Picking a new rear end gear.
04-04-2010, 10:54 AM
#11
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Thread Starter
3.23s are indeed for help meeting CAFE. As for 4.10s not hurtin mileage, I don't believe that for a second. If a truck previously had 3.73s, a swap to 4.10s might not hurt MPG. But a jump from 3.23 to 4.10? Really? I'm sure it'll **** & get like never before, but cmon. Why doesn't GM put 4.10s in all their trucks then? Answer in red.
Results are gonna vary in terms of MPG, whether some gain or lose. That & efficiency are tied in many factors. It's no 1 size fits all blanket statement. In no order, driving habits, tune, cam, convertor & gear all tie into the where's it most efficient/ MPG as far as I'm concerned.
Results are gonna vary in terms of MPG, whether some gain or lose. That & efficiency are tied in many factors. It's no 1 size fits all blanket statement. In no order, driving habits, tune, cam, convertor & gear all tie into the where's it most efficient/ MPG as far as I'm concerned.
True (on the efficiency statement). But this truck is remaining realistically stock (well no internal engine mods or converter). I just figured if anything the 3.23s were hurting it. I guess they may be beneficial if you just drive on the interstate at 70 MPH forever.
I will agree too that 4.10s would be an extreme step though.
According to my RPM calculator 4.10 is right at 2200 RPM at 70...but 3.73 is 2000RPM.
I dunno. I guess Id have to bite the bullet and find out myself
04-04-2010, 11:18 AM
#12
Let us know what u go w/. I'm curious as to what u choose & your results as far as MPG. I've no doubt you'll like the extra pep. 
I'm partial to the 3.42s, but if I had anything 3.23 or smaller, I'd upgrade to 3.55 at least (if they make em for our trucks) but prolly I'd go to a 3.73 in that instance. Like I said, IDK if they offer a 3.55 at all; if anyone does, it's prolly in a aftermarket gear. I prefer if I ever upgrade to 3.73, to use OEM or I hear good things bout Yukon.
Some guys like a lower numerically if goin turbo or F/I.
I'm partial to the 3.42s, but if I had anything 3.23 or smaller, I'd upgrade to 3.55 at least (if they make em for our trucks) but prolly I'd go to a 3.73 in that instance. Like I said, IDK if they offer a 3.55 at all; if anyone does, it's prolly in a aftermarket gear. I prefer if I ever upgrade to 3.73, to use OEM or I hear good things bout Yukon.Some guys like a lower numerically if goin turbo or F/I.
Last edited by fastnblu; 04-04-2010 at 11:25 AM.
04-04-2010, 01:32 PM
#13
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Thread Starter
Let us know what u go w/. I'm curious as to what u choose & your results as far as MPG. I've no doubt you'll like the extra pep. I'm partial to the 3.42s, but if I had anything 3.23 or smaller, I'd upgrade to 3.55 at least (if they make em for our trucks) but prolly I'd go to a 3.73 in that instance. Like I said, IDK if they offer a 3.55 at all; if anyone does, it's prolly in a aftermarket gear. I prefer if I ever upgrade to 3.73, to use OEM or I hear good things bout Yukon.
Some guys like a lower numerically if goin turbo or F/I.
I'm partial to the 3.42s, but if I had anything 3.23 or smaller, I'd upgrade to 3.55 at least (if they make em for our trucks) but prolly I'd go to a 3.73 in that instance. Like I said, IDK if they offer a 3.55 at all; if anyone does, it's prolly in a aftermarket gear. I prefer if I ever upgrade to 3.73, to use OEM or I hear good things bout Yukon.Some guys like a lower numerically if goin turbo or F/I.
I think in such a heavy truck with my size tires it could only be beneficial.
04-05-2010, 11:10 AM
#15
You said your tires measure 31” tall. From my experience, a 3.73 gear with that tire size will give you the best all around performance. You could take this a step further. Find out what RPM the engine makes the most torque, and then select a gear that will allow you to be at or near said RPM at highway speeds.
Example:
Tire Height – 31”
Axle Ratio - 3.73
Trans OD Ratio – 0.70
Target HWY Speed – 70 mph
Now for the math:
70 mph = 73920 ipm (inches per minute)
31” tire dia. = 97.34” circumference
73920 ipm/97.34” circumference = 814.8 tire rpms
814.8 tire rpms*3.73 axle ratio = 3039.5 driveshaft rpms
3039.5 driveshaft rpms * 0.70 trans OD ratio = 2127.6 engine RPMs.
So with a 31” tire, 3.73 axle ratio, and a 4L60E trans, you will get the best MPG at 70 MPH with an engine torque peak around 2127 RPMS (+/- 200-300 rpms).
Of course you need to factor other things like vehicle weight, weight of cargo etc., but you get the picture.
Example:
Tire Height – 31”
Axle Ratio - 3.73
Trans OD Ratio – 0.70
Target HWY Speed – 70 mph
Now for the math:
70 mph = 73920 ipm (inches per minute)
31” tire dia. = 97.34” circumference
73920 ipm/97.34” circumference = 814.8 tire rpms
814.8 tire rpms*3.73 axle ratio = 3039.5 driveshaft rpms
3039.5 driveshaft rpms * 0.70 trans OD ratio = 2127.6 engine RPMs.
