Won't crank cold
 

I've got a strange problem since replacing the engine in my '99 Boxster. When I try to start the engine when the engine is cold, it doesn't crank right away. I have to try starting it several (5-10) times before it will crank. Once it cranks, it starts right up. Once it's hot, it will crank the first time, every time.

That seems weird, and so I have no idea what could be causing it. Do any of you have any suggestions?

My 2¢ says it's the starter.

Check wires to starter
chaffed/rubbing/arc'ing against frame/other wires
loose connection?
touch wires / make sure they're not hot after trying to start it
a few times / resistance builds up heat in wire
then if all is ok...starter is failing
Chris

As a quick test for the starter problem, switch on your headlights and see if they dim when you twist the the key. If the starter fails to turn over and the lights dim, it means the starter motor is drawing current but failing to spin up. Could be a failed starter or faulty bendix.
If the lights remain bright when twisting the key, could be a faulty ignition switch (my guess) or starter relay. Put a voltmeter on the bendix wire (second person required)and see if you have 12 volts there when the key is in the start mode.