Hey Everyone,

I currently have stock 3.73's and i've been running 35's for quite some time. I've finally ready to drop some money to change the gears. Looking at the charts, it looks like 4:30's are the ratio to get me back to "stock" specs. Who out there is running 4:30's, and do you wish you had gone to 4.56 instead? Also, looking at parts lists, they have bearing kits, and then there are master install kits. Do I really need a master install kit or just new bearings? There is a huge difference in price. Lastly, I do spend quite a bit of time off road, would you recommend I get a true-trac? Thanks!

 

I've seen talk of 4.56 and 4.88 for larger tires.....

 

6.0 came stock with 34s and 3.73s. What do you pull you need those higher RPMs for? Very different situation than the modular gasser where people normally go that deep.

 

I have an aftermarket turbo too, and it has a greater turbo lag. This combination combined with the larger tires and I can definately notice the difference. I spend alot of time off road and i've noticed a huge differnce on lack of slow speed power when driving back roads. I've had to use low range on several occasions that my friend and his stock superduty easily get through in 2wd. I have plenty of power once the turbo spools but for slow crawling its a night and day difference. Even driving around town, taking off from a dead stop I can notice the loss.I've never done a gear change but i can only assume that getting more inline to stock (or slighter lower ) would be beneficial

I sometimes pull a small trailer, about 6k pounds and on the highway its not bad, but I really want this for all the four wheeling I do

 

That makes more sense. Did you get your SRL tune adjusted for the PMax? I thought Gearhead got the lag issue worked out, or at least significantly improved compared to untuned trucks. Riff Raff makes a billet wheel for the Pmax:
Riffraff Diesel PMax Billet Wheel for Ford 6.0L 03-07

As far as how deep to go, one big point is to keep the top end in check, I wouldn't go any deeper than 4.30s, that puts you at 2200rpm at 75mph. The F550 came as deep as 5.38 stock and unloaded that's a miserable drive, north of 2500RPMs to roll 65mph; that's obviously an extreme example but the 6.0 doesn't have the headroom for RPM on the top end like the gassers do. I don't think 4.10s would be worth the cost for the minimal change, so 4.30 I guess sounds best for you. 4.56s would be the edge end of tolerable on the highway empty IMO (2400rpm@75mph with 35s), unless you for sure wanted bigger tires.

 

Thanks for the replies everyone. Yes I do have a custom tune from Gearhead diesel and it makes a huge difference. When the stock turbo went out, I ordered a powermax and also bought some custom tunes from Gearhead diesel to accomodate the new turbo. Once the turbo was installed I drove the truck around the block and it actually felt like the truck had less power overall. I got back home and ran the updated tunes. The truck has a ton of power...once the turbo spools. I have not seen that wheel from Riffraff so I'll check it out now. Thanks/

 

Sounds like you have a problem. I can chirp the tires from a stop and 1st to 2nd if I hold the pedal down. Once I got the atlas40 FICM tune, from Ed@ ficmrepair.com, the turbo lag all but disappered, stock turbo, stock PCM tune.

 

I have an 06 CCSB with Toyo MT 295/65/20s (35.5" actual height) and last year changed from 3.73 to 4.11 gears. At 70 mph I am at 2000 rpm, so that gives you a good sense of what you would see.

A couple of suggestions:

1) add a Truetrac LSD in the rear and toss the OEM tracklok in the trash. Best $550 I have spent. Works almost as well as a locker when needed (for those that don't rock crawl their super duty), and is great on the street and while towing.
2) use a crush sleeve eliminator (solid pinion shim) in the rear axle. This will save you from the common super duty problem of worn out (noisy) pinion bearings and a leaking pinion seal.