Drop Trunk Dimensions

[BrewCityCobra]

So a quick question to the group. I am getting ready to start laying out a drop trunk design and was wondering - how "deep" are they? Specifically, using the lower sheetmetal as a datum, I was wondering how far down the bottom of the drop trunk extends?

Any help would be greatly appreciated.

Thanks!

[FLPBFoot]

Mine is currently in the trailer so can't get to it easily to measure but around 4 inches +or- The gas tank is the limiting factor and the bottom of mine sits about 1/2" above the top of the tank.

[OSU Cowboy]

My MK3.1 with Cobra Earl's drop trunk kit measures ~ 8" from the upper trunk shelf down to the modified drop trunk surface. I'm measuring just over 4" from the top of the rear lip - which was the original pre-modified trunk floor - down to the drop trunk surface.

[phileas_fogg]

My lower drop trunk was ~5" deep. You can easily mock up your box using poster board or card board.

Here's a description of the fabrication process from Post #158 of my build log (https://www.ffcars.com/threads/phileas_foggs-mk-4-roadster-build.508121/#post-4776313):

I then fabricated the various panels for the 17 1/2” x 26” x 5” lower trunk floor. I chose to fabricate the lower trunk box rather than just buy the Russ Thompson box for a couple of reasons. First, I wanted to practice on something a little more complex than the upper trunk box before tackling the passenger foot box expansion. Second, if you’re going to leave the rear frame members in place, you have to clearance the RT panels yourself. If I’m going to do that, I may as well make the panels. Third, I wanted every available inch of trunk space. That meant custom panels.

For those of you inclined to do this mod yourself, here are some lessons I learned:

1. The trunk framing is NOT square. For me, the left side of the 3/4” tube running between the rear roll bar mounts was a full 1/4” higher than the right side. I know this because when I fabricated the lower trunk wall panels they didn’t join. At first I thought I’d made a mistake, but subsequent measuring and inspecting and assembly off the car showed I had in fact made a square, non-joining-up box. I ended up remaking the lower left wall and sloping it so that I got a non-square box. If you don’t tell I won’t.

2. Use a piece of scrap aluminum to get 90* bends on the longer panels with your 30” Harbor Freight metal brake. First, make your bend as usual. You’ll find that the only the outermost 2-3” are at 90* and that the part you just bent up is bowed such that the middle is only at ~75*. No big - just insert that scrap aluminum between the brake and the work piece:

https://farm5.staticflickr.com/4438/36185660502_66ca45737b_k.jpg (https://flic.kr/p/X8AYbj)IMG_1856 (https://flic.kr/p/X8AYbj) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

and bend a second time. Repeat everywhere you see the need.

3. There is no elegant way to notch the aluminum panels so that they clear the frame members. I used a jig saw and a lot of trial fitting. I probably spent an hour on each piece and they still look like crap. Good thing they’re getting covered up!

4. I used a bunch of patch panels to cover gaps between the major panels and to provide strength in the corners. I numbered the patch and whatever panel they went on. Note the notch in patch #4 below; that’s a result of Lesson Learned #3 immediately above.

https://farm5.staticflickr.com/4316/36217571431_d775d63837_k.jpg (https://flic.kr/p/XbqwbK)IMG_1825 (https://flic.kr/p/XbqwbK) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

5. Round off the corners of your pieces with a file. If you don’t you’ll bleed.

6. Don’t get too concerned about putting the box on the car after go-kart. I tried to come up with an assembly method that did not require dropping the gas tank, but I’m pretty sure I’ll have to do that anyway. Just leave yourself enough feed/return hose between the tank and filter/hard line such that you can get the tank out of the way.

I can’t call this a lesson learned because I haven’t actually done it, but it MAY be better to fabricate a shallow tub for the bottom rather than use a flat piece of aluminum like I did. That would let you make the walls of the lower trunk box L-shaped instead of Z-shaped. The tradeoff is that with the tub method you’re guaranteed a row of rivets around the side walls of your box.

Finally, I’m glad to have this project done. Even though I spent more time on the lower trunk than I should, and even though the results are not particularly pretty, it was cheap and I’m sure I’ll appreciate the extra storage. I definitely recommend tackling this project.


John

P.S. If you want pictures of each of the panel, just click on any of the pictures. That will take you to my Flickr album, and you can scroll around to find what you want.

https://live.staticflickr.com/4307/36156850561_b67b5430db_4k.jpg (https://flic.kr/p/X64iZc)IMG_3753 (https://flic.kr/p/X64iZc) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

https://live.staticflickr.com/1759/40666659400_64e199baa9_4k.jpg (https://flic.kr/p/24Xzg31)IMG_4468 (https://flic.kr/p/24Xzg31) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

https://live.staticflickr.com/878/40643547040_312aa92509_4k.jpg (https://flic.kr/p/24VwNx3)IMG_4465 (https://flic.kr/p/24VwNx3) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

[BrewCityCobra]

My lower drop trunk was ~5" deep. You can easily mock up your box using poster board or card board.

