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Yes I know, another vacuum advance question.
My main problem is I live overseas and shipping costs of parts are often much more than the cost of the part. Not to mention a very poor exchange rate.
O.K. I am running a comp cams extreme energy cam, flat tappet. About 10-1 compression. 77 350 HEI. I have my distributor set up at 16 degrees idle, 35 all in at 2,900. Idle set at 800. Manual trans. Timing starts advancing about 950.
have about 11.5 inches of vacuum with vacuum advance disconnected. About 13.5 with POS vacuum can connected.
Currently the vacuum can I have on it starts to move at 4 inches of vacuum and is fully advanced at 20 inches. It also pulls about 23 degrees of total advance at the crank. About 11 or 12 at the distributor. But I'm not thinking it ever really gets pulled all the way with my vacuum readings.
I go on Summit Racing's web site and they list a ton of vacuum cans for a HEI distributor. But none of the listings tell you vacuum settings.
I really need to get this dialed in. But need a part number for a online parts place that ships to Australia. Really can't afford to buy 20 or 30 of them and start testing.
Thanks in advance for all your help guys.
Some of the aftermarket vacuum advance cams out there are adjustable. They work very well. That usually means you can change their vacuum setting they kick-in at by a screw and changing the spring tension on the diaphragm. They usually have an octangonal shape and do not look stock however.
If you need the "stock look" Lars has a list of available factory advance canisters, and aftermarket ones, and their settings.
Once you get the vacuum setting right, to what your engine likes, in most cases with today's gas you are going to want to restrict the number of degrees of vacuum advance. There are a couple of "limiters" available, Moroso IIRC, and Lars, they physically limit the amount of movement of the pin in the vacuum can by a little flat piece of aluminum. You could easily make your own if you had a way to measure things. Many stock cans go too far at 20 degrees, and 10-12 engine degrees seems to work better with today's gas and a performance ignition curve.
It's really not that hard to tune this yourself if you are a little handy. I re-curved my own, off the car, and even made a little gadget for measuring the degrees: Out of a protractor. I made the protractor like 7 inches across and I had an accuracy of 1/2 degree.
Well, I have an accel adjustable vacuum can. I tested it. Turned all the way down, starts to move at 14 inches of Vacuum, all in at 36 inches of vacuum. I'm thinking it's junk. And thats as low as it will go. Useless. I also have my original 43 year old can. Starts at 10 inches, all in at 30 inches.
I do appreciate the advice. But the "Adjustable " unit simply wont adjust down low enough. Yes the hex end type. I couldn't care less if it looks original.
I'm looking for one that works. No limiter in the world can help me with the Accel unit.
Have you emailed @lars? You seem to be following the rest of his procedure. He has part numbers for the vacuum cans, which you may be able to order from RockAuto or elsewhere.
There are also ways to limit the total vacuum advance by modifying the distributor. It seems the can you have may be fine, but you need to limit the vacuum advance to 10-12 degrees.
Well, I have an accel adjustable vacuum can. I tested it. Turned all the way down, starts to move at 14 inches of Vacuum, all in at 36 inches of vacuum. I'm thinking it's junk. And thats as low as it will go. Useless. I also have my original 43 year old can. Starts at 10 inches, all in at 30 inches.
I do appreciate the advice. But the "Adjustable " unit simply wont adjust down low enough. Yes the hex end type. I couldn't care less if it looks original.
I'm looking for one that works. No limiter in the world can help me with the Accel unit.
Agreed something seems to be wrong with the Accel can. FWIW I used a Moroso 30 years ago on my 10" vacuum LT-1, and it worked well. At this point your original can seems like it is "tuned" better for your engine. Starting at 10" should be good as long as you have a "street" cam. You just really need to make or purchase a Limiter to get 10-12 degrees vac advance at the engine. 20+ is way to much for today's gasoline.
BTW it'll fit in a regular postage envelope!! Much less shipping!
Last edited by leigh1322; Apr 26, 2020 at 01:39 PM.
