The 2.87 First Gear in the TKO 600 is pretty aggressive, when you consider 2.21 is 1st in a ‘close ratio’ Muncie and 2.48 / 2.52 is the 1st gear ion a TH400 / 350 respectively. I know lots of folks end up going with 3.73s behind their .64 OD TKO-600 in order to make OD ‘useful’ at less than 80 mph. But with the 3.73 rear end, your overall reduction in 1st gear with 3.73s is 10.7. That would be like running a 4.33 behind your TH400. That’s pretty darned aggressive in a big displacement, long stroke engine (455 or 460 stroker) that already makes TONS of torque. 1st gear almost becomes a waste - it’s pure wheel spin for a split second before you have to shift.
I had a .64 OD TKO 600 in front of a 3.42 ring gear and I found that I was never happy on the highway. Even though the engine may not have been technically lugging it just felt ‘soft’ at any speeds under 70-75 in OD. I really needed to be going 80+ to feel comfortable in 5th. And then if I did downshift to 4th from that .64 OD the tach would LEAP to match revs. At speeds between 65-75, I felt like I was either whizzing like a sewing machine in 4th or near lugging in 5th.
I ended up re-building the TKO with a .82 main shaft and swapped in a 3.23 ring gear, and I could not possibly be happier. Overall gear reduction in 1st gear is 9.27. That’s even a bit more aggressive than running 4.11s behind the 2.21 first gear in the stock ‘close ratio’ Muncie. In 5th my overall reduction is 2.64 which is plenty comfortable at 75 mph. And if I need to downshift to pass, its a much more comfortable step. I think the TKO-600 with the .82 OD is tailor made for a 3.23 rear end.
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