Timing & Vacuum Advance 101 - Page 4 - Team Camaro Tech
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post #46 of 80 (permalink) Old Jun 26th, 11, 02:58 PM
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Re: Timing & Vacuum Advance 101

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Originally Posted by HwyStarJoe View Post
But he WROTE AN ARTICLE and you didn't.

Can't really defer to someone who hasn't taken the time to write it up, now can we? You sound kind of jealous Steps.
Conversely, do you always accept everything that is written as gospel truth?

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post #47 of 80 (permalink) Old Jun 26th, 11, 05:36 PM
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Re: Timing & Vacuum Advance 101

Drop it...I think we both know where we stand and its OK.
Johns artucile is a bloody good one, explains things very well in general terms and principles.....
John also has a reputation of knowing what the hell he is talking about..read his stuff Believe it, from reading between the lines on his stuff, hes been there done that and knows what is right and wrong.
My stuff.. been there done that , and just takes Takes Johns articule to the next step practically appling those basic principles to individual reality
I also not John and I have gained our experiance over decades, in parrell, mine is NOT based on his but in parrell and they may differe a little in aproach here and there ...but hey 2 guys ripping engines out will also do the same thing with the same results just as well in doing things in a different order.
I believe John is more informed tham me on post ported vac curves, simply because all my stuff is 1912 to early 1970s.

Quote:
do you always accept everything that is written as gospel truth?
I question everything....
Example...I also breed endangered parrots....look anywhere on the internet, avocado is poisonoius to parrots....If it was the case (not taking that for granteed) my parrot flocks would be sick or dead....If chocolate was piosonous, our house parrot would be dead or sick.....
I have a habit of using, I think, from memory, type phrases, when Im going off others that I have not personally substantuated or not sure 100%.

My Spelling is not incorrect...it is creative

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post #48 of 80 (permalink) Old Jul 8th, 11, 05:20 AM
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Re: Timing & Vacuum Advance 101

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Originally Posted by JohnZ View Post
I'm not familiar with how the Edelbrocks are ported, but you want it connected to whichever port provides full manifold vacuum (sometimes called "full-time" vacuum) at idle, not the one that's a "ported" vacuum source, with little or no vacuum at idle.

I too have an Edelbrock 1407 on a built 350. It has VA on the left ported vac. I asked the guy who just restored it and got it running again and he says stock point dist are always connected to ported vac. I perused the carb owners manual and found this in the tuning section:

Long Duration Camshaft
If the engine has a fairly radical camshaft it may require an excessive amount of throttle opening for idle and/or have low idle vacuum levels. Either condition can lead to poor levels of adjustability and erratic idles.
• Another fix for the above condition is to run as much spark advance as possible at idle. If the distributor is fitted with a vacuum advance unit, connect it directly to manifold vacuum. If you are not able to employ vacuum advance for some reason, then the mechanical curve should have a low limit, which will allow you to use plenty of initial spark advance.

I'm going to study this until I think I have a handle on it and start experimenting with manifold vac.

Great thread!
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post #49 of 80 (permalink) Old Jul 10th, 11, 04:22 PM
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Re: Timing & Vacuum Advance 101

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Originally Posted by Nashville Beth View Post
I found this info in my archives. I don't know who to give credit to, but it's good info:

Vacuum Advance


GM hasn't made vacuum advance units for decades, but they still sell them, made in the aftermarket by Standard Products (and Echlin before that) and boxed by AC-Delco.

All of them provide 16* of advance, and the four calibrations that cover most usages in terms of when they start pulling and at what vacuum level they're fully-deployed are as follows:

VC-1802 (stamped B22) - starts at 8", done at 15"

VC-680 (stamped B1) - starts at 8", done at 16"

VC-1765 (stamped B20 or B26) - starts at 6", done at 12"

VC-1810 (stamped B28) - starts at 4", done at 8" (same as the original Delco "236-16", sold under GM #88924985 and AC-Delco #D1312C). I buy them in bulk for about six bucks each from GMPartsDirect.com. This is the most aggressive unit available, and is the only one that works properly with a "30-30" cam.
Where can I find a VC-1810 (B28), and will it work with an MSD 8360 distributor?

