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Ideal All-Purpose RPM for Re-Gearing

Yoda

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I'm putting 33x10.5's on my 98 TJ with an AX-15 and 4.0L. The motor is going to be stroked and should have peak torque somewhere around 3000RPM hopefully. It will be an all purpose rig, 85% highway cruising during the week, probably 80 miles per day commuting almost all highway. Will play in the woods on the weekends. Mostly rough fire roads, logs, random rocks. Not a dedicated rock crawler or mud bogger.

What do you think the ideal RPM's would be for best MPG on the highway but also good for off-roading when needed? I tend to drive the speed limit or so, about 65-70MPH on the highway.

I was thinking 2500RPM is a good middle ground to shoot for. The .79 5th OD gear, with 33's and 4.56's gives me 2400RPM at 65mph . With 4.88's I'm at 2550RPM at 65mph.

Would 4.56's or 4.88's be better for fuel economy?

Yes I know it's a Jeep not a Honda, so please don't tell me I should have bought a Honda Civic. I somewhat care about the environment and if I can burn less gas while having fun, I'll do it. And if I'm going through everything and re-gearing I might as well try and get the best gas mileage I can while still having fun in the woods.

Thoughts?
 
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JMT

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488’s will be better for fuel economy.
 

machoheadgames

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For those two rpm numbers I would expect mpg to be around the same. 150 rpm isn't going to make or break mpg in either direction. If you will never go past 65 I'd probably just do 4.88. If you will want to drive faster, I'd probably go 4.56 since it's a stroker with more power. On the plain 4.0, I'd definitely do 4.88/33 (and I did).
 
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Yoda

Yoda

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If you will never go past 65 I'd probably just do 4.88. If you will want to drive faster, I'd probably go 4.56
65-70mph is a typical cruise speed. If traffic is moving at 75-80mph I'll jump in but not as common. With 4.88's if I wanted to go 75mph I'm at 2950rpm. 80mph is 3150rpm.

4.56's is 2750rpm @75mph and 2950rpm @80mph.

But....like I said in the first post, most of it's life will be at 70ish.

Which RPM will give me the best fuel economy at 65-70mph?
 

Woodrow

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I have a '97 w/ a Golen stroker, AX-15 and 4.11 gears on 33s. I daily drive it w/ a country road commute. RPM is about 2000 at 60mph in 5th. It will accel up a hill from 60 in top gear but I usually shift to 4th. At 75 on the highway, it feels strong. I think 4.56 would be fine also, but 4.88 might be too much for me. I get about 13 mpg which is down from 15 w/ the 4.0, 31s and 3.07 gears.
 

freedom_in_4low

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as others have said...the difference isn't going to show up in fuel economy.

It might show up in how pleasant it is to drive.

I was happy with 4.56/AX15/33s, but I had a lot of 75mph speed limits where traffic goes 80+. If 65-70 was really top end, I'd probably go 4.88. The reason being is that (IMO) the 4.0's happiness changes a fair amount between 2400 and 2550. I like to target closer to 2700-2800 for cruise speed. I'm ~2675 at 65mph (with 35/4.88/NSG370) and would probably downshift to climb a hill at that speed.
 
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Yoda

Yoda

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Not that it is a deal breaker, but how buzzy/loud/annoying is the engine cruising in the 2750ish RPM range if at all? Does the 4.0l care?

FYI...the stroker is going to be a DIY combo of the "modified poor man's stroker" and either a gasket-matched head done by myself or if I want to cough up some coin get the ported TUPY head from Newcomer. Probably a Comp Cam's 231 or 232 cam. Shooting for 9.5:1 compression or so and 87-89 octane. Prioritizing low and mid range torque.
 

machoheadgames

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I've never found it to be annoying at all cruising in the 27-2800 range or even at 3000. I found 2400-2500 to be a bit anemic feeling myself, but that may change with a stroker. I know a big aspect of the stroker is having the torque come alive quicker than the 4.0 which you get with the 4.2 crank. I'd personally do the engine first, then figure out where you want to be from what you have now.

Or like myself and many others did, regear the 4.0, and determine that it's good enough to not want to mess with an engine build anymore. But you sound serious on the stroker so I'd probably do that first and evaluate the ratio to pick after, if you can sequence things that way.

