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| [GMCnet] More on final drive ratios [message #238033] |
Wed, 29 January 2014 20:50  |
glwgmc
Messages: 1014
Registered: June 2004
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Hi Rob,
Yes, 3.5 chain means the Power Drive technology developed by a well known Porsche tuner turned GMC owner which he sold to Manny. It means the gears/chain that transfers power from the output shaft of the torque converter to the input shaft of the transmission are altered from the stock 1:1 ratio to a different ratio that results in an effective 3.5 over all ratio with the stock 3.07 final drive. In combination with the 3.21 final drive the effective over all ratio is .3.67.
Advancing the cam timing 4 degrees results in reducing the torque curve by about 400 rpm according to some, BUT NOT ALL, 455 knowledgeable engine folks. My experience is that it certainly has a beneficial effect according to the seat of my pants. No science here, just seat of the pants.
For flat land the 12 degrees of static distributor advance might well be ok, but where I live it would be too much unless one likes the tinkle sound of pinging. My ears are no longer good enough to hear such sounds reliably, so I tend to be more conservative. If I had a good knock sensor with auto retard I would advance further and let the electronics do their thing.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed & hand crafted
in the 1907 former Masonic Temple building
in historic Kerby, OR
Http://jerrywork.com
541-592-5360
Cell 541-499-1027
.............
Message: 11
Date: Thu, 30 Jan 2014 11:18:21 +1100
From: "Robert Mueller" <robmueller@iinet.net.au>
Subject: Re: [GMCnet] More on final drive ratios
To: <gmclist@temp.gmcnet.org>
Message-ID: <5AB3F62674D448EFBA303C9DAD075C8D@DellDesktop>
Content-Type: text/plain; charset="iso-8859-1"
Jerry,
When you note "a 3.5 chain in the transmission" do you mean you have Manny's Power Drive installed? If yes with the 3.21 to 1 final
drive you've got a 3.67 ratio.
The cam set at 4? advance will have lowered your torque band (I couldn't say how much cause I'd be pulling the number out my nether
regions). What cam did you use?
The sheet Dick supplied with my distributor noted to set the advance at 12?
http://www.gmcmhphotos.com/photos/member-galleries/p32021-dick-paterson-s-distri.html
Which I set at a Slow Idle speed of 600 rpm Ref: X-7525 / Section 6M / ENGINE FUEL SYSTEM / Page 6M-23 / Figure 12 / Step 6.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
,,,,,,,,,,,,,
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] More on final drive ratios [message #238034 is a reply to message #238033] |
Wed, 29 January 2014 21:19  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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The reason for disconnecting and plugging the canister vacuum line is to
make certain that the distributor vacuum advance is not influencing the
static ignition timing. The mechanical advance mechanism NORMALLY does not
to operate below 1000 rpm or so in the GM distributor used on the GMC motor
home. So, it makes no difference if your idle rpm is 750 or 400, as long as
you are below the point of centrifugal advance pull in when you adjust the
static ignition timing. That said, I normally set the idle speed around
750 rpm after timing is set.
Jim Hupy
Salem, Or
78 GMC Royale 403
On Jan 29, 2014 6:51 PM, "Gerald Work" <glwork@mac.com> wrote:
> Hi Rob,
>
> Yes, 3.5 chain means the Power Drive technology developed by a well known
> Porsche tuner turned GMC owner which he sold to Manny. It means the
> gears/chain that transfers power from the output shaft of the torque
> converter to the input shaft of the transmission are altered from the stock
> 1:1 ratio to a different ratio that results in an effective 3.5 over all
> ratio with the stock 3.07 final drive. In combination with the 3.21 final
> drive the effective over all ratio is .3.67.
>
> Advancing the cam timing 4 degrees results in reducing the torque curve by
> about 400 rpm according to some, BUT NOT ALL, 455 knowledgeable engine
> folks. My experience is that it certainly has a beneficial effect
> according to the seat of my pants. No science here, just seat of the pants.
>
> For flat land the 12 degrees of static distributor advance might well be
> ok, but where I live it would be too much unless one likes the tinkle sound
> of pinging. My ears are no longer good enough to hear such sounds
> reliably, so I tend to be more conservative. If I had a good knock sensor
> with auto retard I would advance further and let the electronics do their
> thing.
>
> Jerry
>
> Jerry Work
> The Dovetail Joint
> Fine furniture designed & hand crafted
> in the 1907 former Masonic Temple building
> in historic Kerby, OR
> Http://jerrywork.com
> 541-592-5360
> Cell 541-499-1027
> .............
