Bump up horsepower or regear? Need advice! - JeepForum.com
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post #1 of 32 Old 07-11-2020, 10:49 PM Thread Starter
RedBolide
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Bump up horsepower or regear? Need advice!

I've been driving my TJ on the freeway a lot more, and I'm starting to get a bit frustrated with the performance. I created the problem myself: I decided to put on 33s since I loved the look and most of my driving was local at the time. Now, I need to do some upgrading to get it to perform. Specifically, when I'm on the highway, my speed varies way too much. Downhill I can do 80 no problem, but every uphill drops me down to 60. I figured I'd have two options.

For one, I could try and squeeze out some extra power on my 4.0. My Jeep is basically bone stock. I'd definitely go for a cold air intake and less restrictive muffler/tailpipe. Was thinking of maybe putting in a different cam or throttle body if that's not enough. The other option is to swap the rear gears. It's a stock 03 Sport, so I could gear down a bit.

Basically, I'm wondering which approach is better. I'm trying to prioritize longevity in this Jeep. I want to make sure I'm not straining the drivetrain, but I'd also like to cruise at 70 when I'm on the highway. Any input on what approach is smarter?


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post #2 of 32 Old 07-11-2020, 11:10 PM
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cool air intake, throttle body spacer, cam, exhaust kit, tuner, etc all will add a little more "oomph". gears will also help, but you'll lose mpg's, if that matters. you can also go with a blower kit. a crank driven blower kit should be pretty easy to do, and will help you run the hills, but still be decent on gas. (if you can keep your foot out of it) a blower kit, complete, should cost around 3500. if you swap the rear gears, you'll have to swap the front as well. (or pull the front driveshaft)

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post #3 of 32 Old 07-12-2020, 01:07 AM
Stumptown
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Gears all the way.

You don't say if you are auto or stick, that would change the ratio you would want to go to. Cheapest way to go is grab some axles from a 4cyl, pretty sure they are all geared 4.10. If not, someone will correct me.

This will allow you to keep your engine in its power band on the freeway. Between 2 and 3k is the sweet spot for my auto jeep. With that wicked overdrive it would want to run like 1400 rpms on the freeway, which was terrible. Way out of the power band for the engine, and it struggled to decide if it really wanted to accerate when I floored it.

I geared down to 5.13 for my 33's, and I actually increased my mpg by 2. I have the 4 speed auto, so depending on your transmission your experience may vary. I am still under 3K at 70 on the freeway.

Now I am on 35's, I want to go even lower, but then that means new front axle, so probably not going to do it.

But those 5.13 gears with a 31 inch tire? That was fun!

The other options may get you more power, I don't know, haven't tried any of them, but gears are the answer.
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post #4 of 32 Old 07-12-2020, 03:56 AM
TheBoogieman
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regear it. The other crap does nothing.

Quote:
Originally Posted by jeepinmichguy_ View Post
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GOT IT BACK 6/17. 03' Rubicon/Zone 4.25" combo lift with 4" lift coils up front/Zone hydro shocks/5.13 gears/35" Mickey Thompson MTZ P3 tires/Black Magic brakes. Jeep #17 & 19.
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post #5 of 32 Old 07-12-2020, 08:44 AM
pwmac
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With such a low horsepower motor there is little hope that any increase due to aftermarket additions will be noticable. Make sure the motor is up to snuff with required maintenance like plugs etc.
With 33" tires you will see the greatest benefit with regearing, but the cost is very difficult to justify.
Getting a newer Jeep 3.6 version is motor the only hope.

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post #6 of 32 Old 07-12-2020, 08:46 AM
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Originally Posted by TheBoogieman View Post
regear it. The other crap does nothing.

Well, it does do something - it reduces your bank balance without any meaningful change to the Jeep...

Further, even if you do something more invasive, like cam, blower, turbo, you still need to correct the gearing to realize the true performance gain. So, do the gears first, gear it for the tires and transmission you plan to run, and that will be the best bang for the buck - even though you need to do the front as well.

