Home » Public Forums » GMCnet » [GMCnet] Climbing
| [GMCnet] Climbing [message #116243] |
Wed, 23 February 2011 15:16  |
Mark Stevens
Messages: 9
Registered: February 2011
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Hi,
My '75 GMC has the 455 Olds and standard transmission. We find ourselves
trying to plan trips around not having long climbs as ours doesn't do so
great. It doesn't overheat, or break, it's just slooowwww.
I would like opinions on the mod with the most bang for the buck in
achieving more climbing power.
Thanks,
Mark
Boise
'75 Palm Beach
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| Re: [GMCnet] Climbing [message #116245 is a reply to message #116244] |
Wed, 23 February 2011 15:29  |
thorndike
Messages: 406
Registered: January 2011
Location: Conifer, Colorado
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Is there a way to identify which final drive the P.O. may have installed?
Robert Peesel
1976 Royale 26'
Side Dry Bath
Conifer, Colorado
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| Re: [GMCnet] Climbing [message #116249 is a reply to message #116243] |
Wed, 23 February 2011 15:33 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Jim K sells the gears and reports that MPG does not decrease at all, and may increase slightly because the engine is running in it torque peak.
I can't get to his website right now - it might be down - but look at the reduction gears he sells.
Larry Davick
Fremont, California
The Mystery Machine
'76 (ish) Palm Beach
----- Original Message -----
From: "Mark Stevens" <bridgeguitar@gmail.com>
To: gmclist@temp.gmcnet.org
Sent: Wednesday, February 23, 2011 1:24:44 PM
Subject: Re: [GMCnet] Climbing
Dan,
Does this kill your mileage...not that it's that great anyway?! : )
Mark
On Wed, Feb 23, 2011 at 2:24 PM, Dan Gregg <gregg_dan@hotmail.com> wrote:
>
>
> Mark, providing everything is in order, the final drive will change your
> ability to climb in a GMC. I would think the 355 would do that for you and
> be your "biggest bang for the buck".
> Dan,
> almost 4 yrs. on a 355
> --
> Dan & Teri Gregg
>
> http://danandteri.blogspot.com/
>
>
>
>
> _______________________________________________
> GMCnet mailing list
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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: [GMCnet] Climbing [message #116250 is a reply to message #116243] |
Wed, 23 February 2011 15:58 |
Rick Williams
Messages: 256
Registered: July 2004
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Mark
In addition to the mechanical suggestions you will receive, travel with empty water and waste water tanks and as little fuel as possible. Do not tow anything. Remodel the interior using light weight materials and leave most everything at home.
I have done some of these. I see 1 mpg difference when not towing and definitely more power. I can not quantify whether the other things work but it makes sense that less weight is better.
Rick
Rick Williams
Bliss, Michigan
1978 Eleganza II
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| Re: [GMCnet] Climbing [message #116251 is a reply to message #116249] |
Wed, 23 February 2011 15:55 |
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hnielsen2
Messages: 1434
Registered: February 2004
Location: Alpine CA
Karma: 0
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No change in mileage and we run 3:70's
Howard
----- Original Message -----
From: "Larry Davick" <ljdavick@comcast.net>
To: <gmclist@temp.gmcnet.org>
Sent: Wednesday, February 23, 2011 1:33 PM
Subject: Re: [GMCnet] Climbing
> Jim K sells the gears and reports that MPG does not decrease at all, and
> may increase slightly because the engine is running in it torque peak.
>
> I can't get to his website right now - it might be down - but look at the
> reduction gears he sells.
>
> Larry Davick
> Fremont, California
> The Mystery Machine
> '76 (ish) Palm Beach
>
> ----- Original Message -----
> From: "Mark Stevens" <bridgeguitar@gmail.com>
> To: gmclist@temp.gmcnet.org
> Sent: Wednesday, February 23, 2011 1:24:44 PM
> Subject: Re: [GMCnet] Climbing
>
> Dan,
>
> Does this kill your mileage...not that it's that great anyway?! : )
>
> Mark
>
> On Wed, Feb 23, 2011 at 2:24 PM, Dan Gregg <gregg_dan@hotmail.com> wrote:
>
>>
>>
>> Mark, providing everything is in order, the final drive will change your
>> ability to climb in a GMC. I would think the 355 would do that for you
>> and
>> be your "biggest bang for the buck".
>> Dan,
>> almost 4 yrs. on a 355
>> --
>> Dan & Teri Gregg
>>
>> http://danandteri.blogspot.com/
>>
>>
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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> _______________________________________________
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All is well with my Lord
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| Re: [GMCnet] Climbing [message #116252 is a reply to message #116243] |
Wed, 23 February 2011 16:06 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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| Mark Stevens wrote on Wed, 23 February 2011 14:16 |
Hi,
My '75 GMC has the 455 Olds and standard transmission. We find ourselves
trying to plan trips around not having long climbs as ours doesn't do so
great. It doesn't overheat, or break, it's just slooowwww.
