Home » Public Forums » GMCnet » 455 recommended FD ratio
| 455 recommended FD ratio [message #166469] |
Mon, 16 April 2012 03:07  |
midlf
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Registered: July 2007
Location: SE Wisc. (Palmyra)
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In another thread it appears the 3.70 FD is favored for the 403 engine. What are the thoughts on the preferred FD ratio for a 455 engine? Would that preference be different if most driving will be flatland with only occasional mountains?
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: [GMCnet] 455 recommended FD ratio [message #166473 is a reply to message #166469] |
Mon, 16 April 2012 07:41  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
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Well, in the Eastern flatland with only the very occasional ride over Monteagle, my 23' does justfine with the 455 and the stock final drive. I'll have the Toadstone clipped on the first of May, I haven't decided whether I'll run over Monteagle or opt for I 65 instead. I don't think it will be a great problem though.
Jury's still out on my PB project. I'll have to decide about nest year prolly.
--johnny
'76 23' transmode norris
'76 palm beach
From: Steve Southworth <midlf@centurytel.net>
To: gmclist@temp.gmcnet.org
Sent: Monday, April 16, 2012 4:07 AM
Subject: [GMCnet] 455 recommended FD ratio
In another thread it appears the 3.70 FD is favored for the 403 engine. What are the thoughts on the preferred FD ratio for a 455 engine? Would that preference be different if most driving will be flatland with only occasional mountains?
--
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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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: 455 recommended FD ratio [message #166475 is a reply to message #166469] |
Mon, 16 April 2012 08:06 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
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Steve,
As someone that finally put a tachometer (cheap digital, but it works), I can tell you that the 3.07 was not a good choice for a 60~65 driving plan (to stretch fuel).
A 3.55 is a very good start, I'm not sure I would go to 3.70 unless I was Emery's neighbor and traveling companion.
An engine wants to be near the torque peak at cruise for a lot of reasons that I don't feel like writing about this morning. On our coach, that seems to be about 2400+/-.
Our 455 is not real unhappy, but it sure does not feel appreciated at ~2200 (heavy end of cruise). If I went to a 3.55, then that would be ~2550 and the engine would be better off with that. A 3.70 in the same condition would be ~2650 and that is still well in the engine's operating band. The 3K+ at 70 will still not be a killer, but the piston velocity will be getting to the high end for longevity. We are trying to stay in the 9+ bracket so we can go other places on 4+$/gal.
JimK (he is an Ornimental Sales Guy) reported he got 9.7 on the way home from Shawnee while running 70~75 with a 3.70, so that can't be all bad. (Problem there, I don't know what engine that coach has.)
If I had the resources, I would pop for a 3.55w/LS in a heartbeat.
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: [GMCnet] 455 recommended FD ratio [message #166483 is a reply to message #166481] |
Mon, 16 April 2012 09:34 |
Neil
Messages: 271
Registered: July 2007
Location: Los Angeles and Magalia, ...
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I have a 455 with a 3.70 LSD. We often tow a big trailer. Being on the left coast we have to climb to go almost anywhere.
I love the 3.70 and can go 70 plus mph no problem.
Neil
76 Eleganza now sold
Los Angeles
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| Re: [GMCnet] 455 recommended FD ratio [message #166489 is a reply to message #166470] |
Mon, 16 April 2012 10:44 |
midlf
Messages: 2212
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| emerystora wrote on Mon, 16 April 2012 04:55 |
Other factors in your decision would be if you pull a toad and also how fast do you drive.
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Good points to keep in mind. We will pull a '95 Sidekick. Generally do the speed limits. (Our thirst for speed was satisfied in our younger days with the Corvette. Been there, done that, gots lots of T shirts.)
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: [GMCnet] 455 recommended FD ratio [message #166490 is a reply to message #166489] |
Mon, 16 April 2012 10:53 |
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WD0AFQ
Messages: 7111
Registered: November 2004
Location: Dexter, Mo.
