The gear (incl. tire) ratio.
And maybe the differences of your instruments (if they are not exact,
esp. the speedometer).

Thomas

Noname wrote in alt.autos

Gearing. Manufacturers choose the gear ratios based on the power
of the engine, and what kind of performance they think the customers
want. The two engines have different power characteristics, and need
to be geared differently just to be able to do the same thing.

It's all in the relative and cumulative gear ratios in your transmissions
and differentials and tire sizes.  Mazda's final drive ratio is .8 times the
other.  You take the final ratio of your transmission, let's say 1 to 1, and
an engine turning 2800 rpm turns the drive shaft at 2800 rpm.  Then with a
differential ratio of 3.55 to 1, would drop that down to a wheel rpm at 789
rpm.  Then include the circumferance of the tire to figure out how much
distance is covered by each rpm of the wheel .. different wheel sizes cover
different amounts of ground at the same rpm, resulting in different final
speeds.