Stock 4.0 XJs with the Highest Highway RPMs? - JeepForum.com
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post #1 of 9 Old 10-30-2018, 12:37 PM Thread Starter
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Stock 4.0 XJs with the Highest Highway RPMs?

This question is to entertain an idea I have regarding axle gearing for the 4.0.

What factory transmission/tire size/axle gearing combo resulted in the highest highway rpms on a XJ with the 4.0?

For example, an early TJ Wrangler was available from the factory with this combination...

32rh / 29.5" / 3.73 = 3186rpm @ 75mph

Was there anything comparable with the XJ?



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post #2 of 9 Old 11-01-2018, 10:24 PM
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To the best of my knowledge, no 4.0-era XJ was ever available without an overdrive transmission. I believe it's a .75 OD on the AW-4. I think you could special-order 4.10 gears. Smallest tire available was a 225-75-15, about 28.5" tall(actual measurement)
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post #3 of 9 Old 11-01-2018, 10:31 PM Thread Starter
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Thanks! That's the kind of info I am looking for.

AW4/28"/4.10 = 2767rpm @75mph

My calculations come from grimmjeeper.com, btw.

The reason behind this is to see what rpms Jeep was running the 4.0 at from the factory as a way to demonstrate that the 4.0 is not a low rpm engine. And that when we regear for larger tires, we should not be afraid of going low.

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post #4 of 9 Old 11-01-2018, 10:38 PM
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But then of course, I think the 4.10s were an upgrade optioned with the "off-road package" and probably weren't offered with the 225 width tire in that configuration.
Unless, back in the day, they could be special ordered "stand alone" on an otherwise bone stock, base 4.0 XJ.
anyway, it would be a rare combination.

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post #5 of 9 Old 11-02-2018, 03:25 AM
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Originally Posted by jjvw View Post
Thanks! That's the kind of info I am looking for.

AW4/28"/4.10 = 2767rpm @75mph

My calculations come from grimmjeeper.com, btw.

The reason behind this is to see what rpms Jeep was running the 4.0 at from the factory as a way to demonstrate that the 4.0 is not a low rpm engine. And that when we regear for larger tires, we should not be afraid of going low.

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it is not a high revving engine for sure, not much beyond 4500rpm and not much comfort above 3,500rpm for cruising. In this respect i has a shorter stroke than its 258 ancestor, and is able to rev higher and faster to make it a more highway friendly SUV engine, but it is still nailed by being a straight 6 tractor engine at heart.

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post #6 of 9 Old 01-26-2020, 01:54 AM
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Yes it concerned me too RPM vs speed.
I always wanted to know what should be the correct RPM for like 75 MPH, in order to know weather your XJ has a healthy engine or not.

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post #7 of 9 Old 01-26-2020, 09:06 AM
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3.55s in my stock 2001xj. AW4. 225 75R15 All Terrain tires. Freeway cruising [60 to 70mph] always in the range of 1850 to 2200 depending on incline.
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post #8 of 9 Old 01-26-2020, 09:46 AM
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Originally Posted by BagusJeep View Post
it is not a high revving engine for sure, not much beyond 4500rpm and not much comfort above 3,500rpm for cruising. In this respect i has a shorter stroke than its 258 ancestor, and is able to rev higher and faster to make it a more highway friendly SUV engine, but it is still nailed by being a straight 6 tractor engine at heart.
It was NEVER a tractor engine or anything of the sort.

https://en.wikipedia.org/wiki/AMC_straight-6_engine

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post #9 of 9 Old 01-26-2020, 09:50 AM
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The 4.0 equipped vehicles came with a 3.55 axle in auto trans and 3.07 in manual trans.

3.73 and 4.10s were used in the 86 and earlier XJs and MJs only.

If you're worried about being at too high an RPM on the freeway, don't be.

It was the Brirish that used tractor motors in their cars. Not AMC.

The 230 engine of Jeep's was used in racecars driven by Juan Fangio with triple Weber carbs. I'm sure he revved it a bit above "plow" mode.........

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