Propane conversion ????

[M-317]

As you people all know gas prices are going higher and our cars arn't what i'd like to call fuel efficient vehicles at least in city driving. My question is if any of you know where or how i can get the equipment to convert my 1990 LSC to propane. Also is it possible to convert a fuel injected car to propane because i've done research on cars and all i hear about is carb this and carb that or about desil motors. One more ? if i do convert i have 140,000 should i look at getting a new engine because of all the carbon buildup everywhere? because after all it would be nice to have a clean engine that stays clean.(no carbon) I do us shell premium.

[Bluegrass]

First question is how would you meter liquid propane through fuel injectors without special changes? Propane has less energy in BTUs than gasoline and make less power in the same engine.
Next if you would replace the engine, you can buy a lot of gas with the money spent for the whole project.
Better to get a smaller more efficient car and save the Mark for less use.
Ford has some engines running on hydrogen but even they are down on power compared to gasoline in the same engine.
This alternate fuel thing is not the savings deal that most think. ;)

[cason1]

quote:Originally posted by Bluegrass:
First question is how would you meter liquid propane through fuel injectors without special changes? Propane has less energy in BTUs than gasoline and make less power in the same engine.
Next if you would replace the engine, you can buy a lot of gas with the money spent for the whole project.
Better to get a smaller more efficient car and save the Mark for less use.
Ford has some engines running on hydrogen but even they are down on power compared to gasoline in the same engine.
This alternate fuel thing is not the savings deal that most think. ;)

Exactly. Take the couple thousand you would spend for a new engine and buy a little honda or something like that to get the mileage you want. My Towncar gets anywhere from 20-30 depending on driving conditions and I am quite pleased with that but everyone is different.

[M-317]

well i want to buy a new engine reguardless of what i do fuel wise. I have done alittle bit more reading and a common misconseption about propane is that u lose power and that there is no way meter it. truth be told that u do lose power in the case that you have and older car and your engine is carburated. Cars converted to propane generally suffered a performance loss in the bad old carbureted days. The problem was that propane was metered (or fumigated) into the engine in a gaseous form. The fuel gas displaced air that the engine was drawing which caused a slight loss in volumetric efficiency. Gasoline is metered into the engine as an atomized liquid. The density of a liquid is much greater that that of a gas and so the volumetric efficiency loss compared to pure air is negligible. The other contributor to lower volumetric efficiency is in the restrictive mixer. Nowadays, with modern vehicles being equipped with digital fuel and ignition control and port fuel injection, sequential fuel injection of propane overcomes the volumetric efficiency disadvantages of the propane mixer. Digital fuel and ignition control is a feedback control system. The engine's computer has a preprogrammed plan for controlling the fuel mixture and spark advance as a function of various parameters measured by sensors in the engine. The O2 or Oxygen sensor in the exhaust, for example, tells the computer how much to correct the fuel mixture to the target mixture. A far better means than the best guess provided by the manufacturer in the design of the shape of the gas valve or the size of the metering jets in the carburetor. Impco and Dual Curve both offer feedback systems for controlling propane fumigation carburetors.

As there is no longer a carburetor on modern engines, propane fuel injection would be the logical option for conversions. There is a great deal of development work currently going on in the area of sequential propane injection. There are two means of injecting propane: gaseous and liquid. Each has its advantages but liquid injection has the potential for higher performance . The reason for this is that as a liquid, propane must absorb heat from the air to evaporate which causes the air to cool and become denser. The increased air density effectively increases the volumetric efficiency of the engine and increased volumetric efficiency is the goal of every engine performance modification. Now what i need to know is there anyone out there who knows where to get one because from what is stated here carbs suck for this app and we all have fuel injection making switching over preferable i have seen these kits on the net for as low as 150 to 1500 but i can not buy them and plus i would like to someone with the knowledge in need to install it. if i do this i can remove the catalytic converters because the polution is reduced by 70%. hopfully this works out because lets face it $2.85 a gallon is rediculous and i'm suprised nobody is opting to propane. 1500 for conversion or 2000 for beater honda=new problems, more car insurance, and less space in the drive way. which one would you opt for?

