Increased RPM's ??

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Period cars generally limited to four forward gears, most always ending with a final ratio of 1:1 rely heavily on the rotation that assembly for top speed.. Gear ratio is obviously a big factor, that and a specified tire diameter, in most of our cases of 25.5-26.5" limit top speed to the top speed of all the parts rotational capacity, of which engine rpm is the biggest factor..

If an engine can turn 5400 rpm you divide that by the final drive ratio, or in the case of a toploader typically 1:1, and again by the ratio distributing that rpm and then by the size of the tire.. Remember pi.. 3.14159+/- which gives you a finite speed..

A car that can only turn 5400 rpm with a final drive ratio of 1:1 and a gear ratio of 3.54:1 with a tire size of 26.5" (295/50 15) has a maximum speed of 128 mph.. Not accounting for aerodynamic influences.

The same car with a maximum rpm of 7200 will give you a top speed of 165 mph.

Modern sports cars with 5 and 6 speed gear boxes are less hindered by rpm.. A modern vehicle turning 4800 rpm with a six speed final ratio of .72:1, a rear end ratio of 3.45:1 with a 375/45 tire has a top speed of 172 mph..

Horsepower is a big factor but only to the point at which aerodynamically it becomes physically impossible or impractical to push an object through the air.. Conversely a 900 hp engine that will turn 7200 rpm will still only push a car as fast as a 450 hp car will given the same rpm.. It will however get it to that speed more rapidly.. Not twice as fast but nearly so.



Hope this helps..