Need some gearing advice
#1
11-21-2013, 08:03 PM
Need some gearing advice
Ok, to start I have a 1982 k5 with a 6.2 diesel. Behind that is a stock th350 with a 205 trans case and 3.08 dive axles on 33s, but Im thinking of going to 35s, maybe 38s.
Heres my concern. As you may know these trucks did not come with a RPM gauge so I have no firm idea how many rpms the motor is doing. I know enough that any diesel motor is much happier in the 1800-2400 rpm range. With RPMs in mind, be sound/feel of the motor I feel like Im extremely over revving the engine to get 65mph. I WANT to put a 700r4 monster in this truck so I can get an over drive so I can get a little more speed on the road. Heres what Im not sure about. With the over drive of the 700 I want to get some lower (locking/positrac) gears but I have NO CLUE what to go with... 3.73, 4.10, 4.56... IDK In the end I want to be able to achive at the least 70mph on the highway but would be much happier with 75mph
Can anyone give me some advice as to what I should go with... Also, any ideas of how I can get a RPM gauge?
Heres my concern. As you may know these trucks did not come with a RPM gauge so I have no firm idea how many rpms the motor is doing. I know enough that any diesel motor is much happier in the 1800-2400 rpm range. With RPMs in mind, be sound/feel of the motor I feel like Im extremely over revving the engine to get 65mph. I WANT to put a 700r4 monster in this truck so I can get an over drive so I can get a little more speed on the road. Heres what Im not sure about. With the over drive of the 700 I want to get some lower (locking/positrac) gears but I have NO CLUE what to go with... 3.73, 4.10, 4.56... IDK In the end I want to be able to achive at the least 70mph on the highway but would be much happier with 75mph
Can anyone give me some advice as to what I should go with... Also, any ideas of how I can get a RPM gauge?
#2
11-21-2013, 09:54 PM
ok here is the issue.
those 3.08s are crying in the city with those 33's. thats why you are over revving because its taking so long to get up to speed. Now,for highway thats great. but unless your 90% highway you want something in between. Id go with 3:73s if its mostly city driving. its going to much better then 3.08 in town but its still going to be a little rough at 70. if its mostly highway,3:42 would be considerable with 33s.
those 3.08s are crying in the city with those 33's. thats why you are over revving because its taking so long to get up to speed. Now,for highway thats great. but unless your 90% highway you want something in between. Id go with 3:73s if its mostly city driving. its going to much better then 3.08 in town but its still going to be a little rough at 70. if its mostly highway,3:42 would be considerable with 33s.
#3
11-21-2013, 11:02 PM
What about 3.55s? Im not going to be pulling anything more than a ridding lawn mower with it, but I cant even spin all four tires in the sand in 4high. That seems odd to me
Is there some sorta gear calculator that I can enter EVERYTHING (rpm, trans gear, axle gear and tire size) that will tell me what my speeds will be at a final drive? Im not opposed to a really low gear ie:4.10 or lower as long as I can do (todays) highway speeds. I dont want to have to be hauling this truck everywhere to enjoy it>
Is there some sorta gear calculator that I can enter EVERYTHING (rpm, trans gear, axle gear and tire size) that will tell me what my speeds will be at a final drive? Im not opposed to a really low gear ie:4.10 or lower as long as I can do (todays) highway speeds. I dont want to have to be hauling this truck everywhere to enjoy it>
#4
11-22-2013, 09:14 AM
4x4 and Gear Calculator
Tire Diameter:Transmission Ratio:Transfercase Ratio:Engine RPM:Gear Ratio:MPH: plugged in a few numbers here Planet 4x4 - Gear and 4x4 Calculators I would shoot for 3.73s on 35s or 4.10s on 38s. Remember tires are not actually as tall as they claim to be.
#6
11-26-2013, 10:16 AM
Here you go:
Gear Chart
This chart shows calculated rpm with a 1:1 final drive ratio of a transmission such as your TH350. It does not take into account any slip of a torque converter which can easily add 2-300 rpm at cruising speed.
The colors are more for gas motors, you can disregard them in this situation.
Very important is tire size. Even though the number on the side of your tire says 33" it does not mean that it measures 33", get out a ruler and measure.
If you add an overdrive you will need to multiply the rpm's in the chart by 0.7. Also, if you plan on hooking up a lock up converter to your TH700R4 then take that into account with your cruising speed as well.
We can tell you which is better between 3.08 and 4.88's but YOU have to decide what you want to do. Do you want off the line acceleration or do you want a comfortable cruise speed? Personally, I'd pick my cruise speed, calculate the lowest gear (higher numerical) I could run while keeping the rpm's in check and go with it.
You don't have to worry about spinning all four tires in the sand, you have a 6.2, only 155hp there and a 5,000 rig, just not going to happen.
Gear Chart
This chart shows calculated rpm with a 1:1 final drive ratio of a transmission such as your TH350. It does not take into account any slip of a torque converter which can easily add 2-300 rpm at cruising speed.
The colors are more for gas motors, you can disregard them in this situation.
Very important is tire size. Even though the number on the side of your tire says 33" it does not mean that it measures 33", get out a ruler and measure.
If you add an overdrive you will need to multiply the rpm's in the chart by 0.7. Also, if you plan on hooking up a lock up converter to your TH700R4 then take that into account with your cruising speed as well.
We can tell you which is better between 3.08 and 4.88's but YOU have to decide what you want to do. Do you want off the line acceleration or do you want a comfortable cruise speed? Personally, I'd pick my cruise speed, calculate the lowest gear (higher numerical) I could run while keeping the rpm's in check and go with it.
You don't have to worry about spinning all four tires in the sand, you have a 6.2, only 155hp there and a 5,000 rig, just not going to happen.
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