Author Topic: Vacuum Advance on HEI 350  (Read 495 times)

Offline kopeck

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Vacuum Advance on HEI 350
« on: November 08, 2021, 08:28:57 AM »
Morning,

I have a bone stock, all original '79 C10 with a 350 that has about 90k on it.  I've owned this truck for a long time, over 20 years and I've fought off and on with it pinging at a light load (e.g. going up a small hill or a lazy acceleration) from pretty much the get-go.  I've done all the usual things, checked/verified the timing (multiple times) last year I replaced all the vacuum hoses and the EGR valve, sprayed everything down to check for leaks and I have never been able to eliminate it.

The solution has always been 89 octane gas, 87 it pings, 89 it doesn't.  Well I just filled up with a tank of 89 that I suspect isn't really up to snuff so it's been pinging a bit.  For the fun of it, I disconnected the vacuum advanced canister and low and behold the pinging went away.

I know they make adjustable canisters but before I order one is that the route I should be chasing?  I'm sure the pinging could be the result of something in the old 350 being tired and I do plan to freshen it up in the next year or two but it always starts well and other than the ping runs well and you know what they say about fixing things that are not broken.  It just feels like that canister is adding at tad to much advance in low throttle situations. 

K



Offline kopeck

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Re: Vacuum Advance on HEI 350
« Reply #1 on: November 08, 2021, 09:10:52 AM »
I'm going to reply to my own thread.

After doing some googling it kind of looks like I need something to limit the canister more than adjust it.

The first thing I found was the Crane 99600-1 kit but it looks like that it's NLA.

Doing a bit more digging it looks like the MSD Ignition 84281 HEI Vacuum Advance Stop Plate might be the ticket.  I'm sure any adjustable canister on top of this would really dial it in but I just want to pull some timing out a light throttle.

K


Offline TexasRed

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Re: Vacuum Advance on HEI 350
« Reply #2 on: November 08, 2021, 12:23:51 PM »
OK, I would look/google "vacuum advance stop plate". I don't know how much this forum likes linking. You can use pretty much anyone's adjustable vacuum advance kit. The crane kit was nice because it had almost everything. You had to do a little machine work but it wasn't bad.

The parts you'll need:
Adjustable vacuum advance
a limiter plate you'll have to make
some screws (you'll need the drill and tap for these)
the springs from one of those kits for adjusting mechanical advance (the weights are junk)
timing light

There's a guy that used to post on other forums called ignitionman that has the setup that you need in terms of initial, how fast you want to see the mechanical and then the additional timing for the vacuum advance.

Clear as mud?

Offline VileZambonie

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Re: Vacuum Advance on HEI 350
« Reply #3 on: November 08, 2021, 05:46:47 PM »
You are going down a rabbit hole. You could simply retard the timing if it is over-advanced. Figure out why it is pinging:

What plugs are you running and how do they look?

What is your initial timing and total timing?

Do you have a borescope? Can you get a look in the cylinder to see if you have excessive carbon buildup? You can buy a cheap borescope for your phone for like $10 bucks on eBay.
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Offline JohnnyPopper

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Re: Vacuum Advance on HEI 350
« Reply #4 on: November 08, 2021, 06:22:43 PM »
Too bad water injections systems aren't on the market anymore.

I bought the last one around here back in '87, still have it  8)

I could run 87 in my 3+3 with a 454, fully loaded 5th wheel toyhouse, and 3 brats and cool as a cucumber!
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline kopeck

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Re: Vacuum Advance on HEI 350
« Reply #5 on: November 09, 2021, 07:21:47 AM »
OK, I would look/google "vacuum advance stop plate". I don't know how much this forum likes linking. You can use pretty much anyone's adjustable vacuum advance kit. The crane kit was nice because it had almost everything. You had to do a little machine work but it wasn't bad.

The parts you'll need:
Adjustable vacuum advance
a limiter plate you'll have to make
some screws (you'll need the drill and tap for these)
the springs from one of those kits for adjusting mechanical advance (the weights are junk)
timing light

There's a guy that used to post on other forums called ignitionman that has the setup that you need in terms of initial, how fast you want to see the mechanical and then the additional timing for the vacuum advance.

Clear as mud?

MSD makes a plate that has multiple options, it's $12 bucks so it seems like that might be were I start.  See what I have for full in timing and then start backing it down.

K

Offline kopeck

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Re: Vacuum Advance on HEI 350
« Reply #6 on: November 09, 2021, 07:38:49 AM »
You are going down a rabbit hole. You could simply retard the timing if it is over-advanced. Figure out why it is pinging:

What plugs are you running and how do they look?

