818 Front Gas Tank

[Xusia]

Because there seems to have been some renewed interest of late in a front gas tank, I spent some time making a cardboard template of the shape, which I then transferred to Visio. Below is the shape with some basic measurements:

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The image below shows the shapes I used to calculate the volume:

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At 10" high (which is my plan), it now holds ~11.3 gallons. That's enough for 280-400 miles of street range, depending on actual MPG, of course (I used 25 as my low and 35 as my high).

Assuming a finished weight of 2000 pounds, and that the f/r weight distribution with the gas tank behind the seats is 42%/58%, I estimate this modification will put me at about 45%/55%.

For those that require more capacity, this shape could be as tall as 12.5" and still fit. At that height, the capacity would be ~14.2 gallons, and the weight distribution would about 47%/53%.

I'm hoping to be able to take some pics of the cardboard model in that space so everyone can better visualize.

Some additional details I'm planning for my tank:

I can't remember what exactly it's called, but it's basically a dish to hold fuel near the pickup to prevent starvation. I plan to just drill some holes near the bottom of it rather than use fancy one-way valves.
To keep costs low, I've decided to go with the OEM/FFR pickup, fuel pump, sending unit, etc. This contributed to my decision to make the tank 10" high (that's the height of the FFR tank for which all those aforementioned components were designed).


That's all I can think of for now. I'll post pics hopefully tomorrow. I'd really love to hear people's thoughts. :)

[Joseph]

Since I am a little tall 6'-2" (long legs) would putting the tank in the front let me use some of that area where the tank would have gone for more seat track travel room. My delivery date is not until July so I do not have the kit to look at, although I try to read every posting on this web site so I can learn and I bought the digital download of the manual. Frankly the wookie leg room problem really has me worried. I am assuming that if the tank goes into the front you would lose some of the safety factor of having the tank sandwiched into the middle of the car. If your idea gets a large following maybe some vendor might step up and produce the tank with the safety foam like they put into race cars.

[Xusia]

Hi Joseph,

I don't see having the tank in the front as any less safe than behind the seats - neither position is perfect. Up front, there is plenty of frame structure providing protection. It would take a really nasty hit to get to it. In the back, there is a bit more structure for protection, but the tank is inches from the hot header pipes and engine. If a rear end collision were to push the engine into the tank, I think a fire is likely. Again, neither position is perfect, and in my opinion they are equally safe.

As for you fitting, It can definitely be done. Just realize you will have some problem solving to do. Here are some ways to get more leg room:

Modify the pedals so that the surface is farther away.
Use aftermarket seats with either or both of a steeper incline (~10*), or a really low bottom.
Use a slimmer gas tank, or relocate the gas tank


My requirements for seats that both slide and tilt forward (for access behind the seat) precluded some of the seat options that would have made fitting much easier. I have found some ways to modify the stock seats (keeping the functions I want) and getting a really good fit. I posted a video on it in my build thread.

Anyway, at only 1" taller than me, I wouldn't be too worried about fitting. And if you need any help, I'm happy to do what I can. :)

[RM1SepEx]

A bigger concern is the change in weight bias as your fuel load changes...

[Scargo]

I had a mod done to a stock gas tank where they used three steel hinges for one-way valves on three sides of a chamber. FI on a '64 Nova SS. :) For a tank in the front of a light car, I think some baffling is essential.

I will be using a fuel cell. If I had a street car I don't know how safe I would feel without a fuel cell (bladder in a container). With any boxy, hard-cornered tank I would be concerned about impact and seams bursting. If it's soft enough and welds are perfect it might survive. There is a reason tanks are pressure formed and only have one seam around the perimeter.
What material are you thinking of using? FFR's is steel, yes? I would guess it's also coated inside with POR 15 or a 3M product. I think it's a critical issue if you would ever run E85. Boyd's tanks are aluminum, but I wonder what thickness, alloy and temper?