> Message: 11
> Date: Thu, 30 Jan 2014 11:18:21 +1100
> From: "Robert Mueller" <robmueller@iinet.net.au>
> Subject: Re: [GMCnet] More on final drive ratios
> To: <gmclist@temp.gmcnet.org>
> Message-ID: <5AB3F62674D448EFBA303C9DAD075C8D@DellDesktop>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Jerry,
>
> When you note "a 3.5 chain in the transmission" do you mean you have
> Manny's Power Drive installed? If yes with the 3.21 to 1 final
> drive you've got a 3.67 ratio.
>
> The cam set at 4? advance will have lowered your torque band (I couldn't
> say how much cause I'd be pulling the number out my nether
> regions). What cam did you use?
>
> The sheet Dick supplied with my distributor noted to set the advance at 12?
>
>
> http://www.gmcmhphotos.com/photos/member-galleries/p32021-dick-paterson-s-distri.html
>
> Which I set at a Slow Idle speed of 600 rpm Ref: X-7525 / Section 6M /
> ENGINE FUEL SYSTEM / Page 6M-23 / Figure 12 / Step 6.
>
> Regards,
> Rob M.
> Sydney, Australia
> AUS '75 Avion - The Blue Streak TZE365V100428
> USA '75 Avion - Double Trouble TZE365V100426
> ,,,,,,,,,,,,,
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] More on final drive ratios [message #238089 is a reply to message #238072] |
Thu, 30 January 2014 10:16 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Matt, as to why some Tech Writer composed a manual for us knuckle dragging
neanderthals to use that had some misleading information in it is anyone's
guess. Perhaps he (or she) was under a production mandate and had to "do
something, even if it is slightly inaccurate ". ( grin). One of my GM
service manuals says the distributor turns clockwise, and another one says
counter clockwise. I guess "stuff happens" is the only plausible
explanation. I seem to remember working on a European vehicle that had both
a vacuum advance as well as a vacuum retard canister on the hall effect
distributor. It had a very specific rpm range that the tech had to use when
making adjustments to timing. If you turned the distributor a tiny bit too
much, the rpm would change and so would the vacuum, then you were chasing
your tail trying to get it within specs. One thing i do know, if the
computer is controlling timing, you aren't. Ain't technology great??
Jim Hupy
Salem, Or.
78 GMC Royale 403
On Jan 30, 2014 6:36 AM, "Matt Colie" <matt7323tze@gmail.com> wrote:
>
>
> James Hupy wrote on Wed, 29 January 2014 22:19
> > The reason for disconnecting and plugging the canister vacuum line is to
> make certain that the distributor vacuum advance is not influencing the
> static ignition timing. The mechanical advance mechanism NORMALLY does not
> to operate below 1000 rpm or so in the GM distributor used on the GMC motor
> home. So, it makes no difference if your idle rpm is 750 or 400, as long as
> you are below the point of centrifugal advance pull in when you adjust the
> static ignition timing. That said, I normally set the idle speed around
> 750 rpm after timing is set.
> > Jim Hupy
>
> Jim,
>
> I know what you have written to be accurate, but then why in bloody blue
> blazes did some moron specify the base timing as 8°BTDC at 1100RPM?
> At that speed any change in timing changes the speed and thus the timing.
> You are trying to hit a dancing target.
>
> It is almost impossible to do alone and I did finally give up and set my
> base at something like 850.
>
> Matt
> --
> Matt & Mary Colie - Members GMCMI, GMCES Going to MontgomeryThe majestic,
> once snow covered glacier Chaumičre is in for the winter.
> '73 Glacier 23 With 4 Rear Brakes that pull as they should
> SE Michigan - Twixt A2 and Detroit
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| Re: [GMCnet] More on final drive ratios [message #238108 is a reply to message #238033] |
Thu, 30 January 2014 12:04 |
Jon payne
Messages: 495
Registered: May 2008
Karma: 1
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Senior Member |
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Hi Jim,
Interesting what you said about the mechanical advance will start advancing around 1000 RPM. So to test this and find out what RPM my distributor starts advancing, I could use a timing light and slowly increase engine RPM (via throttle) from 800, for example, and I should not see the timing mark move until the mechanical advance starts advancing. Would this be correct? Of course I would have the vacuum advance canister disconnected and the hose plugged.
So with this information I will know what RPM I should be below when setting the timing. Yes?
