3.73 vs 4.10 debate (V8 TJ)

[Mitch502]

Wasn't too bad. http://www.pirate4x4.com/forum#/topics/2545569?page=2

 

[OhioWrangler]

I would recommend the 4.10's. I started with a few different combinations, with a 4.2L. I found I couldn't go slow enough for the more technical trails for the power I had, tight turns, etc, rocks or not. With the ax-15, you always go to another gear. I now have a v8 with an ax-15, I can idle in second gear on the easier obstacles. I believe it's better to have to much gear than wish you had more, Ron

 

[comptiger5000]

If you're doing a lot of highway running, go with 3.73s. 4.10s will cost you fuel and noise on the highway. For trails, you can always get a t-case with a lower low range if you need more gear.

 

[Fursphere]

My Silverado had a 5.3L and 3.73 gears. Absolutely fabulous on the highways / freeways. Climbing (paved highway) hills? Sucked. Towing a trailer uphill sucked. My current LJ has 3.73s on 33" tires with an automatic transmission. Same problem. Great around town, horrible as soon as I start climbing the hills. (does fine offroad).

With the bigger engine, with taller gears you're just going to make it work harder on the hills. Gearing down is where you get the climbing power / towing power from. If it was mine, I would probably look to 4.56 gears. After all, you shouldn't be doing 70+ down the freeway anyway. Its a lifted Jeep, not a sports car.

If you're concerned about MPG, you shouldn't have put a V8 in it. You're driving a square brick after all...

And one last thing, that AX15 *can* take the extra power from the V8 if you go easy on it (assuming its in good shape).

 

[Mitch502]

My Silverado had a 5.3L and 3.73 gears. Absolutely fabulous on the highways / freeways. Climbing (paved highway) hills? Sucked. Towing a trailer uphill sucked. My current LJ has 3.73s on 33" tires with an automatic transmission. Same problem. Great around town, horrible as soon as I start climbing the hills. (does fine offroad).

With the bigger engine, with taller gears you're just going to make it work harder on the hills. Gearing down is where you get the climbing power / towing power from. If it was mine, I would probably look to 4.56 gears. After all, you shouldn't be doing 70+ down the freeway anyway. Its a lifted Jeep, not a sports car.

If you're concerned about MPG, you shouldn't have put a V8 in it. You're driving a square brick after all...

And one last thing, that AX15 *can* take the extra power from the V8 if you go easy on it (assuming its in good shape).

I don't mind the occasional struggle up a hill if it were going to help my mileage enough. But After researching, it looks like the difference between 3.55 and 4.10 in 5th gear is about 288 RPM...not sure that is enough to justify the swap, especially since 3.73 would not be even that big of a difference.

I know I'm not going to get good gas mileage...I have owned the 5.9L Limited that this engine came in for about 7 years. But I would expect to get similar mileage, and these first few fill ups, I haven't. My TJ has 1.5" spacers and a 1" body lift...suspension is in good shape and I have ZERO problem cruising at 70.

As far as the AX15 goes, it's rated at 300ftlb I think...I'm obviously killing that number (365+fl/lb probably) but the only "weak links" from what I've read will be first gear, or people putting it in fifth for long periods of time when not on the highway....so no clutch drops which I'm fine with and keep it out of 5th around town.

 

[jscusmcvet]

We are talking about a jeep with a v8, so mileage? Go for the 4.10 and have the jeep as it is intended (even if jeep never built it that way!). I cannot see you feeling any regret over the decision once you are wheeling it.

 

[Happy Joe]

Having used many tire sizes and gears over the years; I will vote for the 4.10s the torque of the V-8 being enough to make up for the tire size/gearing mismatch, especially if it has an automatic transmission (4.27/4.30 axle gearing, appear to be unavailable for Dana 35s, seems to be near optimum for 33" (measured diameter) tires, IMO).
If some one is worried about crawl ratio they should mod the transfer case low range gearing or use a crawl box/dual transfer cases etc. to minimize usage/decision conflicts (I only crawl in low range, I only drive roads in high range).
No one that I know worries about fuel mileage in a Jeep; especially a V-8 Jeep... although it takes all kinds...
Highway stress is best addressed with a good riding, comfortable suspension (will also work better off road).

Enjoy!

 

[comptiger5000]

2100 rpm at 70 on the highway is a good cruising range for that engine. It'll climb some pretty good hills in 5th with that gearing. No need to go with lower gears than that unless 1st is too tall (very unlikely, considering it's a TJ, not a tow rig). And a low enough low range solves any gearing issues on the trail (and will make a far bigger difference than 3.73 vs 4.10 would).

 

[Scoutn79]

With an engine that powerful in a vehicle that light at the low altitude you live at and no rockcrawling I would definitely run the 3.73's. There is no need to spin that engine faster at highway speeds and you'll have plenty off the line acceleration...unless you want to race a 1/4 mile car.

Darrell

 

[Mitch502]

At 70mph

3.55 - 2024 rpm
3.73 - 2127 rpm
4.10 - 2338 rpm

I would go with 3.55 (3.73 if that is the tallest available)...

That lower rpm on the hwy will be much more comfortable and the 5.9 has the power to make up for that down low on the trail all day long...

Lower gear ratios (the 4.10 is lower compared to the 3.73) are used to make up for lack of power... with the 5.9..in a jeep, you have power for days and days....and 33 are not a tall enough tire to rob you....heck if you told me 3.55, I would go 3.55 and you would still have plenty of trail power... And low range will get you what you need with virtually any gear set

It's not the gas mileage but the comfort on the hwy to get to the trail... often overlooked is the stress levels of driving getting to the destination and how fatigued that can make driver and passengers..

The whole point of a low range, is to allow you to make the high range as tall as you like for the hwy.... when you are on the trail, put it in low range and you will have all the gear you ever need... it would be crazy to go with crappy highway gears when you have a low range at your fingertips...

2100 rpm at 70 on the highway is a good cruising range for that engine. It'll climb some pretty good hills in 5th with that gearing. No need to go with lower gears than that unless 1st is too tall (very unlikely, considering it's a TJ, not a tow rig). And a low enough low range solves any gearing issues on the trail (and will make a far bigger difference than 3.73 vs 4.10 would).

With an engine that powerful in a vehicle that light at the low altitude you live at and no rockcrawling I would definitely run the 3.73's. There is no need to spin that engine faster at highway speeds and you'll have plenty off the line acceleration...unless you want to race a 1/4 mile car.

Darrell

I'm going to be going to the junkyard one day next week. My wife just gave birth to our first son, so we have been a little busy. I'm going to shoot for 4.10's for now, for ease of installation and getting me back on the road. However, if I find that all I can get at the JY is 3.73/3.55 with the LSD unit, I'll grab that and swap to that gearing in the front.