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Diff ratio - compare revs 3:15 v 3:54

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Greyhounds_AMX View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greyhounds_AMX Quote  Post ReplyReply Direct Link To This Post Posted: Mar/13/2019 at 9:22am
But you can have both if you run 3.54's with a T5.
1968 AMX 390 / T5
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vinny View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vinny Quote  Post ReplyReply Direct Link To This Post Posted: Mar/13/2019 at 10:59am
I had a few GM vans with I think 3.54 and 700R4 or newer so not bad, couldn't fault them. With 1 to 1 in the Rambler I like the 3.15 as a compromise.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Mar/13/2019 at 12:19pm
A 1:1 transmission high gear doesn't have to suck. It doesn't have to force a compromise axle ratio...if the lower gears in the transmission are a high enough (numerically) ratio. That is where AMC screwed up.

Most AMC manual and automatic transmissions have a 2.5:1 low gear and a 1:1 high gear. That sucks. The ratio spread simply is not wide enough to allow for one axle ratio that produces good low speed performance and good high speed performance. Most cars end up with a compromise gearing that doesn't make them truly good at anything.

...unless you bought Borg-Warner overdrive. Low gear is the same 2.5:1 but the high gear is now 0.7:1. You can run a high axle ratio for good low speed performance but drop into overdrive for high speeds. That 3.54 axle ratio becomes a 2.50 after the overdrive is engaged. It's absolutely perfect.

AMC got smarter in later years too. Starting in about 1975 they switched to 3 speed manual transmissions with low gears around 3.2:1 and 4-speed transmissions with low gears around 4.2:1, all with 1:1 high gears. These transmissions got themselves off the line very well with axle ratios in the 2.5:1-3.08:1 range and produced excellent highway cruising.

They got smarter on their automatic transmissions with the Eagle when they introduced the wide ratio lockup TC A998. A 2.7:1 first gear and a true 1:1 high gear. A 2.35:1-3.08:1 axle works perfectly with these. My Eagle gets itself off the line just as well with it's A998/2.35 as my Hornet does with it's A904/2.73.


Wide ratio 3 and 4 speed transmissions are your friend. AMC engines have a broad torque curve that works well with wide ratios.

'66 Marlin: 327/T10/3.54 Twin Grip
'72 Wagoneer: 360/TH400/3.31
'73 Ambassador: 360/TF727/3.15
'77 Hornet: 232/TF904/2.73
'84 Eagle: 258/TF998/2.35
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