It's odd that your car would run leaner just by changing the pipe. As a matter of fact, the RDL Turbo pipe closely resembles the shape and size of the Nova (Rex, RB) pipe. I would check to make sure you don't have a leak at the exhaust port gasket. Make sure it's really snug. I've cut headers and changed out pipes on cars within the same race day and not had the dramatic temp change you're having. Also, 230 is a good temp area for this engine. If you're not flaming out, there really isn't a problem.