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Old 04-17-2018, 03:57 PM   #11
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Not exactly. We are indeed recommending that Karma spend money. The axles he bought for the 4x4 conversion are 3.73s. So, he would need to regear both going to 4.10s. That's an additional $500 to $1000 to consider depending on parts and labor

Frankly, with 35s I think your going to lug the 6.0 on long grades which does raise EGTs and the transmission is going to be hunting in overdrive.

I'm at 2000 rpm at 67 mph with 35s. Just about right and with an 80HP PCM tune and a 40HP FICM tune I make 15-18 mpg. I don't think your going to get much better with a 4x4 van with a 4" or 6" lift. With 3.73s you might have longer legs for the freeway but you need the gearing for not just pulling a trailer but for a diesel that has a lower power band than the gasser. 35" tires are massive, heavy wheels to turn. Just my 2 cents. It would be interesting to hear the perspective of a 6.0 owner running 35s and 3.73 gearing.

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Old 04-17-2018, 04:38 PM   #12
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Great point Herb. I feel guilty and promise to try and do better next time.

Karma, you really really need a locker for whatever differential you decide on. And onboard air along with plenty of lights for sure. And don't forget bumpers....you need some bumpers.
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Old 04-17-2018, 04:40 PM   #13
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Not exactly. We are indeed recommending that Karma spend money. The axles he bought for the 4x4 conversion are 3.73s. So, he would need to regear both going to 4.10s. That's an additional $500 to $1000 to consider depending on parts and labor

Frankly, with 35s I think your going to lug the 6.0 on long grades which does raise EGTs and the transmission is going to be hunting in overdrive.

I'm at 2000 rpm at 67 mph with 35s. Just about right and with an 80HP PCM tune and a 40HP FICM tune I make 15-18 mpg. I don't think your going to get much better with a 4x4 van with a 4" or 6" lift. With 3.73s you might have longer legs for the freeway but you need the gearing for not just pulling a trailer but for a diesel that has a lower power band than the gasser. 35" tires are massive, heavy wheels to turn. Just my 2 cents. It would be interesting to hear the perspective of a 6.0 owner running 35s and 3.73 gearing.
Yup more parts/money......

I'm a DIYer..... but have never done gear swap..... do you think i'll be fine with 3.73 gearing with 33" tires with 4" lift (95% hwy driving).

I have seen pics of rigs with 4" lift and they do look more proportionate than a 6" one. Was only leaning for 6" because it gives a better turning radius on one of the vendors kit (something to do with smaller pitman arm) and I keep hearing that people with 4" initial lift end up wanting a 6"
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Old 04-17-2018, 04:44 PM   #14
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33's would certainly give you a better chance. I had around 4" of lift, maybe 5 with 33s on my E350 and it seemed about right. I didn't feel like I wanted to go higher.
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Old 04-17-2018, 05:09 PM   #15
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Ya, why not try the 3.73s since that's what's in the axles. Then you could upgrade later to 35s if you want. If you want to stay with 3.73s you could then get a tune for the taller tires and better shift points. Maybe play around with one of these gear calculators:
Differential Gear Ratio Calculator | West Coast Differentials
4x4 related Calculators, Crawl Ratio, Gears Tires Sizes, etc..

Generally speaking a set of 3:73s with 33s would give you the most stock like feel. Anything lower you will gain some low end.

33s: 3.73
35s: 4.10
37s: 4.30
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Old 04-17-2018, 05:25 PM   #16
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Great point Herb. I feel guilty and promise to try and do better next time.

Karma, you really really need a locker for whatever differential you decide on. And onboard air along with plenty of lights for sure. And don't forget bumpers....you need some bumpers.
Yup looking for those..slowly finding bargains for all the upgrades. Yesterday picked up a dieselsite coolant filter from local CL.

But dang as of now 4x4 conversion is still up in the air until UJOINT comes up with an a Kit adaptable to 2013+ axles
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Old 04-17-2018, 05:29 PM   #17
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Coolant filter is a great idea.

You've likely already considered the Expo Vans/MG coil conversion? I think you had another thread about your 4xe conversion if I remember?
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Old 04-17-2018, 05:53 PM   #18
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Coolant filter is a great idea.

You've likely already considered the Expo Vans/MG coil conversion? I think you had another thread about your 4xe conversion if I remember?
Yes, that is correct. Well long story short, as of today neither have a kit they can ship to me....... All this tax return money and my hands itching
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Old 04-17-2018, 05:56 PM   #19
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Well that stinks! Stick it in a mattress somewhere. One of those outfits will likely be able to figure something out pretty soon I'd think?
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Old 04-17-2018, 06:27 PM   #20
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I'm on the same page as JoeH, and others. Based on the conversation so far my final answer would be 4:10. But as was mentioned I say run what you have first and see what happens. Sounds like the gears are already stuck in the axles and if your not cracking them open for any other reason it won't mater much to have to change now or later. Operative part is your not opening up the diffs for any other reason before install.

I only have experience with my van but in it's current trim my 6.0 likes to live between 2200 and 2500 RPM. Which is where it is most of the time with 4:10's. I'm still on the SMB size of 285's on 16's. I've thought about at the next set of tires going to next size up on 17 rims but I'm content with things for now. Calm weather on highway I'm somewhere around 15-16mpg. Town only driving it's a lot less than that. IDK, I really haven't kept track, but it's way better than the 10mpg I've done in other vehicles.

Just a couple more thoughts about possible issues with being to high geared. On my van the key to getting better millage is speed, further above 70 I go the more fuel, and torque converter locked. When I say above 70 the physics really mean air speed as in 30mph headwind plus ground speed kills millage and gearing is part of that. I could also see a potential killer of millage could be not only gear hunting between 4 and OD but the converter constantly locking/unlocking. I keep a lazy eye on my TQ indicator to keep it locked as much as possible by throttle control and manually dropping out of OD when pulling a mountain. When I'm not in town my TQ is locked all the time for millage, heat and longevity of everything.

Another thing that I rely on at times that the my current gearing provides is the scenario of going 70 (ish) and I need to go to full military power for a mile to get away from some "situation" I can hold the throttle open and the trans won't down shift because I'm already above the max shift RPM for OD.

Lastly, pulling 4th gear on large climbs is something to think about in the gear equation. I hear your planning to be light weight but too high of 4th gear on some climbs could be just a tad to high to keep the turbo breathing and be forced to, God forbid, drop to 3rd. Kind of normal for me to see 3rd on a big climb (Vail Pass) pulling a trailer but I would hate to be trapped between 3rd and 4th gear empty every time.

Anyway just some of my thoughts on what could happen being too high geared with a van like ours. But truethfully, I don't really know for sure. Try the 3:73s and report back.

"One live test is worth a thousand expert opinions" - Vernher Von Braun.


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I've got a 6.uh oh and run 4.10 with 35's and stock tune most the time. No issues what so ever and it's great on the hwy.
And just be careful when MSD gives advise. He owns a 6.0 and knows about them but I don't think he's happy about it. Hasn't really embraced acceptance.

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