school me

3.55 gears will take off much faster than the 4.11 gears. It will also run at lower RPMs. I have 3.73 gears in mine and at 65 I am running around 1600 rpm and the truck I am driving while mine is in the shop I think has 3.55 and runs at 1400 RPMs at the same speed. Mine will start moving a lot easier with a heavy load because of the lower gearing where this truck likes to jump when it takes off. They are both CAT motors and the only difference is mine is 625 hp and the loaner is 550 hp and the loaner has a 13 speed instead of an 18 like mine.

I have no rev limiter on mine and even it does not want to run at 1700 rpm. It does run well between 1500 and 1600 on the interstate. I don't like to be that high up in the RPM range(1700) because it does not leave much room. Most of the trucks are limited to 2100 rpm but mine for some reason does not have that limitation.

 

I don't know much about stick truck regs as far as what they allow you to pull on the two lane, but on the bigroad, I am assuming 80000. With 525 hp and 4:11s, that setup should pull 80 grand easily. But IMO, that's too much gear for 80000 lb loads. 3:55s would give you the longer legs to stretch out and stroll, yet still be able to pull decently. No you won't have that incredible pulling ability that you have, but overall, the engine and you would like the longer legs of the 3:55s

What do you mean by longer legs?

You are running that truck near its limit. The engine is running above the sweet spot where you get the best of all worlds, namely economy and performance. The 3:55s should put the engine right where it wants to be. So instead of feeling like a dog at the end of its leash, she should feel like the big dog on the prowl. Would be a much more enjoyable ride.

Now Cnsper pulls big loads. I run the same setup as he does, because those big loads require a lot more grunt to just pull them through the wind. Your 525hp and 4:11s and an 18 would be great for a heavy hauler pulling 160000. But if you're not pulling that heavy, it's actually hurting you for the way you want to run.

 

You mentioned 75 mph and the interstates, and so I thought you were running the bigroad. If your bread and butter is on the back roads of Minnesota, I'd stick with the 4:11s.

 

huh? what have i missed over the decades?

 

with 4.11's you come out of the loading pit much easier which equates starting faster from my perspective. the set up you have is excellent for the job application. i have no idea how the one forum member concluded that a 3.55 rear will pull quicker than a 4.11 rear. top end is different as obviously the taller(smaller) the rears the higher the speed for the most part.your truck drive train rocks for the specific job it is doing.don't let anyone tell you otherwise.

my truck has 3.42's,fairly long legged actually,(turns 1650ish at 80,pulls all the way to 2250ish+ on 11r24.5's) and i get absolutely left sitting still from a dead stop by most company trucks BUT absolutely walk them down and leave them miles behind when i get it going,the exact opposite of the one member's logic. i'd prefer 3.55's or 3.70's for my job application which is severe duty but not as severe as logging especially if you are coming out of the woods.

just inserting my little bit of experience that seems to fit trucking/trucks as i have witnessed and done it. i am thinking that caspar has lots of torque with that 625 and a low revver from the factory.some engines are set from factory to be low revvers and others are set to rev higher.mine is set for 2100 from factory but exceeds that by a bit.some are set for 1800 and that is all they do if that.

confused? i am.

 

-You'll have to downshift earlier and more often on the hills with the 3.55's.
-3.55's will lower your rpms for a given highway speed.
-Reverse will be faster with the 3.55's
-You may find you need to start in a lower gear...or two lower gears with the 3.55's If you need to start in low gear now you may want to stay with the 4.11's