Captain Underpan, Deux

A word about COVID-19. Not long after I made my last post here the nation locked-down due to a global pandemic of a dangerous respiratory virus. Everyone knows that right now, of course, but if this blog persists more than a few years it won’t necessarily be obvious what was happening outside of the context of the build.

The pandemic and its response has crashed the stock market and the real economy, prompting a $2 trillion federal aid package. Something like 20 percent of everyone is out of work. I myself am still “working” from home but am functionally unable, as of yesterday, to do the state court visits my job normally requires. My wife is working from the dining room table and we’re both still being paid, at least for now, and remain healthy.

But currently 200,000 or so Americans are confirmed to have the virus and some 3,000 have died, as the epidemic’s trajectory continues relentlessly upward. The world is a very scary place and frivolities like this car project have largely taken a back seat, even as I knock off the last few dozen tasks on my punch list. The Maryland Motor Vehicle Administration offices are closed, some reportedly converted into drive-through virus testing sites. So instead of getting the car on the road this month, it may be a while.

That said, here’s what happened through February as I (blissfully, ignorantly) worked to make the aluminum undertray.

First I had to make two “stub-out” bits to cover the exhaust pipes on each side just aft of the engine crossmember. These are simple U-shaped bits, mainly, about 8 inches long, reaching from where the pipes exit under the engine to just past the muffler flanges.

I got them in and screwed them to the main underpan piece with self-tapping sheet metal screws, then set about making transition pieces to get to the wider full muffler parts. Once there I knew I could just drape aluminum over the mufflers and the tunnels would be done.IMG_4807

But then I looked at the fan shroud. There’s a doghouse in the back of the Raby DTM, housing the oil cooler. Near the bottom, on the passenger side, there’s a rectangular exhaust port for the hot fan air to come out. I needed to duct that down and out of the engine bay… Simple!

Or maybe not!

What followed was a week and a half of CAD. The doghouse port was just above and inside the exhaust pipes on that side, so at first I endeavored to duct the air down next to my newly-made stub-out. The problem? Not enough room next to the transaxle.


After three or four iterations of the above swaged, weirdly shaped prospective shunts, finally I decided to duct into the stub. That meant making a fairly complicated flange:



This was followed by an interlude in which I (somehow) imagined I should fab up a thermostatically-controlled system to allow oil cooler air into the engine compartment for warm-up.

I bounced these ideas off the experienced people at the Speedster Owners Group, who told me I was crazy—and not in a good way. Eventually I settled on


—and got on with the rest of the job.

Making the transition pieces was fairly easy, but I hadn’t fully reckoned how I was going to install the muffler bolts once the exhaust was shrouded. Two of the three bolts are on top, making access tricky with even thin open wrenches, and the aluminum tunnel shape left no room to turn the fasteners. VXAE7472

This prompted another several days of pondering. Weld the bolts in as studs? Re-make the transition pieces as split for installation after the mufflers are bolted on? There was no way to do anything!

I finally decided to open up the top of the tunnels and make patch pieces to cover the outboard bolts.

I still had to cut and fold the center piece between the mufflers, then make the muffler covers themselves, plus fold in the louvres. It was late February by this time and the rough shapes were all slowly coming together.

But roughly.



By Leap Day I had all the main pieces fit up with sheet metal screws and I knew I could finish the part. The question then was, “Can I do this so it looks good enough to sell in a public auction to people who demand quality?”


And also: will it work as designed?

There were two main groups of problems yet to tackle. First and most relevant: the stub-out tunnels over the exhaust pipes looked very close to the axle boots. This would not have happened had the original, slip-on ones not leaked, but the convenient aftermarket bolt-on accordian-style ones are significantly bigger. I could not yet be sure there would be no interference when the car’s suspension dipped over bumps. Second and not far behind was the look of the part. It could not look exactly or even very much like the original part—the shapes of the frame and exhaust were too different—but I need it to evoke the spirit of the 1955 effort. It had to look purposeful and professional: neither perfectly machine rendered nor bodged together by drunk monkeys.

As of February 29, it was too much the latter.


Next thing was to fold in the louvres. This material the pre-made vents is made of is too thin to risk brazing so, in lieu of rivets I cut the openings a little small and folded over the edges to capture the folded edges of the louvered panels before tapping them down with a hammer. It works and looks pretty clean.


The flanged round hole is for the transaxle oil plug.

From here it was a series of taking-off, trimming, fettling, putting-on exercises. In order to facilitate the installation of this part, I drilled the screw holes and installed 6-32 nutcerts in the center piece, plus the part of the outside edge piece where the stub-out tunnel pieces would fit.

The muffler surrounds were riveted to the outside part.

All of this took many hours as I re-adjusted the parts (sometimes with tin snips, sometimes with a hammer, and always with 220 grit sandpaper and wire wheels) to deburr the edges, smooth the seams and tighten up the fit.

Then I made finish trim strips out of flat bar to reinforce the parts and help improve the look of it.


Everything was marked and drilled to match the existing holes with some precision.

I also formed a part to relieve the shift gate cable…



—and made a bit to attached the middle panel to the outside one.

Then it was on to the “patch panels” to fit over the top part where I’d cut it to access the flange bolts.

The slot on the bottom to fit a tab so the part could be partially secured without screws, since reaching them down there would be awkward.

Socked in on top with temporary sheet metal screws, then changed out for rivet nuts and stainless 6-32s.


With that squared away it was just a matter of installing the heat shielding tape….IMG_5049


With the pan off, I jacked up the Spyder three inches and measured clearances between the exhaust pipes and the axle boots. They still cleared, and three inches is more “up” motion than I plan to allow in the suspension; I’m going to install limiting straps set at 2 or maybe 2.5 inches to prevent any “jacking” of the rear suspension.

The pan fits and includes panels and shrouds to direct all the cooling air out under the car. As of today there are still a couple of ugly gaps still on the top side, invisible when it’s installed but unacceptable to me. I’ll fix those, finish the final few ducting screws and riv-nuts and get the piece back on the car after initial shake-down trials show there are no oil leaks or other matters that need taming.

Otherwise, calling it done.

Time on task: 110 hours.




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