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Old 04-12-2009, 07:36 PM
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re-gearing a 4 cyl with 31's

what kind of gears do you think i should run?

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Old 04-12-2009, 07:43 PM   #2
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A little more info on your rig would be good and what you'll be doing with it. and what gears are in it now. Why do you think you need to regear?

I ran my 2.5 with 31's and 4:10's with my 5spd and it did just fine. But when I put my 32x11.50x15 BFG M/T's on it, it became the little jeep that could on the freeway.

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Old 04-12-2009, 07:52 PM
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its a 4 cyl auto, i dont kno what gears it has right now cause its a jeep that i may be buying im just trying to get an idea, i drove it today and it didnt feel like it has any power i mean obviously its got a 4banger but im just lookin for ideas to get it to where it run highway speeds okay
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Old 04-12-2009, 08:47 PM   #4
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Originally Posted by claygrassmann View Post
its a 4 cyl auto, i dont kno what gears it has right now cause its a jeep that i may be buying im just trying to get an idea, i drove it today and it didnt feel like it has any power i mean obviously its got a 4banger but im just lookin for ideas to get it to where it run highway speeds okay
Best advice.. buy 4.0L
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Old 04-12-2009, 08:49 PM   #5
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A stock TJ 4 banger will have 4:10 ratio to help with the low powered 4 banger, but I think that the 4:10 ratio also contributes to its turtle-like take off speeds.

IMO the auto tranny and a 4 banger is a bad combination. You're better off with a manual tranny. My 4 banger does great at highway speeds. You just gotta remember that it's no corvette, so it will take a hair longer to get up to speed from a dead stop.
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Old 04-12-2009, 08:50 PM   #6
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ya, nothing really wakes that motor up. great motor and it will last forever, but nothing is gonna make you happy from a red light.

i don't know what gears a tj auto 4 banger has, is it 4.10? if it is, its really not worth the money. if you did change, go to 4.88, the lowest you can fit. 4.10 to 4.56 is not all that noticeable. don't ask me why i know that by accident
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Old 04-12-2009, 11:02 PM   #7
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I got my spec sheet for mine, and it is 4.10 normally.
you wont be able to race light to light ever. but it gets up there with the best of them, and mines at 145,000 miles so dont worry about how long itll last.

as for the tires, I'm buying my 31's this week and from countless questions Ive learned its really not as important to regear, just know that your speedometer will be ever so slightly off.
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Old 04-12-2009, 11:42 PM   #8
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I'm buying my 31's this week and from countless questions Ive learned its really not as important to regear, just know that your speedometer will be ever so slightly off.
FYI the speedo gears are now running about $60 to $70 bucks now.
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Old 04-12-2009, 11:57 PM   #9
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Originally Posted by jpdocdave View Post
ya, nothing really wakes that motor up. great motor and it will last forever, but nothing is gonna make you happy from a red light.

i don't know what gears a tj auto 4 banger has, is it 4.10? if it is, its really not worth the money. if you did change, go to 4.88, the lowest you can fit. 4.10 to 4.56 is not all that noticeable. don't ask me why i know that by accident
No offense but I'd beg to differ on the topic about how nothing wakes a 4 banger up. If they are built correctly a 4 banger will beat a 4.0 in torque and HP. That is if you dont do on to the 4.0 as you did to the 2.5 L. Check out this thread on another forum I'm a part of.
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This guy knows how to build a rig.

Edit...I can't directly link this thread for some odd reason. If you would like more info on the great build this guy did, PM me and I'll link you. I can copy and paste the specs here...
internals
crank turned 10/10 -tri metal bearings
forged pistons 60 bore size- chromoly rings/ forged wrist pins
block bored over 60
balanced rotating assemblies
clifford cut 426 cam shaft- tri metal bearings
clifford hardened hydro lifters
clifford hardened push rods
clifford hardened double valve springs/ locks
deck of block zeroed to raise compression- 10.5:1
head ported and rebuilt with new valves/seals
after that is basic rebuild of all other parts, pumps/plugs/gaskets

external
accel 8mm wire
plug gap 50
accel coil
4.0 tb
4.0 tbs
19lb type 2 injectors
borla 4-1 header
fomoco fan
custom run 2.5 exhaust w/flowmaster super40
rusty's conical adapter w/kn ram filter
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Old 04-13-2009, 09:25 AM   #10
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No offense but I'd beg to differ on the topic about how nothing wakes a 4 banger up. If they are built correctly a 4 banger will beat a 4.0 in torque and HP. That is if you dont do on to the 4.0 as you did to the 2.5 L. Check out this thread on another forum I'm a part of.
Login

This guy knows how to build a rig.

Edit...I can't directly link this thread for some odd reason. If you would like more info on the great build this guy did, PM me and I'll link you. I can copy and paste the specs here...
internals
crank turned 10/10 -tri metal bearings
forged pistons 60 bore size- chromoly rings/ forged wrist pins
block bored over 60
balanced rotating assemblies
clifford cut 426 cam shaft- tri metal bearings
clifford hardened hydro lifters
clifford hardened push rods
clifford hardened double valve springs/ locks
deck of block zeroed to raise compression- 10.5:1
head ported and rebuilt with new valves/seals
after that is basic rebuild of all other parts, pumps/plugs/gaskets

external
accel 8mm wire
plug gap 50
accel coil
4.0 tb
4.0 tbs
19lb type 2 injectors
borla 4-1 header
fomoco fan
custom run 2.5 exhaust w/flowmaster super40
rusty's conical adapter w/kn ram filter
no offense, but to me that is retarded. but thats fine, and that was cool for that guy.

the dollar amount in that build is no where near logical for 99% of the people asking how to get a little more power out of their 4 banger.

and i'd like to see how much difference that really made on a 125 hp motor. most of the gain was from the .060 over bore, thus increasing the displacement. most people asking this question are not going to increase the displacement of their 4 cylinder, unless it needs a rebuild. and boring that poor motor that much makes the cylinder walls very thin
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Old 04-19-2009, 08:33 PM   #11
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It cost the guy $1500. To me that is a fraction of the headaches for a 4.0 swap, and that is about the same price your going to buy a reman 2.5 for. PM me and I'll link you to this build page. He had it dynoed and it came out to be more HP and Torque than the stock 4.0 has.
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Old 04-19-2009, 08:36 PM   #12
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Also $450 out of the $1500 is for the Borla header. The $1500 includes the non internals too.
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Old 04-19-2009, 08:42 PM   #13
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with all that machine work, and parts, its hard to believe there's only a grand there minus the header.

that machine work is well over 500 bux easily, i'd waiger closer to a grand alone. i just had a valve job on a 4.0 head and it was over 300 alone, and that was my shops price through the machine shop.
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Old 04-19-2009, 08:56 PM   #14
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I wouldn't even consider building up a 2.5L like that, and if you believe all those parts plus the machine work can be done for only $1100, I think you might have misunderstood him. As Jpdocdave said, even a valve job is would cost a significant portion of that. I had a valve job quoted recently and the machine shop said to be prepared for between $500 and $600... just for a stinking valve job so $1100 for all those parts and work you quoted doesn't sound real at all.
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Old 04-22-2009, 01:34 PM   #15
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Well I can give you his email adress and he can tell you. I am just telling you what he told all us at 4bangerjp.com. You can look up his build if you would like, his forum name is "yjmechs" It is under members projects.

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