FAQ: Fuel Economy Mods


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FAQ: Fuel Economy Mods

1. How to turn your 45RFE (Single .75 OD) into a 545RFE (Dual .75/.67 OD)

Many of the older Dodge Rams, Dakotas, Durangos, and even Jeeps came with the first version of the 45RFE transmission with the SINGLE .75 overdrive programmed into it.

A few years later Chrysler updated the software and programmed the 2nd overdrive into the SAME EXACT transmission and then gave it a new name…545RFE.

Both the 45RFE & 545RFE are mechanically IDENTICAL! The only difference between the two is software/programming-related.

This means if you own a 45RFE… you can add a second overdrive simply by changing your TCM.

Here is how you do it:
1) You needed to look for a TCM out of a 2001 or 2002 Jeep Grand Cherokee with a 4.7/RFE package with any of these part numbers:

After you get this TCM:

2)Simply remove your current TCM and install the RL041504AG

3)You now have a DUAL (.75/.65) overdrive 545RFE transmission, enjoy!


2. GEARS & SIMPLE MATH... Correcting the factory gearing can increase your fuel economey by 2-3MPG and increase off the line + towing performance at the same time.

For increased performance & fuel economy… (Have your cake and eat it too)

RPMS alone do NOT dictate fuel economy. One of the biggest misconceptions is that lower RPMS get you the best fuel economy… and that is absolutely not true. The “LOAD” on the engine at any given RPM has everything to do with fuel economy. So increasing your RPMs does not always mean worse fuel economy.

I have personal experience with going from 3.55 gears to 4.56 gears in my 2002 4.7L 1500 Ram with a 45RFE transmission. You will need to know what transmission you have or at least what your overdrive gear is in your transmission to do the math.

45RFE Transmission- .75 overdrive
545RFE Transmission- .75/.67 overdrive

For best all-around performance & fuel economy, you should attempt to get your RPMs to 2000RPMS@60MPH.

The Math-
Transmission overdrive ratio x rear gear ratio = OVERALL GEAR RATIO

2) FIND YOUR RPMS AT ANY SPEED (Using your OVERALL gear ratio)


This is all you need to know to figure out what is best for your truck. I will give you a quick example:

45RFE with 3.55’s and 32″ tall tires:
.75 x 3.55 = 2.66 <— OVERALL GEAR RATIO
60MPH X 2.66 x 336 / 32″tires = 1677 RPMS

45RFE with 4.56’s and 32″ tall tires:
.75 x 4.56 = 3.42 <— OVERALL GEAR RATIO
60MPH X 3.42 x 336 / 32 tires = 2154 RPMS

I hope this math helps you decide what is best.

3. Electric Fan = 10RWHP + 3-4 MPG!

Adding an electric Fan has been DYNO PROVEN to add 10RWHP. That additional 10RWHP helps increase your MPG by as much as 3-4MPG. Hands down a very worthwhile mod for both HP and MPG performance.

4. POWER WIRE (AIR RAM)= 8-10 RWHP & under a light foot has been known to increase MPG by 1-2MPG.

The POWER WIRE was originally designed to increase HP… hens the name “POWER WIRE” but after several years of our customers reporting noticeable MPG gains we had to take a closer look… and the fact is, under a light foot the POWER WIRE can improve MPG by up to 2MPG in some cases. BUT this is under a light foot! You must remember that each time you hit Wide Open Throttle with the Power Wire installed your engine will consume 2.5 percent more fuel but at all part throttle positions the O2 Sensors will keep the AFR nailed to 14.75:1 so the POWER WIRE will NOT create an overlean condition as some think.

5. JET STREAM SCOOP (AIR RAM)= 1-2MPG! (2002-2008 RAM)

The JET STREAM SCOOP has been known to increase fuel economy by 1-2MPG at steady highway speeds. It’s a great mod and will work with ANY induction system that draws the air from the passenger’s side wheel well.

6. COLD AIR INTAKE = 10-12 RWHP & 2-3MPG.

Choosing an intake that uses the largest Inner Diameter, is free from obstructions places the filter in the coolest location will make the best gains. Just remember NON-Restrictive, NONturbulent Cold Air makes the most power. Chose your system with this in mind and you will have the best.

We recommend our line of S&B intakes, they are high quality and priced affordable. They are currently the best intake going for the Dodge Ram. 10 out of 10 customers report back positive feedback… Yes, that’s everyone who has installed one!