Can you blow up a motor by the revolutions being up to high driving down the road?

Yes, every engine has a "red line." If there is an RPM guage, the redline is clearly marked by red numbers. If you redline it too much, you can tear it up. But under normal conditions, that shouldn't be occurring. About the only way to redline one is to be drag racing, or just revving it constatntly in nuetral, and most new cars have a "governor" built into the PCM that will not allow you to redline it.

Yes, you can. Many cars do not have a built in rev limiter and/or are equipped with a transmission allowing the driver to select the gear ratio. This makes it possible to reach very high engine speeds. SSome things that can happen at excessive engine rotational speeds:

-Oil film can break down at high pressure locations such as between cam and lifters/followers, main bearings, and rod bearings. This is equivalent to running the engine without oil. This is bad.

-Valve float - Valve springs can fail to close the valves fast enough and in an interference (non-freewheeling) engine this can cause impact damage between piston and valve.

-As engine speed increases, so do forces on connecting rods. Connecting rods can break, but it is more likely to break a rod bearing bolt. In either case, this can hammer internal engine parts causing additional damage in a fraction of a second. Shrapnel can exit at dangerously high speeds. Block and crank are usually scrap metal at this time. Fires can occur.

-Torsional forces can shear the crankshaft. The crankshaft becomes unbalanced and can weld itself at the main bearings. Pistons closer to the front of the engine lose their load and can briefly accelerate to even higher speeds, possibly breaking rods. Pistons at the rear end lose time with the valves and can impact them. Dangerous shrapnel can be ejected from the engine. Fires can occur.

It is usually best to operate the engine only at speeds specified by the manufacturer. The engineers who designed the engine have determined that this speed is safe.