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Old 01-12-2021, 12:00 PM   #1
Kilohertz
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Default Help decipher GM distributor vacuum canister numbers

Hi folks,

I'm in the process of restoring my 49 Ford F-47 with the 239 flathead, and am starting by getting the engine running nicely. It hasn't run in years, I have it running now and am starting to make some mods.

I decided to start by machining a GM distributor to fit in place of the Loadomatic. It turned out great and engine fired right up...I am now fiddling with the fine tuning of advance both mechanical and vacuum. All of the references I have found are quoting NAPA/Echlin parts numbers, the VC1765 type etc. I have been unable to find any cross reference to the original GM numbers, and of all the GM dists I have here, none of them have NAPA cans in them, they are all original.

Has anybody found a list of vacuum canisters that reference the original numbers such as are found stamped i.e. 503 15? I know the 15 indicates total crank * at full advance but I want to know begin "Hg and final "Hg.

Any help would be greatly appreciated.

Cheers

PS for now I have an adjustable timing light and hand vacuum pump.
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Old 01-12-2021, 12:38 PM   #2
Charlie ny
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Default Re: Help decipher GM distributor vacuum canister numbers

Kilo,
I've made a few of these distributors and have found the NAPA VC- 1802
works best. Flat Jack Meyer may have something to add. What's most important is
controlling max mech adv and the rate of mech adv.
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Old 01-12-2021, 01:12 PM   #3
Kilohertz
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Default Re: Help decipher GM distributor vacuum canister numbers

Thanks Charlie,

Nice to hear from one of the very well respected people on this group. I have read many, many pages of info about advance and these Delco distributors...I have 2 prime candidates, both early 70's as they seem to have the least amount of mechanical advance. First one is 1112047 which is from a '72 350 truck, max mechanical of 18* crank, which I think it pretty close. Could probably fiddle with the rubber bushing on the pin to get a bit more, maybe up to 20-22*. I just found another one yesterday, 1112844, '74 Nova etc. but I can't find any info on it yet, and there are no stamped numbers on the weight base. That one came with a 14* canister which is the lowest I have found yet, going to test with my vacuum pump today, but would be nice to find original specs for it as well. It's stamped 502 14.

My ultimate goal for this engine will be dual 94 carbs, or a single 4 bbl depending on what I can find, aluminum heads of 7.5 or 8:1, possibly a new cam...that's about it. I want to get it running nicely before any serious modifications so I know I have a good baseline to work from.

The truck is a long way from being able to drive so I won't be able to road test/tune...I am just having fun right now playing with the engine.

All of the NAPA units are special order from our local dealer, I'll decide once I get a little more experimenting under my belt.

Thanks for your help!

Cheers


PS my manifold vacuum at idle is currently 16-17"Hg

Last edited by Kilohertz; 01-12-2021 at 03:52 PM.
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Old 01-12-2021, 03:25 PM   #4
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Default Re: Help decipher GM distributor vacuum canister numbers

Tuning the flathead require some thought on carburetors. Tuning for street requires a very lean mixture in cruise and a rich mixture in ower. When I worked withRrichard we were looking for the safest lean mixture we could get away with, running an AF of 15.5/16. To do this you need allot of advance (28/30) This gave the best economy. 22MPG with the L-100 cam. However, this left acceleration in a slug plus detonations. trying several carburetors. he settled on the Edelbrock 500cfm unit. out of the box it's quite rich, ut ran great, Cruise AF in the 13's. We knew how to get econmy but now time to get some power. Bring the timing back to 18/20 @2000 and getting the Af in arund 13 flat brought the 3800 lb HT back life. It took some time to find the right jets and rods for the carb but the ignition worked out with o problem 16 mach all in at 2k 4 deg inital. 8/10 deg vacuum adv and the economy was back. We did this because we like the challenge Engine runs on 91 Oct no alky gas and lighting the tires is not a problem just expensive. The engine is a mild 276, L-100 Edelbrock 65cc heads and 4bl intake. No porting a valve mods wer made. runas stock There is a reason for this.
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Old 01-12-2021, 03:56 PM   #5
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Default Re: Help decipher GM distributor vacuum canister numbers

Kilo,
I incorporate an adjustable stop in my 8BA / sbc distributors which allows finite
mechanical advance adjustments. Swapping bushings is OK but the overwhelming

positive response to the adjustable stop has been very encouraging...changes are easily made without removing the distributor from the motor. I have a couple brand new 1802 cans on the shelf and if you'd like to try my adjustable mech adv get back to me....cas5845@yahoo.com.....
If you have not already degreed your crank pulley think about doing it...for
the most part you can then dial in the distributor with a timing light.

