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HEI Vacuum Advance Cans

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abarnett

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1965 Chevelle Malibu 4DR
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Discussion starter · #1 ·
Got a 402 big block, 111 lobe separation, so low vacuum at idle. 17 degrees base timing, which I like, aiming for 30-34 at idle with vacuum advance, running manifold vacuum of course. Got +20 degrees centrifugal advance if you're concerned about that.


The vacuum advance can that was in the distributor crapped out, replaced it with a Standard Products VC211 can a few months ago. It crapped out at some point shortly afterwards. Discovered that this weekend, so ordered and just installed a VC1853 from Napa.

It should produce 15 degrees (7.5 at the distributor) of advance between 11-12.5"mg. I get that by 13" (tested with a vacuum pump), so that's good. Gets my idle timing up to 32 degrees, which is great. Car idles GREAT when I use my vacuum pump to deploy the vacuum advance can.
Problem is, it's supposed to start advancing between 5-7"mg. Mine doesn't start advancing until 9"mg. Tested with the vacuum pump, both by eyeball (physically watching for movement of the arm), as well as in the distributor with a timing light. No advance until 9"mg.

Car doesn't make enough vacuum when warmed up to keep the can deployed, so I get a timing black hole where vacuum falls off, so advance goes down, so vacuum declines more, so vacuum goes down...and I'm left with my base 18 degrees advance and very little vacuum.

I don't want to buy a 3rd can and wind up with it either crapping out in a couple months, or not being in-spec. Does anyone have a specific can/mfg that you can recommend? I'll order online, in person at a parts store, I don't mind either, just want it to run cleaner and make more vacuum for my brakes and the vacuum modulator on the transmission.
 
#2 ·
You need to install an adjustable can. Set it to its softest setting so it pulls it at idle and limit its travel to give you the advance you want. Manifold vacuum of course.

The transverse way to do it, albeit less popular, would be to recurve it with less mechanical advance and plug the can into ported vacuum.
 
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Discussion starter · #3 ·
I forgot to mention that I installed the MSD limiter plate shortly after the initial engine install. I'm concerned that was the reason that the last 2 vacuum advance cans failed. Is that likely, or did the old can give out after many years of use, and the new one was junk?

Is there a specific can you would recommend? I see multiple listed at several vendors, with the "adjustable" part not exactly being consistent.

I see a Proform 66952C, and according to a review from 10 years ago the "adjustable" part is the vacuum level that it begins pulling in, with the lowest setting of 3.5"Mg. That would work for me I'd think.

There's also an Accel 31035. That's adjustable to some degree, looks like it can't be adjusted to start advancing any sooner than ~6"mg. When warmed up, I'm making a shaky 8"mg at idle. I'm concerned it won't deploy reliably, especially if it is at all off-spec.

There's a Summit-branded unit, but it's not clear what the adjustment changes. Wonder how long it will take for vendors to attach the installation notes to all of the products they sell. They'd definitely sell more (at least to me!) if they included instructions to specify how the product is intended to be installed and how it functions.

I'm not entirely opposed to recurving the distributor, but I'm not sure my engine will tolerate 30+ degrees of base timing. Granted, static compression is in the 8s, but I run cheap gas and want the car to run safely even when ambient temp is 100F.
 
#4 ·
abarnett said:
Got a 402 big block, 111 lobe separation, so low vacuum at idle. 17 degrees base timing, which I like, aiming for 30-34 at idle with vacuum advance, running manifold vacuum of course. Got +20 degrees centrifugal advance if you're concerned about that.


The vacuum advance can that was in the distributor crapped out, replaced it with a Standard Products VC211 can a few months ago. It crapped out at some point shortly afterwards. Discovered that this weekend, so ordered and just installed a VC1853 from Napa.

It should produce 15 degrees (7.5 at the distributor) of advance between 11-12.5"mg. I get that by 13" (tested with a vacuum pump), so that's good. Gets my idle timing up to 32 degrees, which is great. Car idles GREAT when I use my vacuum pump to deploy the vacuum advance can.
Problem is, it's supposed to start advancing between 5-7"mg. Mine doesn't start advancing until 9"mg. Tested with the vacuum pump, both by eyeball (physically watching for movement of the arm), as well as in the distributor with a timing light. No advance until 9"mg.