[ekooke]

M-317,
Propane or LP efficiency has little to do with liquid or gaseous states; it's simply that there's way more heat energy in a pound of gasoline (or diesel fuel) than any other fuel that can be safely toted around. All the oil companies are constantly researching these things, with small fleets of converted vehicles operating on a wide variety of fuels. After all, if it turns out that there is a fuel that can power a vehicle more cost-effectively than gasoline or diesel, the oil companies would also want to be in charge of THAT, whatever THAT turns out to be. smile.gif

[ August 19, 2005: Message edited by: ekooke ]

[88LSCinSW-FL]

Gotta stop lurking long enough to address this one, since it's a topic I have some interest in and it seems people are already trying to shoot you down. If you're seriously interested in trying it, like I am, don't let the naysayers drag you down and talk you out of at least researching it further before deciding what to do. The option to buy a smaller and more efficient car is always there.. it isn't going to go away just because you read a few websites and considered the conversion.

Finding info on converting newer vehicles to LPG has been a royal pain in the arse for me these past few months. Most info is from Canada, the UK, and Australia. Closest I've come so far is to find a UK site that sells conversion kits for their F150s with the 5.0:
http://www.lpg-kits.com/ford.htm

I also found this UK site that has a wide selection of tanks. They have toroidal (doughnut-shaped) tanks up to 95 liters gross capacity.. which I think calculates to 25 gallons before you take into account the 80% fill thing w/ propane tanks. Cylinders are also available:
http://www.tinleytech.co.uk/sizes.html

If you are not terribly good with metric conversions, I suggest just typing "metric conversion" into Google and picking one of the several free sites available.

Here's some other links I've stumbled across over the past few months that you may or may not find to be of use:
http://www.wps.com/LPG/

^^^ Although this site is about a carbed application, (an old Rambler) it seems anytime I go researching propane conversions I always end up hitting this site. Couldn't hurt to do a little reading there. Also discusses how to make an emergency gas can for a propane conversion.
http://www.oldengine.org/unfaq/leadfoot/lpg.htm

^^^ (I think I got the above mainly for the links page)
http://franzh.home.texas.net/lpinfo/index.htm
http://www.propaneguy.com/www.propaneguy.com/Index.html
^^^ Canadian site, selling plenty of propane goodies.


And here's a little random inspiration for ya: http://www.caranddriver.com/article.asp?section_id=26&article_id=2279&page_number=1

Like I said.. don't let people talk ya out of at least researching it a bit more. Many people mean well by trying to inject the "common sense" thing.. but all it really does is keep you from thinking about alternatives. Probably also a few people out there (not saying anyone here specifically) who at some level don't want to see anyone else try anything different that might make your car stand out over theirs. (don't ask me why.. personally I hate that mentality) I kinda wish more people would either not respond if they're going to respond negatively to these type questions, or make more effort to provide useful information in support of the topic BEFORE saying stuff like "you can also just go get an econo-box and be done with it".

Hell, you can even go the performance route with it. That V10 Vic in the above link isn't the only warmed-over propane car I've heard of. I recall stumbling onto some forum where a guy was talking about his (I think) twin-turbo Vette and running that on propane. I may go back and look for that again someday, just for a little more inspiration. Anyway, the performance loss can be compensated for.. but mainly if you do a total propane conversion vs. being able to still run gas. Propane apparently likes higher compression.. a different A:F ratio.. I've seen at least one site listed above advertise "propane cams" for converted cars.. and there's always boost.

I think what drives me to continue researching propane is that I'd like to see if propane's low temperatures can be harnessed in a boosted application.. as sort of a half-arsed intercooler/aftercooler. Ideally I'd like to be able to run that 95 liter/25 gallon (20, really, w/ 80% fill) toroidal tank, and maybe a 5-10 gallon gasoline fuel cell in the trunk for those times when filling up on propane just isn't possible.

NOTE: I am in no way affiliated with any of the sites listed above. They're listed merely for research purposes. I cannot vouch for the accuracy of the information, nor can I vouch for the credibility of any of the vendors. Proceed at your own risk, YMMV, and all that.

Sorry if this post turns out to be a mess.. I've been jumping around all over it, dropping in links as I dig them up again.

Whatever you decide to do, good luck with it. I will probably pick up a more fuel-efficient car within the next year or two for short trips into town. However, with having this spinal disease and the pain in my back worsening on almost a daily basis, having the comfort of my LSC's seats under me is something I'd consider a propane conversion for just so I could continue to drive a far more comfortable car while saving a bit on fuel prices. I gave up my 32 city/39 highway '94 Escort LX for a reason.

OK, back to lurking for me.