The stock intake is not restrictive. The stock exhaust is not restrictive. Both are beyond the capacity of the stock 4.0 to suck in or blow out. Therefore, increasing the capacity of either is a waste on a stock 4.0.

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post #7 of 32 Old 07-12-2020, 08:58 AM
jtec
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" I'm trying to prioritize longevity in this Jeep"

if you need the "MPH" why not original size tires? least expensive.

Want the 'look' - regear. Ca Ching.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #8 of 32 Old 07-12-2020, 09:24 AM
2jhanna
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Personally I consider being able to go uphill at 60mph in a brick not bad.
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post #9 of 32 Old 07-12-2020, 09:30 AM
sh00ttok1ll
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Regear.

It's not even a question. Until you get your final drive ratios correct nothing else you do will have the desired impact.
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post #10 of 32 Old 07-12-2020, 09:40 AM Thread Starter
RedBolide
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Wow, I really appreciate the responses! I think regearing might be my best bet. I should have specified in my post, I've got the 5 speed. It seems like performance gains aren't going to do me much without regearing anyway, so it might be best to regear. My engine is running perfectly as-is (I'm obsessive with my maintenance). So I think y'all have convinced me. Time to gear up!

As for a few specific responses, the 33s were great for a while. I love the look, and I did virtually no highway driving until now. I just like my TJ too much, so I've been doing some road trips (even though I have a much more suitable highway driver). Nothing like 600 miles in a TJ packed full of tools! And as for the idea of the 3.6 swap, no, NEVER. I hate those motors with a passion. I've pulled too many out of JKs with 100k miles to ever touch another one.

Seriously, thank you all for your feedback! This is a great forum to be in!
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post #11 of 32 Old 07-12-2020, 10:23 AM
2jhanna
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Since you have a 5 speed, how's your performance if you down shift into 4th, or even 3rd. Keep an eye on rpm, but this is a similar effect to regearing.

I am multi-talented, I can talk and piss you off at the same time.

jhanna
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post #12 of 32 Old 07-12-2020, 10:42 AM
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Quote:
Originally Posted by 2jhanna View Post
Personally I consider being able to go uphill at 60mph in a brick not bad.
No sh**! Indeed.

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post #13 of 32 Old 07-14-2020, 06:11 AM
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Quote:
Originally Posted by 2jhanna View Post
Since you have a 5 speed, how's your performance if you down shift into 4th, or even 3rd. Keep an eye on rpm, but this is a similar effect to regearing.
Yep. Drive around using the first four gears only (pretend 5th gear doesn't exist), and imagine a peppier 1st gear. That's a good approximation of a regear.

What RPM range do you keep it in on the highway? Lots of folks keep it too low. 2-3K is really too low. Mine really doesn't like being below 2300 or so (still feels like it's lugging at constant speed on a flat road), and 2700 is the sweet spot for cruising for me. Don't be afraid to rev it higher, the 4.0 will happily chug along all day at 4K without any issue.

I'm still running the stock ratio (3.73) with 33" tires. I have the 6-speed, and I can count on one hand the number of times I have had it in 6th in the last five years.
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post #14 of 32 Old 07-14-2020, 07:39 AM
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Quote:
Originally Posted by JEK3 View Post
I'm still running the stock ratio (3.73) with 33" tires. I have the 6-speed, and I can count on one hand the number of times I have had it in 6th in the last five years.
I had 3.07s, auto and 33s for a short time.

Quote:
Originally Posted by jeepinmichguy_ View Post
TheBoogieman is a jerk.
GOT IT BACK 6/17. 03' Rubicon/Zone 4.25" combo lift with 4" lift coils up front/Zone hydro shocks/5.13 gears/35" Mickey Thompson MTZ P3 tires/Black Magic brakes. Jeep #17 & 19.
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post #15 of 32 Old 07-14-2020, 08:46 AM
2jhanna
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Quote:
Originally Posted by TheBoogieman View Post
I had 3.07s, auto and 33s for a short time.
Remove front drive shaft. Shift t-case into 4lo.

Problem solved.

I am multi-talented, I can talk and piss you off at the same time.

jhanna
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