Jon
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: [GMCnet] More on final drive ratios [message #238157 is a reply to message #238108] |
Thu, 30 January 2014 18:14 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Jon, it will vary by a couple of hundred rpm, depending upon which springs
and flyweights are in your distributor. Yes, you have the procedures down.
Happy tuning. (grin)
Jim Hupy
Salem, Or.
78 GMC Royale 403
On Jan 30, 2014 10:04 AM, "Jon Payne" <embrep@sbcglobal.net> wrote:
>
>
> Hi Jim,
>
> Interesting what you said about the mechanical advance will start
> advancing around 1000 RPM. So to test this and find out what RPM my
> distributor starts advancing, I could use a timing light and slowly
> increase engine RPM (via throttle) from 800, for example, and I should not
> see the timing mark move until the mechanical advance starts advancing.
> Would this be correct? Of course I would have the vacuum advance canister
> disconnected and the hose plugged.
>
> So with this information I will know what RPM I should be below when
> setting the timing. Yes?
>
> Jon
>
>
> --
> Jon Payne
> 76 Palm Beach
> Westfield,IN
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] More on final drive ratios [message #238289 is a reply to message #238072] |
Fri, 31 January 2014 19:51 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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| Matt Colie wrote on Thu, 30 January 2014 07:36 |
| James Hupy wrote on Wed, 29 January 2014 22:19 |
The reason for disconnecting and plugging the canister vacuum line is to make certain that the distributor vacuum advance is not influencing the static ignition timing. The mechanical advance mechanism NORMALLY does not to operate below 1000 rpm or so in the GM distributor used on the GMC motor home. So, it makes no difference if your idle rpm is 750 or 400, as long as you are below the point of centrifugal advance pull in when you adjust the static ignition timing. That said, I normally set the idle speed around 750 rpm after timing is set.
Jim Hupy
|
Jim,
I know what you have written to be accurate, but then why in bloody blue blazes did some moron specify the base timing as 8°BTDC at 1100RPM?
At that speed any change in timing changes the speed and thus the timing. You are trying to hit a dancing target.
It is almost impossible to do alone and I did finally give up and set my base at something like 850.
Matt
|
Matt, I don't think that is an accident nor a mistake by a tech writer. Depending on whether you have a 455, 403 or a California engine, you will see that engine speed at which to set the base timing is very well thought out. The base timing will determine overall timing throughout the entire rpm band. If you look at the centrigugal advance curves, the intent is to just get the centrifugal advance in the very initial start of influence when setting the timing. On Ca engines, the static timing is set at 2000 rpm, just st the start of intermediate centrifugal advance.
Bob de Kruyff
78 Eleganza
Chandler, AZ
[Updated on: Fri, 31 January 2014 19:52] Report message to a moderator |
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| Re: [GMCnet] More on final drive ratios [message #238302 is a reply to message #238289] |
Fri, 31 January 2014 20:58 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Bob, What you said about ignition timing California 403 olds engines
aroused some curiosity in me, so, I fired up my trusty laptop and did some
research. Cal equipped delco distributor, #1103309 according to the GMC
maintenance manual clearly states that the rotor turns clockwise. It does
not. Typo in my book. It also states that mechanical centrifugal advance at
2200 rpm is 0, 11 degrees at 2600 rpm, and finally 16 degrees at 3400 rpm.
It also says to set base or static timing at 12 degrees at 2000 rpm. That
is below the point where centrifugal advance starts to pull in. If one
believes the same book that tells you that the rotor turns clockwise. Just
what I read. Others results may vary.
Jim Hupy
Salem, Or
78 GMC Royale 403
On Jan 31, 2014 5:51 PM, "Bob de Kruyff" <NEXT2POOL@aol.com> wrote:
>
>
> Matt Colie wrote on Thu, 30 January 2014 07:36
> > James Hupy wrote on Wed, 29 January 2014 22:19
> > > The reason for disconnecting and plugging the canister vacuum line is
> to make certain that the distributor vacuum advance is not influencing the
> static ignition timing. The mechanical advance mechanism NORMALLY does not
> to operate below 1000 rpm or so in the GM distributor used on the GMC motor
> home. So, it makes no difference if your idle rpm is 750 or 400, as long as
> you are below the point of centrifugal advance pull in when you adjust the
> static ignition timing. That said, I normally set the idle speed around
> 750 rpm after timing is set.
> > > Jim Hupy
> >
> > Jim,
> >
> > I know what you have written to be accurate, but then why in bloody blue
> blazes did some moron specify the base timing as 8°BTDC at 1100RPM?
> > At that speed any change in timing changes the speed and thus the
> timing. You are trying to hit a dancing target.
