6.4L Power Stroke Engine and DrivetrainDiscussion of the 6.4L Power Stroke diesel engine and drivetrain in the 2008 Super-Duty trucks. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 6.4L Power Stroke engine.
Change from 488 to a 373/taller rear end on my '08 F450?
Hello,
I'm Donna, the designated typist, chief cook and bottle washer for Jim, who has had an F250, F350 and now, a 2008 F450. We also have a different/smaller trailer now and so we don't need the torque. Jim has mentioned several times changing to a taller rear end -- wondering what the cost would be, if anyone's done this, etc. (I tried to type what he said, but if there are any obvious bloopers in this message, it's my fault -- I don't know a torque from a tocque. ;o)
Thanks,
Deere John (a/k/a Donna)
Your F-450 has a Dana S110 rear axle with a 11.8" ring gear. That's bigger/heavier duty than the Dana 80 rear axle in F-350 DRW (Dooley) pickups.
So your choice of rear axle ratios is probably severely limited. The only ones I know about are the 4.88 you have, the 5.38 that was optional on F-450 chassis cabs with gasoline engines, and the 4.30 that was optional and is now standard in the F-450 pickup.
I'm certainly no expert on rear axle ratios, but you should check with someone who is. Maybe the guy that answers the phone at Randy's Ring and Pinion can tell you if other ratios are available for your Dana S110 axle. Note they don't include F-450 on their website, so they probably can't help. but maybe they can. Randy's Ring & Pinion
If you changed out the ring gear and pinion for the 4.30 ratio, that's about an 11 percent change. So your engine RPM would go down by 11 percent at the same speed (with a calibrated speedometer). So if you see 2,600 RPM at your current highway speed, you would see about 2,300 RPM at the same speed with the 4.30 rear end and a calibrated speedometer.
How much does that cost? Not my area of expertise, but I've heard around $1,000 to $1,500 for each differential. So if you have a 4x4, you're looking at $2,000 to $3,000 total. You can buy a lot of diesel for $2,000.
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Last edited by SmokeyWren : 07-11-2008 at 07:12 PM.
Reason: typo
Very expensive, because there are no taller tires that will fit on the stock wheels, so you have to buy wheels too.
Stock size tires are LT225/70R19.5 with 653 revs/mile. The only other sizes made for 19.5" wheels by name-brand tire makers are 245/70R19.5 with 620 revs/mile, which will give you a 5 percent reduction in engine revs at the same speed. And 265/70R19.5 with 606 revs/mile, which will give you about 7 percent fewer engine RPM at the same speed. Those two bigger tire sizes both need 7.5" wide wheels instead of the 6.75" wide wheels you have now.
Michelin - but not Goodyear - also makes a 285/70R19.5 with 587 revs/mile. That's about 10 percent difference than stock, or about the same as going from a 4.88 to a 4.30 rear end. Those wide tires require 12.2" minimum spacing between the duals, so the stock wheels are definitely not a candidate. Michelin Americas Truck Tires XDE®2+ Page
Going up to "real truck" tires in size 9x22.5 will require 22.5" wheels that are 6.75" wide. Those tires have 538 tire revs/mile, so that would give you a 17.5 percent reduction in engine RPM at the same highway speed. So instead of 2,600 RPM, you could cruise at about 2,150. That's between the equivalent of a 3.73 and a 4.10 axle ratio. Goodyear Commercial Truck Tires - Unisteel G149 RSA Details
Last edited by SmokeyWren : 07-12-2008 at 06:24 PM.
Very expensive, because there are no taller tires that will fit on the stock wheels, so you have to buy wheels too.
Stock size tires are LT225/70R19.5 with 653 revs/mile. The only other sizes made for 19.5" wheels by name-brand tire makers are 245/70R19.5 with 620 revs/mile, which will give you a 5 percent reduction in engine revs at the same speed. And 265/70R19.5 with 606 revs/mile, which will give you about 7 percent fewer engine RPM at the same speed. Those two bigger tire sizes both need 7.5" wide wheels instead of the 6.75" wide wheels you have now.
Michelin - but not Goodyear - also makes a 285/70R19.5 with 587 revs/mile. That's about 10 percent difference than stock, or about the same as going from a 4.88 to a 4.30 rear end. Those wide tires require 12.2" minimum spacing between the duals, so the stock wheels are definitely not a candidate. Michelin Americas Truck Tires XDE®2+ Page
Going up to "real truck" tires in size 9x22.5 will require 22.5" wheels that are 6.75" wide. Those tires have 538 tire revs/mile, so that would give you a 17.5 percent reduction in engine RPM at the same highway speed. So instead of 2,600 RPM, you could cruise at about 2,150. That's between the equivalent of a 3.73 and a 4.10 axle ratio. Goodyear Commercial Truck Tires - Unisteel G149 RSA Details
Not trying to highjack this thread but the tire info is something I'm interested in. I have an 08 F350 4x4 with single rear wheel with 18 inch rims. On my 02 I had 16 inch rims and was able to go from a 265x75 to a 235x85 with no real change. I've tried to find some taller tires for the 08 but can't find anything compareable to the 275x70 that are on it. Any thougths? Thanks.
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2008 F-350 King Ranch CC LWB 4x4
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