Aero: Front Splitter

The biggest concern with making a splitter for me was that it had to be fairly easy to take on and off for loading and unloading, so the entire build is made with that in mind. I think I’ve accomplished that, as by releasing 2 pins and 2 dzus fasteners, the splitter can be lifted free from its mounts.

The constraints that the splitter must live in for a D Prepared car are:
It may not be further rearward than the leading edge of the front wheel opening.
It must fit below the silhouette of the car as viewed from above.

Given that, the first thing to do was measure measure measure and make a template:




Next I wanted to make a set of mounts that would do most of the work of locating the entire assembly both laterally and longitudinally. I had a fairly large length of 1/8″ Aluminum Angle, and went to town with the drill and sanding drums. The hook portion will take care of the longitudinal location, and the mounts will be placed flat against the chassis mounts to locate them laterally.


With all the ‘easy’ stuff done, I wanted to make the base of the splitter so that we could start working off of something more consistent that cardboard. The material I chose was 1/8″ Dibond, which is 2 thin sheets of Aluminum with a solid plastic core. A single sheet wouldn’t be strong enough, so I used some of the stronger 3M Double Sided tape to bond 2 sheets of Dibond together.


I spread out some steel and lead to evenly press the 2 sheets together.


After more measuring and fitting, I finally had a starting point:


Now that I had it at a reasonable height, I could start measuring out to build the chassis mounts. Once those were fixed in place, I drilled out 3/8″ holes in the mounts and welded the ‘hooks’ I made to the backs of them, so that the weld metal wouldn’t interfere with the splitter mounts.



With the rear of the splitter fixed in place, I could start making a mount for the fronts. I built it to bolt to existing holes in the bumper support. Harbor Freight actually had excellent ends for the 3mm cable I used. I used a pair of Forked Cable Ends for the chassis side, drilled out to use 1/4″ quick release pins, and used a pair of Eye Terminals for the splitter side.



Finally having the splitter hung and being supported 100% by the car was a big moment for me, as the end was in sight and it finally started looking useful. I noticed however that in order to actually get my hands under the bumper and crash structure, the crash bar needed to be notched:


With all of the mounts sorted, it still felt like it had a bit more flex than I was comfortable with. I used a length of 1/2″ aluminum angle along the rear edge of the spoiler to add strength. Fortunately, I had Superman there to help with the riveting work.


For the air dam, I used 1/8″ ABS as it’s sturdy and easy to work. To join the ABS to the Dibond, I picked up some garden / paver edging from Home Depot Racing Supply. It’s nice and sturdy plastic, but also very light.


Everything got disassembled for a couple coats of paint to keep the rust at bay:



And finally, put back together to be viewed in all its majesty 😀



I think maybe she might need a wash. Before then, there’s lots more work to do in the month or so before the next event.

Aero: Rear Spoiler

First off: the swearing.

Remember the duck-bill template I originally made to trace out the contour of the trunk? Well, it turns out that 2D objects don’t act the same as 3D objects, so when we bent everything to the correct angle of the dangle to sit on the mounts, it was several different kinds of caddywompus. I had to have a bit of a re-think and start almost from scratch.

The solution was to cut the template out at with the material at the correct angle on the trunk, but I had no way of doing that consistently without a fixed datum to start from and reference, so the first thing I needed to do was affix the central lower-mount to the trunk. Which meant I needed to finish fabbing up those mounts.

If you enlarge the picture, you’ll notice that the 1/8″ holes are countersunk. This is because for the brackets to fit flush on the trunk, I need to grind down the ends of the rivets. Countersinking those holes gives the end of the rivet something to grab ahold of after the end is shaved off.



Each bracket will get a wing-head quarter turn fastener to keep things quick-release.



With that done, I got the central bracket mounted to the trunk and worked on the template from there. Once it started getting close, I had a good reference off of the template for where to mount the other 2 quick release fasteners, and finish making the template. Using clecos on the template helped ensure that every time it went on the trunk, it was in exactly the same place.



Unfortunately I ruined a large piece of ABS using the original template, leaving it too small to work for my purposes, so I had to  cut another blank out from scratch. But seeing it start to come together definitely buoyed morale.



Next, some rubber / cushioned edge trim went on to fill the air-gap and make sure no further trimming was necessary on the bottom edge.



From there, it was time to measure it for the top edge and do the final shaping. By rule, it’s allowed to be 10″ from the bodywork and not extend out past the edges of the fenders. Here I’ve already mounted the brackets for the body mount struts that support the upper edge.



The body mount struts use standard hardware sizes, but have a very nice square nut that fits the brackets to facilitate tightening everything into place without a tool on that nut. Wherever possible, however, I like to keep my metric car with metric hardware, so I made my own ‘square’ nuts using some M6 x 1mm nylock nuts and the disk sander:



As expected, and by design, the trunk still works! 2 quarter turn fasteners, and it lifts open with the spoiler still in place.



12 more holes and 15 rivets later, et voilà, job’s a good ‘un.
I may yet paint those brackets black so they blend in a bit better, but for now things are pretty darn good as is.



And of course, the money shot. I think the car is finally starting to match that license plate!


Harness Anti-Sub Strap

The 1st event of the season was a very loud reminder that I needed to do something about the anti-submarine strap on the 5 point harness. The angle and length it’s at, and on my particular seat, it essentially falls down to the floorboard every time the driver undoes their belts, which made strapping the next driver in far more annoying than necessary.

It’s a little thing, but at autocrosses with smaller attendance numbers, we’re often finding ourselves rushing drivers in and out of the car about as quickly as possible before it’s time to go again. In fact, at the 1st event we were the only 2-driver car in our heat, and even doubling up on our runs to cut down on driver-changes I ended up having to do 2 runs back-to-back to close the run group out. Sub-optimal (ha! sub!)

Fortunately endurance racing has figured this out eons ago. I sourced a short length of 1/8″ rubber surgical tubing, tied it to the belt and the front seat mount, and called it good.

The subsequent event had a very similar setup with us being the only 2 driver car in the heat, and we were able to manage just fine now that we weren’t having to fumble around with the belts nearly as much. I even managed to spend some time gathering tire temp data.  Win all ’round!


Split Lip Bumper Repair

My front bumper has had a split in it for ages, that’s been progressively getting worse. Honestly, it’s impressive that it’s lasted as long as it has, through nearly 10 years of dedicated autocross use.

I found a piece of *cough* scrap sheet metal to make a patch to strengthen the area:


I figured 10 rivets would be a nice, round number. It obviously doesn’t need that under static conditions, but when you hit a cone at 50 mph, more is probably better.



After a couple minutes on the drill press, then belt sander to debur, I positioned it on the bumper to transfer the holes through.


Final positioning before riveting it in place.



And the rivets in. Job done. And just picking up the bumper I can feel that it’s far stronger now, with a lot less flex overall.