> >
> > It is almost impossible to do alone and I did finally give up and set my
> base at something like 850.
> >
> > Matt
>
> Matt, I don't think that is an accident nor a mistake by a tech writer.
> Depending on whether you have a 455, 403 or a California engine, you will
> see that engine speed at which to set the base timing is very well thought
> out. The base timing will determine overall timing throughout the entire
> rpm band. If you look at the centrigugal advance curves, the intent is to
> just get the centrifugal advance in the very initial start of influence
> when setting the timing. On Ca engines, the staic timing is set at 2000
> rpm, just st the start of intermediate centrifugal advance.
> --
> Bob de Kruyff
> 78 Eleganza
> Chandler, AZ
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] More on final drive ratios Hijacked to Ignition Timing [message #238304 is a reply to message #238302] |
Fri, 31 January 2014 21:18 |
Nelson Wright
Messages: 147
Registered: May 2004
Karma: 0
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Senior Member |
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Guys,
I haven't been following this to closely, but I would like to mention that on my 78 Cal 455 that the vacuum advance also had a vacuum retard port. This unit sort of has a neutral point about halfway between full advance and full retard. As I had no idea where to get the proper vacuum for the retard feature I replaced it with a standard advance unit.
Nelson Wright
Orlando FL
78 Royale rear bath
On Jan 31, 2014, at 9:58 PM, James Hupy wrote:
> Bob, What you said about ignition timing California 403 olds engines
> aroused some curiosity in me, so, I fired up my trusty laptop and did some
> research. Cal equipped delco distributor, #1103309 according to the GMC
> maintenance manual clearly states that the rotor turns clockwise. It does
> not. Typo in my book. It also states that mechanical centrifugal advance at
> 2200 rpm is 0, 11 degrees at 2600 rpm, and finally 16 degrees at 3400 rpm.
> It also says to set base or static timing at 12 degrees at 2000 rpm. That
> is below the point where centrifugal advance starts to pull in. If one
> believes the same book that tells you that the rotor turns clockwise. Just
> what I read. Others results may vary.
> Jim Hupy
> Salem, Or
> 78 GMC Royale 403
> On Jan 31, 2014 5:51 PM, "Bob de Kruyff" <NEXT2POOL@aol.com> wrote:
>
>>
>>
>> Matt Colie wrote on Thu, 30 January 2014 07:36
>>> James Hupy wrote on Wed, 29 January 2014 22:19
>>>> The reason for disconnecting and plugging the canister vacuum line is
>> to make certain that the distributor vacuum advance is not influencing the
>> static ignition timing. The mechanical advance mechanism NORMALLY does not
>> to operate below 1000 rpm or so in the GM distributor used on the GMC motor
>> home. So, it makes no difference if your idle rpm is 750 or 400, as long as
>> you are below the point of centrifugal advance pull in when you adjust the
>> static ignition timing. That said, I normally set the idle speed around
>> 750 rpm after timing is set.
>>>> Jim Hupy
>>>
>>> Jim,
>>>
>>> I know what you have written to be accurate, but then why in bloody blue
>> blazes did some moron specify the base timing as 8°BTDC at 1100RPM?
>>> At that speed any change in timing changes the speed and thus the
>> timing. You are trying to hit a dancing target.
>>>
>>> It is almost impossible to do alone and I did finally give up and set my
>> base at something like 850.
>>>
>>> Matt
>>
>> Matt, I don't think that is an accident nor a mistake by a tech writer.
>> Depending on whether you have a 455, 403 or a California engine, you will
>> see that engine speed at which to set the base timing is very well thought
>> out. The base timing will determine overall timing throughout the entire
>> rpm band. If you look at the centrigugal advance curves, the intent is to
>> just get the centrifugal advance in the very initial start of influence
>> when setting the timing. On Ca engines, the staic timing is set at 2000
>> rpm, just st the start of intermediate centrifugal advance.
>> --
>> Bob de Kruyff
>> 78 Eleganza
>> Chandler, AZ
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
> _______________________________________________
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| Re: [GMCnet] More on final drive ratios [message #238309 is a reply to message #238302] |
Fri, 31 January 2014 21:32 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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"". If one
believes the same book that tells you that the rotor turns clockwise. Just
what I read. Others results may vary.
Jim Hupy""
Yes Jim, the book has lot's of typos including the firing order. I guess one can decide to discount the whole book and everything in it or to recognize that mistakes exist. Also keep in mind that the 403 and 455 specs are very different when it comes to timing and carb settings.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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