I would like opinions on the mod with the most bang for the buck in
achieving more climbing power.
Thanks,
Mark
Boise
'75 Palm Beach
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Mark--a standard GMC isn't always a bad climber and it's all relative but I would check a few basics first:
Is the throttle lever at the carburetor opening all the way when the pedal is to the floor (many pedals are bent)
Are the secondaries opening when the pedal is floored (many are locked out for various reasons such as the choke not fully opening or the linkage is mis-adjusted.
Is the transmission downshifting when required--many downshift switches are mis-adjusted or not working
Is your base timing, vacuum advance and centrifugal advance working
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Climbing [message #116254 is a reply to message #116245] |
Wed, 23 February 2011 16:06 |
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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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Robert,
There are two types of final drives that can be installed in a GMC.
The OEM is a spur gear final drive which has a gear ratio of 3.07 to 1.
There are 10 bolts that hold the cover on. After market gear ratios are
available for this final drive. Unless the PO identified the OEM final drive
externally in some way there is no way to determine the gear ratio.
The second is a planetary gear differential which has a ratio of 3.21 to 1.
There are 8 bolts that hold the cover on. As far as I know there are no
aftermarket gear ratios available for this final drive.
Here's a link to an album Larry Weidner posted on the photosite which shows
the differences:
http://www.gmcmhphotos.com/photos/showgallery.php?cat=4399
Below is a link to a chart that Ken Henderson put together showing the
various ratios and sources for ring and pinion gear sets to achieve those
ratios in the OEM differential.
http://www.gmcmhphotos.com/photos/data/5124/overall_drive_ratios.pdf
Here is a link to Jim K's website showing the ratios he provides:
http://www.appliedgmc.com/prod.itml/icOid/606
Here's a link to the limited slip device Jim K provides. I can be installed
in the OEM final drive only, it cannot be installed in a planetary final
drive.
http://www.appliedgmc.com/prod.itml/icOid/876
Regards,
Rob M.
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Robert Peesel
Sent: Thursday, February 24, 2011 8:30 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Climbing
Is there a way to identify which final drive the P.O. may have installed?
--
Robert Peesel
1976 Royale 26'
Side Dry Bath
Sterling, Va
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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] Climbing [message #116264 is a reply to message #116246] |
Wed, 23 February 2011 16:44 |
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WD0AFQ
Messages: 7111
Registered: November 2004
Location: Dexter, Mo.
Karma: 207
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Senior Member |
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| Mark Stevens wrote on Wed, 23 February 2011 15:24 |
Dan,
Does this kill your mileage...not that it's that great anyway?! : )
Mark
On Wed, Feb 23, 2011 at 2:24 PM, Dan Gregg <gregg_dan@hotmail.com> wrote:
>
>
> Mark, providing everything is in order, the final drive will change your
> ability to climb in a GMC. I would think the 355 would do that for you and
> be your "biggest bang for the buck".
> Dan,
> almost 4 yrs. on a 355
> --
> Dan & Teri Gregg
>
> http://danandteri.blogspot.com/
>
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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Not really Mark. I slowed down from my normal 70 mph. But, I drive using my vacuum gauge for best fuel mileage. AND, I do not like seeing my tach say 3,000 at 70 mph.
dan
3 In Stainless Exhaust Headers
One Ton All Discs/Reaction Arm
355 FD/Quad Bag/Alum Radiator Manny Tran/New eng.
Holley EFI/10 Tire Air Monitoring System
Solarized Coach/Upgraded Windows
Satelite TV/On Demand Hot Water/3Way Refer
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| Re: [GMCnet] Climbing [message #116294 is a reply to message #116271] |
Wed, 23 February 2011 21:09 |
John Sharpe
Messages: 489
Registered: February 2006
Location: Texas
Karma: 1
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Senior Member |
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I think we need to remember a little caution here. Don't lug the engine. If pedal is on the floor don't let the RPMs fall below about 2400. If it does you need to manually shift to a lower gear to keep from causing bearing failure. Remember to shift out when your speed increases.
Lower gear ratios and combinations of chain-drives and switch pitches increases engine rpm. I wouldn't run a 455 above 3200 and 3000 would probably be better for an extended distance. 403s can tolerate a lot more before they start bending push-rods or coming apart.
John Sharpe
Humble,TX
'78 Eleganza TBI
'89 Spectrum 2000 MPI V-10
'40 Ford Panel Delivery TPI
johnasharpe@gmail.com
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| Re: [GMCnet] Climbing [message #116299 is a reply to message #116294] |
Wed, 23 February 2011 21:45 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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In Marine applications, both work boats and pleasure type, I have quite a
lot of experience with rebuilding and rigging both. It was not uncommon to
see 4500 rpm on lightly loaded boats with jet pumps on shallow draft hulls.
