Calgary Jeep Association
4x4 Related Groups => Tech Talk => Topic started by: Jaguar on November 18, 2005, 09:51:04 AM
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Alright, so when you go up a tire size you need/should regear to get back power and gas mileage, right? What's the downside to regearing? Like, why does't Jeep just throw 4.11s in all their stock TJs while keeping stock tires to improve gas mileage? The only thing I could think of, is that Regearing prolly reduces Torque???
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Because only rubicons come with 31" tires which are the perfect match for 4.11 gears.
With 4cyl jeeps, they all come with 4.11 gears.
Tom
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But, if you took a stock sport, with 3.07s and threw 4.11s in with the same tires, would you not get better gas mileage?
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No, it would increase your RPM's therefore, decreasing your gas mileage. The lower gears (numerically higher) are to compensate for larger diameter tires, which will decrease your RPM's. ie: increase tires size, decrease the gear ratio.
In my research I have based my opinion that...
based on a 4.0L standard tranny:
- 3:07 = 27-29" tires
- 3:55 = 29-30" tires
- 3:73 = 30-31" tires
- 4:10 = 31-33" tires
- 4:56 = 33-35" tires
- 4:88 = 35-36" tires
- 5:13 = 37" and up
based on a 4.0L Automatic tranny:
- 3:55 = 27-29" tires
- 3:73 = 29-30" tires
- 4:10 = 30-31" tires
- 4:56 = 31-33" tires
- 4:88 = 33-36" tires
- 5:13 = 37" and up
Based on a 2.5L standard:
- 4:10 = 27-30" tires
- 4:56 = 30-32" tires
- 4:88 = 33-35" tires
- 5:13 = 36" and up
Based on a 2.5L Automatic:
- 4:10 = 27-29" tires
- 4:56 = 30-32" tires
- 4:88 = 33-35" tires
- 5:13 = 35" and up
Again, these are just my opinion, others may disagree, but it should help with your question.
Dan
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I'm assuming the stock sport has a 4.0L as the 2.5L's come with 4.10's. I believe the 4.0L powerband is at alot lower rpm than the 2.5L
In theory you would probably get better gas mileage, but in practice you will probably have more fun as the jeep will accelerate and burn rubber easier, and you will burn more gas. Going from 3.07's to 4.10 would drastically raise your rpm's at a given speed, with stock tires. Therefore the engine rpm would be very high at highway speeds, for the 4.0L
I once changed the gears in a F150 from 3.08's to 3.73 to help with towing, which it did well, but it really changed the driving characterictics of the pick up. Accelerating faster and lowering the top speed. When I drove it nicely, gas mileage improved.
With 4.10's and small stock tires it would also be hard to crawl in 4 low.
It looks like cablesmurf and myself disagree on gas mileage. So I think you should go ahead and re-gear and let us know what happens :wink:
But I totally agree on his gearing suggestions for all around performance
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Anytime power goes through a gear reduction, torque is increased by that reduction. Gear ratios in relation to power and gas mileage is a balancing action with tire size. Put in lower gears with smaller tires and you will have a torquey little beast that is great off-road, but gas mileage will most likely suffer and not be very good at highway speeds because the engine is reving very high. Now put in higher gears (numerically lower) with the same tire size and you will have a nice power band, that is good at high speed and good on gas mileage, but off-road not very good.
There are tables on the out there that show the relationship between gear ratio and tire sizes and shows whether you are in the power side or fuel efficient side. Here go to this link, scroll down and click on "Gear Ratio Guide for Larger Tires" it explains a lot
http://www.quadratec.com/cgi-bin/sgdynamo.exe?HTNAME=tech_corner.html&checked=Y
Also the reason the 4 banger come with 4.10s and the 4.0L don't is because Jeep is trying to compensate for the lack of power in the 4 banger with gearing. The 4.0L with 4.10s and stock tires would be VERY torquey and BAD on the highway and on gas mileage.
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I wouldn't mind throwning my two cents in here. I get exceptionally poor gas mileage from my 3.07's and 33's due to under gearing. The added weight mixed the improper gearing land a lead foot leaves me with a flooded engine. This wastes a lot of fuel and kills my economy, but then again, it's a 50 year old engine design, you should expect much.
its a balance between tourque and fuel economy. gotta find the middle ground somewhere.