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| midlf wrote on Mon, 16 April 2012 10:44 |
| emerystora wrote on Mon, 16 April 2012 04:55 |
Other factors in your decision would be if you pull a toad and also how fast do you drive.
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Good points to keep in mind. We will pull a '95 Sidekick. Generally do the speed limits. (Our thirst for speed was satisfied in our younger days with the Corvette. Been there, done that, gots lots of T shirts.)
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Steve,
That being the case, you will be happy with the 355 and 455. I paid for a 355 but my calculations lead me to believe I got a 370. I have a plan in the works to get back closer to what I wanted, 355. The 370 seems to be a perfect match for the 403, as I hear from others. I try to keep my rpms below 3k. That means, with 245-75 tires, I must not run over 68 mph. Most of the time it works, we do a lot of two lanes. We can pull nearly any mountain in high gear, above 50 mph with the Vibe in tow.
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] 455 recommended FD ratio [message #166493 is a reply to message #166490] |
Mon, 16 April 2012 11:23 |
James Hupy
Messages: 6806
Registered: May 2010
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The coach that Jim K drove to Shaunee was equipped with a 403 engine and
3:70 to 1 final drive. The same combination that Miguel Mendez and I and
several others have. It just puts that 403 in a very happy state. Love it.
Jim HUpy
Salem, OR
78 GMC Royale 403
On Mon, Apr 16, 2012 at 8:53 AM, Dan Gregg <gregg_dan@hotmail.com> wrote:
>
>
> midlf wrote on Mon, 16 April 2012 10:44
> > emerystora wrote on Mon, 16 April 2012 04:55
> > > Other factors in your decision would be if you pull a toad and also
> how fast do you drive.
> >
> >
> > Good points to keep in mind. We will pull a '95 Sidekick. Generally do
> the speed limits. (Our thirst for speed was satisfied in our younger days
> with the Corvette. Been there, done that, gots lots of T shirts.)
>
>
> Steve,
> That being the case, you will be happy with the 355 and 455. I paid for a
> 355 but my calculations lead me to believe I got a 370. I have a plan in
> the works to get back closer to what I wanted, 355. The 370 seems to be a
> perfect match for the 403, as I hear from others. I try to keep my rpms
> below 3k. That means, with 245-75 tires, I must not run over 68 mph. Most
> of the time it works, we do a lot of two lanes. We can pull nearly any
> mountain in high gear, above 50 mph with the Vibe in tow.
> Dan
> --
> Dan & Teri Gregg
> Soft White LED Lighting
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> http://danandteri.blogspot.com/
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>
>
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| Re: 455 recommended FD ratio [message #166495 is a reply to message #166469] |
Mon, 16 April 2012 11:34 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
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| midlf wrote on Mon, 16 April 2012 01:07 |
In another thread it appears the 3.70 FD is favored for the 403 engine. What are the thoughts on the preferred FD ratio for a 455 engine? Would that preference be different if most driving will be flatland with only occasional mountains?
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Steve,
I have a 3.70 LS final drive in a '75 coach with a stock 455 (81,000 miles). Living in Tucson, where the elevation at my house is ~2600 ft, we either drive up or down to go anywhere with plenty of ups and downs in between, so I love the 3.70. We also routinely tow a Tracker (3,000#) and occasionally tow a Jeep, on a trailer (~4,000#), so the 3.70 is a real plus for that. I also generally keep my speed under 65 mph in a (misguided?) attempt to get decent gas mileage.
I would think a 3.55 would work well for mostly flatland driving, but I would defer to the expert on this, Jim Kanomata. By comparison, my Jeep Cherokee has 3.55 gears in it but weighs a third what the 26' GMC weighs, so I don't think a 3.70 ratio would be too low for your coach either.
