More Power

Redbikemark

Redbikemark

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Jun 7, 2022
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Location
Gallatin Tennessee
2004 TJ 80,000 miles. 31in BF Goodrich all terrain tires and 2 in rough country lift kit. Stock in line 6 cylinder with newly added cold air intake with stock exhaust. I would like more power so I don't have to downshift when going up a average (I know, what is average) size hill when driving on the highway. I have talked with a local Jeep shop and they are recommending 410 gears and new better air flow muffler to go along with the cold air intake. I am using my Jeep for more personal transportation than off roading or mudding, will never rock climb with it (don't have the money to build and maintain a rock climber). My question is the gear setup. Will I still be able to drive 70 mph? Currently getting 15 mpg will my fuel economy be effected? Basically needing suggestions and guidance.
 
Please fill in your profile. Without knowing what you currently have for gears or transmission, it makes giving advice way more difficult.

Welcome to the forum🖐
 
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TheBoogieman said:
You must have 3.07 gears. CAI and muffler don't help. Swap in some axles from a 4 cylinder with 4.10s. Much cheaper than regearing it.
Click to expand...
Obi-Wan said:
Please fill in your profile. Without knowing what you currently have for gears or transmission, it makes giving advice way more difficult.

Welcome to the forum🖐
Click to expand...

Stock gears from factory (3.07??) 5 speed tranny
 
Forget any nonsense about adding "power". It's a glorified tractor engine and nothing short of going to a stroker, forced air induction, or V8 conversion is going to have any meaningful difference. Instead, focus on getting the correct gearing, which must be based on your desired tire size.
 
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Redbikemark said:
Stock gears from factory (3.07??) 5 speed tranny
Click to expand...
Look on your differential cover, front or rear, for the small metal tag bolted onto it at its 9 o'clock position. Your ratio will be embossed into it. Take a rag and a flashlight with you, it's likely covered in dirt and the embossing is not usually easily read. The below tag indicates the axle has 3.73 gearing inside it.
Axle Ratio.jpg


There are NO easy bolt on products that will boost power and that includes cold air intakes, throttle body spacers, free-flow mufflers, etc. Yes I know the THEORY of a CAI sounds good but in reality they don't help on a Wrangler. Not to mention they don't really bring in cold air since it's still sucking in hot engine compartment air.

If you have the dreaded 3.07 ratio, regearing to a lower ratio like perhaps 4.10 will bring an immediate dramatic boost in power. The only problem is regearing is not cheap, plan on it costly $1400-1500 and up. Just make sure if you have it done to INSIST they add only a conventional, not synthetic, gear lube to the axles. At the first 250 mile drain and refill, replace it with more conventional (not synthetic!!) gear lube. It's proven that new gears run too hot when lubed with a synthetic which isn't as effective at sinking the heat out as a conventional gear lube is. Heat is the enemy with new gears which is especially a problem during the break-in.

The correct new ratio, if needed, depends entirely on your transmission however. 4.10 would be fine for 31" tires if you have the 5-speed manual transmission. But if you have the automatic, you need a much lower ratio like 4.56 or 4.88. That's because the 4-speed automatic's Overdrive has a .69 ratio which drops the engine rpms too much at highway speeds for conventional higher ratios like 4.10. In ratio-speak, 4.88 is a lower ratio than 4.10. :)
 
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Jerry Bransford said:
Look on your differential cover, front or rear, for the small metal tag bolted onto it at its 9 o'clock position. Your ratio will be embossed into it. Take a rag and a flashlight with you, it's likely covered in dirt and the embossing is not usually easily read. The below tag indicates the axle has 3.73 gearing inside it.
View attachment 335708

But if you have the automatic, you need a much lower ratio like 4.56 or 4.88. That's because the 4-speed automatic's Overdrive has a .69 ratio which drops the engine rpms too much at highway speeds for conventional higher ratios like 4.10. In ratio-speak, 4.88 is a lower ratio than 4.10. :)
Click to expand...

