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Diff ratio - compare revs 3:15 v 3:54 |
Post Reply | Page 123 7> |
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Craigie
AMC Nut Joined: Sep/06/2011 Location: Bris, Australia Status: Offline Points: 369 |
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Posted: Nov/01/2018 at 1:32am |
I currently have 3:54 gearing in my AMC 20 bolted into my V8 Hornet. At highway speeds of 60/65 mph I'm sitting on 3000 revs I am contemplating switching to 3:15 gearing to save a bit on gas costs and not be pushing my motor so hard. I can see myself doing a lot of highway driving in the future. Can anybody comment on what revs I would be sitting on with 3:15 gearing doing those same 60/65 mph highway speeds ? or should I be selecting something else ? From what I have read, my Auto SC/360 came standard with 3:15 gearing. Many Thanks |
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Craigie.........
1968 Dodge Charger "Bullitt" tribute 1971 SC/360 Hornet 1973 "Levi" Gremlin |
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ambassador401
Supporter of TheAMCForum Joined: Dec/02/2012 Location: Finland Status: Offline Points: 243 |
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2670rpm
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68 American
68 Rebel 70 Javelin 71 Ambassador 73 Gremlin A bunch of Jeeps |
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4742 |
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I have two cars, both with 327 V8s, both that I have driven on long (1500+ mile) cross-country trips, and both with the same tires: 1965 Ambassador 3.15 axle ratio. 1966 Marlin 3.54 axle ratio. The Ambassador is noticeably less stressed at speeds over 70 MPH. The Marlin will cruise 75 MPH all day long if I ask it to, but I can tell it would rather not go that fast. Meanwhile the Ambassador is perfectly happy blasting 80 MPH all day. You won't notice much of a difference in fuel economy. The Marlin still gets close to 20 MPG at 70 MPH (3300 RPM). The main thing you notice is less noise, vibration, lower engine temperature, and less oil consumption. I really, really, really want a 3.54 axle with a 3-speed overdrive. Or a 2.87 axle with a really wide ratio 4-speed.
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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Sonic Silver
Supporter of TheAMCForum Joined: Nov/23/2011 Location: East Tennessee Status: Offline Points: 7969 |
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Have2SC's
AMC Addicted Joined: Nov/30/2011 Location: Norwalk, OH Status: Offline Points: 1257 |
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Craigie, IMO, it wouldnt be worthwhile changing from 3:54 to 3:15s. Been there done that. You may want to consider 2:87s if you are looking to make a bigger change to your highway driving rpm's. Lee
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1971 SC360 Hornet 4 speed 1970 Javelin 390 4 speed "Base Model" 1967 Rambler 220 X code 343 4 speed
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raysinvegas
AMC Addicted Joined: Jul/01/2007 Location: Las Vegas NV Status: Offline Points: 2501 |
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I installed a 3.08 from an early 70's CJ and it made a huge difference for me. They are not easy to find according to the shop.
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Andy Ray
64 440H 64 440 Convertible 68 Javelin SST 343 69 Javelin SST 343 69 SC/Rambler |
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LakesideRamblin
AMC Addicted Joined: Dec/21/2015 Location: So. California Status: Offline Points: 2694 |
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I have a 2.73 in my 69 Rambler with an AMC 360 and a Ford 8.8 rear end. Love it. So the AMC 20 2.87, per Lee above, would be a great highway cruiser gear.
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LakesideRamblin
69 Rambler 360 73 Javelin 360 "If you could kick the person in the pants responsible for most of your trouble, you wouldn't sit for a month." T. Roosevelt |
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Sonic Silver
Supporter of TheAMCForum Joined: Nov/23/2011 Location: East Tennessee Status: Offline Points: 7969 |
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amxdreamer
AMC Addicted Joined: Jul/30/2008 Location: Vancouver, BC Status: Offline Points: 8511 |
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I had a 2.87 in my AMX and it was fabulous on the highway....but was boring in town. I went to a 3.31 and now it is way more fun to drive but sucks on the highway! lol That being said I'm gald I made the change.
IMO the 3.15 will be a big improvement over what you have for the highway but will still leave a little bit of fun compared to going 2.87
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Tony
Vancouver, BC 1970 AMX 1972 Badassador AMO#10333 |
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4742 |
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It depends on what gear ratios you have in the transmission and the torque converter stall if it's an automatic. A wider ratio spread or higher stall allows the use of a lower axle ratio without making it a slug off the line. Or overdrive. Just gives you a wider gear spread in the opposite direction. The problem is that most of us are not lucky enough to have a low gear of more than 2.5 or a high gear of less than 1. Some of us are lucky and have the later wide ratio A998 or an overdrive hanging on the back of our 3-speed manual. Those lucky people make fewer compromises in their axle ratio. Do you know who compromises the most on their axle ratio? People with 4-speed manuals. |
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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