Yes, everyone's counting on the frame to protect the tank, regardless of the position. If the car were free to slide sideways or forward on impact then the frame might be very capable of protecting you and the tank. Last year I was caught up in a freeway incident in which traffic suddenly ground to a halt due to a cop blocking a lane. I had nowhere to go and slid to a stop in-between the concrete divider, the cop car and several other cars with literally inches to spare. I was praying that we would get out of there before we got rear-ended. Not that long ago I saw someone run a red light and T-bone another car. It was not pretty. You just never know.
FYI, I am a little cautious and sensitive in this area of discussion because it involves fuel. I was in the famous Parkland Hospital's burn center from a car-gasoline spill accident.

[FFRSpec72]

The closer the fuel tank is to the CofG the better it is in terms of having the car behave consistently.....and lower the better.

[AZPete]

The space in the front is one factor but getting a tank through the frame openings into the space is another. I have tried to get the OE HVAC unit into that space with no success. Most likely a tank will require cutting some frame pieces out, which adds another pucker factor.

[TahoeTim]

why not make the stock tank taller or stretch the footbox forward?

[C.Plavan]

Porsche's have their tanks in the front with 914 mid engines too. I think you would be perfectly fine. Fuel load weight bias will not be a problem at all. Even more so on a street car. I would also say it is safer in front than having the tank near the headers and motor. Remember, there is not a rear bumper on the 818.....

[TahoeTim]

the 914 and the original beetle share a similar tank location

[Canadian818]

why not make the stock tank taller or stretch the footbox forward?

I believe he wants the space behind the seats for storage.

[Xusia]

A bigger concern is the change in weight bias as your fuel load changes...

Mine is a street car. I do not intend to race, so this is not a concern for me at all. The fuel weighs less than 70 pounds, and since I'm not racing, it would probably take more than 2 hours to deplete the tank. I would be lightening the front end by approximately 1/2 pound ever minute. I think I can compensate well enough! :)


The closer the fuel tank is to the CofG the better it is in terms of having the car behave consistently.....and lower the better.

Absolutely. This location is closer to the front axle than the FFR tank is to the rear axle, but... It's much shorter from side to side, and is the same height. Overall, I expect the location change to no have much impact on handling. Also, don't forget the positive effect of weight bias that's closer to 50/50.

I should probably also add that part of my overall plan is to have the car corner balanced. I plan to provide the weights to Jim so he can tell me what spring rates would be optimal. By doing that, the car should be just fine with the location change and without the sway bar.


The space in the front is one factor but getting a tank through the frame openings into the space is another. I have tried to get the OE HVAC unit into that space with no success. Most likely a tank will require cutting some frame pieces out, which adds another pucker factor.

I have a plan for that. It involves cutting the 2 "V" bars and the battery tray out. BUT, I'll be replacing those with other welded in components, and a bolt in frame structure under the tank. I don't think torsional rigidity will suffer. I'm definitely doing it, so when everyone sees it, I think it will make more sense and people will see it will not adversely affect the frame structure.


why not make the stock tank taller or stretch the footbox forward?

Moving the footbox forward was actually my first idea, but it's more complicated than it looks. There's a lot in that area. Moving the tank also give me easily accessible storage IN the car - that's much more practical for a daily driver like I'm building.

[FFRSpec72]

Porsche's have their tanks in the front with 914 mid engines too. I think you would be perfectly fine. Fuel load weight bias will not be a problem at all. Even more so on a street car. I would also say it is safer in front than having the tank near the headers and motor. Remember, there is not a rear bumper on the 818.....

The fuel tank as located by default is within the roll cage tub of the R car and thus in about the safest place. I will have a 1/8 steel firewall between the engine and fuel cell. The rules only require a firewall between the driver and the fuel cell, the bladder is enclosed in a can does not count as a firewall, only in a Formula car would the can alone be legal. I think that the can in front would be fine, I just feel better if it's protected by the cage, I have had first hand experience with how well Factory Five build the cages, I have no issues being on the track in a Factory Five car with approved roll cage.

[Xusia]

Here are some pics and video of the cardboard mock up I made and fitted.

