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reborn55
11-19-2014, 07:42 PM
After 21 years of M-20 and 3:70 rear end and hipo 283 it may be time for a change--I have complete 3:08 sitting in the corner of garage--thinking about changing out the rear ends. Can't really go to overdrive just yet with early model 283 still in car. any opinions. Just a little tired of running 3500 rpm's and more on long trips. getting ready for Route 66 tour in a year or so. May just opt out for crate motor and 200r. thanks. Still liking shifting but running 3500 and above on the interstate for 3-400 miles at a time gets old.

chevynut
11-19-2014, 09:31 PM
Why can't you go to an overdrive transmission?

WagonCrazy
11-19-2014, 09:56 PM
I'm running a nearly stock 350 crate motor with a 600 cfm carb, and a 200-4r trans with a 2000 rpm stall speed torque converter, and 3.55 rear gears in my 9 passenger wagon.
70 mph at 2400 rpms.

if I had a 3.08 in there, the rpms would make this thing waaaaaaaay tooooo sluggish.

reborn55
11-20-2014, 05:49 AM
First--I still like the 4speed and second early 283 where the starter still bolts to bell housing--

chevynut
11-20-2014, 07:15 AM
First--I still like the 4speed and second early 283 where the starter still bolts to bell housing--

Seems like you still have some options. What about a Tremec 5-speed? They bolt right to the stock muncie bolt pattern so you can keep your bellhousing. I think another option is a T5 but I understand they're not very strong.

Rick_L
11-21-2014, 04:40 PM
3500 rpm sounds very high for a 3.70 rear gear unless you cruise pretty fast.

But let's use your numbers. If you go with a 3.08 you still are going to be turning 2900+ rpm at the same speed. Still pretty high by modern standards.

A typical overdrive transmission has a 0.7 overdrive ratio. This would take you to 2450 rpm if you didn't change the axle gear ratio.

The other half of the rear gear swap is that you reduce your torque at the rear wheels in any gear by 18%. This is going to cause you to slip the clutch when starting from a stop, or to downshift to 3rd much more often. In fact 3rd is going to feel like what you have now in 4th. With the overdrive you wouldn't have this performance reduction.

reborn55
11-21-2014, 08:04 PM
I ran the numbers like you did--with my setup and tires I would only decrease the rpm's by about 500 so it is not much of a trade off. Still researching 5 speed as I took it out for a drive today and was a joy to drive. Do like the idea of automatic overdrive and will look into it also. Whenever we take a long trip--usually 200 miles or more a lot of it is interstate where we run 70-75 MPH most of the time if not more. thanks for info

markm
11-22-2014, 10:40 AM
I run a TKO-600 in my 55 with a .060 over 396 with two Holley 600s and cruise 2000rpm at 70mph with a 56 inch wide Dana 60 with 35 spline axles and 3.54 gears and a Powerlock. I Run 275/60/15 tires on Torq Thrust Ds that are 8.5 wide. Biggest complaint with Tremec hard to hit 3rd at 6000 rpm, however, I find the 700R4 in my 56 boring to drive by comparison.