Daniel Dudley

I must admit I would much prefer to eliminate the front Spoiler and undertray and replace with a demi tray that covers to the back of the alternator. But then I rarely drive at speeds that are considered a federal offense. Also in my uninformed opinion, I think these things are to eliminate drag, not add to stability and I would prefer maximum air flow around the engine to an extra MPH added to the terminal velocity. Don't much like the flaps that restrict cooling air to my radiator either especially as they will no doubt open at the speed/load that they would be most effective and are not needed most of the rest of the time. Feel free to bash me with a German Engineering Degree.

m21sniper

Personally, i agree with you Mr.Dudley.

Mongo

well no worries about the belly pan. I found an extra sheet metal screw in my car unbolted the thing in the parking lot during lunch and carried over to our construction area. I asked one of the guys if he had a mallot i could bar and gave me one so I hammered at it, got it straight *kinda* and now I'm ship-shape.

I still can't believe THERE ARE NO EFFING LEAKS!!!! WE DID IT!!!! SHARKY NO LEAKY!!!!!!

SharkSkin

Beyond the obvious streamlining and protection from debris, the belly pan also prevents pressure build-up on the engine side of the radiator. Marc Thomas pointed this out to me and while I was under there looking at things, it made perfect sense. If you look at the pics below, you can see that the oil pan, AC compressor, and alternator all hang down into the slipstream. I can see how the belly pan could turn this area into a lower-pressure area than running without:

Mongo

great pics Dave and great post on explaining this! They will stay on my car

fraggle

I believe the newer ones (87+?) are a different shape from those pics, but I've still got my aluminum one on the way from DEVEK... can't wait to put it on, esp. with the KONI's, springs, etc.. as well as all the stuff I ordered from 928 specialists! (swaybar kit!) oooooo!

'87 S4 5 speed.

SharkSkin

Yes, later cars have longer belly pans... on the early cars it's just a short deflector that ends about an inch behind the front edge of the oil pan.

WallyP

One effect of the front pans - they prevent hot air from recycling forward and going thru the radiator again when you are sitting still in traffic...

I have had a chunk of gravel pop into the belt groove and stall the engine at low speed when I was running with no front pan. Lots of smoke and noise!

Daniel Dudley

Yes you have to have at least enough pan to create airflow through the Rad. You dont want a backwash effect coming up under it. I think the early pan was a model of function and simplicity, but then I grew up reading Hot Rod and lusting after Lotus Sevens. The minimum you can do is add about a two inch lip coming down from the back of the radiator. The demi pan shields the AC and alternator while allowing the heat from the exhaust to flow out freely. My 89 still has the full stock pan all the way back, but the PITA factor leads to procrastination and paralisis.

Ron_H

I am about to replace the bent pulley on my AC compressor that gave up somewhere in Nevada in the middle of nowhere on a VERY hot day. And the rest of the 6000+ miles I spent in HOT and HUMID weather to Pennsylvania and back to California feeling like being in a sauna. There were a lot of critters on that stretch of road in Nevada, and I hit several medium sized birds that were sitting on the roadway feasting on the grasshoppers that the cars were hitting. One of those birds managed to become lodged in the headlight shroud until I pulled it out. Point I am making is that something bent that pulley. $#@*$%#@!! If I had the belly pan, including the front part Dave mentions, on my car, I
may not have needed to rebuild my AC controller, or drain and then re-charge my AC system, or replace the pulley. And my life would have been a bit more enjoyable having operative AC.