Real world feedback on gears @400-450HP - JKowners.com : Jeep Wrangler JK Forum
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post #1 of 9 Old 12-04-2018, 11:42 AM Thread Starter
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Real world feedback on gears @400-450HP

OK, we all know there are exactly 6 Jeep topics. So, yeah this is a repeat. If I were on either side of this equation I think I'd know the answer but, as always, am a bastard child with my set-up.

I'm going to have at least 400HP at the crank, maybe up to 450hp, with my motor selection. To state the obvious I have plenty of gear selection for off-road so I'm really only concerned with on-road performance with my final gear selection. The torque charts tell me I should be about ~80% of the max 480lbft of torque available at 2000 RPM.

My basic question is do I have enough power to be happy with 4.88's on 37-38" tires or would I be looking for more assistance from the gearing? My highest transmission ratio is 0.64 and with this motor 2,000 RPM seems to be the sweet spot for highway cruising (70mph) and good fuel economy.

Any one with around this much HP want to give input of their gear/tire selection experience..... I know it is extremely subjective but that is what I'm looking for. I know what the dry numbers tell me.

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Last edited by toymaster; 12-04-2018 at 12:51 PM.
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post #2 of 9 Old 12-04-2018, 04:32 PM
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I'm running the stock 4:10s with 37s behind my 6-speed RIPPed 3.6

I've had 5.13 gears sitting around for a couple of years, and have not yet been compelled to put them in. It's a bit of a trade off, but the 4.10s are not so bad that I hate them. FWIW.

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Now back to a 2013 JKU Rubicon with "stuff", planning 37's with minimal lift.

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post #3 of 9 Old 12-04-2018, 08:53 PM
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My Jeep has ~42HP + half a squirrel fart but I'd bet you won't want deeper gearing for the street unless your goal is max. acceleration. Let big torque do its job and take care of business for you, no need to wind out a torquey engine unnecessarily.

If you have 80% of max. torque at cruise RPM, you should have "best" MPG and likely not even have to downshift to accelerate. My $.02 = take advantage of that fat torque and let it lug a bit. You can always downshift.

I'm basing this on my F250 w/ 428CJ and no overdrive . Sporty as fuck, but it needs longer legs on the freeway. Engine's plenty happy at 70 MPH, but it treats the gas tank as its personal beer bong

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post #4 of 9 Old 12-05-2018, 05:45 AM
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Iíve got a 2013 and Iím pushing close to 600 at the crank with 5.38 gears and a 4.3-1 atlas and my Jeep overall is way too low. With the stock 5 speed auto Iím pushing 2700 rpms at 65 on the highway


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post #5 of 9 Old 12-05-2018, 08:19 AM Thread Starter
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Quote:
Originally Posted by ExWrench View Post
....If you have 80% of max. torque at cruise RPM, you should have "best" MPG and likely not even have to downshift to accelerate. My $.02 = take advantage of that fat torque and let it lug a bit. You can always downshift....
Yeah, that is what the math is telling me. My highest transmission gear is 0.64 and the next one down is 0.69. I just can't get the "old school" way out of my head.

I plan on sourcing a 10R80, they are not available yet as a crate transmission so I may have to get one out of a wrecked truck. Found a company currently doing their R&D for a controller for it, should be on the market sometime in 2019. I'm running the 6R** in several of my vics now and love it but I'd have to be more cautious in my R&P choice with that transmission spread. The newly available 10 gears can cover a lot of ill and allow me the luxury of running a higher ratio R&P. It just doesn't "feel" right yet, and if I make the wrong choice I'll be kicking myself in the ass....

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.....a dark forum, were people would sometimes be rude but yet be helpful.
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post #6 of 9 Old 12-05-2018, 08:49 AM
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Quote:
Originally Posted by ExWrench View Post
Engine's plenty happy at 70 MPH, but it treats the gas tank as its personal beer bong
This made me laugh out loud! Haha, I feel the same way sometimes with the 6.0L and 5.38s.

Personally, I do a fair bit of highway driving in the mountains and pulling a 3,500lb camper. I prefer the lower gears, but I think 5.13s would better suit me for the highway. I say go deeper if pulling mountain passes regularly and/or pulling a trailer. However, the 4.88s seem to be right with your HP/TQ numbers and will likely still play well with more transmission later on.
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post #7 of 9 Old 12-05-2018, 09:29 AM
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I have a 6.0l/6l80e combo on 40's and have found that 4.88 are perfect for me. Cruising on the highway at 70mph I am right at 1900rpm but it will still break the tires loose on dry pavement when you get on it.

2011 Jeep Rubicon JKU 6.0l VORTEC L96 - 6L80E 6 speed auto
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post #8 of 9 Old 12-05-2018, 09:39 AM
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Quote:
Originally Posted by Riptide9 View Post
I have a 6.0l/6l80e combo on 40's and have found that 4.88 are perfect for me. Cruising on the highway at 70mph I am right at 1900rpm but it will still break the tires loose on dry pavement when you get on it. <a href="https://www.jkowners.com/forum/images/smilies/smile.gif" border="0" alt="" title="Smile" >:-)</a>
Similar setup here with LS3/6L80, 4.88, and 40” Nittos. 70mph right at 1900 rpm in 6th with converter locked.
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post #9 of 9 Old 12-05-2018, 12:41 PM
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I was running 5.13's with 37s until recently. It's a 3.6 with a blower and I also have a manual transmission in a rubicon (transfer case).

Maybe 4.88 if you are an auto transmission on 37s. I think that is about in the same blue range on the gear chart is for 37s, a manual transmission and 5.13's.

Works well on and off road. I think I'm at about 2450 RPM at 65MPH.

I busted a couple of rear pinion teeth on the rear D44 and am now going tons with 5.38's. Still undecided on tire size.
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