Again, go to the link provided by We B Old or formula provided by GMCdp.
http://www.ringpinion.com/Calc_RPM.aspxThe nuumbers do jive at 3.9 and RPM is at about 3K. There is a lot of flex in 100's of RPM's. Not exact science.
With the numbers as close as they are I would be inclined to agree with GMCdp, that your final ratio for the tranny is 1:1 in 4th, pretty much a standard unless OD'd.
Everyone has opinion and the biggest differnce is Stovebolt guys are not making money or getting kickbacks. Be cautiious out there greasshopper!
I think a lot of us on the site know this and would agree - the final decision is yours to live by as it is your truck, your ride, and the way you role. Go back to the begining of the thread, everything you need has been addressed.
1) Drive conservative. ((Devin 55 tractor)
2) Make sure the truck is in proper tune. (GMCdp and Devine 55 tractor)
3) Find optimum RPM for HP and torque. (Dave Fla54Chevy3100 Fla54Chevy3100)
4) Do mthe math. Add in tire height, gears ratios (rear and tranny) to place your driving conditions in the "motors sweet spot" as much of the time as possible.(Dave Fla54Chevy3100)
5) get the optimum R&P.
6) Fine tune with tires.
Eessential there is no more except your followup on choices and outcome.
good luck,
Cavebull
