Conversion help

[Prestong]

We are puting a 6bt in a 90 f-450 it has 5.13 gear ratio in it and zf5speed what will that give us in speed sence it had a v8 7.3 in it and the 6bt will turn less rpms the original truck would only do 55 to begin with

 

[PDM]

Well, if the redlines I used are accurate, (6bt@3000/7.3@3500)55mph=47mph.

Someone was selling a gear vendors overdrive in the classified forum a few weeks back, 47/gv@.78=60mph.

If you would rather change rear end gears, a 3.54 would give you (5.13/3.54)55mph=80mph@3000.
A 3.54 would cruise at 55mph@2062rpm, and the Cummins is very happy somewhere near 2000rpm.

All this is based on the accuracy of your stated 55mph top speed and the redlines I used. Good luck with your conversion!

 

[Fordpickupman]

It'd pull a heck of a load though.......

 

[Joseph Donnelly]

x2 on changing the differential ratio.