Work boats consistently go from slow speed trolling at about 1200 - 1500 RPM
with reduction drives and props, to over 4000 RPM when traveling. I really
have not seen that much crank, bearing, piston related problems after the
engines are fully broken in. See mostly timing chain, lifter, and camshaft
wear with valve guides sticking and burned valves. These applications
commonly have the problem of the coolant and oil temperatures being too low
when sea water cooling is used. These engines with stable oil and coolant
temperatures in the proper state of tune running at 3500 and below should
last for many years with proper maintenence. Many of the GMCs have
accumulated somewhere around 100,000 miles on the clock since they were new
36 years ago, still on the original engines. Sitting idle in constantly
changing humidity and temperature ranges probably has contributed more to
what accumulated wear they have than running down the road at a steady 2500
RPM. Use them, don't park them. If they break and you have to stirr around
inside one, I can not say it strongly enough, keep the work area very clean.
Just a few small pieces of grit can and does wipe out new bearings and
cranks in the first few minutes of running. If you send a crank out for
machine work, clean the crap out of it when you get it home and be very
carefull to clear out all the drilled passages in the crank. That is where
most of the gritty stuff will hide. Same with cylinder heads, water passages
and oil passages as well as ports. Cleanliness is next to Godliness when it
comes to building engines. Trust me, I have learned this lesson the hard
way.
Jim Hupy
Salem, Or
78 GMC Royale 403
On Wed, Feb 23, 2011 at 7:09 PM, John Sharpe <johnasharpe@earthlink.net>wrote:
>
>
> I think we need to remember a little caution here. Don't lug the engine.
> If pedal is on the floor don't let the RPMs fall below about 2400. If it
> does you need to manually shift to a lower gear to keep from causing bearing
> failure. Remember to shift out when your speed increases.
>
> Lower gear ratios and combinations of chain-drives and switch pitches
> increases engine rpm. I wouldn't run a 455 above 3200 and 3000 would
> probably be better for an extended distance. 403s can tolerate a lot more
> before they start bending push-rods or coming apart.
> --
> John Sharpe
> Humble,TX
> '78 Eleganza TBI
> '89 Spectrum 2000 V-10
> '40 Ford Deluxe TBI
> mailto:johnasharpe@gmail.com
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Climbing [message #116301 is a reply to message #116243] |
Wed, 23 February 2011 22:11 |
bukzin
Messages: 840
Registered: April 2004
Location: North California
Karma: 0
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Senior Member |
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[quote title=Mark Stevens wrote on Wed, 23 February 2011 13:16]Hi,
I would like opinions on the mod with the most bang for the buck in
achieving more climbing power.
Thanks,
Mark
++++++++++++++++++++++++++++++++++++++++++++++++++++
Mine seems to creep up those long pulls.
If you are really looking for 'the most bang for the buck'
you might try what worked for me climbing those big hills,
patience.
Very affordable!
Bukzin
1977 Palm Beach
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| Re: [GMCnet] Climbing [message #116302 is a reply to message #116246] |
Wed, 23 February 2011 22:09 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Mark,
Let me but in.
By going with a lower gear ratio in this case is not going to lower
your mileage for few reasons.
The present ratio is so high, the engine is under load to where the
carburettor is dumping in more fuel to pull the coach.
The engine vacuum is low and the ignition timing is lowered .Yes the
engine is turning fewer RPM, but with lower timing and richer mixture,
it is not performing very well.
Also by looking at the engine torque curve, you'll see that it is not
close to being in the torque curve at the lower RPM.
When you go from the stock 3.07 ratio to 3.55 or 3.70, the engine is
now turning In the torque curve to where it has picked up 12-15 HP.
and now operating at higher vacuum.
Higher vacuum gives the ignition timing few degrees more timing which
in itself increases power and mileage and the carburetor will run
leaner.
End result is power and mileage.
Most people will use the new power and drive little more aggressively
so the mileage levels out and end up to where they will tell me that
the mileage is about the same.
The concept is nothing new or strange. I have few people that are
running the 4.10 ratio in their coach and driving 55mph and claim that
they are getting 12mpg.
I know that driving 55 helps a lot, but the fact that the engine is
turning in the torque curve is why they are doing well.
We have almost 3,000 of these 3.55/3.70 units running and seldom find
anyone complain lower mileage. If they complain, we find that the
distributor is not operating properly or something is wrong with the
carburetor.
On Wed, Feb 23, 2011 at 1:24 PM, Mark Stevens <bridgeguitar@gmail.com> wrote:
> Dan,
>
> Does this kill your mileage...not that it's that great anyway?! : )
>
> Mark
>
> On Wed, Feb 23, 2011 at 2:24 PM, Dan Gregg <gregg_dan@hotmail.com> wrote:
>
>>
>>
>> Mark, providing everything is in order, the final drive will change your
>> ability to climb in a GMC. I would think the 355 would do that for you and
>> be your "biggest bang for the buck".
>> Dan,
>> almost 4 yrs. on a 355
>> --
>> Dan & Teri Gregg
>>
>> http://danandteri.blogspot.com/
>>
>>
>>
>>
>> _______________________________________________
>> 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
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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