Gear ratio input

[ifrythings]

Little about the truck, 95 f350 CrewCab 460 4x4 getting converted to a rebuilt idi factory turbo and wide ratio zf5-42 and bw1356.

I'm trying to figure out what axle ratio to run, both diffs are getting replaced and all gears are on hand just not sure what to pick, 3.55 or 3.73 or 4.10.

99% of driving is going to be in town, a small amount on the highway and at the moment no towing though maybe a slide in camper in the future.

I would also like to put 35" tires on it at some point so I'd like to keep that in mind.

From what I could find its looking like 4.10 should be good but that's online gear calculators which isn't real life so what would you choose for gear ratio?

 

[OLDBULL8]

If you want rear wheel torque use 4:11, for mileage use 3:55, but just for a slidein, 3:55 should be good.

 

[no mufflers]

I would do 4.10, that's what's in my truck. I think with the 35" tires even with the 4.10 gearing you will have no problem on the highway. all the other options would work also.

 

[ifrythings]

I'm thinking 4.10 also, with 35" tires driving around town would put me at 1250 rpm and on the highway 2100 rpm. If I went with 3.55, in town would be 1100 rpm and highway 1800 rpm.

I'm not sure where the idea cruising rpm is but the in town driving is what concerns me at such a low rpm. I've only ever driven non turbo idi's and you really need to keep the rpm up for those.

 

[DaveBen]

I have had both 4:10s and 3:73 and I really like the 3:73 for everyday driving. 4:10s are too low even around town with a diesel. You are talking about a torque motor and not a high reving engine.

 

[austin92]

Play with the gear ratio calculators. I chose my gears by putting my rpms at 2400 at 70mph. Taller tires will require lower gears. Might even look into 4.56 on those 35s. You will absolutely hate 3.55


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[tbrumm]

Play with the gear ratio calculators. I chose my gears by putting my rpms at 2400 at 70mph. Taller tires will require lower gears. Might even look into 4.56 on those 35s. You will absolutely hate 3.55

Yep, my vote is for the 4:10's. With 35" tires, the 4:10's will be like 3:55's with stock tires. I like the 3:55's in my truck, but I have stock size tires. I think the 3:55's will be too tall with 35" tires.

 

[ifrythings]

I've been playing with the gear calculator and at highway speeds it's only a 200 rpm difference from 3.55 to 3.73 and 200 rpm from 3.73 to 4.10 or 400 rpm difference from 3.55 to 4.10.

I'm going to be starting a build thread on this soon, my plan so far is to put a 2004 rear end in which is currently 3.73 and a 2006 front end in which is 4.10. I also have a 2004 front end that's 3.73 and the stock axles which are 3.55 I could swap gears into any of these axles. So no matter what I do I have to regear an axle (no I'm not staying with the stock axles).

It seems like at the moment 3.55 and 4.10 are both perfered and not much said about 3.73.

What's a good rpm to be at on the highway? 2400 seems high to me on a turbo engine what about 2000rpm?


Some engine info if this mite help.
I have the ats 093 kit with 3" down pipe and 4" back exhaust, j2 cam, and stock intake, would like to get a bit bigger pump maybe 90cc in the future.

 

[F350camper]

I'd go 3.55s and 35s and let the turbo make the torque.

 

[no mufflers]

What's a good rpm to be at on the highway? 2400 seems high to me on a turbo engine what about 2000rpm?

.

in my opinion I think any rpm from 2,000 to 2,500 would be a good cruising rpm. it really depends on the truck weight and if your towing. I have found that 2,000 rpm is on the low side for towing.

I think in my truck im around 2,200 or so at 65 mph.

 

[austin92]

These trucks could've came with 4.10s stock and on stock size tires could cruise at 70mph. On top of the added weight from the larger tire the engine will have less "leverage" at lower rpms regardless if your pushing 20psi or you're n/a. It needs deeper gearing to turn the larger tires, especially if you're towing. Your egts will be lower, you're u joints will be under less stress, and you will get better fuel mileage at lower speeds with minimal drop at higher speeds. Brand new trucks make 800+ lbs of torque and still offer 4.10s on tires a lot smaller than 35s. Sorry for the rant but I just firmly believe that you will hate towing with anything numerically lower than 4.10 gears.


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[Macrobb]

Having both 4.10 trucks and 4.10 with GVOD(which is almost exactly a 3.55 ratio in double overdrive...
The double overdrive(1600RPM at 60MPH) gearing is /great/ for unloaded/lightly loaded. I've never had trouble with it unloaded, even on decent hills at 60MPH. If you are going 55, you may have to downshift, though, just cause the revs are too low.
If you are doing highway cruising at 70-74, it's perfect. Right at the bottom end of the turbo performance curve at 2000-2100 RPM, and I've hauled an empty dual-axle car hauler trailer doing that.

Hauling a trailer, I often have to downshift into single-overdrive, but rarely below that. I'm pretty sure I was in single overdrive when hauling 16,000 lbs one trip at 55MPH...

Go with the tallest gearing you can easily, you can always downshift. 4th is direct drive anyway, so why not use it if you need to?

 

[93banksidi]

I have stock 3.55's in my truck on 37" tires and my rpms are around 2100 @ 75mph. Id think the 3.73's would be the best bet for city and mild highway on 35's.

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[FarmerFrank]

On my bronco When I went from 31x10.50x15's and 3:55's to 35x12.50x16.5's and 4:10's my 65mph cruise RPMS stayed the same. Not sure if that helps ya but that's my real world experience.

I'll say I've also never had much trouble towing 10k lbs with a NA 6.9 c6 and 3.55's


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[catbird7]

Mine has 4.10 gears, 35" tires, ZF-5spd and I routinely haul slide-in camper. Wish I had 3.73!

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