If all else is unchangedss, you should be able to calculate a new speed at a given engine RPM fairly simply:

take the current ratio (eg 4.10), and divide by the new ratio (eg 3.73). The result multiplied by your current speed at a given RPM (eg 50 mph @ 2700) will give you the new speed.

4.10/3.73=1.099

1.099*50=55 mph @ 2700.

This doesn't guarantee that your engine will be able to turn 2700 with the new rear, but it is a simple conversion for the numbers.

Current fleet (subject to change w/o notice)
\'49 GMC 3/4-Ton , 60 Austin Healey Frog-eye Sprite (some assembly required), 2011 Dodge Avenger, 2015 Jeep Cherokee. No, they don't all run.
My other ride is a (B737)no, (B767)no, A320.... Update... was Embraer E190, now Boeing B787.

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