This is on my 2011 R3, just under 30k miles. Only owned it since April or so.

When going from zero throttle to... anything other than zero, there's a jerk that feels like all the slack is being taken out of the powertrain at once. Sometimes there's an audible clunk, but that might be something in my trunk; usually there's no sound. What makes me think it's driveline lash is:

1. Really delicate throttle application prevents it, and
2. It only happens when I tip the throttle in from zero. If I'm already giving it a little and then roll onto it further, it's completely smooth.

Is some amount of this normal for this car?

 

At low RPM these cars are jerky, jerkier than most others I've driven. So what you describe sounds normal, but it's hard to judge without being there or a video. There shouldn't be any clunks though.

 

Hmm, text-based descriptions are hard to evaluate, but...

...as long as you rule out the noise as being a problem, then yes, it sounds about right. The RX-8 has an extremely light rotation mass for the whole drivetrain, so it can change it's inertia much more quickly than you might expect.

It shouldn't make any noises though, and there shouldn't actually be much slack at all. If noises are linked to the drivetrain, or if you have a lot of slack, then there is a problem that needs solving.

 

So, if what I'm feeling is just due to the absurdly low inertia in the drivetrain, then what's actually happening millisecond-to-millisecond? Is the engine's RPM just changing quickly enough to challenge the ECU for a fraction of a second?

Either way, how would I tell that from slack in the drivetrain? Gotta get the rear wheels in the air, I guess...

 

The lash is nothing to worry about unless it's accompanied by by a noise or excessive wheel hop during any wheel spin. Keep in mind that the stock engine mounts are liquid filled and the stock differential carrier mounts have cavities all in favor of creature comfort. There are remedies for both the engine mounts and the diff. carrier bushings.

- Engine mounts can be drained and then filled with liquid urethane for a more acceptable solution.
- Diff. Carrier bushings can be replaced with Whiteline urethane ones, although the job is not easy, unless you decide to take a shortcut by cutting out a patch out of your trunk floor above the diff. carrier bracket bolts then filling that patch in :D

 

Drove the car yesterday after 5 days of downtime (didn't need to drive). I tried like heck and couldn't get the same feeling. Guess there's no abnormal lash, unless ambient temps significantly affect the hardness of the powertrain mounts or something...