Here's a description of the fabrication process from Post #158 of my build log (https://www.ffcars.com/threads/phileas_foggs-mk-4-roadster-build.508121/#post-4776313):

I then fabricated the various panels for the 17 1/2” x 26” x 5” lower trunk floor. I chose to fabricate the lower trunk box rather than just buy the Russ Thompson box for a couple of reasons. First, I wanted to practice on something a little more complex than the upper trunk box before tackling the passenger foot box expansion. Second, if you’re going to leave the rear frame members in place, you have to clearance the RT panels yourself. If I’m going to do that, I may as well make the panels. Third, I wanted every available inch of trunk space. That meant custom panels.

For those of you inclined to do this mod yourself, here are some lessons I learned:

1. The trunk framing is NOT square. For me, the left side of the 3/4” tube running between the rear roll bar mounts was a full 1/4” higher than the right side. I know this because when I fabricated the lower trunk wall panels they didn’t join. At first I thought I’d made a mistake, but subsequent measuring and inspecting and assembly off the car showed I had in fact made a square, non-joining-up box. I ended up remaking the lower left wall and sloping it so that I got a non-square box. If you don’t tell I won’t.

2. Use a piece of scrap aluminum to get 90* bends on the longer panels with your 30” Harbor Freight metal brake. First, make your bend as usual. You’ll find that the only the outermost 2-3” are at 90* and that the part you just bent up is bowed such that the middle is only at ~75*. No big - just insert that scrap aluminum between the brake and the work piece:

https://farm5.staticflickr.com/4438/36185660502_66ca45737b_k.jpg (https://flic.kr/p/X8AYbj)IMG_1856 (https://flic.kr/p/X8AYbj) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

and bend a second time. Repeat everywhere you see the need.

3. There is no elegant way to notch the aluminum panels so that they clear the frame members. I used a jig saw and a lot of trial fitting. I probably spent an hour on each piece and they still look like crap. Good thing they’re getting covered up!

4. I used a bunch of patch panels to cover gaps between the major panels and to provide strength in the corners. I numbered the patch and whatever panel they went on. Note the notch in patch #4 below; that’s a result of Lesson Learned #3 immediately above.

https://farm5.staticflickr.com/4316/36217571431_d775d63837_k.jpg (https://flic.kr/p/XbqwbK)IMG_1825 (https://flic.kr/p/XbqwbK) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

5. Round off the corners of your pieces with a file. If you don’t you’ll bleed.

6. Don’t get too concerned about putting the box on the car after go-kart. I tried to come up with an assembly method that did not require dropping the gas tank, but I’m pretty sure I’ll have to do that anyway. Just leave yourself enough feed/return hose between the tank and filter/hard line such that you can get the tank out of the way.

I can’t call this a lesson learned because I haven’t actually done it, but it MAY be better to fabricate a shallow tub for the bottom rather than use a flat piece of aluminum like I did. That would let you make the walls of the lower trunk box L-shaped instead of Z-shaped. The tradeoff is that with the tub method you’re guaranteed a row of rivets around the side walls of your box.

Finally, I’m glad to have this project done. Even though I spent more time on the lower trunk than I should, and even though the results are not particularly pretty, it was cheap and I’m sure I’ll appreciate the extra storage. I definitely recommend tackling this project.


John

P.S. If you want pictures of each of the panel, just click on any of the pictures. That will take you to my Flickr album, and you can scroll around to find what you want.

https://live.staticflickr.com/4307/36156850561_b67b5430db_4k.jpg (https://flic.kr/p/X64iZc)IMG_3753 (https://flic.kr/p/X64iZc) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

https://live.staticflickr.com/1759/40666659400_64e199baa9_4k.jpg (https://flic.kr/p/24Xzg31)IMG_4468 (https://flic.kr/p/24Xzg31) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

https://live.staticflickr.com/878/40643547040_312aa92509_4k.jpg (https://flic.kr/p/24VwNx3)IMG_4465 (https://flic.kr/p/24VwNx3) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

This is great. I was messing around with the trunk design over the weekend and had anticipated doing something almost identical to what you did - to help open the trunk up a little bit beyond what the Russ kit would have provided. I'll certainly be checking out your Flickr and build thread. Much appreciated.

[CraigS]

Do you have your fuel tank installed yet? There may be some differences in them so I'd want to have mine before deciding on your depth.