Home » Public Forums » GMCnet » Vacuum Advance Diaphram
| Vacuum Advance Diaphram [message #146161] |
Tue, 11 October 2011 10:29  |
philipswanson
Messages: 282
Registered: January 2004
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Does anybody have the correct part number for the 455 HEI vacuum advance diaphram? The old one we used to use was the Delco 1973577 with a max of 10 degrees. I can't find that P/N any more. Looking for the correct motorhome one, not the Toro. Anyboady have a good part number?
Thanks, Phil Swanson
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| Re: [GMCnet] Vacuum Advance Diaphram [message #146164 is a reply to message #146161] |
Tue, 11 October 2011 11:43  |
James Hupy
Messages: 6806
Registered: May 2010
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Phil, that number should still be good. But in the event that it is not,
there is available from Accel an adjustable one that has a hex screw located
in the vacuum inlet passage that allows for variable tip in. There is also a
mechanical kit that limits the overall total travel of the operating rod.
This allows for max travel and tip in, both ends of the curve. It is not
perfect, but what is? I looked in the mirror this morning, and it wasn't
George Clooney looking back at me. <Grin> The mechanical advance can be
tailored with different weights and springs as well, but beware all who
enter here, this is dangerous territory, too much advance on a 455 at
maximum throttle opening is a recipe for detonation and disasterous engine
damage. Don't ask me how I know.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Tue, Oct 11, 2011 at 8:29 AM, Phil Swanson <woodyman1@sbcglobal.net>wrote:
>
>
> Does anybody have the correct part number for the 455 HEI vacuum advance
> diaphram? The old one we used to use was the Delco 1973577 with a max of 10
> degrees. I can't find that P/N any more. Looking for the correct motorhome
> one, not the Toro. Anyboady have a good part number?
>
> Thanks, Phil Swanson
> _______________________________________________
> GMCnet mailing list
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| Re: [GMCnet] Vacuum Advance Diaphram [message #146173 is a reply to message #146172] |
Tue, 11 October 2011 14:57 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Phil. I never know what the mindset is of a GMCer. Some guys chase rainbows
looking for the pot of gold, and some just look at them and appreciate them
for what they are, a promise from GOD to never flood the earth again like he
did to Noah, and still others want to know the wavelength of the light
refracted through the water droplets, etc. The distributor probably has more
tuning capabilities than the carb if the truth were known. I think that the
Jim's have that cannister and I know that Dick Paterson has them. Like Gene
Fisher says, a GMC gets 8 to 10 mpg depending. If you had a really well
sorted out multipoint fuel injection system with O2 sensor and closed loop
operation along with electronic timing control, perhaps you can do a little
better than that, but it costs so much to get there it does not make
practical sense. I kinda equate all that to the idiot light vs gage
contraversey. Some of us prefer to watch the road, not fret about what a
gage is telling us. By the way, these comments are just my observations,
they are not meant to be critical of anyone for their views.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Tue, Oct 11, 2011 at 12:34 PM, Phil Swanson <woodyman1@sbcglobal.net>wrote:
>
>
> Jim,
>
> I really don't want to get into all the adjusting routine. Looking for a
> plug and play vacuum advance.
>
> Thanks, Phil Swanson
> _______________________________________________
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| Re: [GMCnet] Vacuum Advance Diaphram [message #146176 is a reply to message #146173] |
Tue, 11 October 2011 15:28 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Adding fuel injection and a computer controlled distributor really costs about 2 grand, more or less. I intend to do this (once other things stop robbing my piggy bank) mostly for the drivability. I've never liked carburetors and I understand that so long as you have the fuel injection set-up with a modern EBL, adding a computer controlled distributor is the best bargain around. It seems that a computer controlled distributor does at least as much for the drivability as all the other fuel injection stuff.
This is my understanding based on reading, not actual experience. Frankly I don't know why I'm waiting so long to do this...
Oh, yes I do, my coach drives very well right now. Damn.