All other part numbers above are listed on Napa's website...the 1810 is not--has it been discontinued?

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406, 10:1, comp xr282HR, Dart Iron Eagle 200cc, Holley Contender dual plane, Holley 750 DP
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Last edited by keithl1967; Jul 10th, 11 at 04:36 PM.
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post #50 of 80 (permalink) Old Jul 12th, 11, 02:25 PM
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Re: Timing & Vacuum Advance 101

nevermind--ordered one from AZ--will have it Thursday...

Keith
1967 Camaro
406, 10:1, comp xr282HR, Dart Iron Eagle 200cc, Holley Contender dual plane, Holley 750 DP
Muncie M-20
GM 8.5, 3.73 posi
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post #51 of 80 (permalink) Old Aug 4th, 11, 05:42 PM
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Re: Timing & Vacuum Advance 101

OK, I have read this many times and want to give it a try. The engine (302) was built with a Unilite without vacuum advance. I have one in the box with the advance pot. My engine runs at about 8" Hg. I have emailed the Mallory help desk to get the specs on their advance pots but two weeks later no answer. Any one have those specs??

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post #52 of 80 (permalink) Old Aug 4th, 11, 05:47 PM
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Re: Timing & Vacuum Advance 101

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Originally Posted by scblucam View Post
OK, I have read this many times and want to give it a try. The engine (302) was built with a Unilite without vacuum advance. I have one in the box with the advance pot. My engine runs at about 8" Hg. I have emailed the Mallory help desk to get the specs on their advance pots but two weeks later no answer. Any one have those specs??
Their cans are adjustable. You will need to screw the adjustment screw in until the vac can does not respond over 7" vacuum.
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post #53 of 80 (permalink) Old Aug 4th, 11, 06:44 PM
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Re: Timing & Vacuum Advance 101

I assume the adjustment would be through the hose nipple. I looked for instructions on their site but could find nothing.

68 302 M20 - 85 IROC Z
The older I get the faster I was.
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post #54 of 80 (permalink) Old Aug 4th, 11, 10:18 PM
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Re: Timing & Vacuum Advance 101

And keep in mind as u adjust u also get less advance..generally loose about 1.5 degre for each inch of vaccuum.

My Spelling is not incorrect...it is creative

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post #55 of 80 (permalink) Old Sep 4th, 11, 03:50 AM
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Re: Timing & Vacuum Advance 101

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Originally Posted by JohnZ View Post
Yup - I wrote it originally as a paper in early 2003, shared it on several different forums, and later dressed it up, expanded it, and published it as a feature article in the November, 2003 issue of "Corvette Enthusiast" magazine, when I was the Technical Editor. Here's a link to the published CE article, offered on our CRG site under "Technical Articles".

http://www.camaros.org/pdf/timing101.pdf

In the published version of this it states:

"Tune in next month, when we’ll show you
how to check out those systems, how to “map” your advance curves against their
design specifications and verify proper operation, and pass along some simple tips
and techniques for improving your Corvette’s performance by “tweaking” its
advance systems for peak efficiency."

Was that published? Is it available somewhere?
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post #56 of 80 (permalink) Old Sep 4th, 11, 02:03 PM
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Re: Timing & Vacuum Advance 101

