Hair brained scheme

[housertl]

SO.... My VX will be here tomorrow morning, and I am already thinking of things that I want to mod on it. Depending on whether the CNG fueling station gets added into the Military Exchange gas station near the Pentagon as planned, one of my desired mods is to set the vehicle up as a bi-fuel CNG vehicle. My question is about tank placement. The easiest thing would be to mount a tank into the cargo compartment and call it a day. This would, however, limit me to a tank that would only provide about an 8-9 gallon equivalent capacity, limiting me to about 120-130 miles between fill ups, at 15 mpg, ans would also eat up the entire cargo area. In order to come close to the driving range of the gasoline tank, it would require tanks that are 16-18" in diameter and about 48" long, nessecitating a roof mount. From an aesthetic perspective, I actually think this will enhance the kind of "Moon-Buggy" look that attracted me to the VX in the first place, if done correctly.

My real concern is with structural integrity and handling. I assume that I will be adding 200-300 lbs + to the top of the vehicle, as well as making the truck at least 20-24" taller, which I assume could have serious effects on the center of gravity. Not to mention my concerns about what it could mean if I were involved in a bad accident and they turn into missiles.

Do you guys think that the roof rack mounts would be strong enough to hold that kind of weight, or would it need some kind of reinforcement (exoskeleton)?

[Triathlete]

I believe the roof rack is rated at around 100 pounds. As far as adding that much weight up that high...it would derinately not be a good thing. Just ask the guys that have their spare tire, which weighs a third of your expected weight, how much they feel it up there.
Some of our overseas owners have done LPG conversions, maybe they will chime in.
Also placing a fuel tank on your roof would probably violate some safety laws in most states.

[Vendetta]

Echoing Tri here, yeah... the rack is rated to 110 pounds. Although honestly I'm not sure if that's per rail or for the rack as a whole.

There are plenty of pics on here that show the warning label - here's one:
http://www.vehicross.info/gallery/sh...ize/big/sort/1

I think your thread title pretty much sums it up.
-V

[rsteinmetz70112]

Interesting idea. Using multiple long thin tanks would tend to reduce the added height and possible allow a rack on top of the tanks. A quick google turned up some 2 GGE @ 3,000 psi
9" Diameter x 34.3" Long.

I don't know much about CNG. Is it liquid when in the tank? If so shifting weight could be an issue.

[housertl]

Interesting idea. Using multiple long thin tanks would tend to reduce the added height and possible allow a rack on top of the tanks. A quick google turned up some 2 GGE @ 3,000 psi
9" Diameter x 34.3" Long.

I don't know much about CNG. Is it liquid when in the tank? If so shifting weight could be an issue.

CNG is gasseous when in the tank, which actually makes it safer than LNG (which also requires cryo, as it has to be at -270 or so to be liquid), because it is lighter than air. The tanks on the roof would be fine from a legal perspective, most CNG applications on busses have them there. The tank you speak of would need 9 tanks to equal the 2 tanks that I was thinking of, so the mount would be much more complicated, and might actually end up weighing more. A 8-9 GGE tank that could go inside the vehicle would be about 14" diameter X 38 " long. Realistically, that would be big enough for about 1 weeks worth of driving, and would only cost about $10-12 per fill up. The cost savings is what I am really interested in, but engines also seem to run better on CNG, as there is less carbon fouling on the parts.

[VX KAT]

closer pic of label and the tower structure:

Interesting, the official install instructions DO NOT even mention a weight limit, or show the weight limit sticker in their diagram...bet it's a U.S. ONLY sticker...due to all our attorneys and lawsuits!

[Y33TREKker]

Any reason a combination of tank sizes and placements couldn't be used? If you're wanting to go full CNG, would you actually be removing the stock fuel tank? The space gained would allow for the mounting of some of the tanks there. Even if they had to be custom made to fit in the space, the cost of the custom build would most likely be recouped in little time with the later fuel cost savings.

If you then wanting to mount additional tanks on the roof, they wouldn't have to be as large or as numerous, although I would personally make absolutely sure that they were mounted as solidly as possible to prevent them from becoming "missiles" in accidents like you referred to earlier.

[housertl]

Any reason a combination of tank sizes and placements couldn't be used? If you're wanting to go full CNG, would you actually be removing the stock fuel tank? The space gained would allow for the mounting of some of the tanks there. Even if they had to be custom made to fit in the space, the cost of the custom build would most likely be recouped in little time with the later fuel cost savings.

If you then wanting to mount additional tanks on the roof, they wouldn't have to be as large or as numerous, although I would personally make absolutely sure that they were mounted as solidly as possible to prevent them from becoming "missiles" in accidents like you referred to earlier.

Apparently, doing a full CNG conversion (removing the gas tank) is illegal, but adding a secondary fuel system is fine. I had thought of swapping the gas tank for a smaller one, to see if a decent sized cylinder could fit into the space created, problem with that is that you lose range on extended trips, as CNG can be problematic to find stations for. If you live in TX, no problems, but other places, it really only makes sense if you have a station in your local area (I happen to pass the place that should be getting set up for it on my daily commute). Baker equipment has a system that they will install on ford and GMC vans that has a 500 mile range and has passed crash tests, but looks like rotten arse.

[housertl]

[QUOTE=VX KAT;232279]closer pic of label and the tower structure:

Interesting, the official install instructions DO NOT even mention a weight limit, or show the weight limit sticker in their diagram...bet it's a U.S. ONLY sticker...due to all our attorneys and lawsuits!

QUOTE]

I was actually thinking of attaching the mounting system directly to the rails, and bypass the crossbars, 1) because they are to high up, and 2) because I don't have them. I wonder if that might make it stronger. Perhaps a system that hooked into the factory tower mounts, and then attach it through the roof to a roll cage on the inside.

[samneil2000]

Will you be using your rear seats? If not, you can easily remove them and have a very large flat surface to use for tank(s).

[housertl]

Will you be using your rear seats? If not, you can easily remove them and have a very large flat surface to use for tank(s).

I had wanted to, but I am not above removing it, although I WOULD need to install a rear bucket on the passenger side, so that my kid can ride back there. Not a bad idea actually..... HMMMM. If I built an enclosure over the top of the tank, I could still have a good (maybe even more) amount of cargo space.

[jimonskye]

http://www.ppidts.com/

talk to these guys, they make tanks that weigh less than half a normal tank