Larry Davick
Fremont, California
The Mystery Machine
'76 (ish) Palm Beach
----- Original Message -----
From: "James Hupy" <jamesh1296@gmail.com>
To: gmclist@temp.gmcnet.org
Sent: Tuesday, October 11, 2011 12:57:42 PM
Subject: Re: [GMCnet] Vacuum Advance Diaphram
Phil. I never know what the mindset is of a GMCer. Some guys chase rainbows
looking for the pot of gold, and some just look at them and appreciate them
for what they are, a promise from GOD to never flood the earth again like he
did to Noah, and still others want to know the wavelength of the light
refracted through the water droplets, etc. The distributor probably has more
tuning capabilities than the carb if the truth were known. I think that the
Jim's have that cannister and I know that Dick Paterson has them. Like Gene
Fisher says, a GMC gets 8 to 10 mpg depending. If you had a really well
sorted out multipoint fuel injection system with O2 sensor and closed loop
operation along with electronic timing control, perhaps you can do a little
better than that, but it costs so much to get there it does not make
practical sense. I kinda equate all that to the idiot light vs gage
contraversey. Some of us prefer to watch the road, not fret about what a
gage is telling us. By the way, these comments are just my observations,
they are not meant to be critical of anyone for their views.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Tue, Oct 11, 2011 at 12:34 PM, Phil Swanson <woodyman1@sbcglobal.net>wrote:
>
>
> Jim,
>
> I really don't want to get into all the adjusting routine. Looking for a
> plug and play vacuum advance.
>
> Thanks, Phil Swanson
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: Vacuum Advance Diaphram [message #146217 is a reply to message #146161] |
Tue, 11 October 2011 18:57 |
g.winger
Messages: 792
Registered: February 2008
Location: Warrenton,Missouri
Karma: 0
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Jim,,,,I'm a rookie at distubutors. But dosen't the vac advance back off or "not advance" at full throttle??? No vacume at full throttle??? Was just thinking,,,,,PL
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| Re: [GMCnet] Vacuum Advance Diaphram [message #146233 is a reply to message #146217] |
Tue, 11 October 2011 21:19 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Paul, Yes, when there is an absence of vacuum, like there would be when the
throttle is depressed, the spring in the vacuum cannister overpowers the
vacuum and retards the ignition timing. Just how much that is depends on
spring strength, diameter of the diaphram, etc. The limits of that device
are determined by positive stops that are unique to that particular
cannister, hence separate numbers for the motorhome vs the passenger car vs
the station wagon, etc. Generally speaking in a low compression engine with
large combustion chambers and no "squish" area to suppress detonation, the
generally accepted maximum TOTAL Combined vacuum and mechanical advance
combined with the static timing advance of around 8 degrees, is no more than
36 degrees total. When you are pulling a hill, you lose 10 degrees from the
loss of vacuum. As the RPMs go slower, the mechanical also dials the advance
back a bit. If you can hear an audible pinging under those conditions, the
usual remedy would be to dial back the initial timing a couple of degrees.
Another fix might be to use higher octane fuel. Tuners all have their own
tricks. Joe Mondello had his, Dick Patterson has his, I have mine, etc. No
one has all the answers all the time nor in all areas of the country, as the
altitudes vary, the fuel quality varies, etc. As our engines age, the
ability of the engine to keep the cylinders sealed and vacuum high changes
also. Lots of variables.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Tue, Oct 11, 2011 at 4:57 PM, Paul Leavitt <leavittpaul@yahoo.com> wrote:
>
>
> Jim,,,,I'm a rookie at distubutors. But dosen't the vac advance back off or
> "not advance" at full throttle??? No vacume at full throttle??? Was just
> thinking,,,,,PL
> _______________________________________________
> GMCnet mailing list
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> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Vacuum Advance Diaphram [message #146239 is a reply to message #146233] |
Tue, 11 October 2011 22:40 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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| James Hupy wrote on Tue, 11 October 2011 19:19 |
... Tuners all have their own
tricks. Joe Mondello had his, Dick Patterson has his, I have mine, etc. No
one has all the answers all the time nor in all areas of the country, as the
altitudes vary, the fuel quality varies, etc. As our engines age, the
ability of the engine to keep the cylinders sealed and vacuum high changes
also. Lots of variables.
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Sounds like an advertisement for a computer controlled distributor. Advances until it senses a ping, then backs off a little. (As I understand it anyway!)
Someone once said: "Timing is everything."
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: Vacuum Advance Diaphram [message #146265 is a reply to message #146161] |
Wed, 12 October 2011 08:10 |
philipswanson
Messages: 282
Registered: January 2004
Karma: 0
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Senior Member |
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The GMCMI parts book lists the Napa VC1835 as the proper replacement. If you have an original NOS Delco #1973577 vacuum advance, it is a collector item and you might put it on E Bay because the Corvette and Camero guys are paying up to $100 for them as a correct GM part on their restorations. The Napa VC1835 is not quite the same spec. having a little different vacuum curve and a 12 degree total advance, vice 10, but probably close enough.
Phil Swanson
Bluebird Wanderlodge Wannabe
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