3.90 or 4.10 gears
09-01-2012, 10:28 PM
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3.90 or 4.10 gears
i currently have a 3.42 open diff in a 2004 xcsb 2wd daily driver. truck has a 5.3 with Comp XR-259-HR (206/212 and .515/.522 on a 112 LSA) , air intake,efans, long tubes,y pipe,nelson tune, 100 shot NOS,transgo shift kit,4l60e, 285-50-20 tires (31.2"). i'm going to upgrade the rear diff with a posi and new gears i can't decide on 3.90 or 4.10 ratio and does anybody have any clue what rpm i will be turning @ 60mph with these setups. i currently turn 1550rpm @ 60mph. all help would be greatly appreciated.
09-02-2012, 12:10 AM
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Go to wallaceracing.com for a huge assortment of calculators
09-02-2012, 11:55 AM
#4
If your calculated tire height is close to accurate, I come up with a little less than 1900rpm at 60mph with 4.10’s using the rest of your information. With 3.90’s I come up with approximately shy of 1800rpm at 60mph. Either should still result in somewhat decent economy if you can keep your highway speeds in check, as these engines for the most part seem to get the best mileage at or around 1700 to 1900rpm. I personally would do a gut check to come up with what would best suit your needs by answering to yourself what you expect out of your vehicle, do you normally keep highway speeds down to 60mph or do you like to travel at a higher rate of speed on regular occasions. Do you drive around town for the most part where highway speeds are of minimum impact? Do you intend to swap camshafts in the future and/or torque converters? You didn’t mention a converter, but given the small nature of your current camshaft I’m assuming you’re still on the stock unit. The reason I bring this up is with a little more gear you can get away with a little less converter and still have decent response off the line, enjoy better part throttle response cruising around and better in town economy. Or course if you changed some things around with a looser converter you could still get off line decently with a little less gear for daily usage, but tip-in throttle response will soften up some, yet highway usage would be better. Of course for primarily NA performance usage you may want to throw caution to the wind and go with a steeper gear, looser converter and larger camshaft all combined together for a street terror (especially when you hit it with that 100hp shot), but don’t expect good economy as a result.
09-02-2012, 12:32 PM
#5
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If your calculated tire height is close to accurate, I come up with a little less than 1900rpm at 60mph with 4.10’s using the rest of your information. With 3.90’s I come up with approximately shy of 1800rpm at 60mph. Either should still result in somewhat decent economy if you can keep your highway speeds in check, as these engines for the most part seem to get the best mileage at or around 1700 to 1900rpm. I personally would do a gut check to come up with what would best suit your needs by answering to yourself what you expect out of your vehicle, do you normally keep highway speeds down to 60mph or do you like to travel at a higher rate of speed on regular occasions. Do you drive around town for the most part where highway speeds are of minimum impact? Do you intend to swap camshafts in the future and/or torque converters? You didn’t mention a converter, but given the small nature of your current camshaft I’m assuming you’re still on the stock unit. The reason I bring this up is with a little more gear you can get away with a little less converter and still have decent response off the line, enjoy better part throttle response cruising around and better in town economy. Or course if you changed some things around with a looser converter you could still get off line decently with a little less gear for daily usage, but tip-in throttle response will soften up some, yet highway usage would be better. Of course for primarily NA performance usage you may want to throw caution to the wind and go with a steeper gear, looser converter and larger camshaft all combined together for a street terror (especially when you hit it with that 100hp shot), but don’t expect good economy as a result.
09-03-2012, 09:45 AM
#6
If your calculated tire height is close to accurate, I come up with a little less than 1900rpm at 60mph with 4.10’s using the rest of your information. With 3.90’s I come up with approximately shy of 1800rpm at 60mph. Either should still result in somewhat decent economy if you can keep your highway speeds in check, as these engines for the most part seem to get the best mileage at or around 1700 to 1900rpm. I personally would do a gut check to come up with what would best suit your needs by answering to yourself what you expect out of your vehicle, do you normally keep highway speeds down to 60mph or do you like to travel at a higher rate of speed on regular occasions. Do you drive around town for the most part where highway speeds are of minimum impact? Do you intend to swap camshafts in the future and/or torque converters? You didn’t mention a converter, but given the small nature of your current camshaft I’m assuming you’re still on the stock unit. The reason I bring this up is with a little more gear you can get away with a little less converter and still have decent response off the line, enjoy better part throttle response cruising around and better in town economy. Or course if you changed some things around with a looser converter you could still get off line decently with a little less gear for daily usage, but tip-in throttle response will soften up some, yet highway usage would be better. Of course for primarily NA performance usage you may want to throw caution to the wind and go with a steeper gear, looser converter and larger camshaft all combined together for a street terror (especially when you hit it with that 100hp shot), but don’t expect good economy as a result.
Jarrod, u know I'm so nitpicky, esp. about MPG. But I so much think of the 4.10s, mainly cause of all the guys on PT, whereas before, I woulda never considered them prior to PT, & only thought of a 3.73 when I upgrade (read that as my rear goes) which would be a big jump up from the 3.42s now.
Also, not sure how many of those same 4.10 guys are boosted. But to further complicate, how many of those same have such & such convertor, cam...?
But 3.73s would be my other gear of choice. Plus, I know both are OEM GM gears, therefore quiet. Not sure who makes a quiet 3.90, as it's sure not an OEM gearset.
While I'm not sure on whether he does more city or hwy, & that should definitely be a decidind factor in his decision, myself, I rarely take freeway. When I do, 70 MPH. But I almost never go more than 50 each way. More city drivin for me, rarely gettin above 55. So, I'd hate to kill my around town MPG.
To the OP, that may not matter. And he also didn't say if he planned on stayin N/A. Obviously I'm not anymore, & the Radix pulls u thru w/. less tip in than I needed b4, so in reality the 3.42s are fine, but I always wonder what if.
Tells you a no B.S. approach & doesn't sugarcoat it.
I'm kinda partial to his advice, as I consider him a good friend. And lookin at your sig lineeup, you're partial to LS anything.
Last edited by fastnblu; 09-03-2012 at 10:00 AM. Reason: Info added.
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