wrong gears?
03-09-2010, 01:43 PM
#1
JK Newbie
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wrong gears?
i bought a 2010 wrangler sport with so many options i midas well have got me a rubi... stupid me... but thats not what im curious about. i got an auto... stupid, i know but the wife has to be able to use it once an a while. the build sheet says that i have 3.73 gears (standard with an auto) but my RPM's at 65 are around 1700-1800... when i looked at gearing charts, that was the RPM's for a jeep with 3.21 gears... did i get ripped off? my rig feels so underpowered with rubi 32's and RPM's ar 65 dont lie... what should i do?
03-09-2010, 02:05 PM
#3
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the auto is cool, fun and easy to drive, but the power is lacking sooo bad with these "3.73" gears that are acting and working like 3.21's... am i thinking logically here in thinking i have 3.21's since my rpm's at 65mph are around 1800-1900 max (getting close to 2k rpm's and ill be doing about 70mph)?
03-09-2010, 02:24 PM
#4
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The chart you are looking at is probably for a 3 speed auto without an overdrive with over drive the Rpms are lower
try checking rpms with overdrive off against your chart
Tom
try checking rpms with overdrive off against your chart
Tom
03-09-2010, 02:51 PM
#5
JK Freak
Due to top gear ratio (4th in auto and 6th in the 6th speed) the 3.21 gears with the 6-speed are the same as having 3.73 gears with an auto. I have the 6-speed with 3.21 gears and 32" tires and my engine is at exactly 2K RPM at 70 mph in 6th.
Based on dyno charts I have seen the autos loose about 20 extra horsepower through the transmission compared to the 6-speeds (150 vs. 170 HP at the rear wheels). So the 3.73 gears in an auto theoretically would have worse top gear abilities on the highway if you have 32" tall tires.
No big deal though, just means your transmission will need to downshift a bit more often on the highway for passing compared to mine. Since you have an auto you don't need to do the extra work other than push the pedal down a little further
Based on dyno charts I have seen the autos loose about 20 extra horsepower through the transmission compared to the 6-speeds (150 vs. 170 HP at the rear wheels). So the 3.73 gears in an auto theoretically would have worse top gear abilities on the highway if you have 32" tall tires.
No big deal though, just means your transmission will need to downshift a bit more often on the highway for passing compared to mine. Since you have an auto you don't need to do the extra work other than push the pedal down a little further
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03-09-2010, 04:55 PM
#8
JK Junkie
Yeap, 1800-1900 is correct for 3.73s. That's where my Jeep used to cruise at before I installed larger tires, gears and a Flashpaq.
Ideally, you need to cruise at 2200-2300+ RPM is you don't want the transmission to shift out of OD on an incline or head wind.
Ideally, you need to cruise at 2200-2300+ RPM is you don't want the transmission to shift out of OD on an incline or head wind.
03-10-2010, 07:46 AM
#9
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most charts are for with a manual tranny set at a 1:1 engine:driveshaft ratio (5th gear in a 6-speed, 4th gear in a 5-speed), the auto usually gets more revs because it takes more power to overcome the drag of the torque converter as well as to power the hydraulic pump of the transmission that the manual doesn't have to deal with as it has a clutch that is used instead.