Car doesn't make enough vacuum when warmed up to keep the can deployed, so I get a timing black hole where vacuum falls off, so advance goes down, so vacuum declines more, so vacuum goes down...and I'm left with my base 18 degrees advance and very little vacuum.

I don't want to buy a 3rd can and wind up with it either crapping out in a couple months, or not being in-spec. Does anyone have a specific can/mfg that you can recommend? I'll order online, in person at a parts store, I don't mind either, just want it to run cleaner and make more vacuum for my brakes and the vacuum modulator on the transmission.
Click to expand...
Yep. My go to can is the VC 302 from RockAuto.

STANDARD MOTOR PRODUCTS VC302 Distributor Vacuum Advance | Shop Now at RockAuto

STANDARD MOTOR PRODUCTS Ignition Parts and More for Your Vehicle at Reliably Low Prices. Fast Online Catalog. DIY-Easy. Your Choice of Quality. Full Manufacturer Warranty.
www.rockauto.com

Starts at 3-6“ of vacuum, all in by 7-9” of vacuum, provides 10* of advance at the crank.

I have bought many of them, each I tested work as expected.

I dial them in with manifold (not ported) vacuum.
 
Discussion starter · #5 ·
lucifershammer said:
Yep. My go to can is the VC 302 from RockAuto.

Starts at 3-6“ of vacuum, all in by 7-9” of vacuum, provides 10* of advance at the crank.
Click to expand...
I'll set timing to 28 degrees and see how the engine responds at idle. Not sure if 10 will be enough or not. Thanks.
 
#6 ·
abarnett said:
I'll set timing to 28 degrees and see how the engine responds at idle. Not sure if 10 will be enough or not. Thanks.
Click to expand...
You could try the VC 233. It’s supposed to start at 3-6”, all in 9-12”, but gives 20* at the crank so you would have to limit it.

I have never tried one of those though - you could confirm the specs if you try it and let us know. ;)

STANDARD MOTOR PRODUCTS VC233 Distributor Vacuum Advance | Shop Now at RockAuto

STANDARD MOTOR PRODUCTS Ignition Parts and More for Your Vehicle at Reliably Low Prices. Fast Online Catalog. DIY-Easy. Your Choice of Quality. Full Manufacturer Warranty.
www.rockauto.com
 
#7 ·
abarnett said:
I'll set timing to 28 degrees and see how the engine responds at idle. Not sure if 10 will be enough or not. Thanks.
Click to expand...
Actually was going through my notes, the VC 262 might be what you are looking for. Supposed to start at 3-5“, all in by 9-11”, and supposed to provide 15* at the crank. I have never tried this one either (the most I usually go for is 10*.)

STANDARD MOTOR PRODUCTS VC262 Distributor Vacuum Advance | Shop Now at RockAuto

STANDARD MOTOR PRODUCTS Ignition Parts and More for Your Vehicle at Reliably Low Prices. Fast Online Catalog. DIY-Easy. Your Choice of Quality. Full Manufacturer Warranty.
www.rockauto.com
 
#8 ·
I’m using the crane can but unfortunately I do not believe they are available any more. The other guys sound like they know what cans to be looking at.

As far at your failures, I don’t know if the limiter caused it or just luck. Either would be equally likely. Just make sure that you are limiting the can by stopping it from its starting position of zero (if that makes sense) instead of preloading it. Do a search of Dave Ray here. He has posted lots of pictures over the years.

Can you tell us what you’re idle speed is and more details about the cam? Duration at .050” lift? Advertised duration. Or a part number. That’s going to help.
 
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#9 ·
abarnett said:
I forgot to mention that I installed the MSD limiter plate shortly after the initial engine install. I'm concerned that was the reason that the last 2 vacuum advance cans failed.
Click to expand...
I've been using the MSD limiter plate on my HEI's vacuum advance for over 10 years and I have not had any issues with my VA unit (Pertronix HEI and VA).

abarnett said:
When warmed up, I'm making a shaky 8"mg at idle.
Click to expand...
You really need an adjustable VA unit that will provide "full pull" at a vacuum level that is a couple In/Hg below your engine's vacuum level @ idle rpm.... not just beginning to pull (or at mid pull). The reason is If your engine had a larger/more radical cam, the vacuum level at idle would not be steady.