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: 455 recommended FD ratio [message #166503 is a reply to message #166495] |
Mon, 16 April 2012 13:09 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
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| Carl S. wrote on Mon, 16 April 2012 11:34 |
I would think a 3.55 would work well for mostly flatland driving, but I would defer to the expert on this, Jim Kanomata. By comparison, my Jeep Cherokee has 3.55 gears in it but weighs a third what the 26' GMC weighs, so I don't think a 3.70 ratio would be too low for your coach either.
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Oh yeah - JimK will be consulted if I $decide$ to do this now. The whole front frame clip is out and disassembled so I have to give it some thought. Although I have one of the GMC FD change-out gurus close by.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: 455 recommended FD ratio [message #166508 is a reply to message #166503] |
Mon, 16 April 2012 14:18 |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
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What size tires?
The Revcon does 3K at 60 on 16.5 X 9.5 tires. I'm not sure what the final drive is.
I'm also not sure about the RPM on a stock tac but I measured the speed with a GPS.
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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| Re: 455 recommended FD ratio [message #166509 is a reply to message #166469] |
Mon, 16 April 2012 14:24 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
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| midlf wrote on Mon, 16 April 2012 01:07 |
In another thread it appears the 3.70 FD is favored for the 403 engine. What are the thoughts on the preferred FD ratio for a 455 engine? Would that preference be different if most driving will be flatland with only occasional mountains?
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If you have an original torque converter, the 3.07 original will still be slipping at 55mph (well, it always slips) because the torque converter has a stall of around 2200. I have a switch pitch which is much tighter (1800 stall or so) and so the original 3.07 will work fine. I rarely tow. I always seem to be in mountains, but shifting down is not so bad.
When I had a 355 fail, I went to an "original" because of the switch pitch. In a comedy of errors, I apparently ended up with a 2.73. I will be going to Casa with Western States, and that will be another 190 miles one way. I have come about 400 so far. I may swap it out one of these times, but towed over the Grapevine, going North. Hey, you can go 55 in second gear without breaking 3000. And at 62 mph (my happy spot) it is so quiet, I hardly know the engine is running. It will be interesting to play with it for a bit. It's a cruiser.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: 455 recommended FD ratio [message #166772 is a reply to message #166469] |
Wed, 18 April 2012 21:55 |
Jim Galbavy
Messages: 1443
Registered: August 2007
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Steve,
As many have stated, it all varies with how and where you drive. My "73 455 KOBA has a stock 307. I have towed here in Florida where the highest grade is an overpass. ... never felt the car or towdolly. I drove the mountains of NC, VA, WV and PA with no real problem (once I learned that I needed a fan clutch). I've even driven the Skyline Drive. I normally drive 62 to 70 mph depending on speed limits. My sweet spot seems to be around 62-63 mph.
jim galbavy
'73 x-CL ANNIE
Lake Mary, Fl
[Updated on: Wed, 18 April 2012 21:57] Report message to a moderator |
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| Re: 455 recommended FD ratio [message #166778 is a reply to message #166772] |
Wed, 18 April 2012 22:30 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
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I'm certainly not against any of these ratio changes, in fact I may do one at some point, but one side of me thinks that as long as I have adequate ratio spread for how I drive, I really don't care if I go up ahill in 2cnd or 3rd. I do almost all mountainous driving and my 3:07 final drive does require 2cnd and sometimes 1st gear. My feeling is so-what? Whatever I do, I don't want to give up the ability to kick down during passing maneuvers at 65 or so and kick it down into 2cnd. So, I guess what I'm thinking is overall ratio coverage rather than the ability to stay in 3rd all the time. Gradeability from a stop is certainly an issue, but so far I've always been able to launch no matter where I've been (other than on grass of course).
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: 455 recommended FD ratio [message #166779 is a reply to message #166778] |
Wed, 18 April 2012 22:33 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
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I should probably add that my 403 on flat lands is very content to cruise at 70+ with great fuel economy. I also ran the entire route 66 route pulling a heavlly loaded microbus and never realized I needed any other ratio. That was my pre GMCNET experience however.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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