Tank armor question

Fuel cell fill necks have a flapper valve in them that won't allow fuel to escape if the cell is compressed and/or inverted.

A drop-in that mimics the original tank's shape would be nice but those are the ones that cost big bucks. A universal fuel cell is under $300 and I had a local fabricator build me a cage for it for $275. Now that I have the knowledge and equipment I can probably build one for a third of that. I'm thinking of digging out my old tank from my parents' basement and cutting the top off to use it as the holder for the fuel cell. At least it'll look like the original tank from the outside.

I'd do both tank armor plus rear seat divider

the rear seat divider should add the same structural strength to the rear of the car, if you do it right, that the convertible rear seat divider gives. Ford put it on convertibles for a reason. It helps. I can just weld a plate to my existing rear seat divider and box it in on the sides in front of the wheel wells.

So, I wouldn't discourage someone from doing both, especially on a regular commuter.

Polar moment - having weight behind the rear wheels is a good thing

Rusty67 said:

The reason the added wieght helps is that it gets the car closer to a 50/50 weight ballance.

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That's part of it, but it's not that simple. Putting weight that far back helps (I believe) move the polar moment (the center point the weight of the car rotates around) of the car farther back, versus putting it right over the rear wheels. I'm no expert, but that's how the argument was made. As you turn, it's beneficial to have the polar moment farther back on our cars to increase oversteer. Therefore, a weight behind the rear wheels is better than one on the rear wheels:

RST Tips & Tricks

The only downside, possibly, is more squat/wheelie action if you've got too much weight back there.

Edit: For Auto-X cars and "tossability", you actually want the weight closer to the center to move the polar moment closer in - it helps in rapid transitions side to side. But with the understeer most of our cars have, having a weight way back out there helps to swing the rear around and bring it closer to neutral. But do a test - fill up your tank, load up the rear with some more weight (tied down) and see how it feels around your favorite corner. Keep it safe, of course . . .

I would definitely get the tank armour. My godfather is the one that invented the design for the Mustang version, so I have the original model in mine. I just wouldn't feel safe without it. A little extra money for extra protection never hurt.

Fuel cells and tank armor

ron67fb said:

Fuel cell fill necks have a flapper valve in them that won't allow fuel to escape if the cell is compressed and/or inverted.

A drop-in that mimics the original tank's shape would be nice but those are the ones that cost big bucks. A universal fuel cell is under $300 and I had a local fabricator build me a cage for it for $275. Now that I have the knowledge and equipment I can probably build one for a third of that. I'm thinking of digging out my old tank from my parents' basement and cutting the top off to use it as the holder for the fuel cell. At least it'll look like the original tank from the outside.

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That's what I did with my 70 Fastback. I removed the stock tank and had a metal fabricator weld in a rectangular box (or sunken bathtub as I call it). I chose the dimensions so that it would fit many 20 gallon fuel cells. Fuel cells should be replaced every 5 years and this is a method to ensure that those replacement costs are manageable -- by allowing me to buy standard low cost cells. There is Fuel Safe that makes a drop in replacement, but it would seem that the problem with their approach is that their cell is so expensive that replacement costs are too high. The good thing about their product is that cosmetically their design is nicer and simple. In my case, I couldn't run my exhaust betwee the rear leaf spring and the fuel cell bathtub. The tub hung lower and was wider than the stock tank.

Always with the tradeoffs.

I'm still not happy. I want to fabricate a steel floor to go over the fuel cell. I also would caution ANYONE installing armor to WATCH OUT that they do not use too thick of a plate. Think about it. If you're driving in fog with passengers in the rear seat and you have to stop -- and you get rear ended by someone in an SUV -- a thick plate will not crush. There is nothing to stop the plate from moving forward except a cheep door and the back seat. That plate will be the leading edge of a guilotine (no spell check) that will maim your passengers. The guage of the armor should be thin enough that itr can crush, but not allow fuel into the passenger compartment. Remember, car designs have evolved in terms of safety because they allow energy absorption by the car's structure and not the occupants. The armor is only as strong as the structure it's bolted to! Your goal IMHO should be to protect against cabin fire, not to build a tank -- especially if the vertebrae of your passengers in the back are placed at risk.

I've always approached my restomod with the goal of building the car better than Ford originally did. I'm using a Jaz fuel cell (and those people are stunningly useless in giving information about their product). I will use no filler neck. Bad idea. In almost any serious rear end collision, the filler neck will crush creating a certain fire if the check valve does not close. Remember the stock car fire than burned Dale Earnhart Jr? Filler neck. Unless you're sloppy at the gas station, you should have no gas smell. In fact, a gas smell tell me that the installation (venting) is wrong.

I hope to post pics of my car as guidance and example to fellow builders who are noodling on how to do this. It's an engineering problem and in the day of the Internet, it's nice to get dirty and create something.

Post scriptum: If you install no fuel cell and no armor but are concerned about the issue of safety, I think this: You'll be safer anyway because you'll be a more thoughtful driver. Since I started working on this problem, whenever I have to come to a stop on the freeway because of traffic, I always leave a few extra car lengths of spacing and I LOOK UP AT MY REAR VIEW looking for the bozo dialing a cell phone barreling down on my rear bumper. Here's the morality question of the day: If you see someone closing at 50MPH over your speed toward your rear bumper would you jump lanes to avoid getting hit KNOWING that the guy in front of you will get hit?

My SS fuel tank I designed and is to be made from 16ga. 201 stainless.
View attachment 264538
It is currently in pieces as I haven't welded it together yet. I will put foam in it. I picked up a fill plate from ebay to mark the holes. It's same width & length as a stock tank but a little taller.

the rear seat separator also helps with torsional rigidity. RacerX- nice custom piece

Here's the morality question of the day: If you see someone closing at 50MPH over your speed toward your rear bumper would you jump lanes to avoid getting hit KNOWING that the guy in front of you will get hit?

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hell yes.....unless it's full of kids, then i'd probably just run away and leave the car