| Final Drive Ratio Final Decision Rationale [message #237618] |
Mon, 27 January 2014 10:37  |
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SeanKidd
Messages: 747
Registered: June 2012
Location: Northern Neck Virginia
Karma: 4
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I have the stock 3.07...and cannot back-up my driveway without a running start...I upgrading Stephanie's '66 Mustang to a 3.20:1 from the paltry 2.83:1 and realized marked seat of the pants improvement in torque and acceleration....Among other deciding factors, what was everyone's rationale for choosing their FD ratio? 3.55 or 3.77 or...
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: Mon, 27 January 2014 12:16] Report message to a moderator |
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| Re: [GMCnet] Final Drive Ratio Final Decision Rational [message #237620 is a reply to message #237618] |
Mon, 27 January 2014 10:42  |
Jeff Marten
Messages: 199
Registered: August 2013
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Mine has the 3.21; installed by the PO. I can't give any real feel for benefit over the stock 3.07 as this is the only GMC I've driven.
At some point I may upgrade to the lower ratio chain drive.
> To: gmclist@temp.gmcnet.org
> From: fiatkidd@yahoo.com
> Date: Mon, 27 Jan 2014 10:37:52 -0600
> Subject: [GMCnet] Final Drive Ratio Final Decision Rational
>
>
>
> I have the stock 3.07...and cannot back-up my driveway without a running start...I upgrading Stephanie's '66 Mustang to a 3.20:1 from the paltry 2.83:1 and realized marked seat of the pants improvement in torque and acceleration....Among other deciding factors, what was everyone's rational for choosing their FD ratio? 3.55 or 3.77 or...
> --
> Sean and Stephanie
> 73 Ex-CanyonLands 26' #317 "Oliver"
> Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms,
> Fluorescent Mineral Capital of the World, New Jersey
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1985 Gulf Stream 34' Sun Stream
1964 Falcon 'Vert
1980 Bradley GTE
1999 Chevy Tahoe
2005 Saab 93 Aero
1987 Suzuki Intruder 1400
1978 Glastron/Carlson CV23
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| Re: [GMCnet] Final Drive Ratio Final Decision Rational [message #237624 is a reply to message #237623] |
Mon, 27 January 2014 11:00 |
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SeanKidd
Messages: 747
Registered: June 2012
Location: Northern Neck Virginia
Karma: 4
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| WD0AFQ wrote on Mon, 27 January 2014 11:56 |
Sean, we have the 355 from Jim K. The warranty is one reason we have this one but also the get up and go from a stop will thrill you. Makes same difference as on the stang. It will give you the backing power you need to pull the driveway. Teri really gets aggravated when I floor the thing and then run up on the stop sign before shoving the reaction brake pedal down and throwing everything onto the floor. It goes, it stops.
I have the 300 rear end in the 65 fastback. That came with auto A code. I have a top loader in now but have a t 5 ready for install. I am not changing the final drive in this car.
Dan
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I was trying to find the 3.5:1 left overs from the comet station wagon...we wanted to maintain the 4-lugs. The big cam, valves and triple offy really makes a lot of torque in the 6
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: Mon, 27 January 2014 11:02] Report message to a moderator |
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| Re: Final Drive Ratio Final Decision Rational [message #237627 is a reply to message #237618] |
Mon, 27 January 2014 11:15 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| SeanKidd wrote on Mon, 27 January 2014 11:37 |
I have the stock 3.07...and cannot back-up my driveway without a running start...I upgrading Stephanie's '66 Mustang to a 3.20:1 from the paltry 2.83:1 and realized marked seat of the pants improvement in torque and acceleration....Among other deciding factors, what was everyone's rational for choosing their FD ratio? 3.55 or 3.77 or...
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Sean,
This is really a simple situation. GM didn't have the 3.42 that they later determined was the right FD for our coaches. So they shipped the closest that they had. Not only is the 3.07 just barely acceptable for a light coach doing 70 (the pre-Arab oil embargo speed limit), as soon as you slow down, you will fall off the low end of the engine's torque curve. This is not desirable for a whole lot of reasons I will not go into here and now.
The fact is that with our 9500# coach, it is problematic even on flat ground. My seat of the pants dyno tells me that the torque peak is in the 2400 region, and 60mph is only about 19~2000. The torque converter isn't even completely out of stall yet.
One of the big things on my list is a 3.55. If our coach was heavier, I would go for the 3.77. I already know the the cruise would love it.
If you read the reviews here, you will find that there is no fuel consumption increase with the higher numerical final drive.
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: Final Drive Ratio Final Decision Rational [message #237632 is a reply to message #237629] |
Mon, 27 January 2014 12:19 |
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SeanKidd
Messages: 747
Registered: June 2012
Location: Northern Neck Virginia
Karma: 4
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| WD0AFQ wrote on Mon, 27 January 2014 12:33 |
| Dan Borlase wrote on Mon, 27 January 2014 11:21 |
The general conscience is...455cid-355...403cid-370 (411 if towing heavy weight)
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Yep, what our friends above have stated. This is a very worthwhile upgrade for many of us. I even dropped a broken governor gear down into Dans, when we were along side a New Mexico interstate one morning. He never complained. 
Dan
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Is there an issue with a 3.70:1 in a 455 (regarding sweet spot on the curve) BTW I'm running a Melling MTO-1 cam if that matters.