The goal is to have the VA rod at full pull at idle vacuum. Most of the time, you set this adjustment so the spring tension within the adjustable VA is loose (... so that the VA arm is at "full pull" at about 2" Hg below engine vacuum at idle rpm). If the spring tension was tighter... and you were not getting a full pull on the VA rod at idle, the amount of advance provided by the VA would fluctuate with engine vacuum level at idle. This change in advance would affect your timing and engine rpm (inconsistent idle). When the VA provides full pull at idle, the amount of advance is consistent to provide a steady idle. The bigger (more radical) your cam, the more significant this adjustment becomes.
 
#10 ·
RifRaf said:
I've been using the MSD limiter plate on my HEI's vacuum advance for over 10 years and I have not had any issues with my VA unit (Pertronix HEI and VA).


You really need an adjustable VA unit that will provide "full pull" at a vacuum level that is a couple In/Hg below your engine's vacuum level @ idle rpm.... not just beginning to pull (or at mid pull). The reason is If your engine had a larger/more radical cam, the vacuum level at idle would not be steady.

The goal is to have the VA rod at full pull at idle vacuum. Most of the time, you set this adjustment so the spring tension within the adjustable VA is loose (... so that the VA arm is at "full pull" at about 2" Hg below engine vacuum at idle rpm). If the spring tension was tighter... and you were not getting a full pull on the VA rod at idle, the amount of advance provided by the VA would fluctuate with engine vacuum level at idle. This change in advance would affect your timing and engine rpm (inconsistent idle). When the VA provides full pull at idle, the amount of advance is consistent to provide a steady idle. The bigger (more radical) your cam, the more significant this adjustment becomes.
Click to expand...
Well said
 
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Discussion starter · #11 ·
2/75NastyNewbs said:
Can you tell us what you’re idle speed is and more details about the cam? Duration at .050” lift? Advertised duration. Or a part number. That’s going to help.
Click to expand...
I set the stop limiter such that it prevents the VA can rod from pulling any further towards itself. It doesn't 'preload' the rod, it just stops the rod from travelling any further.

I don't know what the idle speed is, tach isn't working at this time. Just by ear I'd say around 750rpm. It's set high enough that hot oil pressure is 35-40psi.
Cam is a single pattern hydraulic flat tappet Erson HIFLOW-1H. .542 LIFT, 228 duration at .050. 111 lobe separation. I'd link the cam card, but their website has been down for at least a couple weeks for "upgrades".

RifRaf said:
I've been using the MSD limiter plate on my HEI's vacuum advance for over 10 years and I have not had any issues with my VA unit (Pertronix HEI and VA).

You really need an adjustable VA unit that will provide "full pull" at a vacuum level that is a couple In/Hg below your engine's vacuum level @ idle rpm.... not just beginning to pull (or at mid pull). The reason is If your engine had a larger/more radical cam, the vacuum level at idle would not be steady.

The goal is to have the VA rod at full pull at idle vacuum. Most of the time, you set this adjustment so the spring tension within the adjustable VA is loose (... so that the VA arm is at "full pull" at about 2" Hg below engine vacuum at idle rpm). If the spring tension was tighter... and you were not getting a full pull on the VA rod at idle, the amount of advance provided by the VA would fluctuate with engine vacuum level at idle. This change in advance would affect your timing and engine rpm (inconsistent idle). When the VA provides full pull at idle, the amount of advance is consistent to provide a steady idle. The bigger (more radical) your cam, the more significant this adjustment becomes.
Click to expand...
Everything you've said here makes perfect sense, and also lines up with what I've read in Ignition 101 and several other well-made write-ups on the subject. I'm looking at the Pertronix D9006. Hopefully get it on order tonight and install next week.
 
#12 · (Edited)
It sounds like you’re doing all the right things. You’re in the ballpark timing wise for that cam to be happy at idle. That cam isn’t very radical by any means so the vacuum at idle should be plenty. That’s why I asked you what your idle speed was.

Put that new can in, adjust the carb and report back. Maybe bump that idle up a little too but 750 sounds about right
 
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#13 ·
I agree with 2/75NastyNewbs. The cam specs you posted do not seem that radical and I would imagine you will achieve a vacuum level higher than 8” at idle rpm once you get the initial timing with the correct VA dialed in.

