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Username Post: Vacuum advance 327        (Topic#362479)
bolake 
Poster
Posts: 57

Age: 73
Loc: Northern MN
Reg: 09-05-17
09-07-20 02:43 PM - Post#2802948    

Been looking over 55 chevy belair with 327 I just bought. Starts and runs good but noticed the vacuum advance on distributor , the tube that runs to carburetor has been purposely disconnected from carburetor, and the fitting in carb has a rubber plug cap on it. Anyone have insight for doing this?

If your not the lead dog the view never changes


 


acardon 
Ultra Senior Member
Posts: 11418
acardon
Loc: DFW TEXAS
Reg: 03-25-05
09-07-20 04:31 PM - Post#2802951    
    In response to bolake

The vacuum advance pot may be leaking and that was a quick fix. No reason that I know of to disconnect it on a street driven car. Check that it holds vacuum.

Don
66 Corvair (driving)
57 2dr HT (driving)
56 2dr HT (waiting to be restored)


Edited by acardon on 09-07-20 04:32 PM. Reason for edit: No reason given.

 
bolake 
Poster
Posts: 57

Age: 73
Loc: Northern MN
Reg: 09-05-17
09-08-20 05:00 AM - Post#2802984    
    In response to acardon

Pumped it up to 15" let it set for 15 seconds, didn't leak. Guess I will hook it up and see what happens Thanks

If your not the lead dog the view never changes


Edited by bolake on 09-08-20 07:01 AM. Reason for edit: No reason given.

 
japete92 
"6th Year" Silver Supporting Member
Posts: 1488
japete92
Loc: No. Virginia
Reg: 01-18-13
09-08-20 06:59 AM - Post#2802991    
    In response to bolake

  • bolake Said:
Been looking over 55 chevy belair with 327 I just bought. Starts and runs good but noticed the vacuum advance on distributor , the tube that runs to carburetor has been purposely disconnected from carburetor, and the fitting in carb has a rubber plug cap on it. Anyone have insight for doing this?




Recommended reading:

https://www.chevelles.com/threads/ignition-101.189...

The 'amount' of advance? At idle, initial timing plus vacuum advance
is best at approx 22-24 degrees BTDC. Vacuum advance connected to 'full manifold' (the carb port that's below the throttle plates).

Initial timing (w/o vacuum advance) around 12, and vacuum advance around 10-12 works very well. Recommend trying a few different combinations to determine the 'best' settings.

Your cam will determine the amount of 'vacuum' you have available. Adjustable (for 'vacuum') advance 'cans' are available.

Pete




Edited by japete92 on 09-08-20 07:00 AM. Reason for edit: No reason given.

 
bolake 
Poster
Posts: 57

Age: 73
Loc: Northern MN
Reg: 09-05-17
09-08-20 07:04 AM - Post#2802992    
    In response to japete92

Thanks for information, Was trying to figure why it was purposely unhooked from carburetor, Put the vacuum on it pressure holds. Will hook it up and see what happens.

If your not the lead dog the view never changes


 
55 Shaker 
Member
Posts: 1561

Age: 70
Loc: north central IL.
Reg: 03-13-06
09-08-20 08:09 AM - Post#2803000    
    In response to bolake

Maybe from the last time they set the timing, and forgot to hook it back up.

The older I get, the more dangerous, I am !!!!


 
bolake 
Poster
Posts: 57

Age: 73
Loc: Northern MN
Reg: 09-05-17
09-08-20 09:26 AM - Post#2803010    
    In response to 55 Shaker

Could be, will hook it up later and start it up, see what happens. Plugged it into the carburetor port. Runs, idles fine, just a hair faster idle then when its unplugged. Seems if they had forgot to plug it in after timing they wouldn't of put a rubber cap on the carburetor port.

If your not the lead dog the view never changes


Edited by bolake on 09-08-20 02:34 PM. Reason for edit: No reason given.

 
bolake 
Poster
Posts: 57

Age: 73
Loc: Northern MN
Reg: 09-05-17
09-08-20 04:17 PM - Post#2803046    
    In response to japete92

After reading your information from GM engineer about vacuum, 2 things come to mind on my engine. (1) I'm wondering if the vacuum line was left off the vacuum port on carb & plugged to help cool idle temperature. (2) The car has front disc brakes conversion with the dual master cylinder with booster and by plugging the carb port would help with more vacuum for the booster.

If your not the lead dog the view never changes


 
japete92 
"6th Year" Silver Supporting Member
Posts: 1488
japete92
Loc: No. Virginia
Reg: 01-18-13
09-09-20 06:38 AM - Post#2803095    
    In response to bolake

  • bolake Said:
After reading your information from GM engineer about vacuum, 2 things come to mind on my engine. (1) I'm wondering if the vacuum line was left off the vacuum port on carb & plugged to help cool idle temperature. (2) The car has front disc brakes conversion with the dual master cylinder with booster and by plugging the carb port would help with more vacuum for the booster.