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Woah, sweet! thanks for the info guys! This cleared up alot of things for me. I can definately see why it's easier to snap axle shafts with the larger tires and lower gears...... But with my little 4cyl, I don't think I'll have to worry about that too much :)
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so... i just put 31" a/t's on my 01 TJ Sport (4.0L) manual transmission.
should i re-gear now?
lol, i swear if anybody has a computer question, i can help... but i'm lost here with this stuff.
i'll owe lots of people free computer tech support if they can help me out! :D
-Andre
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Don't waste the money, are about looking at about $1500-2000 to regear both front and rear for parts and labour. I would wait until you go to 33s or 35s. Just add performance parts like high flow intake and exhaust and these will take care of most of the power lost.
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.... This wastes a lot of fuel and kills my economy, but then again, it's a 50 year old engine design, you should expect much.
its a balance between tourque and fuel economy. gotta find the middle ground somewhere.
It's definitely a balance thing. That 50 yr old technology was, on my TJ and in stock form, capable of 23-24mpg. TJD60's was getting 24-25mpg. For a 4.0L engine that's not bad at all considering some of the new vehicles get this mileage or even slightly better but in an under 2.0L package and a light unibody car. I don't buy this "outdated engine technology" mindset at all. The older TJs were more economical than the newer (2000+) TJs and Rubicons. And with a regular distributor. Go figure. I believe the 4.0L engine to be quite economical in its class and even better than some smaller class engines. People modify vehicles, make them heavier, harder to roll down the road and then blame "old technology". The new manufacturing "standards" also amuse me. Make the vehicle heavier, slower and then wonder why the economy suffers. So let's throw more electronic gizmos in the mix to fix this. Making it even heavier and more complicated and less efficient as soon as one of those componenets is in less than 100% shape. Shame.
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.... This wastes a lot of fuel and kills my economy, but then again, it's a 50 year old engine design, you should expect much.
its a balance between tourque and fuel economy. gotta find the middle ground somewhere.
It's definitely a balance thing. That 50 yr old technology was, on my TJ and in stock form, capable of 23-24mpg. TJD60's was getting 24-25mpg. For a 4.0L engine that's not bad at all considering some of the new vehicles get this mileage or even slightly better but in an under 2.0L package and a light unibody car. I don't buy this "outdated engine technology" mindset at all. The older TJs were more economical than the newer (2000+) TJs and Rubicons. And with a regular distributor. Go figure. I believe the 4.0L engine to be quite economical in its class and even better than some smaller class engines. People modify vehicles, make them heavier, harder to roll down the road and then blame "old technology". The new manufacturing "standards" also amuse me. Make the vehicle heavier, slower and then wonder why the economy suffers. So let's throw more electronic gizmos in the mix to fix this. Making it even heavier and more complicated and less efficient as soon as one of those componenets is in less than 100% shape. Shame.
Its not so much that its outdated tech milan, its that its old tech. But its old tried and true stuff that still works, which IMO, makes it far from outdated.
The 4.0 has seen very few changes over the past 50 years.
Yes there are some older 4.0's that get slightly better milage, but there are also some key differences in those motors.
Those same older 4.0's are not the ones making 195hp and 240lbs of torque.
Most importantly, they arent making these numbers at the same rpm the older version made similar numbers.
I have not driven many older 4.0's that my 03 wouldnt walk all over, in stock form, or how it is now. But the cost of the changed cam timming, additional torque and hp is milage of course.
The 4.0 is still 100lbs heavier then a cast iron small block v8. As much as 300lbs heavier then the new aluminum versions that are out there.
There is no variable valve timming available for 4 litres.
There are no stock 4 litres comming out with aluminum heads, aliminum blocks, or rollerized valve trains. Mustangs have been rollerized since 84 or earlier.
The things mentioned above are becomming standard in a lot of engines, meaning the current tech used on 4 litres is still very basic and old school.
With the exception of an upgraded head around 1993, and the removel of the distributer in 02, there has been little to no change technology wise in the 4 litre for 50 years. Unless you count the addition of more and more computerized ignition timming and cat converters to decrease emission new tech. Which I dont as those things are external add ons.