Once you get the initial timing dialed in, be sure to adjust your carb’s idle mixture screws to achieve the highest vacuum level.
 
Discussion starter · #14 ·
IIRC idle vacuum was around 13" when it had 30+ degrees. Ordered that Pertronix can and a summit-branded HEI recurve kit in the event I feel like messing with that. Summit says it'll be here tomorrow, we'll see!
 
#15 · (Edited)
If the Summit HEI recurve kit looks like the one shown below... just use the springs to change your advance rate. The weights and centerplate are made of junk metal. There are better HEI recurve kits available... but some modifications may be needed to the centerplate to achieve desired results (see link below).
Image

If you want to adjust the amount of mechanical advance your HEI provides by trying different weights and centerplates, I detailed how I was able to dial-in my HEI's timing curve in the link below.
 
Discussion starter · #16 ·
RifRaf said:
If the Summit HEI recurve kit looks like the one shown below... just use the springs to change your advance rate.
Click to expand...
Yes that's the kit, and just using the springs was what I was hoping to try out. Good to know the weights are junk. Do they fly apart, machined/weighted poorly?
 
Discussion starter · #19 ·
Got the new vacuum can installed. I won't bury the lead, it is definitely running better now, took a bit of finagling to get set up, which I will outline below for future people scrolling these forums. 2 major issues:

1. The included allen wrench is WRONG. I've already thrown it into the abyss and can't find it to measure whatever it was, but it's too small, it will strip out immediately. Don't even try using it, it will just strip out the set screw and leave you with a now non-adjustable vacuum advance can that likely isn't set where you want it. Thankfully I bought a big set of miscellaneous allen wrenches at a garage sale years ago for $1. You need a 3/32" allen wrench. It will take a small amount of extra effort to seat-in to the set screw; just rotate the wrench lightly until you can feel it "want" to go in, then lightly apply pressure until it seats.

2. Instructions are wrong.

7. Turn the provided Allen wrench into the port and turn the wrench counter clockwise until it stops. This position will lock the vacuum advance out entirely.
8. Turn the wrench clockwise six complete revolutions to achieve a general vacuum advance setting of 16 degrees.
9. Each additional turn in the clockwise direction will add 2 degrees of vacuum advance.
10. Each additional turn in the counter clockwise direction will subtract 2 degrees of vacuum advance.

This is simply not how it works. It works as RifRaf said in post #9 in this thread, it simply adjusts spring tension/preload on the diaphram.

I did as the instructions said to get 16 degrees (with my base 18 it would've given me 34 degrees, which would be great), and I wasn't getting much. Engine was 25 degrees BTDC and making 9-10" of vacuum. I hooked up my vacuum pump and it took 7" to start moving, and 16" until it was done. I backed the screw all the way out (which really sucked with the valve cover in the way, only getting about 1/2 of a turn each time) and got no vacuum advance. Ok, then I turned in a bunch. Didn't bother trying to count, just spun it until I felt like stopping. Started the car up and applied about 10" of vacuum with the pump, and the engine started running better. Engine vacuum was up to a steadier 10" vacuum, timing was about 30 degrees. Went ahead and turned in maybe another 1-1/2 turns, now she's got 34 degrees advance and a steady 11" vacuum. Car definitely idling much happier. Took it for a short trip and she feels better, definitely doesn't need as much throttle to move down the road. Hopefully get a few more MPGs and cleaner plugs.

Unfortunately, this extra vacuum didn't help the 1-2 shift issue I'm having on my TH400. Line pressure test indicates an issue with the vacuum modulator, which is what got me started down the vacuum advance path. Regardless, this needed to be done, as my can had failed and car wasn't running as well as it should. Thanks for all the help guys.

p40 said:
do yourself a faver and a lot of headache get a progression dist no spring weights or vac cans its well worth the buy
Click to expand...
That progression ignition distributor looks pretty cool. Definitely not in the budget anytime soon. However, I will add that to the folder of miscellaneous electronic gizmos that might be useful or interesting in the future. $500 is a lot, but considering the boards are built in the USA that's not bad. Interesting product. I'd be concerned about the technology getting away from me ie. not having a device that can program it in the future 10-20 years down the road.
 
#20 ·
If you don't physically limit the vac can with a stop to 10*, you will definitely get too much advance at the upper rpms under light throttle.
 
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