I agree with rob on this one. However, a friend of mine with a 4.2L Ford just swapped from a 3:55 to 4:10's and hes gained about 2 MPG. He also got the LSD installed too which take a load off the tranny and motor around town. Stopping and starting, that situation improves your gas MPG. 4.56 is a huge jump though. Would you increase your 1/4 time if you get the 4.56's?

 

gears dude, thats the way to go. Oh and also an Underdrive pulley, the a/c and all other electric power options use power from the engine to run while the car is moving. If you increase the size of the pulley then the engine wont have to work as hard to turn the other pulleys on the engine, like shifting gears on a bike, fewer rotations on a larger gear does the same amount of work with less effort. The fan belt is replaced with a larger one to deal with the increase pulley size, but it is well worth it.

 

If you have a 2002 Ram then you have a .75 overdrive... if you have a 2003-UP then you have a .75/.67 overdrive. So the RPM gain is minimal at the most while in overdrive.

For some reason many people think RPM’s alone are what determine fuel consumption... the fact is RPM’s have a smaller role in your actual fuel economy than you may think. You need to be concerned with the load on the engine at any given RPM... its the load on the engine that consumes the fuel... not RPM’s.

EXAMPLE: If you have an overhead trip computer set it to "INST MPG"... if you don’t have INST then use the "Act MPG" but you will need to RESET it frequently for this example. Now get on the highway and set your speed to 60MPH. You will find that your RPM’s at 60MPH will NOT change as long as you don’t hit a steep hill and downshift. Reset your ACTUAL MPG and monitor your MPG at 60MPH... notice as you hit slight inclines your MPG drop. Depending on the incline the MPG will drop by -1 to 9MPG before downshifting. As you hit a decline your MPG raise by as much as +1-15MPG depending on the decline.... This is more accurate with trucks equipped with the "inst MPG" but you should still be able to get a feel for the point being made.

Even though your RPM’s stay the same, you still have a deviation or tolerance of 10+MPG at the SAME SPEED & SAME RPM the only changing factor is the load on the engine.

Lower the load on the engine and get better fuel economy. The 4.56's only raise your RPM’s by 300-350RPMs at 60MPH...

If you want to figure out what your RPMs would be at ANY speed use these two formulas:

Overdrive Gear x Rear Gear = OVERALL REAR GEAR

SPEED x OVERALL REAR GEAR x 336 / tire hight = RPMs

This formula will tell you EXACTLY what your RPMs should be as long as your tire hight is correct. then when you have the RPMs realize that the gain from your stock gears to the 4.56's is high enough to lower the load on the engine but not enough to KILL fuel economey like many beleive.


SPEED SAFE, AIR RAM

 

Hey thanks for all the great input guys. I really do appreciate it. I haven't been on here in quite some time, but remembered today when I got a PM from nos4fuel. I am sorry to say that I haven't done anything to the truck yet. I am still planning on something. Gears sounds like alot of work, the gains are there, but the cash factor is high. Air intake, pulley, or tune or a combo is probably what I will end up doing. Thanks again to all the gear heads.