What is your initial timing and total timing?

Do you have a borescope? Can you get a look in the cylinder to see if you have excessive carbon buildup? You can buy a cheap borescope for your phone for like $10 bucks on eBay.

No doubt about it, there is some underlying issue.

I'm pretty sure I'm running NGK 7052 now, I was running some flavor of AC Delco before that.  The plugs looked good when I replaced them, no oil fouling or anything like that.  The only reason I replaced them as I needed to replace wires and I figured why not.

The timing is whatever's on the sticker, off the top of my head something like 20 BTDC @ 2000 RPM but don't quote me.  I have checked it multiple times.  That's with the canister unplugged, I can't exactly remember where it goes with the canister plugged in, mid 30s?

The valve guides must be pretty worn on this old girl as she gives a good-sized blue puff on cold startup.  The engine undoubtedly needs to be freshened up but it also runs well, makes good oil pressure, and moves the truck around.  I'm just trying to make it happy until I can pull it and see how worn it really is.

K


Offline Mike81K10

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Re: Vacuum Advance on HEI 350
« Reply #7 on: November 09, 2021, 10:13:27 PM »
Should not be much wear on a 90K engine unless it has been abused.

Offline TexasRed

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Re: Vacuum Advance on HEI 350
« Reply #8 on: November 10, 2021, 12:16:47 AM »
OK, I would look/google "vacuum advance stop plate". I don't know how much this forum likes linking. You can use pretty much anyone's adjustable vacuum advance kit. The crane kit was nice because it had almost everything. You had to do a little machine work but it wasn't bad.

The parts you'll need:
Adjustable vacuum advance
a limiter plate you'll have to make
some screws (you'll need the drill and tap for these)
the springs from one of those kits for adjusting mechanical advance (the weights are junk)
timing light

There's a guy that used to post on other forums called ignitionman that has the setup that you need in terms of initial, how fast you want to see the mechanical and then the additional timing for the vacuum advance.

Clear as mud?

MSD makes a plate that has multiple options, it's $12 bucks so it seems like that might be were I start.  See what I have for full in timing and then start backing it down.

K

The reviews on amazon for the MSD leaves a little to be desired.

Well, I found an extra scroll plate from crane. You have to drill and tap the advance in front of the pin on the vacuum advance. NOT like what Crane describes. Each notch should be about 2 degrees.

https://static1.s123-cdn-static-a.com/uploads/278432/2000_593f642430b4c.jpg  - not my picture, but it's kind of what it would look like.

I would think with the vacuum canister plugged in, you'd get around 20 extra degrees of advance.

Offline kopeck

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Re: Vacuum Advance on HEI 350
« Reply #9 on: November 10, 2021, 06:44:39 AM »
Should not be much wear on a 90K engine unless it has been abused.

It hasn't been abused at all.  It was bought new by my Grandfather and he used it as his chore truck around the farm and then I inherited it in 2000.  I drive it but I've always been easy on it, I guess I wasn't "normal" in my younger years. :-)

It's one of the things I've struggled with.  I suspect it's not all that worn but the heads need some attention and it leaks from all the usual spots.  You don't know until you look but through the years I've learned that you shouldn't just tear down engines just for the fun of it.

K

Offline kopeck

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Re: Vacuum Advance on HEI 350
« Reply #10 on: November 10, 2021, 06:48:16 AM »

The reviews on amazon for the MSD leaves a little to be desired.

Well, I found an extra scroll plate from crane. You have to drill and tap the advance in front of the pin on the vacuum advance. NOT like what Crane describes. Each notch should be about 2 degrees.

https://static1.s123-cdn-static-a.com/uploads/278432/2000_593f642430b4c.jpg  - not my picture, but it's kind of what it would look like.

I would think with the vacuum canister plugged in, you'd get around 20 extra degrees of advance.

Yeah, it seems they overstate the amount each notch retards the timing.  I don't suspect I need a lot which of course which brings up VileZambonie point of me just taking a few degrees out and seeing what happens.  I mean that's free. :-)

K

Offline TexasRed

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Re: Vacuum Advance on HEI 350
« Reply #11 on: November 10, 2021, 11:56:12 AM »
I think some more in-depth analysis of what you have currently is probably in order. For now, I'd ignore what the factory sticker says the timing should be. Let's see what it is at various parts of the RPM range.

What is your initial timing WITHOUT vacuum advance can hooked up?
What is the total timing and the about the RPM it stops advancing WITHOUT the vacuum advance can hooked up?
At idle, what does adding the vacuum advance can do in terms of extra degrees of advance?