Moving Donor Tank Up on the MKIII Roadster

[skullandbones]

While I'm working on a couple of projects in the rear of the roadster, it occurred to me that it may be possible to move the donor Mustang tank up an inch or so without too much modification of the supports and frame structure. I have done a few attempts to find something specific about this without any success. I'm wondering if it has been done. I plan to add a diffuser in this area. The movement of the tank up a little would make this easier. I know that some have done a "dropped butt" mod but I don't want to lower the body by 2.5 inches. I may do a smaller mod of this type later (like the perky butt maybe a little less of it) but right now I'd like to get any existing info on moving the tank. Most of what I found was on the perky but mod on ffcars.com. Any help you can give will be appreciated.

Thank you,

WEK.

[skullandbones]

Bumping this back up to see if I can get an answer with the week end coming up (more traffic).

[CraigS]

I think you may be the first to bring this up. As I remember the tank is pulled up by straps until it hits the bottoms of four vertical square tubes. SO it would seem easy to shorten those tubes. But will the high right side of the tank run into anything? OTOH I am not sure a better diffuser shape is worth raising the weight of the tank upward. I guess it depends on how much you will be running at speeds where a diffuser will help (if it actually will) vs how much gas you need in the tank at those events.

[Jeff Kleiner]

I guess it depends on how much you will be running at speeds where a diffuser will help (if it actually will) vs how much gas you need in the tank at those events.

IMHO if someone is running fast enough for a diffuser to actually work then they are running fast enough that they should be using a fuel cell rather than an OEM Mustang tank.

Jeff

[skullandbones]

IMHO if someone is running fast enough for a diffuser to actually work then they are running fast enough that they should be using a fuel cell rather than an OEM Mustang tank.

Jeff

Jeff, you must have read my mind. I have thought about the custom tank or fuel cell. The trouble is, of all the donor parts that I would get rid of immediately, the tank isn't one of them. I actually like it. It's pretty well done and it fits nicely in the roadster except for the exposed. Not it's fault; it's that perky butt! I really haven't checked into the requirements of when you must have a fuel cell. I have a couple of friends who do track days so I will check with them first. It is something to consider.

I was actually thinking further down the road if the diffuser idea gets old, moving the tank up and dropping the rear an inch or so instead of the full drop butt, would get a similar look (sort of between perky and sagging butt) to the drop butt but less effect on the wheel well area.

I'll have to decide if the mod is worth it. BTW: the cross member I made for my new watts link is a perfect mounting point for the diffuser. I think it might clean up the air flow under the car at that point. Wouldn't it be fun to test the "brick" in a wind tunnel and try some of this stuff?

Thanks, guys.

WEK.

[GThompson]

I did this on my Coupe but I'm not sure how different the frame is in the back compared to the Coupe. I trimmed the 4 posts that the tank rests against about 1-1/2", moved the strap mounting points up the same amount and modified the diagonal piece that them covered up the filler opening in the tank.

http://i183.photobucket.com/albums/x213/ffrgorgo/null_zpseb102c93.jpg (http://s183.photobucket.com/user/ffrgorgo/media/null_zpseb102c93.jpg.html)

I did this so the body would fit over the tank a bit better, might be able to make a lower cover for the tank.

[skullandbones]

Hi GT,

I never would have guessed that a coupe guy would have done this. Never noticed that the tank hung down on the coupe (probably not on the latest gen). Well that's pretty neat the way you solved the filler hole issue. Thanks for showing us. I'm not the first after all! BTW: did you notice any differences about handling or any other change from the mod?

Thank you,

WEK.