Pics:
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Link to the video: https://plus.google.com/107272488473870379365/posts/iq5Hn4kDxBy

[Santiago]

I like this approach, even though I won't be doing it. For some folks I think it makes a lot of sense. My $0.02 on random issues raised:

- Weight Balance: Optimizing CoG trumps static weight distribution for enhancing performance (your polar moment of inertia is independent of xyz static weights), but on a street car...meh. Also, at least some of the losses in rearward bias will actually be recouped by placing upwards of 200 lbs or more worth of the nut behind the wheel back several inches.

- Changing Handling Balance: Not terribly important on a street car that's even modestly close to balanced already. When folks talk about a given car's sensitivity to such changes in weight distributions they're likely either (a) mistaking the cause of an ill-behavior as weight-induced rather than some silly thing done with the throttle (mmm, can we say "user error") or (b) they are genuinely tuned in to the car's performance at 9/10ths or 10/10ths of its performance envelope. For the (a) crowd, fix your foot. For the (b) crowd, they know there is no concern for this on the street and if there is, you probably need to revisit (a).

- Foot box mod: forward of the square tube structure you run into the rear mounts for the front lower control arm. So short of trying to shift the seat towards the center 3" or more, you're stuck

I'm looking forward to seeing how this turns out.

Best,
-j

[TahoeTim]

Santiago
I agree 100% about weight transfer red herring. Back when I raced, it took a couple of laps to get near 100%. Even after you've been at a track like Laguna Seca for years, it still takes a warmup session. On the street it's a silly conversation because you shouldn't be near 100% (safety) and if you think you are, you are fooling yourself.

I, too, want some storage in my 818 but moving the fuel tank is not on my list. I plan to build a trunk box over the trans. I can't believe it's not part of the kit! Herb, where are you? The front fuel tank design with an open top makes for a nice little trunk too.

[Blitzkrieg]

I shoot trap a lot and was going to put my gun case right behind the seats on top of the tank, but moving the tank would work better. How are you going to fill it?

[Xusia]

Thanks a bunch for the positive feedback, guys. It's helpful to hear other's perspectives, and for me, your comments confirm I'm on the right track for my needs/wants.


I, too, want some storage in my 818 but moving the fuel tank is not on my list. I plan to build a trunk box over the trans. I can't believe it's not part of the kit! Herb, where are you? The front fuel tank design with an open top makes for a nice little trunk too.

I plan to build one of those as well. I just thought having some room in the cockpit (besides the passenger seat) would be useful!


I shoot trap a lot and was going to put my gun case right behind the seats on top of the tank, but moving the tank would work better. How are you going to fill it?

I plan to run the filler out to the passenger side fender. There is plenty of room and it should fit well.

[Blitzkrieg]

I like the idea but getting the tank into the car is a problem. What if you made a tank that was triangle and a knotch cut out for the steering rack? Like 12" tall should be around 10gallons. Make it slip in from the top and sit on the frame.

[Frank818]

Also, at least some of the losses in rearward bias will actually be recouped by placing upwards of 200 lbs or more worth of the nut behind the wheel back several inches.

Could you repeat that in other words, plz?

[Bob_n_Cincy]

Xusia
Looks great,
You and I are thinking much the same on the tank.
My reason for the front tank isn't storage. To make my seat low enough and back far enough there is no room for a tank.
I will post my mock up in a week or 2.
Bob

[AZPete]

Xusia, I like your solution of putting the tank in from the bottom. Replacing tubes and/or a steel plate should replace the support. Smart.

[Santiago]

Could you repeat that in other words, plz?

I'm like a partially trained ninja with words Frank...I'll give it a go, but I might cut myself. =)

My thought was that you're taking 70 or so pounds from the original tank area to move it forward, which will obviously lower your rear weight percentage. However, a good number of folks considering this also seem to be doing it for more leg room. This means they'll be moving their seats 6" - 8" further back from where it would have been restricted. So you've got a 200+ lb driver/seat combo that is moving further back (that was the "nut behind the wheel" reference). So this will regain some of the rear weight percentage. I wouldn't expect it to be huge, but with a passenger, the difference between a "normal" seat position and one possible with this mod will be even greater. I'm looking forward to what figures Xusia comes up with once he gets his car scaled.

Best,
-j

[Frank818]

Ha, ok I get it. I didn't picture the driver change at first.

