Home » Public Forums » GMCnet » Advancing cam timing (Adjustable double roller timing chain)
| Advancing cam timing [message #260464] |
Fri, 29 August 2014 14:04  |
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SeanKidd
Messages: 747
Registered: June 2012
Location: Northern Neck Virginia
Karma: 4
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GMCNet,
When I rebuilt engine (455) I installed a Melling MTO-1 high torque cam and cloyes double roller timing chain with adjustable (3 position) keyway. I installed the cam "straight up" with the alignment marks. The engine runs well, good vacuum (19" at idle, 16" in gear) and I've been averaging just about 8 mpg...with my 3.70:1 FD
I plan on replacing my radiator soon, what , if any are the advantages to advancing the cam timing (while I have the radiator out(more room))
Sean and Stephanie
73 Ex-CanyonLands 26' #317 "Oliver"
Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD Honda 6500 inverter gen.
Colonial Travelers
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| Re: [GMCnet] Advancing cam timing [message #260465 is a reply to message #260464] |
Fri, 29 August 2014 14:42  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Sean, there are a lot of factors in play here. With 3:70 final drive on
your coach what is the steady state rpm at the speed you normally drive?
What heads do you have on the engine, is it a 403 or a 455? Did you degree
in the new cam to determine lobe centerline or just assemble it on the
marks? Which intake manifold/carb combination are you using? Headers or
iron manifolds?
The generally accepted belief is that advancing the CAM TIMING moves the
point of maximum torque down the rpm scale, whereas retarding CAM TIMING
moves it up the scale. Some combinations of compression/valve sizes, port
shapes, header diameter and tube length, intake and carb/air cleaner
combinations will respond to changes in cam timing differently than other
combinations will. It can be helpful or not, depending upon what you wish
to accomplish.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Aug 29, 2014 12:04 PM, "Sean Kidd" wrote:
> GMCNet,
> When I rebuilt engine (455) I installed a Melling MTO-1 high torque cam
> and cloyes double roller timing chain with adjustable (3 position) keyway.
> I installed the cam "straight up" with the alignment marks. The engine
> runs well, good vacuum (19" at idle, 16" in gear) and I've been averaging
> just about 8 mpg...with my 3.70:1 FD
>
> I plan on replacing my radiator soon, what , if any are the advantages to
> advancing the cam timing (while I have the radiator out(more room))
>
> --
> Sean and Stephanie
> 73 Ex-CanyonLands 26' #317 "Oliver"
> Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD
> Honda 6500 inverter gen.
>
> Colonial Travelers
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: Advancing cam timing [message #260467 is a reply to message #260464] |
Fri, 29 August 2014 15:51 |
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SeanKidd
Messages: 747
Registered: June 2012
Location: Northern Neck Virginia
Karma: 4
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Thanks Jim, My 455 runs 67 mph at about 3000 rpm, headers, quadrajet, blocked iron manifold, olds "J" heads, std size valves/springs, OEM air cleaner, Patterson dizzy, I did not degree the cam, just assembled with the alignment marks. The only thing I'm looking for would be better economy...highway driving. I drive via my vacuum gauge, trying to keep it "in the green" as much as possible. I achieved 9.5 mpg between virginia beach and Delaware running on rt 113? About 50 mph average and lots of stop lights. I have to remind myself that I'm not in a hurry, and I'm not in my MINI Cooper S. 
7.8 mpg (without towing)last few trips is disappointing
Sean and Stephanie
73 Ex-CanyonLands 26' #317 "Oliver"
Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD Honda 6500 inverter gen.
Colonial Travelers
[Updated on: Fri, 29 August 2014 15:52] Report message to a moderator |
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| Re: [GMCnet] Advancing cam timing [message #260470 is a reply to message #260467] |
Fri, 29 August 2014 16:17 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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You MIGHT gain a slight increase in vacuum by advancing 4°. Fuel economy is
largely determined by how far open the throttle plates are. Obviously,
steady state 60 mph will achieve a bit more fuel mileage than 70 mph. Wheel
alignment, tire pressures, terrain, road surface, all play a part as well.
