Using OpenAL, have any of you done any work to vary the pitch of a looping sound to mimic an engine running at different speeds?

Yeah, it's easy. There is a source property you can use to set the relative pitch.

And changing that in real-time at any point when a source is playing, (not just on the boundaries of a loop, for instance) doesn't lead to any popping sounds or nastiness?

Got around to trying it myself now. It works fine, even while a source is playing. Yay!

I have been trying to use AL_PITCH to change the pitch of car engine sound.
It is changing the pitch but the effect is very abnormal; it is not realistic at all.

Is there any suggestion from you on how do i change the pitch so that it mimics the engine sound going up and down as the speed increases or decreases respectively in a smooth way.

I will be very thankful for any sample codes and tutorials to accomplish this task.

Thanks in advance.