Slant 6 with 4 speed

Johnny71dusty said

im getting ready to do this exact thing. 1975 od trans in my 198 slant duster , with factory rear I have no idea the gears in those cars but figure its 2.73 wish realm ? does that sound right ? I want the over drive as I take it on long highway trips like moparty and power tour and I think it would help a lot. are you saying its gonna be a issue here or jus that is pathetic with my rear in it ?

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Speed/Tire/RPM calculator

You might want to go play with this calculator to make sure you are staying in your power band. I have a 225 slant with the OD trans in my truck with 3.55 gears and 29" tires. On the freeway, it's barely into the power band turning 2000 RPM at 65. I'm changing to 3.91's to get cruising speed up to 2300 or so.

Just for grins I ran your numbers, with a 27" tire and 2.7x gears, at 65 you'd only be turning 1600 RPM. That may make you happy, or it may not. I found I could barely operate at such a low RPM.