Looking for any info i can find on running 4.56 in a 2wd hemi truck it is a 2012 5.7l automatic 6speed ext cab and i am running 305 50 22 tires i was told i need 4.10 or 4.56 with the cam and everything else that is going on the truck but want to know what the highway rpms are like and street manners from any one that has personal experience with these gear ratios thanks in advance for any info
I have run 4.56's in all of my HEMI trucks and I ran 4.10's in a 2002 Ram 1500 RCSB with a 4.7 because it was what I had to use that the time. I have a 2004 QCSB and a 2011 RCSB. The trucks overall drivability is improved with a 4.56 gear. Fuel economy in the city is better due to the lower gear because it doesn't take so much skinny pedal to get these heavy things moving. On the interstate and highways my fuel economy drops about 1.3mpg at 70mph but I don't drive that fast anyways. You will definitely enjoy driving the truck again with a 4.56 out back.
Now, for engine RPM. To calculate engine RPM at a given road speed I use this formula...
RPM =
MPH x Trans Ratio x Rearend Ratio x 336 / Tire Diameter
So, for instance, let's say you want to know what the engine RPM will be for 60mph.
60 x .67 x 4.56 x 336 = 61,592
61,592.832 / 34 = 1811rpm
For your transmission ratio, we use the ratio for 5th gear which is 0.67:1
If you want to see what your engine RPM will be at different road speeds just change the MPH to whatever you drive and recalculate the formula.
