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What RPM should my 4.0 be running at?


Eddie Greenlee

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So I read a long thread last week about what the proper rpm range the wrangler's should be run. I can not find the thread now but, the main thing i remember is that if I am running my jeep at or around 2000 to 2300 rpms that im doing it an injustice. Could you please set me straight on the proper rpm to run my 97 tj 6cyl 4.0 with 4.10 gears.... thanks again
 
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Eddie Greenlee

Eddie Greenlee

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should I be concerned with upper rpms till i get to 5 gear and 70mph ( now I know when to down shift and not let it lug and all) like should i run the jeeps rpms in 1st -4th to 2500 before shifting, or just with in reason??
 

Jerry Bransford

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Don't be afraid to rev our Jeep engines to whatever rpms you want to while accelerating. If I were running a manual transmission I'd be revving it to no less than 3000 but more likely 3500 to 4000 to merge onto a highway. Consistently keeping the rpms low and never revving to high rpms is a sure-fire way to cause the engine to start developing carbon deposits in the combustion chambers which will make the engine run like crap, ping, etc.
 
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Eddie Greenlee

Eddie Greenlee

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well I just went out for a test drive, and thats a BIG difference ( 3000 to 3500), and will take some getting use to. But my rpms at 70 were more like 2250 in 5th gear. I know that has to do with gearing vs my tire size, but that will change within a year. Thanks for the info, what a difference in speed and torque.
 

jjvw

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I typically shift well past 3k rpm, often getting into 4k. When I regeared, I intentionally put my 70mph at about 2800rpm. 75mph is 3k. It's fine. The Jeep is my daily driver, btw.

2003 Rubicon
 

Mr. Bills

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The "sweet spot" for the 4.2L I-6 in my CJ-6 was about 2,400-2,600 rpm. The sweet spot for the subsequent 4.0L I-6 engines I've had has been a tad higher, but not much.

My '06 LJ Rubicon with 4.0L I-6, 42RLE automatic transmission (0.69:1 OD), 5.38 gears and 35" tires (actually 34.6") turns the following RPM's at 65 and 70 mph (RPM rounded to the nearest 100; Speedometer calibrated with SpeedoHealer and verified with my CHP buddy's radar):

65 MPH

3rd Gear (1.0:1) 3,400
4th Gear (0.69:1) 2,400

70 MPH

3rd Gear (1.0:1) 3,700
4th Gear (0.69:1) 2,700


I can't tell you what the shift points are because my trans is "automatic" and I haven't paid close attention other than the shift points are at the right place.

This online gear calculator may give you hours of enjoyment playing with rpm's, gear ratios and tire sizes: grimmjeeper.com/gears.html
 
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HarleyMick

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Dyno.jpgThe 'sweet spot' for peak horsepower on my 99 TJ is between 5k - 6k rpm, but the red line is at 5,500 and I honor that. When I had the computer reprogrammed I wish I had set the rev limiter at 5,200 rpm instead of just removing it. Even a Golen Stroker will float the valves if you push it too far or miss a gear. I'm considering sending the ECM back to have the rev limit set.
 

Rescue6

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I typically shift between 3500-4000 on the street. No problems doing it that way in every 4.0 Jeep I’ve owned.
 

bluescapegoat

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When I got my first 4.0 6 speed TJ I found myself shifting at 2k rpm, it felt so torquey down low with the short gears.

Started adding bigger tires and started shifting later and mpg went up and it just felt so much more natural to drive.

Generally speaking I just try to keep the revs above 2250 any time I'm asking it to do any work, 2500-3000 daily driving. 4500+ merging. I'm also geared to about 2750 rpm at 70.

The 4.0's a screamer, but she can take it.
 

tworley

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Cruising speed is somewhere around 2600-3000 depending on speed. Daily driver here too
 
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Goatman

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By "sweet spot" I think most people are referring to efficiency not an actual HP number. These engines were designed for torque more than HP. For a manual trans you want to be in the 3,000 rpm range for good acceleration. 4,500 or even a tad more when you need to get moving fast. If you are never getting the engine in the higher rpms under load then you can (will) cause carbon buildup and a cylinder lip can form. Higher rpms can also help get any moisture cleared out of the lubrication system and help keep bearings in good shape.
This is not to be confused with maintaining sustained rpm's in the 4,500 and above range. The heavy rotating mass isn't designed for this unlike a light 4 cyl engine is. (Honda or sim.)
For everyday easy driving the 4.0 is happy in the mid to upper 2k range. But you should include at least a few higher rpm shifts after the engine is warmed up.

I think even with an auto trans you should allow the engine some higher rpms under load every so often to help keep carbon buildup down.
 

freedom_in_4low

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I sit between 3500-4000rpm for about half an hour to stay within 5mph of the speed limit over Monarch Pass (11,300' and 7% grades) in 3rd gear. I then end up getting better than average mpg for that tank because I don't touch the throttle for the next 30 miles going back down the other side.
 
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jjvw

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I sit between 3500-4000rpm for about half an hour to stay within 5mph of the speed limit over Monarch Pass (11,300' and 7% grades) in 3rd gear. I then end up getting better than average mpg for that tank because I don't touch the throttle for the next 30 miles going back down the other side.
My mountain mileage has always been better than flat highways.
 

freedom_in_4low

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My mountain mileage has always been better than flat highways.
mine too. My best tank ever was 19mpg coming from my family's cabin about 8 miles northeast of Estes Park, driving around in Rocky Mtn NP, then going back through Lyons and Longmont to I-25. I averaged a little under 15 on the (relatively) flat stretch between Colorado Springs and Pueblo when I worked down there.
 
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LJBean

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Dec 25, 2019
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Rockwall, TX
My mountain mileage has always been better than flat highways.
What's up with the better mileage at higher elevation? I can get 18+ MPG running 35s on mountain highways in SW Colorado, but struggle to get 13 MPG down on the plains.