 15° (donīt remember it ecaxtly)

I have made a lot trial and error to get to those numbers.

Of course GM gives a **** on your gas milage and wants to avoid complaints.

Last edited by zuendler; 06-14-2018 at 11:03 AM.
zuendler is offline  
The Following User Says Thank You to zuendler For This Useful Post:
OldCarBum (06-14-2018)
Old 06-14-2018, 03:51 PM
  #12  
derekderek
CF Senior Member
 
Member Since: Jul 2015
Location: Westville NJ
Posts: 3,435
Thanked 417 Times in 388 Posts
Default

32 is not enough for light load gas mileage. ALL distributors will give you 32 full throttle above 3000 degrees of advance. At least they can all be timed to that point. You need around 50 degrees for part throttle gas mileage. And you MUST be set up to limit total advance to 32 to 36 degrees at hard throttle. Set your mech advance too high cuz you have no vac advance, you are roasting pistons.

Last edited by derekderek; 06-14-2018 at 03:54 PM.
derekderek is offline  
The Following User Says Thank You to derekderek For This Useful Post:
OldCarBum (06-14-2018)
Old 06-15-2018, 06:19 AM
  #13  
2mnyvets
CF Senior Member
 
Member Since: Jul 2015
Location: Lehigh Valley Pennsylvania
Posts: 122
Thanked 20 Times in 17 Posts
Default

Originally Posted by MBrianB View Post
The instructions for my ZZ502 specifically say to not use vacuum advance.
I would guess you would be way more prone to ping when cruising with a vacuum advance especially if you stomp on it and transition to full power. That being said, I don't think I would eliminate on a street driven car.

Last edited by 2mnyvets; 06-15-2018 at 06:20 AM.
2mnyvets is offline  
The Following User Says Thank You to 2mnyvets For This Useful Post:
OldCarBum (06-15-2018)
Old 06-15-2018, 06:36 AM
  #14  
cooper9811
CF Senior Member
 
cooper9811's Avatar
 
Member Since: Oct 2009
Location: Marysville Ohio
Posts: 599
Thanked 64 Times in 60 Posts
Default

A lot of crate engines are assumed to be for other-than-street-street applications. A strip car has no need for vacuum advance, since it spends a lot of time at WOT or close to it.

Having said that, there is still no penalty for vacuum advance even on the strip - it won't hurt performance, it just isn't necessary if your goal is to go a quarter mile as fast as possible.

Different story on the street - the majority of time is at part throttle, so the vacuum, which changes based on RPM and engine load, allows the timing to be modulated based on load. This can help with fuel efficiency and allow your car to run cooler.
cooper9811 is offline  
The Following User Says Thank You to cooper9811 For This Useful Post:
OldCarBum (06-15-2018)
Old 06-15-2018, 09:43 AM
  #15  
cuisinartvette
CF Senior Member
 
Member Since: Oct 2004
Location: Valencia Ca.
Posts: 66,420
Thanked 946 Times in 873 Posts
St. Jude Donor '05
Default

Learn how to set one up they are an asset
Dont have one on mine but not worried about mpg and overlap is nuts anyways. Same with a carb, well tuned they seem just as smooth as EFI save for extreme hot/cold conditions big deal.

Last edited by cuisinartvette; 06-15-2018 at 09:43 AM.
cuisinartvette is online now  
The Following User Says Thank You to cuisinartvette For This Useful Post:
OldCarBum (06-15-2018)
Old 06-15-2018, 10:19 AM
  #16  
cagotzmann
CF Senior Member
 
cagotzmann's Avatar
 
Member Since: Jun 2011
Location: Sherwood Park Alberta
Posts: 2,055
Thanked 173 Times in 137 Posts
Default

Originally Posted by OldCarBum View Post
I just ordered my new MSD tach drive distributor with the vacuum advance module and it includes a plate to provide the option to remove the module.
MSD also offers the distributor without vacuum advance.
Talking to my local engine builder, he told me it's better to run the vacuum advance on the street as it will increase fuel economy.
I'm building the 496 for my 73 as a hot rod and fuel economy is not something I'm worrying about.
I'm also trying to get rid of as many vacuum lines as possible and wondering if there is any other advantage or disadvantage to removing or keeping the vacuum advance.
What are your thoughts or experiences?
Get the best of both worlds. Use a programmable Ignition module.

I have a MSD 6530 Programmable ignition with a MSD 85551 Distributor. Added a 2 bar map sensor to program the vacuum advance as required.

No need to replace parts to re-curve anything. Complete control of RPM curve & vacuum curve. Great for tuning at your local track or dyno booth as you can make changes between run using your PC.
cagotzmann is offline  
The Following User Says Thank You to cagotzmann For This Useful Post:
OldCarBum (06-15-2018)
Old 06-15-2018, 10:56 AM
  #17  
Peterbuilt
CF Senior Member
 
Peterbuilt's Avatar
 
Member Since: Aug 2006
Location: mount holly NC
Posts: 5,133
Thanked 360 Times in 333 Posts
Default Timing information here.

Peterbuilt is offline  
The Following User Says Thank You to Peterbuilt For This Useful Post:
OldCarBum (06-15-2018)
Old 06-15-2018, 10:57 AM
  #18  
flyeri
CF Senior Member
 
flyeri's Avatar
 
Member Since: Mar 2011
Location: Kernersville NC
Posts: 1,190
Thanked 71 Times in 63 Posts
Default

Originally Posted by MBrianB View Post
The instructions for my ZZ502 specifically say to not use vacuum advance.
Same as my ZZ454. I have a Davis HEI with vac advance on manifold vac port. 12 degrees initial and it idles around 26 degrees or so. No ping at cruise, even lugging in 5th gear.
flyeri is online now  
The Following User Says Thank You to flyeri For This Useful Post:
OldCarBum (06-15-2018)


Thread Tools
Search this Thread
Quick Reply: Vacuum Advance or Not?


Sponsored Ads
Vendor Directory

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2018 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: