Modern Drivetrain Swap into '65 Valiant
Driveshaft speed doesn’t change with respect to engine speed and throttle, since the trans ratios haven’t been changed.
If you changed the rear gear ratio, then the rpmat any given roadspeed has changed by the percentage difference between the gears. You won't notice a small change on the speed-O (which is calibrated for the out=going gears, BUT
You most certainly will see it on the tach as a similar percentage change in rpm ...... for the corrected roadspeed.
Here's what I mean:
going from 3.23s to 3.55s, with no other changes;
With 3.23s, 65=2614rpm with 27" tires.
With 3.55s, 65=2873rpm still with 27s; and both are at zerp-slip.
This is a percent increase in driveshaft speed of 3.55/3.23= plus 9.907%
Your speed -O will now be in error by that 9.907%, reading higher because the driveshaft speed is higher. You may not find this out until you get a speeding ticket.
But; your tach will tell the tale. If you drive the 3.55s at 2614 rpm as you did the 3.23s, then you will be driving at 9.907% slower, or 6.44 mph slower = 60.8 mph.
Your Speed-O only has to be corrected if you can't do the math-correction in your head, or if someone else is gonna drive it.
This driveshaft rpm increase causes your governor flyweight to fly out at a quicker rate, which increases it's pressure, which then over-rides the line pressure+throttle pressure, and this action causes your shifts to occur earlier than before.
You can change your throttle-pressure at the KD mechanism, but if when it is maxed out, your auto upshifts are still too early, then the only other thing you can do is go into the governor and reduce the pressure by delaying the flyweight by making it lighter.
Now, if the auto-upshifts have become too high after the governor swap, then you have to go back to the KD mech and reduce the Throttle Pressure. If you cannot bring the auto upshift speed down far enough to make you happy, then you have installed a too-light governor and will have to swap it out for a slightly heavier one. They call this; Hot-Rodding, lol
You can get around all this Hot-Rodding, by simply manually downshifting the trans, and holding it in gear, until you think the engine is past it's prime, or until it has exploded, whichever comes first. There, I hope that is a lil more clear.
