14. In every instance of 4.0L building that I've seen, there has been excellent success with Airaid throttle body spacers on the '98-and-older intake manifolds. They give noticeable throttle response improvement and do actually increase fuel economy a bit. But the entire staff wondered if it made the same differences on a '99-and-newer intake manifold. And I'll save you the suspense: it didn't. 'Seems the Airaid spacer is an excellent option for anyone with the earlier intake, but the newer manifold improves airflow enough to make the spacer unnecessary.