But, if you still want to make a decision now, I don't think you'd hate 4.88 based on how you say you'll drive it. If you wanted to fly down the road at 80 mph all the time, then you maybe would want 4.56 instead.
 
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TheBoogieman

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Not that it is a deal breaker, but how buzzy/loud/annoying is the engine cruising in the 2750ish RPM range if at all? Does the 4.0l care?

FYI...the stroker is going to be a DIY combo of the "modified poor man's stroker" and either a gasket-matched head done by myself or if I want to cough up some coin get the ported TUPY head from Newcomer. Probably a Comp Cam's 231 or 232 cam. Shooting for 9.5:1 compression or so and 87-89 octane. Prioritizing low and mid range torque.
The 4.0 prefers higher rpms and mine isn't loud at all. I did have a 32rh auto with 4.56 gears and 32s. It got the worst highway MPGs of any Jeep I've ever owned.
 
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Slicknick630

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In my 01 TJ 4.0 4spd trans with 35s and 4.88 gears I run about 3100-3200 rpm at 65 mph if I could do it different I would have done more research to get those rpm’s down on the highway for when I drive out to do some off-roading. I just went with what my local off-road shop told me before I knew what type of wheeling I was going to be doing. I just said I have 35s and want to regear. You give and take with gears that’s for sure. I am definitely interested in what other think and how their setups compare.
 
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freedom_in_4low

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Not that it is a deal breaker, but how buzzy/loud/annoying is the engine cruising in the 2750ish RPM range if at all? Does the 4.0l care?

FYI...the stroker is going to be a DIY combo of the "modified poor man's stroker" and either a gasket-matched head done by myself or if I want to cough up some coin get the ported TUPY head from Newcomer. Probably a Comp Cam's 231 or 232 cam. Shooting for 9.5:1 compression or so and 87-89 octane. Prioritizing low and mid range torque.

I don't notice it, but mine isn't a stroker. You'll have more piston velocity, and being an inline 6 theoretically cancels out the primary and secondary imbalances but I don't have experience there.
 
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machoheadgames

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In my 01 TJ 4.0 4spd trans with 35s and 4.88 gears I run about 3100-3200 rpm at 65 mph if I could do it different I would have done more research to get those rpm’s down on the highway for when I drive out to do some off-roading. I just went with what my local off-road shop told me before I knew what type of wheeling I was going to be doing. I just said I have 35s and want to regear. You give and take with gears that’s for sure. I am definitely interested in what other think and how their setups compare.
From the factory, an 01 auto is 3 speed and the manual is 5 speed. Guessing you have the 3 speed. Most people going with 35's on the 3 speed choose 4.56. There is always some give and take on the gearing vs rpm with the 3 speed auto because you don't have overdrive.
 
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Jerry Bransford

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Not that it is a deal breaker, but how buzzy/loud/annoying is the engine cruising in the 2750ish RPM range if at all? Does the 4.0l care?
The 4.0 doesn't care at all, I loved my 2750 70 mph cruising rpms with my previous TJ with 4.88 and 35's with the 5-speed. My current TJ has 5.38 gears with 35's but with the 4-speed automatic. Its 70 mph rpms are more like 2550 which is not quite enough.
 
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machoheadgames

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The 4.0 doesn't care at all, I loved my 2750 70 mph cruising rpms with my previous TJ with 4.88 and 35's with the 5-speed. My current TJ has 5.38 gears with 35's but with the 4-speed automatic. Its 70 mph rpms are more like 2550 which is not quite enough.
When you move to FL and won't be doing any more heavy wheeling, you could downsize to 33's and enjoy getting some of the rpm back :)

Although I suppose you're set up for 35's in many other ways.
 
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SvtLdr

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Not that it is a deal breaker, but how buzzy/loud/annoying is the engine cruising in the 2750ish RPM range if at all? Does the 4.0l care?
As mentioned above, the 4.0 performs very well at that RPM. By the time you're moving that fast, there are a number of other things that make a lot more noise than the engine.
 

SvtLdr

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When you move to FL and won't be doing any more heavy wheeling, you could downsize to 33's and enjoy getting some of the rpm back :)

Although I suppose you're set up for 35's in many other ways.
Jerry's plans for Florida retirement...
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...oh yeah, that's an ANGRY GRILL!