Captain Underpan! Part 1

From the beginning of this build I planned on making a louvered aluminum tray to fit under the engine and surround the exhaust. The original cars had them (though most were reportedly thrown away in the ’50s), and they would appear to be functionally important: VW engines like their cooling air to be, well, cool—not pre-heated by the headers and heads. Bugs and buses have tin to keep the hot underside of the car isolated from the top where the fan and carbs are sucking, so it seems logical to do the same with the Spyder.

Here’s the look we’re going for, courtesy, once again, of The Spyder Factory:

Here’s where we’re at right about now (actually a week ago):


I never plotted out how long I thought it should take to build this accessory. But if you’d told me at the start it would be more than 100 hours, and that after all that it still wouldn’t look quite right, I probably would have scoffed.

It’s just a flat sheet with two tunnels! How hard could this be?

Well anyway.

First thing was to get the “easy” part under the engine squared away. After determining that a “sled tin” concept that isolated the front exhaust pipes from the cylinders wasn’t advisable, I made a template for the whole engine area out of a big corrugated box back in June of 2019, opening up flaps under the heads and oil pan to let hot air out and give service access. I also provisioned it for a set of louvers to pull in air just ahead of the engine, as original.


IMG_3141I can’t punch louvers in the shop, so I bought some pre-made with the idea that I could fold them into the sheet. The three-wide set was a little wider than what I wanted but I figured it would work OK and look fine, given its position under the middle of the car where hardly anyone would see it.

Looking at the original design against the reality of the Beck style frame and Type 1 exhaust, you start to see how challenging this job is. The Type 547 engine exhaust came out the bottom of the heads, both pipes right next to each other, then curved and went under the engine crossmember, which was helpfully S-shaped to facilitate this. The Type 1 exhaust pipes, by contrast, exit out the front and back sides of the heads, curving around (the back one cork-screwing lazily to create more equal length tubes) far away from each other, with the front pipe passing over the engine crossmember, which was unhelpfully made arrow straight to facilitate easier frame construction and basically thwart my plans for an underpan.

Here’s the pipes on the driver’s side as they go past the motor mount and over the crossmember. The sheet on top of them is my abandoned “sled tin,” which would have blocked air from leaving the engine except out through that small space above the pipes:


After pondering this off and on for months I finally decided to just get on with it.

I also had a picture of a pan made by Beck for use with a Type 1 mill.Arjani bellypan

This one is going on a friend’s CMI car which has the correct engine mount crossmember. Pretty good likeness!

I started by cutting my box template into hardboard. Thence into a 2×4-foot piece of aluminum sheet.


I folded the edges up to make a tunnel under the heads so the cooling air would have to exit under the car.


I folded the louvers in and riveted standoffs to create a half-inch scoop at the leading edge. The bottom of the car is slightly concave, so the added depth here brings it about even with the edges and the couple of bolts holding the seat in. This was February 1.IMG_4736

Next I cardboarded the rear 2/3 pan and made a couple of stub piece to curve up and around the exhaust pipes where they exit over the frame. My idea was to make the second piece independently removable since there was no way to do it all in one piece. This was done February 8-9.



Trimmed roughly and folded, then clamped up under the chassis, the part started to take shape.


At this point, February 10, I started to develop some confidence that the piece might be makable by the likes of me. I was then about 40 hours into it.

Now all that was needed were some hoops over the pipes and mufflers, and some other minor stuff. It was about to get complicated.



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