"Jack Rabbit" starts where the secondaries are open are a no no if you seek
mileage. If you average 8+ mpg currently, I think you are in the ball park
as far as engine tune up is concerened. You might try sneaking up
(advance) ignition timing by a couple of degrees. If you or your
significant other detect any pinging under steady hard pull, retard it
until you can not. Pinging is a big no no. Remember this, if you run no
alcohol fuel, you will see an increase in fuel economy.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Aug 29, 2014 1:51 PM, "Sean Kidd" wrote:
> Thanks Jim, My 455 runs 67 mph at about 3000 rpm, headers, quadrajet,
> blocked iron manifold, olds "J" heads, std size valves/springs, OEM air
> cleaner,
> Patterson dizzy, I did not degree the cam, just assembled with the
> alignment marks. The only thing I'm looking for would be better
> economy...highway
> driving. I drive via my vacuum gauge, trying to keep it "in the green" as
> much as possible. I achieved 9.5 mpg between virginia beach and Delaware
> running on rt 113? About 50 mph average and lots of stop lights. I have
> to remind myself that I'm not in a hurry, and I'm not in my MINI Cooper S.
> 8)
>
> --
> Sean and Stephanie
> 73 Ex-CanyonLands 26' #317 "Oliver"
> Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD
> Honda 6500 inverter gen.
>
> Colonial Travelers
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Advancing cam timing [message #260473 is a reply to message #260470] |
Fri, 29 August 2014 16:58 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Jim,
IIRC the Cloyes set allows you to advance or retard the cam 4° and advancing the cam timing will lower the torque curve by about
300-400 rpm from the zero setting.
I have NO idea how it would effect fuel mileage.
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
USA '75 Avion - Double Trouble TZE365V100426
AUS '75 Avion - The Blue Streak TZE365V100428
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of James Hupy
Sent: Friday, August 29, 2014 4:17 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Advancing cam timing
You MIGHT gain a slight increase in vacuum by advancing 4°. Fuel economy is
largely determined by how far open the throttle plates are. Obviously,
steady state 60 mph will achieve a bit more fuel mileage than 70 mph. Wheel
alignment, tire pressures, terrain, road surface, all play a part as well.
"Jack Rabbit" starts where the secondaries are open are a no no if you seek
mileage. If you average 8+ mpg currently, I think you are in the ball park
as far as engine tune up is concerened. You might try sneaking up
(advance) ignition timing by a couple of degrees. If you or your
significant other detect any pinging under steady hard pull, retard it
until you can not. Pinging is a big no no. Remember this, if you run no
alcohol fuel, you will see an increase in fuel economy.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Aug 29, 2014 1:51 PM, "Sean Kidd" wrote:
> Thanks Jim, My 455 runs 67 mph at about 3000 rpm, headers, quadrajet,
> blocked iron manifold, olds "J" heads, std size valves/springs, OEM air
> cleaner,
> Patterson dizzy, I did not degree the cam, just assembled with the
> alignment marks. The only thing I'm looking for would be better
> economy...highway
> driving. I drive via my vacuum gauge, trying to keep it "in the green" as
> much as possible. I achieved 9.5 mpg between virginia beach and Delaware
> running on rt 113? About 50 mph average and lots of stop lights. I have
> to remind myself that I'm not in a hurry, and I'm not in my MINI Cooper S.
> 8)
>
> --
> Sean and Stephanie
> 73 Ex-CanyonLands 26' #317 "Oliver"
> Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD
> Honda 6500 inverter gen.
>
> Colonial Travelers
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Advancing cam timing [message #260478 is a reply to message #260475] |
Fri, 29 August 2014 17:07 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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If I was going into the front of the engine anyway, I might consider
advancing the cam. Otherwise, I wouldn't consider removing all the "junk"
from up there & replacing it for the likely difference.
JMHO,
Ken H.
On Fri, Aug 29, 2014 at 6:03 PM, Sean Kidd wrote:
> My gut tells me cruising rpm at or near peak torque would be optimum. I
> guess I'll look up some of the dyno's members have posted and make an
> educated guess.
