Krampus

I was thinking of changing out the rear diffuser on my car to the GT4 design because I prefer the look of it to the factory one. But I noticed that there is a disclaimer " A direct fit, some models may require minor modifications. ". I've called a couple Porsche dealership parts departments and as expected nobody knew what was ment by that. Even looking in their system they could not find any information on any modifications required.

I just wondered if someone else had done this swap and if so what needed to be modified. Also if anyone had any pictures of a boxster with the GT4 diffuser installed.

Krampus

Wow 73 views at not a single response. The parts department led me to believe this was a popular swap, and that someone on the forums might be able to answer my question.

tomhartzell

Just conjecture on my part, but I believe they may be referring to the mods that might be required similar to adding the aero kit for my '12 Cayman S. (https://www.suncoastparts.com/product/987C2AERO.html)
The airflow and handling of the car changes a lot when the aero kit is installed, and Porsche sells it with a "front bumper spoiler lip" that must be installed along with the fixed wing spoiler in the rear. If just the larger rear spoiler were added without the front spoiler lip, there would be considerably more downforce on the rear of the car which could adversely affect its handling at high speeds. (And with my Cayman, I wouldn't be surprised if it actually inhibited its performance even with the front spoiler lip until I got to very high speeds; the Porsche design engineers are scary smart when designing the aerodynamics of their cars.)

Rebuttals / corrections / updates gladly solicited.

Krampus

I will agree with you on their thoughtful engineering. I just wonder how much difference there is in having a little more open space for air to exit vs the 2 large holes it had currently. Not that I will ever drive the car fast enough to test it as its not a track car by any means.

Leicht

tomhartzell

I suspect the handling might not be adversely affected if you're only going to be driving at highway speeds or lower. If I were considering it, I would shoot a note to PCNA or one of the PCA gurus for any airflow and handling considerations or drawbacks associated with installing it. My specific questions would include whether the car would now be more prone to understeer or oversteer as a result of the change.

Krampus

Just FYI for anyone looking at this thread to think about this for their car. I found the info needed over on Planet-9. From everything I have seen there is no modification being done. Not sure but I guess that portion is just a CYA policy for whomever is selling the parts.

http://www.planet-9.com/981-diy-disc...all-981-a.html