There is a follow up somewhere. very good
In the mean time these are the basics
Quote:
The ball park and principle is basically the same be it a ford dodge rolls royce ...all internal combustion engines...it just has tweak changes to suit cam profiles and bore to stroke variations
Ball park for pre pollution manifold vac dizzies
8 to 12 degre intial ..that is what it fires up on (idle no VA)
8 to 18 degs depends on the cam/idle charactoristics and how inefficient the carbed engine is at low rpms Idle
Total intial plus cent 32 to 36 on modern fuels all in around 3000 rpms
VA has 2 specs, the amount of degrees and the vac range it works in
Should be all in at the idle vac with no VA..idling on the intial that to +1"..so fires up and then pulls the VA to the idle advance....the intial should be kept as high as possible but ..well 14 is getting maxed out, loads starter armitures and solenoids try keep below 12The amount in the VA is the difference between the idle advance, extablished with experimenting with the intial and no VA attched and the intial ..keeping low to get as much in the VA as possble for economic cruising
At cruise the intial +cent+ VA should not go above about 45 degs....keep in mind that the cent will/ may not be all in at the cruise rpms THAT IS why plotting the curve on graph paper is so important and why when free reving total everything can get up around the 50 /54 in some cases and not be an issue.
Stuff I have picked up with 30/40 yrs of tuning modding timing/dizzies from old vintage 5.5 to 6:1 compression cars that where designed to run on British pool fuels (60 to 65 octane between 1939 and 1954 thru to Hi Compression engines running propane (105.110 octane) and inbetween leaded and unleaded fuels.

My Spelling is not incorrect...it is creative

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post #57 of 80 (permalink) Old Oct 1st, 11, 02:06 PM
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Re: Timing & Vacuum Advance 101

Great Timing...Pardon the pun..

Reading this thread caused the ole light bulb in the head to go off.

I purchased my 69 a few months ago. The motor, a forged 355 roller with all the right stuff, was in it with about 200 miles on it and runs great. Built by a Racing Engine Builder.

My only observation is a little rich off idle. Carb is adjusted spot on.

MSD 85551 Non VA Dizzy.

So I read this and realize I need VA. So just for the heck of it I decide to check out how the mechanical advance curve is set.

Pull the cap a rotor and 1st thing I see is the big heavy advance springs. Way wrong. Then I realize NO Advance weights and vaguely remember the seller saying something about locked out. At the time I assumed he was talking the VA was locked out. Doh!

Ordered the new MSD 8361 today along with the VC1810 advance can

I never really thought about it as the motor ran so strong. Maybe having the 5 speed helps but I'm guessing I'll see some major improvements with the new VA Dizzy.

I can only assume the Initial/Final timing is set around 35*. I'll check it out later today.
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post #58 of 80 (permalink) Old Oct 1st, 11, 03:51 PM
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Re: Timing & Vacuum Advance 101

I never posted the answer to my question about the follow up article by JohnZ. It can be found at: http://www.camaros.org/pdf/map_advance.pdf

These 2 articles are fantastic for someone like me that didn't know a thing.
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post #59 of 80 (permalink) Old Oct 1st, 11, 04:41 PM
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Re: Timing & Vacuum Advance 101

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Originally Posted by Vega$69 View Post
Then I realize NO Advance weights and vaguely remember the seller saying something about locked out. At the time I assumed he was talking the VA was locked out. Doh!

Ordered the new MSD 8361 today along with the VC1810 advance can

I never really thought about it as the motor ran so strong. Maybe having the 5 speed helps but I'm guessing I'll see some major improvements with the new VA Dizzy.

I can only assume the Initial/Final timing is set around 35*. I'll check it out later today.
Old drag racer's trick but remember, at the strip, you come off the line at high rpm and make it go higher from there. Driving in the street to the market is a whole different can of worms. VA and MA make the care much more drivable. When I got my Z, it too was locked out, no VA, no MA (breaker plate had acutally been tack welded!!!). Getting these systems up and running made driving it like night and day.

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post #60 of 80 (permalink) Old Oct 1st, 11, 06:54 PM
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Re: Timing & Vacuum Advance 101

Quote:
Old drag racer's trick
Its no "trick" that is what one does for dedicated track racing where the rpms dont go below the power rpm band width.
Which is sort of using a dizzy as a fixed magnito.
And why track cars often have remote very heavy duty portable starter motors on trollies

My Spelling is not incorrect...it is creative

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