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Old 12-30-2020, 06:51 AM   #360
John V
No more BMWs
 
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Join Date: Apr 2005
Carmudgeonly Ride: Ram, MS3, CX-5, RX-8
Location: Glenwood, MD
Posts: 14,753
Nick's post reminded me that I've done some stuff worthy of updating this thread.

First of all, this happened:



Suffice it to say it's challenging to register a car like this in Maryland. In five years, when the car is 20 years old, I have options, but for now this works.

Going back to last year, when I ditched the FD RX-7 gearbox and went to the 4-speed, I needed to clearance the unibody a little. Part of the internal mechanism for the shifter wanted to occupy the same space as the trans tunnel sheet metal. So I did the rational thing and cut a rectangular hole just big enough to fit the gearbox. There was really no way to close it back up from the bottom, so I put it off. You can get a sense for it in the image below. It was about a 3" x 4" rectangle and it opened up the underside of the car to the interior.



Given that I'm off work for two weeks I bit the bullet and tackled this. That meant removing the entire dashboard. Super super not fun.

The tricky part is there are multiple layers and varying thicknesses of sheet metal forming the unibody. As viewed from the interior, the top layer is about 16-gauge, pretty thick. The next layer down is also roughly 16-gauge. Then there is a bottom layer of roughly 22 gauge, so very thin. The approach I took was to cut the opening into a circular shape on the sides, clean up the squared-off ends, and form two curved pieces of 16-guage to bridge the top and bottom layers. That's in the picture below. It took a long time because I don't really have any metal forming tools, so it was just all manual bending by hand. That bridged the top and "middle" 16-gauge layers of the unibody and made everything strong again. I then just folded up the 22-gauge bottom layer and tacked it into place. Hard to describe but it turned out okay. Welding sheet metal is a little tricky and I'm not a welder.



So that fixed the sides, I then made a "cap" of 16-gauge and welded that in. The welds on the leading side look abysmal but they're actually well-penetrated, I just didn't take a lot of time to make them look pretty.



So, that project done, next I updated my gearbox mount. This is version 2. Version 1 was made from .080" wall, 1x2 rectangular tubing. I was worried it wouldn't be strong enough and it wasn't. After the dyno session it had a bit of a bend in it. I decided to scrap it and make a new one out of 0.120" wall, 1x3 tubing. This one came out really nice.



Last step here is to reinforce the center section which was cut out for bolt access by adding a couple of pieces of angle steel, then prime and paint it.

Now that the car is registered I can take it out on the road and work on some of the areas of the tune that are hard to hit on the dyno. Side benefit is the car is a riot on the street, although it's geared a little bit too short.
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