In my case I won't change the location, so it would be a full 70lbs moving to the front. But then if the car is well balanced the way it is now and I don't plan on moving the driver's seat location and I plan to fab a trunk in the rear (I won't have a tranny in there cuz mine is transversal), maybe it's just pointless for me to change the location of the tank. I'll think about it.

[Xusia]

I like the idea but getting the tank into the car is a problem. What if you made a tank that was triangle and a knotch cut out for the steering rack? Like 12" tall should be around 10gallons. Make it slip in from the top and sit on the frame.

I actually started with that idea, but the volume was just too small (more like 6-7 gallons, if I recall). I'll calculate it again for reference and post. I'm in CA for work at the moment, so it will have to wait until later this week or the weekend.

Also, sliding in/mounting from the bottom is better because in order to do so from the top you'd need to remove the windshield (it obscures a very large part of that triangular entry space).

[Xusia]

Sorry it has taken me so long; I've been traveling for work for the majority of the past 2 weeks. I was able to mock up shapes this last weekend, calculated the volumes Sunday, and I finally have time to post the results.

To review, the question was about a shape that could slide into the same area up front through the existing triangle shape - to avoid cutting the frame. That's a larger shape, but you can't get the tank out without removing the windshield. So I also did a shape that can be inserted from the bottom.

The space has 18.5" from the top of the bottom set of frame tubes, to the top of the top set of frame tubes. I don't think all that space is usable though, because I think some space is needed for things that poke out the top like fuel lines and electrical connections. In case I'm wrong, I'll post vumes for both 18.5", and 17". NOTE: My volume estimates account for the thickness of the material.

Front Mounted Tank Inserted From The Top
Below is the 2D mockup of the shape. I took pictures from several angles to try and show the clearances. they are tight to maximize volume. The last 2 pics show the shape as it would sit in the bottom of the space. Volumes are: 18.5"=12.6, and 17"=11.6.

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Front Mounted Tank Inserted From The Bottom
Just one pic on this one. Volumes are: 18.5"=6.9, and 17"=6.3.

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CONCLUSION
The bottom tank (as I'll call it) is just too small. The "top" tank could work, but I'd personally hate to have to remove the windshield to remove it. This begs the question of how big of a deal is it really to have a removeable gas tank? I know it sounds like we should, but I've NEVER had the need to remove a gas tank from any vehicle I've ever owned. I'm not seeing how this car would be any different, so it seems highly unlikely I'd ever need to deal with it. I don't mind modifying the frame, but if I don't have to, all the better.

Thought?

[FFRSpec72]

You would just have to make sure that the pump plate (and filter) and fuel gauge plates are accessible as I don't think you would need to remove tank if you can replace those items. Also you will need a fill, I assume this will be from the side? if so that will reduce pumpable fuel, would be better if you can get this from the top of tank.

[Blitzkrieg]

I don't need to remove the tank at all, inless it got punctured from crash. The reason behind the slipin tank is I wouldn't have to cut up my nice 818 frame and I could bolt it in.

[TahoeTim]

So we are back full circle, the factory tank location is still the best. Your two designs have serious drawbacks.

Buy a boyd tank, make your box up front for storage and move on.

[Xusia]

So we are back full circle, the factory tank location is still the best. Your two designs have serious drawbacks.

Buy a boyd tank, make your box up front for storage and move on.

I disagree the FFR location is "best." They ALL have drawbacks. You may prefer the FFR location - and that's fine for you - but other people (like me) have different priorities. The Boyd tank will not work for me, AND I want a front tank (for many reasons). I would appreciate if you contributed positively to the discussion, rather than telling us we are wrong.

[Bob_n_Cincy]

So we are back full circle, the factory tank location is still the best. Your two designs have serious drawbacks. Buy a boyd tank, make your box up front for storage and move on.

