what gears

[john1977]

Can anyone suggest what rear gears that I should go with. Have a 77, 350/340hp that starts its power band at 2400rpm tied to a TH350 with 2400 B&M stall conv. and 3:08 gears. Looking to get a little more low end but at the same time still be able to run down the highway with out pushing the engine to hard. What would be a good gear for what I want to do?

 

[80redbeast]

I have 4:10's that were in the car when I bought it last year. Put a new 350/300HP in last year. It screams on the higway at 70mph. One day might change to 3:73 or 3:54. Love the way it jumps off the line, though. Im not ready to give that up. It make the kids in the ricers look like asses.

 

[patsnitrovette]

Then you might be happy with a 3.55 - 3.70 gear.

 

[GTR1999]

I'd use 3:55's too

 

[Hib Halverson]

Can anyone suggest what rear gears that I should go with. Have a 77, 350/340hp that starts its power band at 2400rpm tied to a TH350 with 2400 B&M stall conv. and 3:08 gears. Looking to get a little more low end but at the same time still be able to run down the highway with out pushing the engine to hard. What would be a good gear for what I want to do?

It's tough to give a useful answer to this because the tire size and the intended use of the vehicle are not given, however, a preliminary answer is that, with a power band that starts at 2400 and a 2400 stall converter seems to indicate the engine is a little lacking down low. If the intended use is hi-po street and the tire size is reasonably close to stock, I'd suggest 3.55 gears. If the use is street/strip drag racing, I'd suggest 3.70s or 4.11s.

 

[john1977]

Right now I'am using stock tire size 2:25/70 15s. In the spring I plan to put 2:55/60-15s on all 4. The way it is now with the 3:08s it is just on the verge of breaking the tires loose. Would like to know I can smokem if I want and at the same time still be able cruise down the highway with out pushing it to hard. Do not really take any long trips, just cruise-ins and car shows mainly local . Farthest driven in any one day would be 100 miles.

 

[81 Corvette]

i've got 3.54 with my th 350. When i cruise on the highway, i'm turning over 3k. most of the time i'm turning 3500 cause i like to pass people.

I figure that if the the c6 can run a 3.42 gear, then 3.54 is a good long term gear for me. long term = richmond 6 speed adn a few more ponies.

 

[Glensgages]

Maybe 81 Corvette can confirm my calculations, but with 255 tires, 3.55 gears, and a non-locking THM350, at 50 MPH, you'd turn 2440 RPM, at 70 it'd be 3460, and at 90 it'll twist 4390;

if you choose 3.70 gears, simply multiply the above by 1.0422 ( x 1.0422) to find RPM at same speeds.....

 

[john1977]

I'am pretty sure I have 3:08s now, just by counting driveshaft revolutions. With the stock 2:25/70-15s it turns 2500 at 55 mph and 2700 at 65 mph. If I went with 3:38s instead of 3:55s do you think I would notice much of an improvement in my low end? Also since I should have the differential out today does anyone know of any place in Ohio that can do the work just so I don't have to ship it out.

 

[80redbeast]

I'am pretty sure I have 3:08s now, just by counting driveshaft revolutions. With the stock 2:25/70-15s it turns 2500 at 55 mph and 2700 at 65 mph. If I went with 3:38s instead of 3:55s do you think I would notice much of an improvement in my low end? Also since I should have the differential out today does anyone know of any place in Ohio that can do the work just so I don't have to ship it out.

DOnt forget that your speedometer gear will need to be replaced so that your speedo is accurate

 

[Glensgages]

I'am pretty sure I have 3:08s now, just by counting driveshaft revolutions. With the stock 2:25/70-15s it turns 2500 at 55 mph and 2700 at 65 mph. If I went with 3:38s instead of 3:55s do you think I would notice much of an improvement in my low end? Also since I should have the differential out today does anyone know of any place in Ohio that can do the work just so I don't have to ship it out.

john1977:

"Assuming" the 225s are 27.4" tall, 2500 RPM at 55 MPH is 3.36 gears, but 2700 at 65 MPH equals 3.08 gears.....
:confused
It is entirely possible that at 55 MPH, the converter is still 'slipping' a bit, resulting in higher RPM than expected with a traditional 'tight' converter.

If it were me (and I'm probably in the minority on this), I wouldn't spend the time or money just going up a 'single' ratio-increment
(i.e.: 3.08-to-3.36, or 3.36-to-3.55),
as I don't think you'd REALLY notice it via your 'butt-dyno'.

If you are truly not going to be driving it far from home, with most driving on two-lane roads, in-town, or to Shows/cruises, throw as much gear at it as you can find.
I think you'd really enjoy the off-the-line acceleration offered with 3.73s:
even my wimpy Cross-Fire smokes the tires at-will

I believe you can only run up-to and including 3.70/3.73 gears in your OEM series-3 carrier:
4.11 and deeper gears (if you can even find them) would require the series-4 carrier.

 

[81 Corvette]

Also since I should have the differential out today does anyone know of any place in Ohio that can do the work just so I don't have to ship it out.

This is the place that did mine. http://www.4wddiv.com/indexhome.htm they are in Ohio, but probally quite a bit of a haul for you. Mark is the guy I dealt with. No complaits from me.

 

[81 Corvette]

Maybe 81 Corvette can confirm my calculations, but with 255 tires, 3.55 gears, and a non-locking THM350, at 50 MPH, you'd turn 2440 RPM, at 70 it'd be 3460, and at 90 it'll twist 4390;

if you choose 3.70 gears, simply multiply the above by 1.0422 ( x 1.0422) to find RPM at same speeds.....

:L Without digging up my gearing file, i'll agree