4.10 vs 4.56 gears

[RobertN]

I have already researched it and the saginaw in my truck will except up to 5.38's with out a carrier change and it is a full floating rear end. It is basically the same rear end as the 350 truck, cutaways and motorhomes without the dual tires.

Most trucks do not go lower than 4.11's, for good reason. You're just taching to high. The numbers you mentioned earlier don't sound too high, but when you run sustained speeds that high, your mileage will be terrible, and your pulling advantage will not be that great at 4.56.

Since you have 2wd, and can change gears without carrier changes, try 4.11 first.

Also, look up the charts on your motor. There should be a HP/torque curve chart for it. Compare your rpm to where your HP and torque are.

 

[Builder]

Most trucks do not go lower than 4.11's, for good reason. You're just taching to high............

I think it's because they want their truck to have fuel economy ratings that match their competitors.

What can really help is a truck with more gears in the tranny.

 

[RobJ]

On many differentials, 3.73 and taller(ie 3.55, 3.00) use a smaller carrier, while lower gears(ie 3.90, 4.11,4.27) use a larger carrier.

If you can change gears without changing carriers, then the price is not to bad($500 around here). If you have to change the carrier, then plan another $250-500 or more, depending on what you want.

When I changed the gears in my old firebird I had to change the carrier. went from a 2.41 to a 3;73. I wasn't sure if there was another cust off somewhere.

Rob

 

[Builder]

When I changed the gears in my old firebird I had to change the carrier. went from a 2.41 to a 3;73. I wasn't sure if there was another cust off somewhere.

Rob

Nope, the cut-off is much higher. Sorry man.

 

[RobertN]

When I changed the gears in my old firebird I had to change the carrier. went from a 2.41 to a 3;73. I wasn't sure if there was another cust off somewhere.

Rob

It really varies by differential. In my old '70 Jeep CJ5, the cutoff was at 3.73. If you had higher 3.73 or higher(ie 3.23) and switched to something lower(3.90, 4.11, 4.27, 5.38), the Dana 27/30/44 diffs required a different carrier.

When I re-geared my old '89 F250 from 3.50's to 4.11's, the corporate rear-end did not need a new carrier.

 

[john_bud]

John,

I run 4.30's up to 85-90 with O/D on, 4.88's up to 80MPH with O/D on and 5.38's up to 70+ with O/D in a manual trans. As long as he has an O/D gear in his tranny, he should be fine with 4.10's or 4.30's.

If his "drive" gear is 1 to 1 then he should avoid anything numerically higher than 4.10's, IMO.

Yeah, but what RPM are you running for those speeds? About any rpm over 2000 and the economy tanks quick. You could run up to the red line, but who want's to spend that much on fuel?

jb

 

[bx23barry]

Yeah, but what RPM are you running for those speeds? About any rpm over 2000 and the economy tanks quick. You could run up to the red line, but who want's to spend that much on fuel?

jb

While low rpm generally burns less fuel than high rpm, "lugging" at low rpm will burn as much or more fuel than turning higher rpm without lugging. I drove a work truck (chevy 350 1/2 ton) with 3.07 gears. It was a real "dog" and got less than 10mpg with the 1000+ lbs of tools/parts it always hauled around. Put 4.10 gears in it and gained mph and power. It was a much better truck with the lower gears.

 

[Builder]

Yeah, but what RPM are you running for those speeds? About any rpm over 2000 and the economy tanks quick. You could run up to the red line, but who want's to spend that much on fuel?

jb

I'd doubt 4.10's will run anywhere close to the redline. I've had many a gas truck with 4.10's that would go 100 mph and be close to redline. With 4.30's you'll start seeing the redline come up sooner, but I'd bet he could still go 85+ MPH. You would have to do the calcualtions to find out. And you'd have to know if he has an O/D trans or his final gear is 1 to 1. I'd doubt 2000RPM is the sweet spot for a 350 gas, heck that's just a few hundred over the sweet spot for a diesel.

 

[art]

To run engines at that type of RPM for a few hours straight will so to speak take the starch out of that engine by 50! I certainly wouldn't want to try it with a multi weight oil.
I like the 4:10's best for a maximum. You might find that headers would make a good differnce in the horsepower but for any work or money spent you'd better be sure your going to keep it for a while if it works.