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So I have been looking for a 928 off and on for about a year. More off than on. And the other day I was looking over pictures of a car that just popped up on Bring A Trailer, which is now quite a different web site than it originally was, and their were pictures of the underside of the car with a vented belly pan. This is the first car I have ever seen with a belly pan. So were belly pans optional ? Did they get removed and never replaced when they were worked on or do they have a tendency to get ripped off easily when driving over normal road debris? I am guessing they are not particularly important for aerodynamics or cooling as up unit this car I have not seen one on a car yet. Cheers Paul
they came on the later cars stock. most of the time they get busted and just left off. some have vents that keep the motor mounts cool so they dont bake to death
It seems like a lot of the trays get damaged when the car's front suspension sags over time. Plus they are too often put back without all the screws needed, dangle some and get damaged. Those front mounting tabs are bent and break after just a few parking bumper slide-overs.
The trays shown so far are the front tray for '87 and later cars. That one keeps junk from getting up into belts and such, and can save a lot of grief by helping the car pass over stuff that would otherwise rip the alternator or air-conditioning compressor off the engine.
There's a second aluminum tray that's installed behind the plastic one on the car. It protects the bellhousing and the exhaust to about where the catalysts are installed. Metal because of the heat.
The trays do contribute some to engine bay cooling. The front edge carries the back of the plastic chin spoiler too, so it doesn't droop too low and get caught on stuff. In the picture above, those two ducts protruding up are used to push air to the motor mounts area, near the exhaust. Those are not part of the aftermarket tray shown, but must be harvested from the old tray and pop-riveted to the new one.
I ran my 1988 with no belly pans for several years, it was a disaster. It ate accessory belts annually and the alternator cooling hose lasted maybe 5,000 miles. Finally I bought all new belly pans, there are new aluminum ones available from 928 International. With the pans in place, the engine sound inside the car is completely different. Clearly designed for undertrays, don't leave home without them.
The two center bolts (red arrows) are often forgotten to be put back after a bellypan removal for service, ask me why I know, it happened two times when I got my car back from a service. These two missing bolts will make the belly pan rattle.
The front lines up with the rear of the S4+ plastic nose section, with screws through that section to little tabs that hang from the bottom radiator support. I made a separate aluminum cross-piece that hangs from the original location for those front ears on the frame, and more securely manages the height and strength of the pieces there.
The rear of the main pan sits on top of the front edge of the rear pan. The aluminum rear pan has ears that screw to the frame at the front, and separate support brackets that go to little tabs on the tub at the rear. If you decide to mount the front tray without the rear one, you'll need to figure out a way to support the back edge a little better.
Near the rear of the main tray, there are tabs that accept screws up into tinnerman-style speed nuts, accessible through holes in those NACA-style scoops for the motor mounts. In addition, there are two reliefs that each accept a 6mm capscrew and a washer that fit up into tapped holes in the steering rack. I swapped in 1/4" SS fender washers there to spread the load around some on the plastic tray material. This seems like an area where vibration and the tiny original washers really need the help.
I put 6mm NutSerts into the frame where the tray brackets attach. Much more secure than the little hex-head sheet-metal screws used originally.
Otherwise, The original tray is still doing the job OK on mine. I know the guy who takes it on and off, so no serious worries about getting it back on correctly.
78-86's also all came with a belly pan, though it was really just a lower shroud bridging the gap between the radiator bulkhead and the oilpan, with reliefs for the A/C compressor and alternator. Some were steel, some aluminum, all roughly the same shape. Here's an aluminum one, stripped in the process of repainting:
I've taken off and replaced those belly pans many times over more than ten years, but never had any idea there were screws inside the air ducts!
I will examine and install next time I'm underneath!
The screws go up through holes in pan just behind the actual ducts, fit through the holes in the little tabs that are part of each duct, and engage speed-nuts on tabs that are part of the crossmember.
02-18-2017, 06:32 PM
Belly pan