The 42RLE OD truly sucks. I'd even run a 5.13 gear, which is what I'm planning for, with an automatic and 31" tire!

Gear
Road RPMs at given speed in miles per hour10 MPH35 MPH70 MPH
11592557211144
288030806160
356119623924
438713542707

Even if I lost OD, I could still drive up to 55 MPH without worrying.

Gear
Road RPMs at given speed in miles per hour10 MPH35 MPH55 MPH
1159255728756
288030804840
356119623083
438713542127
 
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Assuming your 2707 rpms at 70 mph is with 31" tires and 5.13, yeah that'd be a great highway rpm. I got 2700-2750 rpms at 70 with my first 5-speed/4.0/35"/4.88 setup and it was perfection on the highway.
 
Before changing gear ratio be sure of your final desired tire size. Many people start with 31’s and then move to 33’s .
 
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GPK03X said:
Before changing gear ratio be sure of your final desired tire size. Many people start with 31’s and then move to 33’s .
Click to expand...

31" is what I am looking for. no plans to go to a bigger tire size......I don't want the body to be any higher off the ground than it is...
 
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Jerry Bransford said:
True, though if he went with 5.13, a good suggestion by Irun, that'd be the best available ratio for the 33's too since 5.38 isn't available for his TJ.
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I've come to realize that there are only two gear choices for a 42RLE and stock axle housings:

- Non-Rubicon = 5.13
- Rubicon = 5.38

Tire size doesn't much mater for the later automatic. The manual is a different story and gearing is very much driven by tire size.
 
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Redbikemark said:
No plans for 33's.....I had an 03 wrangler sport with 31's and 4 inch lift....to hard to get in Jeep so on the 04 I just purchased I went with 31's with 2in lift and so far it is perfect....
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Based on the calculated highway rpms of 5.13 I'd go for that ratio even with 31's. Certainly no less than 4.88. Edit; this recommendation is only for those with the 42RLE automatic transmission.
 
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GPK03X said:
Po has the 5 speed,hope you guys talking about the 42rle isn’t confusing him on gear selection
Click to expand...

Good point. OP, fill in your profile. It helps us more easily know what you are running. With the banter that takes place in these threads, details like that often get buried. The profile is a way for us to quickly get useful information!

Back to the regularly scheduled program, OP, here are numbers based on a 30.75" tire and your NV3550.

Gear 4.8810 MPH35 MPH70 MPH
Road RPMs at given speed in miles per hour
12138748414968
2124243488697
374125945188
453318663733
538913622725


Gear 4.56
Road RPMs at given speed in miles per hour10 MPH35 MPH70 MPH
11998699313986
2116140638127
369324244848
449817443488
536412732546

Here's the calculator to enter your own numbers:

http://www.grimmjeeper.com/gears.html
 
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One point to remind, I acquired a TJ with the cold air intake. It was zero benefit, just sounded weird, actually annoying. If you can go back, kept the original, I would seriously go back.

To the other posts, all my research is none of these add “power”.

What it sounds like you’re looking for is better gearing in axles, and that will deliver what you want.

These guys have a ton of threads solving that, and it’s good info.

I would say, there are options, you can start looking for new axles online or local already geared at 4.10, 4.88 whatever, or you can get yours regeared.

No somehat simple engine tweaks or adds will deliver what you want from my experience.
 
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How to make a TJ feel more powerful- drive something with less power for a few days. The effect lasts like 10 minutes but it is exciting.

Failure to provide a full profile can result in a 25 point penalty- just fyi- plus we can’t stalk you as easily, so help us out. Yours may have parts we need.

Gearing is where it’s at. The 4.0 doesn’t have the the capability to compensate for improper gearing for the tire size. Gearing is not a mod, it is a correction to keep the rpms, power and drive ratios working as designed.

Boy that sounded good, If Jerry hits LIKE I’m going to feel all mushy.
 
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