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paging dr. hornbrod, and others who feel like chiming in..


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Don's my best choice on this question, but I felt like getting everyone's input...

 

I'm selling all of the mods on my lifted truck, save engine and intake/header.

 

Have a full 98 conversion to 4x4/ 5 speed, and I'm dropping it to a 3 inch lift with 31's.

 

My question is reguarding gearing. I currently have a d30 and d44 with factory 4.10's. With that in mind, a 5 speed has a higher geared overdrive than an auto.

 

I'm wondering if this is my optimal choice in gearing, or if I should install the 3.73 d30/d44 combo that I have?

 

Just want to know the facts of what I'm getting myself into.

 

 

Also, this will be a street truck/utility truck. It won't see much offroad time, but it will be heavy. Sliders, custom bumpers, plow, and winches front and rear (eventually). I intend for it to be useful. Right now it is a lawn ornament until I wheel it once in a blue moon, and the tire size is too much and causes issues. I want something that will get me or others out of trouble, and help me with towing and plowing duties. It will see interstate time as well as tow a tow dolly with weight up to that of an xj.

 

 

Opinionsd/ideas on optimal running gear?

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Here is a great site that I use alot...

http://www.grimmjeeper.com/gears.html

 

Just plunk in your factory specs on one side and go nuts on the other and it will tell you all the numbers you need to know...

 

Really your the only one who can tell you what gears to run based on your driving...

 

I prefer to get my RPM's as close to stock as possible for the best economy if a DD which most trucks are some sort of DD...

 

I hope this helps you some...

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The 5-speed overdrive ratio changed a few times but, in the overall scheme of things, none of them are enough different from that of the AW4 to indicate a different choice of ratio based on the transmission.

 

As I have posted a number of times, I ran the lifted '88 MJ on 31s with 3.73 gears the entire time it was lifted and used for wheeling. 31s and 3.73s results in exactly the same overall final drive ratio as stock tires with 3.54 gears. It's very drivable on the street, but could use a bit more gear for a better off-road crawl ratio. IMHO 4.10s are the optimum gear ratio with 31" tires.

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Yep, I agree. I run 4.10s with 31" on the AW4. It runs about 200-300 RPM higher across the board than it with the stock 3.55 gearing and stock tires, but mileage actually increased 2-3 MPG on the highway and stayed about the same in town. I think the 4.10 ratio w. 31" tires is ideal for the AW4 and it's .75 final O/D ratio. :cheers:

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WIth the AW4, 4.10 would be great. For the AX15, I fear it may be a bit high, but I say try it and see how it goes. If nothing else, just skip 1st.

 

 

that math computes to the gearing actually being a little low.

 

 

 

if it were, high, 1st would be necessary.

 

should be fine then, according to you guys.

 

 

 

thanks hornbrod, eagle, jeepman. my biggest concern is being able to do 70mph without redlining it.

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my biggest concern is being able to do 70mph without redlining it.

Redlining it?

 

How fast do you drive? Redline is 5,000 RPM. With 31x10.50s and 4.10 gears, in 5th gear 70 MPH is 2440 RPM. Does your truck do 150?

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my biggest concern is being able to do 70mph without redlining it.

Redlining it?

 

How fast do you drive? Redline is 5,000 RPM. With 31x10.50s and 4.10 gears, in 5th gear 70 MPH is 2440 RPM. Does your truck do 150?

 

Eagle, it was a figure of speach. I didn't say that I DO redline it...just that I don't want to.

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when reading the beginning of the post i'm thinking go up to 3.73, but then toward the end with the weight, utility, plowing, and occasional pulling i was thinking keep the 4.10. its a toss up imo.

 

you are definitely more likely to make money selling the 4.10 axles though.

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when reading the beginning of the post i'm thinking go up to 3.73, but then toward the end with the weight, utility, plowing, and occasional pulling i was thinking keep the 4.10. its a toss up imo.

 

you are definitely more likely to make money selling the 4.10 axles though.

 

especially since the rear is already SOA

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The nice thing is you already have both sets of axles with the gearing already done so if you decide on going 3:73's and find it too sluggish then you can eaily swap out to the 4:10 axles...

 

I am setup with 3:73 gears and 31x10.5x15's and a 4.0L HO (275HP) AW4 + I weigh in at 4000LBS and @100KPH (60MPH) I am at 2000RPM...

I am currently 13MPG City and 18MPG Hwy I have installed an overhead console with fuel info to monitor my realtime MPG numbers so I try to get as good as I can but I am too hard on the accelerator some times as the truck is too much fun to drive...

 

I will be upgrading to 33's which will lower my RPM and may have to upgrade to 4:10's in my near future..

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Yep , 410's with 31"s you won't regret it , my 456"s are too steep for 31"s as we all know but the 410"s are perfect . A nice blend of performance and function .

I can still use first even with the 456"s , I just don't need to ... :yes:

Actually installing my gears helped with milage since most of the roads in town are tall hills , way better than the ever hated 307's .

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Even with 205/75/R15 tires, 4.88 gearing, you'd would only be pushing 4500 RPM at 94 MPH.

