928 S/4 Engine Undertray - do I need one?
 

I need some advise around the undertray please. In short, my car does not have one, and as luck would have it there is one for sale close by.

Does my car need one? Will fitting one greatly improve my car or should I spend the money on other things on the to do list?

Thanks in advance.

I have it in my mind that the undertray will protect the engine bay by preventing water and grime to be sucked up into it. This is especially important in environments where salt may be used to clear roads. Probably, however, it is also advisable if you drive in the rain as well. I would buy one.

My underhood temps went down a lot with the undertray. My exhaust manifolds run hotter than on the average 928, though.

I would plan on buying one eventually, but your decision depends on the price of the one close to you and what's on the "to do" list. If new fuel lines or refreshing the trans fluid lines is on the list that should take priority as failure in those areas is often fatal to the car. Same goes for timing belt/water pump and tensioner rebuild.

Mike

Buy it! It's nearby they are not that easy and high $ to ship

Get one !
There are numerous tales here of unwanted things ran over that caused damage that could have just skidded off the undertray. Try having a plastic bag getting caught in your alternator !
Get one !

Are new undertray's still availble from Porsche? mine needs a front and rear undertray, I might even acquire some front vents and put them back in.

Yes: good protection for vital engine and exhaust parts, and run's cooler with the front undertray including the two naca-ducts for both motor mounts cooling.
Buy the much stronger and better aftermarket front aluminum undertray instead of the factory default plastic one, and move the two naca-ducts from an original one (takes seconds to drill out the rivits, and re-install them with lock-nuts. I did so a few years ago, and happy that I did so).

Yes:
928 504 021 02 protective plate, front
928 504 029 02 protective plate, back

But do not buy the original front plastic version one, as per my above writing: buy the much stronger and better aftermarket front aluminum undertray.

What's the views on fitting the under tray without the naca ducts vs no under tray, ie will the motor mounts get to hot with the tray on with no ducts?

The ducts are N/A right?

Mine came to me with no under tray fitted.

Ducts are available from Porsche, 928 504 021 02 which includes two ducts and a disposable fiberglass tray as a "mounting suggestion".

Seriously, the factory front tray is very fragile, and won't do much to protect the engine vitals. The aluminum tray from 928 International is quite sturdy, but as you note does not include ducts. Personally I think an aluminum tray without ducts is far better than a factory one with, and if you can find a used/trashed factory tray then you can salvage the ducts.

If you live in a winter climate with lots of wet snow, the plastic tray is not very good. In pulling into a driveway that had not been plowed, the build-up of snow tore mine right off. If you are going to replace the tray I strongly suggest the aluminum one.

Trust me, it definitely does not snow where the OS lives!

Thank you for the advice, all. I will go and have a look at it this weekend. If it is as per the photos I will get and fit it.

I do not expect to have snow in my driveway (it is winter here, temp around 15 Celsius at night - 23 daytime. You can see some winter pics here. http://www.facebook.com/media/set/?s...0385106&type=1

Unless its cheap, save your money and spend it on parts that are alot more important.

If you happen to drive anywhere around Phoenix or Tucson, you need the undertrays to deflect road hazards (such as an 18" section of oil drilling pipe) away from the oil pan, alternator and everything else hanging off the front of the motor. I know from firsthand experience x2. This is one example of the bellypan sacrificing itself. I was able to "repair" this one (second pic), but in the other instance it was a goner.