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Advancing cam timing [message #260479 is a reply to message #260473] |
Fri, 29 August 2014 17:10 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Rob, yes, BUT. You have to take into account all the variables. Where is
the keyway machined into the crank? Where are the sprocket teeth relative
to the hobbing pin on the cam? Where is the keyways cut into the crank gear
relative to the key in the crank and tdc? etc, etc. All that stuff was done
by humans somewhere between hangover monday, and week end anticipation
friday. That is why I asked Sean if he degreed the cam in. I have seen
stock GM parts so far out that I had to slip the timing chain one tooth to
get it close. Just sayin'. If all the stars and planets happen to align on
assembly day, what you say can be true. Odds are, based on my experience,
it is far more likely to be wrong by 7 or 8 degrees than it is to be right.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Fri, Aug 29, 2014 at 2:58 PM, Rob Mueller
wrote:
> Jim,
>
> IIRC the Cloyes set allows you to advance or retard the cam 4° and
> advancing the cam timing will lower the torque curve by about
> 300-400 rpm from the zero setting.
>
> I have NO idea how it would effect fuel mileage.
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> USAussie - Downunder
> USA '75 Avion - Double Trouble TZE365V100426
> AUS '75 Avion - The Blue Streak TZE365V100428
>
> -----Original Message-----
> From: gmclist-bounces@temp.gmcnet.org [mailto:
> gmclist-bounces@temp.gmcnet.org] On Behalf Of James Hupy
> Sent: Friday, August 29, 2014 4:17 PM
> To: gmclist@temp.gmcnet.org
> Subject: Re: [GMCnet] Advancing cam timing
>
> You MIGHT gain a slight increase in vacuum by advancing 4°. Fuel economy is
> largely determined by how far open the throttle plates are. Obviously,
> steady state 60 mph will achieve a bit more fuel mileage than 70 mph. Wheel
> alignment, tire pressures, terrain, road surface, all play a part as well.
> "Jack Rabbit" starts where the secondaries are open are a no no if you seek
> mileage. If you average 8+ mpg currently, I think you are in the ball park
> as far as engine tune up is concerened. You might try sneaking up
> (advance) ignition timing by a couple of degrees. If you or your
> significant other detect any pinging under steady hard pull, retard it
> until you can not. Pinging is a big no no. Remember this, if you run no
> alcohol fuel, you will see an increase in fuel economy.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
> On Aug 29, 2014 1:51 PM, "Sean Kidd" wrote:
>
>> Thanks Jim, My 455 runs 67 mph at about 3000 rpm, headers, quadrajet,
>> blocked iron manifold, olds "J" heads, std size valves/springs, OEM air
>> cleaner,
>> Patterson dizzy, I did not degree the cam, just assembled with the
>> alignment marks. The only thing I'm looking for would be better
>> economy...highway
>> driving. I drive via my vacuum gauge, trying to keep it "in the green" as
>> much as possible. I achieved 9.5 mpg between virginia beach and Delaware
>> running on rt 113? About 50 mph average and lots of stop lights. I have
>> to remind myself that I'm not in a hurry, and I'm not in my MINI Cooper
> S.
>> 8)
>>
>> --
>> Sean and Stephanie
>> 73 Ex-CanyonLands 26' #317 "Oliver"
>> Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1
> LSD
>> Honda 6500 inverter gen.
>>
>> Colonial Travelers
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Advancing cam timing [message #260482 is a reply to message #260480] |
Fri, 29 August 2014 18:05 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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That was the case when I asked about the cam I'm running in the Cad500.
Ken H.
On Fri, Aug 29, 2014 at 6:33 PM, Larry wrote:
> Be careful. Some aftermarket cams come with 2-4* of advance built into
> them. Another 4* could be way to much. Find out what cam it is and check
> with the cam builder as to the built in advance before you go messing
> with it. JWID
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Advancing cam timing [message #260492 is a reply to message #260479] |
Sat, 30 August 2014 09:00 |
|
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Jim,
Agree with all your points; my intent was to explain to non gear heads what the effect of advancing the cam had on the engine.