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Old 01-12-2021, 05:30 PM   #6
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Default Re: Help decipher GM distributor vacuum canister numbers

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Being a Corvette owner, I frequent The Corvette Forum, specifically the "C2" section. I remember this being covered in detail there. I took a quick look, but couldn't find it. They do allow guests there, so perhaps you should spend some time over there if we can't help.
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Old 01-12-2021, 06:08 PM   #7
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Default Re: Help decipher GM distributor vacuum canister numbers

Here is some info on vacuum advance units for GM distributors I found a good while ago. Scroll down past the first few pages to the column listings. The document gives starting and max advance for each part. I used the unit that maxed at 8 degrees on my distributor.
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File Type: pdf Vac Adv Spec (1).pdf (119.5 KB, 37 views)
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Old 01-12-2021, 06:38 PM   #8
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Default Re: Help decipher GM distributor vacuum canister numbers

Charkey's adjustable Mech advance modification, maked the GM distributor a very useful product for all applications. Giving the user more latitude in tuning the ignition advance. this way yiu can try different advance settings, quite easy to find the right one. However, it must work with the carburetor and AF meter. Takes alittle putzing.
Gramps. .
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Old 01-12-2021, 10:35 PM   #9
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Default Re: Help decipher GM distributor vacuum canister numbers

I found an adjustable vacuum advance unit online (but don't remember the source). It adjusts with an Allen wrench through the vacuum nipple, just like a Ford. In fact, it looks just like a Ford, only with Chevy mounting.
As you tighten the Allen screw (turn clockwise) it compresses the spring to slow the rate of advance and and also reduces the amount of vacuum advance.

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Old 01-12-2021, 11:11 PM   #10
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Default Re: Help decipher GM distributor vacuum canister numbers

Quote:
Originally Posted by 40 Deluxe View Post
I found an adjustable vacuum advance unit online (but don't remember the source). It adjusts with an Allen wrench through the vacuum nipple, just like a Ford. In fact, it looks just like a Ford, only with Chevy mounting.
As you tighten the Allen screw (turn clockwise) it compresses the spring to slow the rate of advance and and also reduces the amount of vacuum advance.
I've had two of those (a Mr Gasket and an Accel, same unit). Both failed within a year or so.
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Old 01-12-2021, 11:32 PM   #11
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Default Re: Help decipher GM distributor vacuum canister numbers

Awesome info guys, Thank you! Just got back in the house from the shop...lots to digest...I'll read and research and get back to you in the morning. I made some good progress today, testing cans and such...so much fun.

Your help is very much appreciated.

Cheers

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Old 01-13-2021, 05:34 AM   #12
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Default Re: Help decipher GM distributor vacuum canister numbers

A question was brought up about the small amt of mechanical advance I use?? I'm not tuining for Horsepower here, I' turning for acceleration . When tuning for HP you'd advance the timing for max torque. In the stock car we lost the pull off the corners and found 16.20 worked best.
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Old 01-13-2021, 08:49 AM   #13
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Default Re: Help decipher GM distributor vacuum canister numbers

use an adjustable can and the (usually supplied) stop.
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Old 01-13-2021, 12:06 PM   #14
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Default Re: Help decipher GM distributor vacuum canister numbers

Good morning fine fellows,

Been reading for a while now and have digested all comments. I'll reply chronologically..

Charlie, I think I accidentally ended up with a few VC1802 as when I made my vacuum tests yesterday I found 2 that started at 8"Hg and ended at 14-16"Hg even though they are marked with the factory markings, not NAPA. One was on the '72 350 unit which is currently in my flathead and is functioning, the other was from my '74 Pontiac 455. So those should be fine but thank you for the offer of yours.

Yes degreeing the crank pulley is on my list, but I borrowed my friends Snap-On variable timing light which should accomplish the same result, but might be more cumbersome.

