Mathematically the difference is equal to the ratio difference .
So since the overdrive ratio is .73; and the standard is 1.00;
going from 2200 is;
2200/(.73/1.00) =3014rpm; right on target; speed remaining the same..
the ratios are ;
3.09--------1.67------1.00-- .73od versus
- -2.66--1.92--1.40--1.00 ; unless you got a close ratio, then
-- 2.47--1.77--1.33--1.00
the tires on that yellow Dart appear to me to be quite a bit taller than 26.6.
According to the math; for 60=3012 with 3.45s; those tires are 22.9 tall. Obviously; either 1)you don't have 3.45s. or 2) your speed-O is out.
If in fact those tires are 26.5; then the math points to about 4.00 gears.
But to me, those tires look to be more than 28 tall. If that was true, then the rear gear would have to be closer to 4.30s
Here is the Formula so you can figure it out for yourself;
Mph= (rpm x TR)/( 1056 x R1 X R2 x R3)
where;
Mph is Miles per hour
TR is Tire Rollout ( ~diameter times pi which is 3.1416)
R1 is the rear gear
R2 is the trans gear
R3 is any other multiplier you may have installed
1056 is a constant that spits out a usable number for Mph
Here is an example;
Mph= (rpm x TR)/( 1056 x R1 X R2 x R3)
For TR =26.5 x 3.1416 =83.252
and 3.45s
Mph=(3012observed x 83.252)/(1056 x 3.45 x 1.00) = 68.8 mph..
This would point to an error of 68.8/60=14.67%.. Could be the Speed-O, or could be the rear gears, and could possibly be complicated by an error in the TR. Or even in the tachometer.