If your mechanically inclined you can do what I did. The spring inside the can retards the timing and vacuum advances the timing right?
so if yours is not advancing as soon as you need it too or not fully at idle as you need it to, you therefore need less spring or more vac.
since more vacuum may not be an option then less spring is what you are left with.
i fashioned a spring inside the cap that would pull on the timing rod so that less vacuum would pull the timing where I needed it and fully advanced at idle vacuum. Baisically an external spring pulling against the internal spring inside the vacuum can. Some experimentation as to the strength of that spring will be necessary.
next I figured I only needed maybe 12* of vacuum advance. So I figured out how much timing the full movement of the rod from the vacuum can advanced the timing ( using a timing light). Then measured the total distance the rod moved full travel using micrometers.
full timing was 20*. Since I only needed 12 I divided 12 by 20 and got. 0.6.
then measured total travel of the rod that advances and got say .475” ( don’t remember the actual movement)
them multiply .6 by .475 to get .285.
so .285” is the total movement I want to get only 12* of advance.
then I weld, carefully with wire welder, don’t even try a stick welder.( you could use jb weld too I suppose) up the slot that the rod moves in and file it back (rat tail file) to get my .285” of movement.
now I have a vacuum can that starts and advances fully with much lower vacuum due to the spring and a total movement of 12* due to the slot being shorter.
Done.
Last edited by REELAV8R; Apr 26, 2020 at 04:36 PM.
If your mechanically inclined you can do what I did. The spring inside the can retards the timing and vacuum advances the timing right?
so if yours is not advancing as soon as you need it too or not fully at idle as you need it to, you therefore need less spring or more vac.
since more vacuum may not be an option then less spring is what you are left with.
i fashioned a spring inside the cap that would pull on the timing rod so that less vacuum would pull the timing where I needed it and fully advanced at idle vacuum. Baisically an external spring pulling against the internal spring inside the vacuum can. Some experimentation as to the strength of that spring will be necessary.
next I figured I only needed maybe 12* of vacuum advance. So I figured out how much timing the full movement of the rod from the vacuum can advanced the timing ( using a timing light). Then measured the total distance the rod moved full travel using micrometers.
full timing was 20*. Since I only needed 12 I divided 12 by 20 and got. 0.6.
then measured total travel of the rod that advances and got say .475” ( don’t remember the actual movement)
them multiply .6 by .475 to get .285.
so .285” is the total movement I want to get only 12* of advance.
then I weld, carefully with wire welder, don’t even try a stick welder.( you could use jb weld too I suppose) up the slot that the rod moves in and file it back (rat tail file) to get my .285” of movement.
now I have a vacuum can that starts and advances fully with much lower vacuum due to the spring and a total movement of 12* due to the slot being shorter.
Here's my old original can. Notice how the rod doesn't go all the way to the back stop. Not sure if that's normal. This one starts to move at about 10 inches of vacuum. Will this be OK to use if I limit the stroke down to about 10 degrees of total advance at the crank?
Don’t see why it wouldn’t.
If you decide to do the spring idea, use one strong enough to give you full vacuum advance at idle vacuum. I think you’ll find it much peppier when letting out the clutch.
Mechanical coming in at 950 may be a bit early, more like 1100 to 1200. The engine will let you know if it’s herky jerky starting out.
Well, if the goal is to have all of the vacuum advance in at idle. None of the cans I have will work. Back to a part number for one that does from a place that ships overseas.
Well, if the goal is to have all of the vacuum advance in at idle. None of the cans I have will work. Back to a part number for one that does from a place that ships overseas.
The Accel unit I mentioned is all-in at 8 in hg. At least it was out of the box (check the link!). Yours may have failed internally, but it should be all-in at idle.
Here's my old original can. Notice how the rod doesn't go all the way to the back stop. Not sure if that's normal. This one starts to move at about 10 inches of vacuum. Will this be OK to use if I limit the stroke down to about 10 degrees of total advance at the crank?
Yes that would be good one. Can I assume your engine makes at least 12-14" at idle or more? The 18 may indicate it gives 18 degrees advance, so you need to add a limiter plate to restrict it to about 10. OK it starts moving at 10" When is it all done moving? How high? That number needs to be less than your vacuum at idle.
Originally Posted by 4-vettes
Well, if the goal is to have all of the vacuum advance in at idle. None of the cans I have will work. Back to a part number for one that does from a place that ships overseas.
Hmmm.... you are connecting this to a full time manifold vacuum source aren't you? The port should read 12-14" or better at idle. And you already said you tested the can and it works. Just test the can again for a few minutes and see if it holds vacuum and is not not leaking. Then you're good.
If the port reads zero at idle it is a ported vacuum source and you do not want to use it. That was only for 70's emissions and the engines run bad, and run hot. Find another port.
You could quite literally measure how much that rod moves total, assume that is 18 degrees, and make a plate of some sort to stop the rod to at about 55%. Then test.
Since you are 10,000 miles away, here's Lars paper on vacuum cans.