If you spec out a crane cam for a 4 litre, have a look at cranes listing.
"AMC 4 litre, 1965 - presesnt"
Not even a sb chevy can do that, since they changed a lot of the bearing journals and what not after 69.
Like the saying goes, you cant get blood from a stone.
Without drastic changes to the ignition timming, valve train and timming, internal component compositions, etc etc etc, the 4.0 will pretty much stay the way it is. Not great on fuel but durable, reliable, and a very healthy lowend torque motor.
thats my 2 cents anyways.
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Oh, and one more tid bit.
The older tjs were already electronic ignitions. The removal of the dristributer simply consolidated some parts and allowed for the computer to have mroe control over ignition timming during warm up.
Both sparks are already strong enough that a change to either doesnt really make a difference.
Not like swapping out traditional points for something like a chevy HEI system does, where it doubles or triples the power of the spark, allowing for a much more efficient burn.
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Good info Bill. Man apparently knows his stuff.
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ya... but who asked you anyways Bill
:lol: :lol: :lol:
just kiddin. Good 'nfo. I want more info on the Cam mods.
As for you Milan... yer heavier, slower, and technically built from outdated technology but we still put up with you.
:mrgreen: :mrgreen: :mrgreen:
j/k
:D :D :D
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I want more info on the Cam mods.
Go to the Crane Cams website and all the info is there. There is a guy I wheel with that put a performance cam in his 4.0L with 33s, and the freakin' thing goes. When he steps on the skinny pedal, it throws you back in your seat. I think it is defnitely worth the money because cams are only about $250.
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Go to the Crane Cams website and all the info is there.
This the one? Linky (http://www.cranecams.com/?show=browseParts&lvl=2&prt=5&Vehicle_Type=Truck&Cylinders=6&Engine_Make=AMERICAN%20MOTORS&Year=1991&Engine_Size=258%20C.I.&partNumber=753905&partType=camshaft)
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more options here (http://www.cranecams.com/index.php?show=browseParts&lvl=2&prt=5&Vehicle_Type=Auto&Cylinders=6&Engine_Make=AMERICAN%20MOTORS&Year=1997&Engine_Size=243-258%20C.I.)
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Well you missed my point somewhat bnine, though I appreciate the info you provided. Sure its old and heavy. But my point was "so what?". It does not need anything new and yet it works as well as or better than most newer engine designs. The distributorless ignition was just an example of that something not really needed and only making the system more complex with no real gain anywhere. Aluminum heads and blocks, roller rockers, titanium valves, etc. Yeah I like them but guess what? They don't seem to give the new engines better fuel economy than that old iron block 6. They just make the engines they replaced better. Well then put the same stuff in the 6 and it will also be better...again. Just because it's old does not mean it's bad and just because it's old and there's newer stuff out there it does not mean it needs to be replaced....is all I was getting at.
Just like some of us, Apex....:D:D:D
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:lol: :lol: :lol:
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Well you missed my point somewhat bnine, though I appreciate the info you provided. Sure its old and heavy. But my point was "so what?". It does not need anything new and yet it works as well as or better than most newer engine designs. The distributorless ignition was just an example of that something not really needed and only making the system more complex with no real gain anywhere. Aluminum heads and blocks, roller rockers, titanium valves, etc. Yeah I like them but guess what? They don't seem to give the new engines better fuel economy than that old iron block 6. They just make the engines they replaced better. Well then put the same stuff in the 6 and it will also be better...again. Just because it's old does not mean it's bad and just because it's old and there's newer stuff out there it does not mean it needs to be replaced....is all I was getting at.
Just like some of us, Apex....:D:D:D
Oh ya, I agree with you 100%, its definately a "not broke so dont fix it" type of motor.
The only benefit I see to the new ignition is sealing and and some room under the hood, as in not looking so busy.
Its true lots of these fancy motors see similar milage to what the old six does.
The big difference is efficiency. For some of their 25 mpgs they are making motors put out 250 plus hp.
Or in the extreme cases like a vette, you have a 400 horse sbc that gets 22 on the highway.
