3.73 vs 4.10 debate (V8 TJ)

[Mitch502]

I recently swapped a 5.9L Magnum motor into my 2001 Wrangler. It was originally a 4cyl, so it has 4.10's with a D30/D35 combo. Obviously that D35 is going to detonate if I keep driving it or the first time I take it off road.

I'm getting a 8.8 this weekend probably, and can probably find one that is 3.73 easier than 4.10, but you know...4.10's, right??? I already have a Dana 30 with 3.73's that is getting junked that I can take the gears out of, so gear swap expense isn't a concern.


My question is regarding fuel mileage. I never plan to go over 33's, and my off-roading is limited to camping and tight trails that we have here towards the east. No rock crawling or anything, but I do drive a lot on the highway to take trips to where I can wheel. The 5.9L is mated to a AX-15

Will 3.73's give me better fuel mileage, to a noticeable and worthwhile degree? Obviously it will be "better" but I don't want to give up the fun of 4.10's with the 5.9L for a 1MPG difference.


Thanks,

Mitch

 

[JeepN95YJ]

Obviously there is no way to accurately predict difference in mpg. Having swapped multiple engines and driven lots of different combinations of tire, gear, and engine, I'd say that with the 5.9 torque you would be happy with either gear set. Mpg will be within 1-2 either way.

If I were making the swap, personally, I'd hold out for the 4.10 gearset in the 8.8. I think it would match the 5-speed, engine, tire size about perfectly.

 

[Mitch502]

That was my thought process. I'm driving it now with 4.10's, and it's a beast. The ZJ the 5.9L came out of was 3.73's, and was also powerful. MPG difference between the 2 is about 1-4MPG it seems, but with this being the first week of driving the TJ post swap, it's hard to tell. I also don't have cruise control on the TJ, which doesn't help matters. I've managed to sell the Dana 35 for $300, and don't want to break it before he comes and gets it

Any additional information will be nice if someone could chime in, but as I type this someone replied to a message saying they have a 4.10 8.8 (open, not LSD unfortunately) for $75 caliper to caliper. So I'll be getting that unless someone convinces me to go 3.73.

 

[MOguy]

I have no experience with engine swaps but I have bad a couple vehicles regarded. With the higher ratio it is easier to "crawl". Not sure if that is a concern of your or not?

 

[Mitch502]

I have no experience with engine swaps but I have bad a couple vehicles regarded. With the higher ratio it is easier to "crawl". Not sure if that is a concern of your or not?

Generally speaking, no. My off-roading is limited to tighter trails with VERY little to no rock crawling

 

[gwittman]

With 33" tires, I would go with go with the 4.10 gears. I run 4.56 gears with 33" tires and that is perfect for my heavier, lower powered vehicle. I don't think you would be happy with the 3.73 gears even with a lighter vehicle with more power. I ran 4.10 gears for a while with the 33" tires before I got the 4.56 gear installed. That did not work well with my vehicle. It was sluggish and did not like 5th gear (OD) at all.
.
I run 31" tires when I am not going off-road. Acceleration is nice but rpms are high on the highways. Not a big deal but not what I prefer.

 

[SilicaRich]

Hard call. I feel like 4.10 gearing would be a better compromise for mpg and power. You'll be hovering around 2.5k RPMs @75mph with 33s and 4.10 gearing.

Good to see you back around

 

[Cottontail]

I hope the ZJ you pulled the 5.9 from was trashed. That's a pretty rare Jeep to part out.

If I understand gears it's as much or more about tire size than engine size. Engine size and power are more likely to damage axle shafts, u-joints and the like I believe.

I'd go with 4.10s and call it a day.

 

[Mitch502]

The ZJ was totaled, but I might have been able to sell it... Check my signature for the build

 

[Mitch502]

I'm thinking I'm going to stay 4.10 and then if I want to swap, I can do so pretty cheaply...

 

[SilicaRich]

If I understand gears it's as much or more about tire size than engine size. Engine size and power are more likely to damage axle shafts, u-joints and the like I believe.

Mostly about matching your gears with your tire size+final drive ratio+engine powerband for further clarification.

 

[Mitch502]

Right. I'm using the same size tire and engine, so I know 3.73 did fine before (haven't compared trans ratios)

 

[SilicaRich]

Right. I'm using the same size tire and engine, so I know 3.73 did fine before (haven't compared trans ratios)

AX15 has a final drive ratio of .79. For comparison people regear to 4.56 with 33" tires and the 4.0. Considering most V8s love lower RPMs I would assume taller gears would be more appropriate for the 5.9. However, I assume. I have no knowledge of the 5.9's powerband

 

[Mitch502]

AX15 has a final drive ratio of .79. For comparison people regear to 4.56 with 33" tires and the 4.0. Considering most V8s love lower RPMs I would assume taller gears would be more appropriate for the 5.9. However, I assume. I have no knowledge of the 5.9's powerband

The auto from the ZJ had 3.73, and the trans 4th gear ratio was .69.

So I'm going to be turning higher RPM's no matter what it seems.

 

[Cascade Wanderer]

Another vote for 4.10's, and I gotta say, you must be pleased with the big jump in power from a 4 cylinder to a big ol' V8!

Tough swap? Or pretty straightforward?

Guy