I was under the impression that the 4.0 liked it higher up closer to 3k for cruising.

 

4.11s have an extra spline? Huh? Do you mean that the pinion is larger? Has nothing to do with splines. All Dana 30s in XJs, TJs, YJs, ZJs, MJs, WJs, JKs are 27 spline.

The AW4 is a 4-speed with overdrive (aka torque convertor lock-out). It's taking data from the tps, vss on the tcase and probably more and deciding when to upshift and downshift. Low load cruising down the road? It'll be in overdrive. Going up hill, etc. needing more throttle to maintain speed? It'll be in 3rd or 4th.

I'm not sure what you're trying to figure out. To make your transmission behave as though your jeep is completely stock you need to regear AND replace the speedo gear in the tcase. With larger tires (spinning slower at the same mph as stock) your driveshaft will be spinning faster than stock. So, to get back to factory final drive ratio you need to regear to 4.10s and use the appropriate speedo gear (should be larger i think) to make the speedo/odo and TCU think that everything is as it left the factory.

I've never hear about this 2200 rpm shenanigans but at 65 mph my engine is running at a little over 2500 rpm (4.10s and 31" tires). I like it that way. 2200 seems low to me and seems like it would have to downshift at highway speed to accelerate.

 

Well i'm not really trying to figure anything out persay; just wondering what rpm is concidered "lugging the motor"

I'm not trying to talk myself out of regearing. I def want to. When i posted that question i was on the wall about 4.10s or 4.56s.

I decided to go with 4.56s because my main driving is on country roads and city with about 6-7 miles of highway.

when i used the calc i mainly set it for the back roads @ 50- 55mph and 4.10s would be to low of an rpm for me @ 50. with some minor inclines the tranny would be gear searching. and that costs mpgs.

even on the highway wich is the Atlantic City Expressway, the part of it that i travel has a max speed limit of 55mph. So i'll do 60-65 at most. I don't ever see the 65mph speed limit of the expressway.

Plus the fact I can't completely count out the possibility of ever getting bumpers.

I never go faster than 65 anyway. So 4.56s for me.

So thankyou Mwildmann...

 

I think that lugging the motor applies to the manual transmission crowd more than anything. Like not downshifting far enough and trying to accelerate, the engine will make that angry grumbling sound (usually below 1000 rpm). That's how my car (a 5-speed) tells me I didn't go deep enough.

In terms of lugging an automatic, I don't think that really happens. And I'm interpreting the term "lugging" as putting a heavy load on a motor that isn't running fast enough. Which is bad because the engine isn't spinning fast enough to generate really good oil pressure while under that heavy load.

Is there an optimum rpm? Sure there is. Do I know what it is? Nope. I don't even bother trying to figure out mpg on my junk because i never replaced the speedo gear since i'm about to go to 33s. I probably will once the new shoes are on though. Plus it's just a toy and I don't care.

I think that your choice of 4.56s is a wise one. If I hadn't stumbled on my axles that were already geared to 4.10, that is what I would want. I got a hell of a deal too cause the PO didn't know what he had. Maybe I'm rambling now. Good luck to you, boss!

 

thanks brotha.

I only sweat it alittle because she's my DD. I know i won't exactly at stock mpgs, but getting close would be good. I'm gonna try and get the speedo cal. this week. and do mpgs with my 33s. so we'll see how close my estimation of 15-16 is...lol

 

Also, keep in mind that fuel economy is far more affected by such things as weight, powertrain inefficiencies, aerodynamics, tire tread pattern and driving style rather than final drive ratio.

 

Hmm mine seems to like the 2200 a lot. Like I get damn good gas mileage like 21 mpg with 4.5 and 31s. Ill have to try the higher rpms and see but I doubt it

 

driving @ 3k will only get you speeding tickets and sh1ty mpgs.

Defwillp..whoever told you that is on some serious crack.

2-2200 is what i read. not 3k. thats funny..lol

 

i was reading the thread and also have some aw4 problems so i went looking for mentioned thread^^^^^^^^^^^^^^ found it not on jeepforum but on naxja so here it is if anyone else needs it. hope it answeres some of your question.
http://www.naxja.org/forum/showthread.php?t=1053970

 

Thanks for getting into the convo, guys, some points you're making are things I was thinking, just forgot about.

There has to be a sweet spot for every vehicle/person combo. We don't have a lot of hills in my commuting route in AZ, so I can get by with lower rpm's without down shifting.

I would think that the computer in an auto would not let the motor lug itself. Thanks for pointing that out MWildmann

I also know that mileage will be helped if the motor doesn't have to work as hard to accelerate (which it's doing right now in mine). But there is a point where that affects final drive ratio. So it seems that you'd want to figure out which one is more important.

4.10 gears will help my final drive it seems, and 4.56 will help my city mileage (among other things). I have a hard time believing that it will get better mileage on the highway with 4.56's than 4.10's at this point. Like someone else pointed out, it's probably very minimal compared to drag, heavy bumpers,

I think it all started when some guy seemed appalled when I would consider 4.10's to the point where it set off warning bells. Often the most vocal people are the most unsure, so they counteract their lack of explanation with volume.

I'm getting enough tanks of gas under the belt here and taking enough notes that I'll definitely have some idea of how much my highway mileage is affected.

There's no way it's 3K though... that' nearing cruising rpm territory for my motorcycle. The 4.0 is a tractor motor.

 

I heard "Tractor motor" so that's my queue. Lol. Seriously, I'm running an actual IH 258 tractor motor in my 85 Xj with the original 2.8L 3.31:1 gearing on 31x10.50R15s. Forget speed cause its all torque. My OD RPMs at 65mph is 2100. Keep in mind whe selecting gears that the basic gearset was 3.55 for autos and 3.07 for standards. Now use this basic formula to determine what your Xj "acts" like it has: Current gear ratio X Stock tire size / New tire diameter = Effective gear ratio. EX: 3.31 X 26 / 31 = 2.68:1 gear ratio. (Yes I know that's high but my motor makes three times more power so it acts like a stock 4.0 w/3.55s till I regear) By plugging a different tire size/ gearset in, you should be able to do the math to bring the end result as close to 3.55 for autos and 3.07 for standards for best performance/fuel economy.

 

OP. just do whats right for you. All we can do is offer our experience and opinions.
And opinions are like a$$holes. we all have'm.GL.

 

Ain't that the truth