Ron, thank you for chiming in with your expertise. Yes an AF meter has been on my want list for a few years now..one day, hopefully soon. I think I have located a 4bbl intake, waiting for my friend to go see him and determine what it is, another local flathead rodder friend has the Edelbrock 390 CFM carb on his '32 roadster and he loves it. I still like the "look" of dual 2bbls but it's all about what I can find locally. I'll contact Charlie about the stop mods.

Tubman and 40cpe, thanks! Yes I have visited the Corvette site numerous times and that is where I have found most of the original Delco info, and the excellent article by Lars Grimsrud.

And as for the adjustable vacuum units, it's a great idea, but I am hoping once I get this dialed in, I won't be monkeying with it again, (ya, right, we know how that goes) I have enough cans here that I should be able to find one that will work, and maybe incorporate Charlie's mods.

I need to figure out a shop exhaust system so I can run the truck for more than 30 seconds at a time, gets pretty thick in there. It's also freezing outside so any time with the doors open, takes a while to build up heat again.

Today's project is to figure out radial movement of the vacuum canister acting on the points plate so I can figure out the distance traveled per * of advance. Then I can build a stop for the canister and mount it in the appropriate location. Sounds like fun. I knew high school Trig would come in handy one day....40 years later.

Thanks everyone!

Cheers

Last edited by Kilohertz; 01-17-2021 at 09:33 PM.
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Old 01-13-2021, 03:03 PM   #15
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Default Re: Help decipher GM distributor vacuum canister numbers

Quote:
Originally Posted by Kilohertz View Post
Hi folks,

I'm in the process of restoring my 49 Ford F-47 with the 239 flathead, and am starting by getting the engine running nicely. It hasn't run in years, I have it running now and am starting to make some mods.

I decided to start by machining a GM distributor to fit in place of the Loadomatic. It turned out great and engine fired right up...I am now fiddling with the fine tuning of advance both mechanical and vacuum. All of the references I have found are quoting NAPA/Echlin parts numbers, the VC1765 type etc. I have been unable to find any cross reference to the original GM numbers, and of all the GM dists I have here, none of them have NAPA cans in them, they are all original.

Has anybody found a list of vacuum canisters that reference the original numbers such as are found stamped i.e. 503 15? I know the 15 indicates total crank * at full advance but I want to know begin "Hg and final "Hg.

Any help would be greatly appreciated.

Cheers

PS for now I have an adjustable timing light and hand vacuum pump.
I just completed setting up my GM distributor from Charlie a little while ago.
I used the Crane adjustable vacuum can (99601-1).

I followed the guidance on the pdf attachment.

On the STOCK GM canisters, on the two numbers you mention on the canister mounting bar, the three numbers usually signify the last three numbers of the Delco-Remy/GM part number and as you stated, the last two numbers signify the number of CRANKSHAFT degrees the vacuum advance can allows. The real trick is knowing the first 4 of that long GM #......
Attached Files
File Type: pdf GM Distributor tuning 11-17-13 (1).pdf (575.7 KB, 23 views)

Last edited by 1948F-1Pickup; 01-13-2021 at 03:30 PM.
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Old 01-13-2021, 07:57 PM   #16
Kilohertz
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Default Re: Help decipher GM distributor vacuum canister numbers

Quote:
Originally Posted by Charlie ny View Post
The real trick is knowing the first 4 of that long GM #......

And that's the chart/table/list I've been trying to find. I'm not going to pursue it too much more as I think the with measurements I made with the vacuum pump, I have found that one of mine should be workable with a fixed stop at whatever advance my engine decides it likes.

Appreciate the pdf, I'll read it tonight when I get back in the house.

Cheers
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Old 01-17-2021, 08:56 PM   #17
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Default Re: Help decipher GM distributor vacuum canister numbers

Send me a address and i will send you a adjustable vac advance for the chevrolet ......
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Old 01-18-2021, 11:55 AM   #18
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Default Re: Help decipher GM distributor vacuum canister numbers

Quote:
Originally Posted by BUBBAS IGNITION View Post
Send me a address and i will send you a adjustable vac advance for the chevrolet ......

Thank you Jim!! pm sent
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