Im sure if similar upgrades were ever added to the l6 you would see similar results. Basically the same milage, just better hp and torque for that mileage. They have already shown that trend over the years. The mileage has never changed by a whole lot, but they do seem to squeeze a little more power out of them as time goes on.
I also agree it doesnt need replacing. I personally love the simple straight forward approach used in our jeeps. From the age old proven motor, to not having to worry about power window and abs systems.
Sort of off topic, but I just had a co worker pay 1800$ for an abs controller on a chev half ton with 30k on it. Lucky for us we dont have to deal with situations like that with our "old" tractor motors, and relatively simple in todays standards jeeps :D
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Oh ya, I agree with you 100%, its definately a "not broke so dont fix it" type of motor.
The only benefit I see to the new ignition is sealing and and some room under the hood, as in not looking so busy.
Yup.
Its true lots of these fancy motors see similar milage to what the old six does.
The big difference is efficiency. For some of their 25 mpgs they are making motors put out 250 plus hp.
Yup.
Im sure if similar upgrades were ever added to the l6 you would see similar results. Basically the same milage, just better hp and torque for that mileage. They have already shown that trend over the years. The mileage has never changed by a whole lot, but they do seem to squeeze a little more power out of them as time goes on.
Yup.
I also agree it doesnt need replacing. I personally love the simple straight forward approach used in our jeeps. From the age old proven motor, to not having to worry about power window and abs systems.
Sort of off topic, but I just had a co worker pay 1800$ for an abs controller on a chev half ton with 30k on it. Lucky for us we dont have to deal with situations like that with our "old" tractor motors, and relatively simple in todays standards jeeps :D
Yup.
No that there's anything wrong with disagreeing but it's nice to be able to agree. :D
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I got 35's on my 01 tj auto with 35" pro comp tires .. i have it geared with 4:88 and like everyone else i still get bad gas milege
on the highway i get 450 kms to 60 L of gas at 105kph with cruise on . my rpms sit at 2900 if i go 120 i get about 300 kms to 60L of gas at 3200 rpms
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so... i just put 31" a/t's on my 01 TJ Sport (4.0L) manual transmission.
should i re-gear now?
lol, i swear if anybody has a computer question, i can help... but i'm lost here with this stuff.
i'll owe lots of people free computer tech support if they can help me out! :D
-Andre
Hey Andre,
I've been running BFG 31"s for about 3 years now on my '01 TJ Sport with 3.07's and a 2" daystar lift. It hasn't been the end of the world. I get about 440km out of a tank of gas (~18-20mpg). 5th gear is pretty much useless without a downhill pitch and a tailwind though!!!. Power's good in town in gears 1-4. I did add a K&N cone, a big intake, throttle body spacer, and Banks exhaust. I'm going to regear (probably 4.10's or 4.56's) this summer and go to 33"s, and I'll be stopping there. If I were you, I'd either wait like I did, or if you want to regear now, gear to what you think your ultimate tire size will be. Also, think about whether or not you want lockers, and you might as well do that when your diff's are open. Going to 33's is a big step because of the gears, lockers (if you want), need for bigger rims, the tires, bigger spare tire carrier, maybe flares, lift kit, etc. It's sort of all or none IMO.
Anyway, hope that helps.
BTW, I hate PC's, and will be ordering my new MacBook Pro on the same day as my gears!!!
-J.
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I got 35's on my 01 tj auto with 35" pro comp tires .. i have it geared with 4:88 and like everyone else i still get bad gas milege
on the highway i get 450 kms to 60 L of gas at 105kph with cruise on . my rpms sit at 2900 if i go 120 i get about 300 kms to 60L of gas at 3200 rpms
I think that you are overlooking some other aspects of why you may be getting less that average mileage from your rig, although you should be quite happy if your getting 450k's out of a tank. I would be.
The jeep is not the most aerodynamic vehical on the road. :wink: And putting a lift kit on and adding 35's will add all sorts of negative impact on the aerodynamics of a jeep. Plus the weight of the extra components and the extra weight of the tires and the additional resistance of the tires on the road and the additional wind they have to push.
Like Milan was saying before. There are not too many new jeeps on the road that are getting better milage then you, even if their brand new. :wink:
8)