Vacuum Advance can for 71

[dshanks]

Hi all, I have the distributor going back in this weekend, and I wanted to make sure that I've covered all my bases. I remember I read a while back that the 71 vacuum can was a piece of junk designed to meet emmissions standards and should be replaced when performance is an issue.

I was wondering if someone could simply provide a part number that I could pick up at a local autoparts store. The motor is basically stock with headers and edelbrock performer cam/intake, The dist. is stock with updated ignition.

Id like to do the springs, but from what Ive read, thats a whole different story, sounds complicated, and quite honestly above my head.

Any suggestions?

Derrick

 

[Bill75]

Derrick,

You might be suprised on the amount of improvement recurving your distributer makes by changing the springs and replacing the vacuum advance can. Crane makes a kit with springs and an adjustable diaphram for around $40 from your local shop, $30 from Summit plus postage. The instructions are pretty well done and Lars also has a paper available on the procedure as do others. It's not hard at all to do just takes a little testing to dial in the right springs and engine timing but no big deal.

I'm sure NAPA or Autozone has a replacement vacuum can if you want to just replace the existing one.

Here's a pic of mine under surgery:

Good luck, Bill

 

[Nutmegger]

Any of the cans from that era are junk. Napa does make a can but I cannot recall the number. If you are of a mind to wait a hour or so I can find the number.

THe springs are VERY eay to change the curve that results is a different matter and the weights play in the equation biug time also.

Stand BY

 

[Nutmegger]

There are two cans that people say are good to try.

Napa VC 1802 is a little less aggressive than VC 1810. Since I don't know a lot about the insides of yuour engine go by the following guidelines. The 1810 can works well on high perf small blocks like the old 365 HP 327 or the old 1970 LT1 Vette / Z28 engines. Both shared the same solid lifter cams. The 1802 can is suggested for milder engines like the 300 HP 327 or some of the lower power smogger 350's.

 

[dshanks]

Thanks for the help guys. I think Ill be stopping by NAPA for the vc1802. Im not running anything too hot.
Since I've been working on this car in my buddies garage now for 7 months, I really need to get it out. I may try to do the springs later, after I get the car home, and the money to have it professionally done. This is my first time for a project anywhere near this size (frame on resto), and I've been easily learning all the way, thanks to this site!
Thanks again for all your help.

Derrick

 

[JohnZ]

Vacuum advance can selection depends on your manifold vacuum at idle (with the can connected to full manifold vacuum, not "ported" vacuum).

If you have 16"-18" of vacuum, use the VC-680

If you have 14"-16" of vacuum, use the VC-1765

If you have 10"-14" of vacuum, use the VC-1810

 

[dshanks]

Vacuum advance can selection depends on your manifold vacuum at idle (with the can connected to full manifold vacuum, not "ported" vacuum).

If you have 16"-18" of vacuum, use the VC-680

If you have 14"-16" of vacuum, use the VC-1765

If you have 10"-14" of vacuum, use the VC-1810

How do I know how much vacuum I have, and what happened to the vc1802?

 

[JohnZ]

Never heard of the VC-1802; the three I listed will cover just about any application. The VC-680 is stamped "B1", the VC-1765 is stamped "B20", and the VC-1810 is stamped "B28".

Use a vacuum gauge connected to a full manifold vacuum source (like the vacuum fitting behind the carb, on top of the manifold). While you have it connected, it's a good time to adjust your idle mixture screws - adjust for highest steady vacuum.

 

[dshanks]

Since Im not after every last bit of HP, is there a way that we could estimate which one I need and get close enough to where I need to be. Heres some details about what Im running:

71 350 4 speed. Stock block, pistons, etc. New head job, slightly modified if any- heavier springs, roller tip rockers, cleaned up, with a 3 angle valve job. Edelbrock performer (not RPM) cam, lifters, and intake. Remanufactured Q-jet Carb, headers, a/c removed, clutch fan removed. Crane cams ignition box and the points have been removed...

Thats about all I can think of at this point...

 

[JohnZ]

You need to put a vacuum gauge on it and measure your idle vacuum; that number will allow you to select the correct vacuum advance unit. The vacuum gauge is about $15.00, and is a primary tune-up tool.