Last edited by leigh1322; Apr 26, 2020 at 10:23 PM.
Oh yes, I'm real certain what vacuum port I'm using. And yes with some timing in as I stated above. Aprox. 13.5 inches of vacuum. But this can just starts to move at 10..... 30 inches for full vacuum advance. If I limit it down it'll still be in the neighborhood of 20 inches to reach full vacuum advance.
Oh yes, I'm real certain what vacuum port I'm using. And yes with some timing in as I stated above. Aprox. 13.5 inches of vacuum. But this can just starts to move at 10..... 30 inches for full vacuum advance. If I limit it down it'll still be in the neighborhood of 20 inches to reach full vacuum advance.
what engine makes 30” of vacuum at idle? You sure about how much it takes to fully pull it in? That number sounds way too high to me.
what engine makes 30” of vacuum at idle? You sure about how much it takes to fully pull it in? That number sounds way too high to me.
It is. 17" of hg is max for any HEI can.
A VC1703 will start at 3-6" and is 5* at 7-9"hg. That would give you 10* crank advance at idle.
A VC-1838 will start at 7-9" and 7* at 10-12" . That is 14* crank. advance.
The 18 on that can is part #, and means zippo
In response to the last couple of posts. Yes I am absolutely certain of the readings. I am using a matco tools vacuum gauge. Verified by readings off my EFI . I am indeed running about 11 inches of vacuum at 800 RPM with no Vacuum advance connected. 13.5 inches of vacuum with vacuum advance canister that I am certain is bouncing around in the middle of its throw. Yes. I have measured with a vacuum gauge all of the vacuum measurements I have posted. NO, I am not a "Nubie". I am a 60 year old professional Harley Davidson Mechanic. I have owned this car for over 30years.
the original can was on my car from new. It's 43years old. Perhaps the high readings are because the diaphragm is 43 years old. And it was on a car that back when new was hooked up to ported vacuum. And run threw a thermo switch. I really doubt the factory was concerned with idle vacuum. Only emissions.
As per the "Accel" can I have. Bought that back in the 90's . Not sure why I didn't pitch it years ago. It never did work properly. Always made my car overheat. But I had it laying around so to speak so I measured it.
what I want/need is a can that starts pulling at about 7 or 8 inches of vacuum. And is all in at 12 crank degrees at 11 inches of vacuum.
all the part numbers on Lars papers dont match up with current part numbers on Summit Racing and or other similar online retailers. When I put in something like "B28" into summit's search engine. I get motorcycle parts and carpets.
none of the listings for Standard Motor products vacuum canisters give specs on vacuum needed to max them. And none of the part numbers match what Lars has on his report.
looking for a part number that I can order from an online company that will ship overseas, without excessive shipping fees. Please don't tell me to "pop on down" to the local "XYZ" auto parts store.
there not interested in shipping overseas.
If someone could please help would be greatly appreciated.
Thank you
O.K. , so far not much in the way of a part number that works in todays world. So I go out to the garage, armed with a vacuum gauge. And I do some playing around with the vacuum can that came with my Proform "Race" Distributor.
yes laughable, anything but "race".
Anyway, it seems the other 2 cans are just too old to think about getting right. The Taiwanese can. Well it's junk but what do I have to loose.
I find if I shim the back side of the slot to hold the rod slightly into the can. It raises the start of the advance to, well, where ever I want it. About 8 inches of vacuum as a start point I'm thinking would be good. I'm thinking it's so low now that I may be getting some additional timing in when I floor it. And that would explain my less than great power when I floor it.
soooo, weld in the back side of the slot to hold the rod slightly into the can. File it until I can get 8 inches of vacuum to just start to move it.
Now keeping in mind, this thing is giving me roughly double the vacuum timing I'm looking for.
weld in the front of the slot and file it till the rod hits at about 11.5 Inches of vacuum. Now I realize that this may not be perfect. But I'm thinking it'll get me in the ball park.
pulling the bottom stop up I should be able to compensate by resetting the distributor. Once in place and base timing set. I can measure exactly how much vacuum advance I am getting and if necessary, file abit from there.
I'm thinking what do I have to loose?
As per the adding a spring idea. I've looked at this and for the life of me can't figure out how to install such a spring.
still , would be great to get a part number that I can order.
Last edited by 4-vettes; Apr 27, 2020 at 07:39 AM.
I agree......instead of driving yourself crazy, read the Lars Vacuum Advance specs and facts sheet he wrote. It has part #'s and where to get his vacuum advance lever stop.
Vacuum advance