Here's more info:

http://www.superchevy.com/how-to/additional-tec h/1...

Was/is the engine set up/built for racing only?

Question 1: Timing does impact temps, BUT the only reason to not have vacuum advance is if the engine is only being asked to perform at high rpm; basically at wide open throttle.

Q2: More likely it's plugged to simply eliminate the vacuum leakage 'unplugged' would cause. BUT, if the cam installed is long duration with a short separation angle it is suited for high-rpm drag racing, with a high-end, sharp torque peak. Manifold vacuum will be very low to non-existent. Plugging that carb port won't change that.

If you have nothing better to do, here's some cam shaft info:

http://forum.grumpysperformance.com/viewtopic.php?...

Why did a previous owner do what he did? No clue. If this engine is planned for street driving, it needs vacuum advance.

I've attached some tid-bits about vacuum advance.

Just trying to be helpful.

Pete






Attachment: vacuum_advance_READ_FIRST_overview.pdf (129.42 KB) 10 View(s)



Edited by japete92 on 09-09-20 10:56 AM. Reason for edit: No reason given.

 
acardon 
Ultra Senior Member
Posts: 11418
acardon
Loc: DFW TEXAS
Reg: 03-25-05
09-09-20 06:42 AM - Post#2803096    
    In response to bolake

You have to plug the carb port to set timing or you will have a vacuum leak. The vacuum advance pot doesn't use any vacuum unless the manifold vacuum changes, and then it's so little, it will not affect the booster. The vacuum advance is a closed system, unlike the booster and PVC systems, which have to replinish the vacuum when operated.

Don
66 Corvair (driving)
57 2dr HT (driving)
56 2dr HT (waiting to be restored)


 
Rick_L 
Member #409
Posts: 27749
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
09-09-20 09:48 AM - Post#2803110    
    In response to bolake

Retarded timing produces heat in the coolant.

Advanced timing puts less heat in the coolant.

So you want the vacuum advance hooked up.



 
IgnitionMan 
Valued Contributor
Posts: 3802

Reg: 04-15-05
09-09-20 10:58 AM - Post#2803114    
    In response to japete92

I see a lot of "disconnect the vacuum advance, it doesn't do nothin'" all the time on the tech boards, total hot air from all sorts of supposed tuners that literally refuse to understand vacuum advance.

NOT hard to get the vacuum advance set up right, then use it to supplement idle and no load cruise, on full manifold vacuum, and to use a stop to set the total degrees the advance gives when plugged in.

Most people I see posting on timing issues and problems have no idea how to set a vacuum advance up to work right, let alone connect it to the full manifold vacuum fitting.

One very good vacuum advance information source is a whole package, lets you get it done right, that I send out to everyone for free.

Easy way to get the whole package, ask for it at this email address,

gmvacuumadvancemodificati ons@gmail.com





 
bolake 
Poster
Posts: 57

Age: 73
Loc: Northern MN
Reg: 09-05-17
09-09-20 12:43 PM - Post#2803122    
    In response to japete92

Pretty sure not setup for racing. Put the gauge on the vacuum port on carburetor, idling at 13. Notice when I hook up vacuum I have slightly higher idle, maybe 100 rpm's. Just took it for a 5 mile run seem to run good. Will do some experimenting. Thanks to all for the information.

If your not the lead dog the view never changes


 
japete92 
"6th Year" Silver Supporting Member
Posts: 1488
japete92
Loc: No. Virginia
Reg: 01-18-13
09-09-20 01:24 PM - Post#2803127    
    In response to bolake

  • bolake Said:
Pretty sure not setup for racing. Put the gauge on the vacuum port on carburetor, idling at 13. Notice when I hook up vacuum I have slightly higher idle, maybe 100 rpm's. Just took it for a 5 mile run seem to run good. Will do some experimenting. Thanks to all for the information.



The attachment I posted earlier came from "Ignitionman' . He sent it (and other data) to me in response to an email request I sent him to the address he posted. He sent it totally free; no adds. Recommend the info.

AND, just to make sure we are communicating, ALL the 'numbers' I posted were timing 'degrees' BTDC.

Pete






 
bolake 
Poster
Posts: 57

Age: 73
Loc: Northern MN
Reg: 09-05-17
09-09-20 02:27 PM - Post#2803130    
    In response to japete92

OK Thanks I have already got the info from him

If your not the lead dog the view never changes


 


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