Will my road speed increase at same RPM with higher torque?

Only with people that ask stupid questions

 

the only way to speed a truck up at a given rpm is to go higher in the trans overdrive ratio numerically, or change rears to a lower numerically number 3.73 to 3.55 for instance or change to tall rubber if you are running metric tires

 

glad someone mentioned tire circumfrence

 

What are you looking for? Better fuel economy? Change the gears, and ditch the cat. Is it your truck and what year?

Mike

 

your acceleration will increase
speed no

 

But not the first time - only the same question repeatedly .

 

Let's give the guy a break, there are those times that each of us has gotten into a rut of misunderstanding. That's why he asked the question, and to his (and everyone elses) benefit, I hope he steps away with a better understanding. For starters, vehicle speed is a direct function of engine speed and gearing, not horsepower or torque. Just because and engine can develop 1650 lb-ft of torque at 1200 rpm, does not mean it will always be producing that torque at that rpm. Same with horsepower...it varies with the fueling, and thus is the maximum power produced at a particular rpm with maximum fueling.

On to your power/economy question. Let me first say that I don't run any Acerts in my fleet. I have an "E", a "C", a "B", and an "A" model; but in no way does it qualify me as to the 'real world' of Cat's latest and greatest (well, however you classify it!). Anyway, what popped out to me is the 3.73 rears with LP 22.5's. That seems to be an awfully low gearing for the Acert Cat, and it could be the cause of your fuel mileage complaint--that's how I interpret your postings. By my calculations, at 58 mph, you would be turning around 1348 rpm, not 1300; which is fine if you were cruising at 60 mph all day long. However, at 1500 rpm, you would be going 64.6 mph--Cat's recommended maximum cruise rpm and thus, your maximum recommended cruise speed. Anything over 64 mph, and your gulping fuel!

Cat recommends gearing the Acerts to run 1325 to 1400 rpm at 65 mph, with a max cruise speed of 1500 rpm. You don't mention your normal cruise speeds nor your current average fuel economy, so I'll let you do the math. Here are some helpful gearing formulas:

Engine RPM = (Veh Speed in mph * Trans Ratio * Axle Ratio * Tire Rev per mile) / 60

Veh Speed in mph = (Engine RPM * 60) / (Trans Ratio * Axle Ratio * Tire Rev. per mile)

[FYI, the constant of '60' in each formula is for the conversion from minutes (as in revolutions per minute) to hours (as in miles per hour) or vice versa.]

Startability = (engine's clutch engagement torque * trans low gear * axle ratio * tire rev per mile) / (10.7 * gross vehicle weight)

[the '10.7' is constant, and make sure the gross vehicle wieght is your total weight, not just the GVWR of the tractor. It is usually 80,000 lbs, 85,000 lbs, or whatever your normal max weight will be. Make sure your low gear is the low hole ratio...for a super 13 (RTLO1x913A) it would be 12.31 (low forward), or 13.22 (low,low reverse). I don't know what the Acert clutch engagement torque is. The "E" model was 940, so I speculate somewhere between 940 and 1000. Perhaps one of the CAT guys can help you out with that number.]

In general, regarding startability, you want:
>14 -- turnpike applications
>16 -- general highway use
>25 -- on/off highway use
>30 -- severe on/off highway applications

I personally don't think going from 1650 to 1850 torque will help your fuel economy. As goes, it will take more fuel to develope the 1850 than 1650, and thus the power increase becomes a wash. I do acknowledge that there is that magical line with any engine where, when underpowered, it will use more fuel; however, I don't think you are anywhere near underpowered for 45,000 lbs.

Play with the numbers...going from a 3.73 ratio to something along the lines of a 3.58 and see how that affects your engine rpm at your desired cruise speed. Unfortunately, gearing changes don't come cheap. With that in mind, you could simply change tire size from a LP22.5 to conventional 11R22.5's or LP24.5's (around 493 rev/mile), or even conventional 11R24.5's (around 471 rev/mile). You just might find reason to switch to a larger tire when it comes time to buy new rubber.

Good luck.

 

If a tree falls in the forest and no one hears it, does it make a sound??? JEEEEEEZZZZ...........