I'm looking into a 91 S4 and have seen that it does not have the two protective plates mounted under the engine behind the front spoiler. They are available from Porsche at about $600 total. Are there any other suppliers out there and are they required.

Thanks

 

There are several aftermarket options out there... contact any of the big three for more info.

 

They are not protective plates; the belly pans are for aerodynamic and engine cooling purposes.

Most run with them removed after belly pan damage from poor driving skills, driver impairment, or poor front shock absorbers.