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
USA '75 Avion - Double Trouble TZE365V100426
AUS '75 Avion - The Blue Streak TZE365V100428
-----Original Message-----
From: James Hupy
Rob, yes, BUT. You have to take into account all the variables. Where is
the keyway machined into the crank? Where are the sprocket teeth relative
to the hobbing pin on the cam? Where is the keyways cut into the crank gear
relative to the key in the crank and tdc? etc, etc. All that stuff was done
by humans somewhere between hangover monday, and week end anticipation
friday. That is why I asked Sean if he degreed the cam in. I have seen
stock GM parts so far out that I had to slip the timing chain one tooth to
get it close. Just sayin'. If all the stars and planets happen to align on
assembly day, what you say can be true. Odds are, based on my experience,
it is far more likely to be wrong by 7 or 8 degrees than it is to be right.
Jim Hupy
Salem, OR
78 GMC Royale 403
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Advancing cam timing [message #260494 is a reply to message #260492] |
Sat, 30 August 2014 09:28 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Rob, I was not arguing with you at all. There are so many variables in this
deal, I was just trying to protect my butt from all the rail birds out
there who have little or no experience with the installation of camshafts,
custom or factory. Seems that there are a few more lurkers out in GMC land
lately, that are like a baby bird. All mouth and asshole with no substance
in between the two. (Grin) I would love to give answers like Gene Fisher
does. Just a link, folks, just a link.
Jim Hupy
On Aug 30, 2014 7:00 AM, "Rob Mueller" wrote:
> Jim,
>
> Agree with all your points; my intent was to explain to non gear heads
> what the effect of advancing the cam had on the engine.
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> USAussie - Downunder
> USA '75 Avion - Double Trouble TZE365V100426
> AUS '75 Avion - The Blue Streak TZE365V100428
>
> -----Original Message-----
> From: James Hupy
>
> Rob, yes, BUT. You have to take into account all the variables. Where is
> the keyway machined into the crank? Where are the sprocket teeth relative
> to the hobbing pin on the cam? Where is the keyways cut into the crank gear
> relative to the key in the crank and tdc? etc, etc. All that stuff was done
> by humans somewhere between hangover monday, and week end anticipation
> friday. That is why I asked Sean if he degreed the cam in. I have seen
> stock GM parts so far out that I had to slip the timing chain one tooth to
> get it close. Just sayin'. If all the stars and planets happen to align on
> assembly day, what you say can be true. Odds are, based on my experience,
> it is far more likely to be wrong by 7 or 8 degrees than it is to be right.
> Jim Hupy
> Salem, OR
> 78 GMC Royale 403
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Advancing cam timing [message #260495 is a reply to message #260492] |
Sat, 30 August 2014 09:20 |
Sammy Williams
Messages: 522
Registered: August 2010
Karma: -2
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Senior Member |
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Personally i'd consider this: Leave the engine alone. It runs. It runs
well. reducing weight and changing driving style will yield some savings in
fuel, and I'd imagine far more then just changing cam degrees. If your able
too, and wish to change your shelving to aluminum (overhead cabinets) If
your not using the stove in the kitchen, replace it with a unit you would
use (like a convection oven/microwave) Ditch the other microwave then. Do
you really need all that junk on a 2 day trip? If not, do not pack heavy.
If your gonna full time, consider travelling light. Take that you ill use,
not all the trinkets you want on a spur of the moment.
Lastly: consider QUALITY fuel-- the good stuff from top line gas vendors
Use the octane rating your engine's maker calls for if possible avoid
alcohol gas, if you cannot, use a gas stabilizer or what I call "octane
booster."
Quality fuel, optimum tuning not driving like a madman and not carrying 12
elephants WILL improve your mileage.
Remember its the TRIP, not the destination that makes a LOT of fun in the
GMC. :)
S. Williams
On Sat, Aug 30, 2014 at 9:00 AM, Rob Mueller
wrote:
> Jim,
>
> Agree with all your points; my intent was to explain to non gear heads
> what the effect of advancing the cam had on the engine.
