Using the original BMW underbody shields...

[bwh13]

Being the cars are 16 years old at a minimum, I would guess that most don't even have the shields anymore, I know mine didn't when I bought it.

Given the engineers spent a lot of time determining the cooling requirements of the engines and designed the necessary duct work and shields to ensure air moved through the radiator properly, it would only be natural to replace the shields if they are missing.

This would be especially true with the swaps since the engines generated more power and heat.

Any air that doesn't get forced through the radiator is wasted air; it won't carry away any heat if it doesn't go through the radiator fins.

I noticed several shields missing from my car (underbody right below radiator, a side radiator sheild, metal one back below the trans) all of which are designed to direct airflow through the radiator or smooth the flow under the car.

By smoothing the undercar flow, the air will pick up heat better and remove it from the cars heat sources.

Anything to make the air go through the radiator is beneficial, look at the newer cars that have those aftermarket aluminum shields to seal off the area between the radiator support and the grill. This forces the air to go through the radiator, instead of up over the engine, giving them a bit more cooling capacity. The gap between the radiator and support on our cars is a prime example of where we can improve the airflow through the radiator.

[FredK]

Hey, do you know what the part number is for that "cardboard" splash shield is?

[bwh13]

The undercar plastic piece that covers the entire front area from the radiator core support back under the oil pan is 51 71 1 965 899. It bolts to the wheel well liners and the brake duct pieces on the 88+ 325i and 325is and the 318is.

[FredK]

Holy crap, it's $93 at Pelican! I'm glad one of my cars still has it!

[BeirBrennerE30]

are you talkin about the metal shields that seperate the driveshaft from the exhuast? if so those are the only "shields" or ducts that i removed as they really dont do very much the way my exhaust sits now...

[FredK]

No, he's talking about the plastic splash shield that the brake duct backing plates attach to. It attaches to the front body of the car.

[bwh13]

There is also a metal shield that goes below the trans, which acts as a diffuser, smoothing the undercar air flow...BTW I paid the $93 for the plastic shield since I can't find one in the salvage yards...

[Axxe]

Lol, these cars are refrigerator boxes aerodynamically, no underbody tray is going to fix that.

[bwh13]

Ture about the aero qualities, but my point is that anything to help with cooling is worthwhile, and smoothing the undercar flow will allow the air to pick up more heat from the engine and exhaust, freeing up the radiator to manage the coolant to air heat exchaging better.

[M42Technik]

Glad this came up.

Would this work with an OEM skidplate? I am missing this part as well. There's a huge gap behind that valence, hah. I'm going to get this anyways, I hate not having it. I thought that was the right part, thanks for the number.

EDIT: And don't feel bad ponying up the cash, almost all junkyard ones are probably bent out of shape or missing anyways.

[BDSax]

i got one from th junk yard that was cracked, i just got a sheet of polycarbonate and cut it to shape and bolted it on