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: Final Drive Ratio Final Decision Rationale [message #237777 is a reply to message #237618] |
Tue, 28 January 2014 09:00 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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| SeanKidd wrote on Mon, 27 January 2014 09:37 |
I have the stock 3.07...and cannot back-up my driveway without a running start...I upgrading Stephanie's '66 Mustang to a 3.20:1 from the paltry 2.83:1 and realized marked seat of the pants improvement in torque and acceleration....Among other deciding factors, what was everyone's rationale for choosing their FD ratio? 3.55 or 3.77 or...
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Sean,
I went with one of Jim K's 3.70 final drives in my 455 equipped 26 footer. I live in the Southwest where there is very little flat ground and I tow almost all the time. The 3.70 gives me a lot better throttle response off the line while keeping the engine in the torque band. It also is easier on the transmission.
Most 3/4 ton trucks (7500# -8500# GVW) of our motorhome's era had 4.10 rear end ratios and most 1-ton's (10,000# - 10,500# GVW) had 4.56 ratios. Most used similar sized tires as well. It only makes sense to have as low (high numerically) a ratio as you can get, within reason.
I usually don't drive much over 65 anyway because fuel economy is usually more important to me than time. It has made a big difference in the drivability of the coach. Highly recommended.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Final Drive Ratio Final Decision Rationale [message #237784 is a reply to message #237618] |
Tue, 28 January 2014 09:35 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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My Royale came with a Cinnabar 3.42 from my beloved PO. That seems to be a really good compromise between cruising RPM and acceleration / climbing. It seems to always be in the sweet spot of the torque curve on the highway, and climbs and accelerates as well as I'd have any right to expect, except at high altitude, which will hopefully be much improved when I finally get my TBFI installed.
But I suppose there's not much of a down side to going with a higher numerical ratio... seems like it doesn't really hurt gas mileage, and should help if you pull a towd or trailer (or spend a lot of time on low-speed roads).
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: Final Drive Ratio Final Decision Rationale [message #237788 is a reply to message #237618] |
Tue, 28 January 2014 09:52 |
Ultravan Owners
Messages: 443
Registered: March 2013
Karma: 0
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Here is a calculator you can use/play with to see what your RPMs might be.
http://www.ringpinion.com/Calculators/Calc_RPM.aspx
Using this calculator I put the following numbers in.
GR = 3.07 Tire Height = 31(complete guess) and Speed = 65 the RPMs for an Auto came to 2221RPMs
The only change was GR
GR = 3.55 Tire Height = 31(complete guess) and Speed = 65 the RPMs for an Auto came to 2568RPMs
Again the only change was GR
GR = 3.70 Tire Height = 31(complete guess) and Speed = 65 the RPMs for an Auto came to 2677RPMs
Now I know if you had a more detailed calculator, with AT ratio too, that the numbers could be different. At least this will give you a ballpark idea.
The calculator I perfer was used on PowerBlock TV, but I could not find it fast enough, before I had to leave the house.
That calculator allows you to put your engine in the RPM range you are looking for at the speeds you plan to use it at.
Tony (Ontario Canada)
Marie and I are blessed to have had a 2nd chance to buy our farm.
Still hoping and more importantly praying to be able to build a garage.
Our 1970 Ultravan #520 has an Olds Toronado 455 in back.
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| Re: [GMCnet] Final Drive Ratio Final Decision Rational [message #237824 is a reply to message #237623] |
Tue, 28 January 2014 14:14 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Too many holeshots and powershifts to second have nearly done for my T5. Soon as I get the engine in my 05 Ranger, the toad trans goes to my rebuilder. It's overdue.
--johnny
From: Dan Gregg <gregg_dan@hotmail.com>
To: gmclist@temp.gmcnet.org
Sent: Monday, January 27, 2014 11:56 AM
Subject: Re: [GMCnet] Final Drive Ratio Final Decision Rational
Sean, we have the 355 from Jim K. The warranty is one reason we have this one but also the get up and go from a stop will thrill you. Makes same difference as on the stang. It will give you the backing power you need to pull the driveway. Teri really gets aggravated when I floor the thing and then run up on the stop sign before shoving the reaction brake pedal down and throwing everything onto the floor. It goes, it stops.
I have the 300 rear end in the 65 fastback. That came with auto A code. I have a top loader in now but have a t 5 ready for install. I am not changing the final drive in this car.
Dan
--
Dan & Teri Gregg
Dexter, Mo.
http://danandteri.blogspot.com/
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Final Drive Ratio Final Decision Rationale [message #237842 is a reply to message #237784] |
Tue, 28 January 2014 17:24 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Mark,
It has been noted here that "supposedly" a ratio of 3.42 was "on the design boards at GMC" when GM pulled the plug. Whether that is
true or not I have NO idea!
BTW as Mr. Erf says; "8 to 10."
Regards,
Rob M.
Sydney, Australia
-----Original Message-----
From: Mark
My Royale came with a Cinnabar 3.42 from my beloved PO. That seems to be a really good compromise between cruising RPM and
acceleration / climbing. It seems to always be in the sweet spot of the torque curve on the highway, and climbs and accelerates as
well as I'd have any right to expect, except at high altitude, which will hopefully be much improved when I finally get my TBFI
installed.
But I suppose there's not much of a down side to going with a higher numerical ratio... seems like it doesn't really hurt gas
mileage, and should help if you pull a towd or trailer (or spend a lot of time on low-speed roads).
--
Mark
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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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