 

I hope you're not seriously thinking overrevving is a problem, unless you're hammering on it in the lower gears and not watching the tach.

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I run 3.73's with 31 STT's great for the daily driving, and if I really need a compound low the tera 4:1 2 low his really come in handy for short hauling assorted junk including retrieving boats from deterioriated boat launches. If I had a stock Tcase I would go with 4.10's. :cheers:

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my biggest concern is being able to do 70mph without redlining it.

Redlining it?

 

How fast do you drive? Redline is 5,000 RPM. With 31x10.50s and 4.10 gears, in 5th gear 70 MPH is 2440 RPM. Does your truck do 150?

 

Eagle, it was a figure of speach. I didn't say that I DO redline it...just that I don't want to.

No, you said you were worried about redlining it. And I was pointing out that with 4.10 gears you would be a LOOOOOOOOONG way from ever approaching redline even at extra-legal highway speeds. Remember these engines were designed before most people had overdrives. The standard setup from AMC typically was 3.08 gears for the I6s and 3.15 gears for the V8s, and on stock tires we cruised at 3000 RPM at 72 MPH -- all day, for hundreds of miles. Y'all (not just you, Pat) have gotten so accustomed to the ridiculously low engine speeds the factory pushed out the door that you think anything over 2,000 RPM is going to blow up the engine. Not so.

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my biggest concern is being able to do 70mph without redlining it.

Redlining it?

 

How fast do you drive? Redline is 5,000 RPM. With 31x10.50s and 4.10 gears, in 5th gear 70 MPH is 2440 RPM. Does your truck do 150?

 

Eagle, it was a figure of speach. I didn't say that I DO redline it...just that I don't want to.

No, you said you were worried about redlining it. And I was pointing out that with 4.10 gears you would be a LOOOOOOOOONG way from ever approaching redline even at extra-legal highway speeds. Remember these engines were designed before most people had overdrives. The standard setup from AMC typically was 3.08 gears for the I6s and 3.15 gears for the V8s, and on stock tires we cruised at 3000 RPM at 72 MPH -- all day, for hundreds of miles. Y'all (not just you, Pat) have gotten so accustomed to the ridiculously low engine speeds the factory pushed out the door that you think anything over 2,000 RPM is going to blow up the engine. Not so.

 

lol...I have no quarrels with high RPM's. The truck has bounced off the rev limiter quite a few times, and caused no worry to me.

 

that said, I was using a figure of speech when I said "redline". what I should have said is that I don't feel like running @#$%ing ridiculous high rpm's at constant. I like gas mileage...it doesn't need to hit 3,000 rpm at a constant.

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Speaking of high RPMs: I'll never forget the first time I brought the MJ back to Hesco for my first dyno run about a year after I had installed their crate engine and done some exhaust and intake mods. The man himself, Lee Hurley did the test, while I watched. He made several short runs up to 5000 ear-splitting screaming RPMs while I cringed, held my breath, and waited for the engine to explode. It didn't, and when he handed me the the new printouts, it was a pretty good increase in torque/HP over the originals.

 

Since then I've had 3-4 more dyno runs all done by Lee (he likes MJs :D) after other mods I've done to confirm the improvements, and I'm not nervous anymore. These engines can spool up pretty well for short bursts, as all the ricers in my town now realize, although I don't do it often since I've snapped and axle w. the freaking D35. It's fun though..

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that said, I was using a figure of speech when I said "redline". what I should have said is that I don't feel like running @#$% ridiculous high rpm's at constant. I like gas mileage...it doesn't need to hit 3,000 rpm at a constant.

If I were a betting man, I would be willing to bet that with two otherwise identical MJs, one that ran 3,000 RPM at 70 MPH would deliver better gas mileage than one with stock gears and a 5-speed, that runs 1960 RPM at 70 MPH. There's just nothing like running UNDER the torque curve to boost your gas mileage ... NOT.

 

3,000 RPM is not "@#$% ridiculous high rpm's" for these engines -- it's the speed they were designed to run at.

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that said, I was using a figure of speech when I said "redline". what I should have said is that I don't feel like running @#$% ridiculous high rpm's at constant. I like gas mileage...it doesn't need to hit 3,000 rpm at a constant.

 

 

Don't fear the rpms. :D Freeway speed and vehicle design FAR outweigh rpms when it comes to mpgs. most of the energy used at 70 mph is used to push the air out of the way. Think of it as the engine needs x amount of power to push through the air at Y speed. rpms matter little in the equation since the engine will consume about the same amount of gas to accomplish the same task (pushing a brick along at 70mph), whether at 2500 or at 3500 rpms. There is a sweet spot (usually the torque peak), but it's a big sweet spot since our trucks have a large flat torque curve. :D

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There is a sweet spot (usually the torque peak), but it's a big sweet spot since our trucks have a large flat torque curve. :D

 

True for stock engines, not so much for strokers though. Not so flat. But even for a stock lawn and garden engine in good health it's wise to spend 50 bucks or so to get a dyno run done to see exactly where the efficiency and peak sweet spots are, otherwise you're just guessing.

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