teddycarnut

Have chance to swap my 411 rear end for a 313 or something close, Would you do to improve ride and fuel economy. never race and drive about 2000 miles a year. I am told gear change is great improvement in both and easy to swap whole unit.

MOXIE62

I would go even lower then that, or higher, whatever the correct term is. I have a 306 in my 63 and can cruise down the road a little over 2000 RPM. Not only gas saver but quiter and cooler.

DZAUTO

The 55-64 full size pass cars and 56-62 Corvettes shared the SAME removable rearend center sections.
The ONLY ratios that were available in these rears were: 3.08, 3.36, 3.55, 3.70, 4.11, 4.56. There was never such a ratio as 3.13,
ALLLLLLLLLLLLLLLLLLLLL of the above ratios were available in NON-posi and posi.
Changing the center section is a relatively simple task. With experience, the center section can be changed in 45min (MOST folks will probably require 1 1/2-2hrs).

Below is a comparison of posi(left) and non-posi 3.08 center sections.






Going from a 4.11 to a 3.36 or 3.08 will significantly lower your hiway rpm and noticeably improve fuel economy. The ONLY downside is that it will not be as responsive from a dead stop (and with today's gas prices, that is a non issue for me). Also, the ride will SEEM smoother (but it really won't be) because of less noise and vibration as a result of the lower hiway rpm. These cars NEVER had the ride of a full size 4dr family sedan.

C.T.

If your driving is mostly local, I wouldn't.

wmf62

depends on what engine you have and what your transmission's 1st gear ratio is. my 1st gear is 2.66 and my RER is 3.36; around town I do NOT like it...

Bill

GTOguy

I have a 2.56 first gear in my '65 GTO with a 3.36 rear gear and I love it. Excellent all around gear. I like a 3.23 even better. But my 389 puts out about 430 foot pounds of torque....so that could be part of it.

MikeM

Take heed. What kind of driving and what kind of roads do you drive on?

tomy62

This thread is right on point for me. I have a 4.11 posi behind a close ratio 4 speed behind a 340 horse 327. I think a 3.70 would be about perfect for me. Lose a little acceleration and maybe a slightly sluggish take off but quieter highway operation, smoother, run cooler and better mileage. I have no idea as to the cost but I am guessing I would go with an aftermarket gear set. I’m going back to lurking now.

wmf62

you've got a double 'whammy', t he 340hp (low on low end torque) and the (i'm guessing..) 2.20 1st gear

the rule of thumb for drivability is 1st gear times RER should be at least 10. so 2.20 x 4.11 = 9.04 2.20 x 3.70 = 8.14 (worse...)

my SS700: 2.66 x 3.36 = 8.94 with ZZ4 engine (as I said, I don't like it, but too much trouble to change..)

my MY6 has/had a 3.09 x 3.36 = 10.38. a pleasure to drive around town and has an overdrive 4th gear

GCD1962

2.88 lst gear and 3:36 rear in my '57 Chev. Very fast off the line.

wmf62

2.88 x 3:36 = 9.68; pretty close

68hemi

I have 3.08s in my 57 with a Saginaw 4 speed (don't know what the 1st gear ratio is) and it is great but then again I have a 383 stroker engine 450-475 h.p.

OLDED

My 59 has the 4:11 posi which is no fun on any kind of open road. I installed a T5 for the overdrive 5th. gear - changed the personality of the car. Still has the low 1st. gear while rolling effortlessly down the interstate with 70+ mph. traffic.