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> USAussie - Downunder
> USA '75 Avion - Double Trouble TZE365V100426
> AUS '75 Avion - The Blue Streak TZE365V100428
>
> -----Original Message-----
> From: James Hupy
>
> Rob, yes, BUT. You have to take into account all the variables. Where is
> the keyway machined into the crank? Where are the sprocket teeth relative
> to the hobbing pin on the cam? Where is the keyways cut into the crank gear
> relative to the key in the crank and tdc? etc, etc. All that stuff was done
> by humans somewhere between hangover monday, and week end anticipation
> friday. That is why I asked Sean if he degreed the cam in. I have seen
> stock GM parts so far out that I had to slip the timing chain one tooth to
> get it close. Just sayin'. If all the stars and planets happen to align on
> assembly day, what you say can be true. Odds are, based on my experience,
> it is far more likely to be wrong by 7 or 8 degrees than it is to be right.
> Jim Hupy
> Salem, OR
> 78 GMC Royale 403
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Advancing cam timing [message #260496 is a reply to message #260494] |
Sat, 30 August 2014 09:34 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Crap, put my foot in it again, didn't I. Someday I will learn to see where
my message is headed BEFORE I hit the send key. I thought I was sending
that off net to Rob Mueller. Sorry if I offended anyone with my choice of
consonants and vowels.
Jim Hupy
On Aug 30, 2014 7:28 AM, "James Hupy" wrote:
> Rob, I was not arguing with you at all. There are so many variables in
> this deal, I was just trying to protect my butt from all the rail birds out
> there who have little or no experience with the installation of camshafts,
> custom or factory. Seems that there are a few more lurkers out in GMC land
> lately, that are like a baby bird. All mouth and asshole with no substance
> in between the two. (Grin) I would love to give answers like Gene Fisher
> does. Just a link, folks, just a link.
> Jim Hupy
> On Aug 30, 2014 7:00 AM, "Rob Mueller" wrote:
>
>> Jim,
>>
>> Agree with all your points; my intent was to explain to non gear heads
>> what the effect of advancing the cam had on the engine.
>>
>> Regards,
>> Rob M.
>> The Pedantic Mechanic
>> USAussie - Downunder
>> USA '75 Avion - Double Trouble TZE365V100426
>> AUS '75 Avion - The Blue Streak TZE365V100428
>>
>> -----Original Message-----
>> From: James Hupy
>>
>> Rob, yes, BUT. You have to take into account all the variables. Where is
>> the keyway machined into the crank? Where are the sprocket teeth relative
>> to the hobbing pin on the cam? Where is the keyways cut into the crank
>> gear
>> relative to the key in the crank and tdc? etc, etc. All that stuff was
>> done
>> by humans somewhere between hangover monday, and week end anticipation
>> friday. That is why I asked Sean if he degreed the cam in. I have seen
>> stock GM parts so far out that I had to slip the timing chain one tooth to
>> get it close. Just sayin'. If all the stars and planets happen to align on
>> assembly day, what you say can be true. Odds are, based on my experience,
>> it is far more likely to be wrong by 7 or 8 degrees than it is to be
>> right.
>> Jim Hupy
>> Salem, OR
>> 78 GMC Royale 403
>>
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
>
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| Re: [GMCnet] Advancing cam timing [message #260498 is a reply to message #260496] |
Sat, 30 August 2014 09:39 |
Olly Schmidt
Messages: 1265
Registered: February 2014
Location: Germany and Scottsville, ...
Karma: 8
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Senior Member |
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James,
on the contrary, I had to forward your choice of words and bird remarks
right away to a friend of mine, as a very fitting analogy.