So with a 31” tire, 3.73 axle ratio, and a 4L60E trans, you will get the best MPG at 70 MPH with an engine torque peak around 2127 RPMS (+/- 200-300 rpms).
Of course you need to factor other things like vehicle weight, weight of cargo etc., but you get the picture.
Last edited by axisT6; 04-06-2010 at 07:31 AM.
04-05-2010, 08:21 PM
#16
Teching In
Thread Starter
Ahh, that's some good info. Thanks!
I'm going to calculate my gas mileage on a long trip hopefully soon and see what I'm working with as a base line. Like I stated, I figure if the 3.73s don't make too drastic a change in MPG then it sounds like a plan to me
I'm going to calculate my gas mileage on a long trip hopefully soon and see what I'm working with as a base line. Like I stated, I figure if the 3.73s don't make too drastic a change in MPG then it sounds like a plan to me
04-09-2010, 01:46 AM
#17
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SImpleGreen. I am verifying it but I went from 15-16mpg to 19.11mpg by going from 342 1 legger to tru trac 373. I went 411 miles on 21.5 gallons.
I am breaking in my rear so I am just driving cruise control 90% of the time.
100 miles to go to complete the rear end.
I am breaking in my rear so I am just driving cruise control 90% of the time.
100 miles to go to complete the rear end.
04-09-2010, 05:05 AM
#18
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I just went fro 342 to 373 + truc track. Once I break it in, Ill give you an update. My co-worker has posi 373 on his 05 'burban and it hauls ***. IT accelerates fast from 0mph. He drives it like a Sports car some times but I like how his accelerates.
Check out this thread on gear selection and install
Check out this thread on gear selection and install
You said your tires measure 31” tall. From my experience, a 3.73 gear with that tire size will give you the best all around performance. You could take this a step further. Find out what RPM the engine makes the most torque, and then select a gear that will allow you to be at or near said RPM at highway speeds.
Example:
Tire Height – 31”
Axle Ratio - 3.73
Trans OD Ratio – 0.70
Target HWY Speed – 70 mph
Now for the math:
70 mph = 73920 ipm (inches per minute)
31” tire dia. = 97.34” circumference
73920 ipm/97.34” circumference = 814.8 tire rpms
814.8 tire rpms*3.73 axle ratio = 3039.5 driveshaft rpms
3039.5 driveshaft rpms * 0.70 trans OD ratio = 2127.6 engine RPMs.
So with a 31” tire, 3.73 axle ratio, and a 4L60E trans, you will get the best MPG at 70 MPH with an engine torque peak around 2127 RPMS (+/- 200-300 rpms).
Of course you need to factor other things like vehicle weight, weight of cargo etc., but you get the picture.
Example:
Tire Height – 31”
Axle Ratio - 3.73
Trans OD Ratio – 0.70
Target HWY Speed – 70 mph
Now for the math:
70 mph = 73920 ipm (inches per minute)
31” tire dia. = 97.34” circumference
73920 ipm/97.34” circumference = 814.8 tire rpms
814.8 tire rpms*3.73 axle ratio = 3039.5 driveshaft rpms
3039.5 driveshaft rpms * 0.70 trans OD ratio = 2127.6 engine RPMs.
So with a 31” tire, 3.73 axle ratio, and a 4L60E trans, you will get the best MPG at 70 MPH with an engine torque peak around 2127 RPMS (+/- 200-300 rpms).
Of course you need to factor other things like vehicle weight, weight of cargo etc., but you get the picture.
04-10-2010, 04:33 PM
#19
You said your tires measure 31” tall. From my experience, a 3.73 gear with that tire size will give you the best all around performance. You could take this a step further. Find out what RPM the engine makes the most torque, and then select a gear that will allow you to be at or near said RPM at highway speeds.
Example:
Tire Height – 31”
Axle Ratio - 3.73
Trans OD Ratio – 0.70
Target HWY Speed – 70 mph
Now for the math:
70 mph = 73920 ipm (inches per minute)
31” tire dia. = 97.34” circumference
73920 ipm/97.34” circumference = 814.8 tire rpms
814.8 tire rpms*3.73 axle ratio = 3039.5 driveshaft rpms
3039.5 driveshaft rpms * 0.70 trans OD ratio = 2127.6 engine RPMs.
So with a 31” tire, 3.73 axle ratio, and a 4L60E trans, you will get the best MPG at 70 MPH with an engine torque peak around 2127 RPMS (+/- 200-300 rpms).
Of course you need to factor other things like vehicle weight, weight of cargo etc., but you get the picture.
Example:
Tire Height – 31”
Axle Ratio - 3.73
Trans OD Ratio – 0.70
Target HWY Speed – 70 mph
Now for the math:
70 mph = 73920 ipm (inches per minute)
31” tire dia. = 97.34” circumference
73920 ipm/97.34” circumference = 814.8 tire rpms
814.8 tire rpms*3.73 axle ratio = 3039.5 driveshaft rpms
3039.5 driveshaft rpms * 0.70 trans OD ratio = 2127.6 engine RPMs.
So with a 31” tire, 3.73 axle ratio, and a 4L60E trans, you will get the best MPG at 70 MPH with an engine torque peak around 2127 RPMS (+/- 200-300 rpms).
Of course you need to factor other things like vehicle weight, weight of cargo etc., but you get the picture.
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