Hi Tim
I have no choice, my son and I don't fit in the car comfortably with a Boyd size tank.
I'm a little over 6' and my son is 6'3" and both weigh 250+.
You mentioned "serious drawbacks". I don't see any drawbacks.
Bob

[Scargo]

I too, don't think this is black or white. I am picking up my kit tomorrow, but from what I see in photos, I think you have an option for a front mounted tank.
I feel compelled to say that things are going to be tight up front and safety is a real concern of mine. A solid front-end collision, or one where the front suspension is involved, might drive parts into the tank. I sure hope you will consider a custom fuel cell.

Now, why not remove the "V" and make a sturdier, removable triangular part? Add gusseting to this part and extend it to overlap additional plates on the frame that hold nuts or use nuts and bolts that extend into the passenger compartment area. Don't drill through the frame, but add plates with holes.
Then, much more elaborate: Could you rework the steering and use a different rack to gain additional room by moving it out of that area?

[Blitzkrieg]

The thing about "crashing" 818 is the car is it's so low if you hit another car you're going to go under it and it's going to go right at the windshield. The front of it is a wedge with no bumper really. If you get in a front-end collision with enough force to crush the frame to the suspension you have a slim chance of getting out with out major injuries.

[Scargo]

The thing about "crashing" 818 is the car is it's so low if you hit another car you're going to go under it and it's going to go right at the windshield. The front of it is a wedge with no bumper really. If you get in a front-end collision with enough force to crush the frame to the suspension you have a slim chance of getting out with out major injuries.
Please..! Are you suggesting that if you have a bad front-end crash you might as well not worry about burning to death?

[RM1SepEx]

Crash issues are the same no matter front or existing FFR location, depends where you get hit. The key is a bulkhead that forces the fuel out the bottom vs into the cockpit. The best crash protection for a tank would be using the tunnel area for the tank as it would be the least likely to get crunched. Occupant protection is provided by th 1/8 bulkhead, are you going to do the same for your front tank? Are you going to have holes under it for fuel to dump onto the ground if the tank gets crunched?

The stock tank has areas removed corresponding to suspension point attachments, making it better than the Boyd tank, less likely to get damaged.

This is a low production car, you can't expect the same crash worthiness of a high volume car that has Gov regs and testing. If this stuff bothers you, I suggest you look at a used Porsche Boxster as a comparable.

[FFRSpec72]

Crash issues are the same no matter front or existing FFR location, depends where you get hit.

Oh so not true with the R as the gas tank location is within the front and rear roll hoops, not true if you put the tank in the front, safest place is within the cage.

[Blitzkrieg]

We are talking about a street car here, not a track car. If you are racing on the street thats your choice but if you wrap the car around the tree it's on you. As for the safest location on the car for the tank, there is none. You are not going to find a 100% safe spot on the car. If you think the tank will get crushed wrap it in flame retardant material then in carbon fiber.

[Scargo]

I'm not going to say how goofy this conversation has gotten. I'm not going to continue this line of conversation or staunchly defend my position.
I will say that I have an engineering background and worked many years for a respected group of registered professional engineers that dealt with failures of every description.
I was a safety representative for a corporation and a building of over 100 people.
I've been on fire. I've had car wrecks, motorcycle crashes and totaled a car at Watkins Glen when my ball joint failed.
I have a fully track/race prepared STi with six point cage, six point harness, fire extinguisher and I use a Hans device and wear a fire-retardant racing suit. I don't take safety lightly. I already have a five nozzle fire suppression system for my 818. I like to think that I have gained a bit of wisdom in my old age.
To cross your fingers and say it won't be me if I behave myself is the main reason I take issue. Nor do we need to be fatalistic because it is a kit car.
There are many satisfactory solutions to a gas tank and some are far safer than others.

[ruckus racing]

Only read about half... whats the weight ratio and range of running 2 fuel tanks on a street car. Factory and front?

[FFRSpec72]

We are talking about a street car here, not a track car. If you are racing on the street thats your choice but if you wrap the car around the tree it's on you. As for the safest location on the car for the tank, there is none. You are not going to find a 100% safe spot on the car. If you think the tank will get crushed wrap it in flame retardant material then in carbon fiber.

Once again the safest place on the R or the S is going to be within the cockpit, is it 100% safe, not but on the S or the R it will be the safest place and yes I will have a Kevlar bladder on my fuel cell to make it even safer