:D
--
Best regards
Peer Oliver Schmidt
PGP Key ID: 0x83E1C2EA
'76a Eleganza II, VA
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Best regards
Olly Schmidt
PGP Key ID: 0x18a9 3a1f 4196 bf22
'76a Eleganza II, VA
'73 Sequoia, SH, Germany
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| Re: [GMCnet] Advancing cam timing [message #260501 is a reply to message #260496] |
Sat, 30 August 2014 11:10 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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James Hupy wrote on Sat, 30 August 2014 10:34Crap, put my foot in it again, didn't I. Someday I will learn to see where my message is headed BEFORE I hit the send key. I thought I was sending that off net to Rob Mueller. Sorry if I offended anyone with my choice of consonants and vowels.
Jim Hupy
Well, yes there is no like key here, but we do have sigfiles. Over at FB, you get a lot of questions with no reference information.
Rob, Jim and anybody else interested.....
Now, to the subject at hand.
What I most recall is the work up on the Chrysler V-8 318 & 360. We were looking at changes to the intake manifolds and so there was a lot of dithering with a well developed engine. As such, it became very clear that the torque peak speed could be shifted with a manifold change, but changing the cam timing from there essentially "rocked" the torque curve around the torque peak (also the peak of volumetric efficiency).
As a multi-decade engine development guy, I an tell you for a matter of fact that changing the cam timing will have little effect at moderate manifold pressures - Meaning road load vacuum. I actually ran a test for a company that was marketing a centrifugal cam timing controller to a fleet to save fuel. Well, it could improve the shape of the WOT power curve a little, but at less than WOT (like driving) it made little difference in the delivery vans that were the target.
In engine build, I would always provide a timing for #1 intake. Many of the cams we got had a specification and many times the stock cam drive was not dead on. So, we also had a box of offset keys. We also did runs with the cam intentional offset. This is pretty easy on a lab engine as everything is marked and all the build data is unambiguously recorded. An experimental engine technician (aka dyno-jock) could go undress the front of most engines and swap in a different key in less than an hour. Some things get real easy when an engine is alone in the middle of a large room.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Advancing cam timing [message #260533 is a reply to message #260464] |
Sat, 30 August 2014 17:48 |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma: 3
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Senior Member |
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SeanKidd wrote on Fri, 29 August 2014 14:04GMCNet,
When I rebuilt engine (455) I installed a Melling MTO-1 high torque cam and cloyes double roller timing chain with adjustable (3 position) keyway. I installed the cam "straight up" with the alignment marks. The engine runs well, good vacuum (19" at idle, 16" in gear) and I've been averaging just about 8 mpg...with my 3.70:1 FD
I plan on replacing my radiator soon, what , if any are the advantages to advancing the cam timing (while I have the radiator out(more room))
Sean,
There have been great comments on the advance issue. One thing I have read, not experienced, I am very careful to add, is that because the main goal of engine design in 1970, or soon after, was not power, dependability, efficiency, but meeting emissions regulations and because of that the cams were retarded from ideal 4 degrees. Therefore, if some cams were advanced 4 degrees, you might be back at stock, where it is said additional power was found along with the sweet spot in horsepower for passenger cars, arrived at during those days when emissions wasn't such a large consideration.
Some measurement and reporting on your results would be enlightening. Not having been on the spot, I can't vouch for this, besides quoting what I remember reading. I just checked in an Oldsmobile performance book and no mention of this, only "trust your cam supplier, and degree anyway to make sure."
Best,
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
[Updated on: Sun, 31 August 2014 19:44] Report message to a moderator |
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| Re: [GMCnet] Advancing cam timing [message #260535 is a reply to message #260494] |
Sat, 30 August 2014 18:32 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Jim,
I know you weren't arguing with me and even if you were I CAN TAKE IT. ;-)
I agree with the baby bird statement as well!
In "Hobokenese" we'd say they didn't know S#!T from SHINOLEA! ;-)
Regards,
Rob M.
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of James Hupy
Rob, I was not arguing with you at all. There are so many variables in this
deal, I was just trying to protect my butt from all the rail birds out
there who have little or no experience with the installation of camshafts,
custom or factory. Seems that there are a few more lurkers out in GMC land
lately, that are like a baby bird. All mouth and asshole with no substance
in between the two. (Grin) I would love to give answers like Gene Fisher
does. Just a link, folks, just a link.
Jim Hupy
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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