[ August 19, 2005: Message edited by: 88LSCinSW-FL ]

[StanTheMan]

Hey, thanks for "coming out" of the "Lurking" state. I think most of us are open to good discussion about various topics relating to the LSC but when you think of the reality (dollars, cents, and time involved) in some projects, it doesn't have a payback. But then, research and new developments rarely reap profits at first. I still remember the early 80's when I laughed at the use of PC's (toys) for serious business use.....

[Bluegrass]

No shoot down intended but only to bring the issues that have to be delt with to light in order to help make a decisions to procede based on money and time versus the end result.
I have had lots of ideas over the years only to have someone somewhere go ahead and do the same thing I had in mind in as little as 9 mo. later.
Recent case in point. Building and marketing a lawn mower type engine powered low priced outboard boat motor, 10 year ago. Now it is being done, saw the add in Field $ Stream.

[ekooke]

I worked with several groups back in the late 1970s that:
1. converted a 1951 Ford to run on grain alcohol that was distilled from field corn, and we used a solar-powered still. The alcohol-powered car averaged about 13 mpg, while its previous gas powered version managed 18 mpg all-around.

2. built a hybrid gas electric car from an Opel GT (tiny Corvette looking thing) that had a 15 hp gas engine and 8 12v storage batteries; it got an AVERAGE of 40 mpg, city & highway. All that stuff was fun, but we had a lot of ideas back then, and all it took was time & money.

Neither idea proved to be practical, since it cost more (in the case of the alcohol-powered car) to make the alcohol than just buy the gas outright. The Opel hybrid definitely cost less to run, but we sunk about $6,000 into it, when gas was about $0.70/gallon, and there was also the matter of disposing of the batteries & getting new batteries 3~4 years down the road. This battery dispose/replace thing is what's going to kill today's hybrid/gas vehicles and the environuts will really be up in arms then.

Converting a vehicle to propane isn't tough, but the stuff comes from the same place that the oil does, so I can't really see any long-term benefits. If propane becomes the road fuel of the future, it's ALSO going to bear the brunt of the highway taxes when it's sold as a motor fuel.

[M-317]

ok it's time to face the fact that oil is a finite resource that is severly outdated and keep in mind i do know that propane is a by product of the making of gasoline or a byproduct of something. The truth is that oil cos. are researching alternatives but the only reason they are is so they can get the patents before any of the little people can get the money to do the same. Then of course them having the patents and all they keep them and as a result they have the final say weather or not these "alt" fuel vehicles make to production. lets face it we have the tech to make an electric car break the sound barrier (it has been done), Hydrogen if burnt is 10 times more cumbustible to the weight of gas so no one can say nothing produces as much power as gas that's bullsh*t. Why do think the nay sayers say what they say because they really havn't thought about or learned about how the alternatives are there but the only reason they havn't made it to production is because one oil cos will lose money and plus no one has the imagination to make the alts better, more powerful, and more efficient, at least here in USA and under the watch of bUSH(lets not get political). I mean lets look at the history of internal combustion engines we came from whimpy little 2 cylinders with 5 horsepower and a top speed of 20 mph, if that fast, to what we have now v12's, engines that put out up to 6,000 horse power and can reach i think somewhere 350 mph plus :eek: (record breaker for piston engines) so no one can honestly say we can't find some way to make alts better.

[M-317]

HERE IS SOME FOOD FOR THOUGHT. As propane actually has a higher calorific value than gasoline, its stoichiometric ratio—the ideal air-fuel mixture—is 15.7:1 versus gasoline's at 14.7:1. The smaller injectors obviate the need for any change to the car's stock powertrain controller. And with an octane value of 104, propane is ideal for high-compression engines.
Because the car's fuel-injection system operates with liquid propane, the car requires a so-called distribution block to recirculate the propane to purge vapor. In most vehicles, the dome-light switch could activate this as the driver opens the door, readying the car for an immediate start.

[ekooke]

M-317,
You can dance around this one all you want, but the fact remains that there's less heat energy in a gallon of propane (LPG) than there is in a pound of gasoline, as follows.
Gasoline = 115,000 btu/ gallon (average)
LPG = 84,000 btu/ gallon
The above are DOE figures, verifiable on its website.

Philips Petroleum in Bartlesville OK has been running its service trucks around town on LPG since 1977 and they've tried all kinds of tuning tricks to the drive trains of these vans, and they still fall 10~15% short of the fleet average of comparable gasoline-powered vehicles. This is strictly due to the energy content of the various fuels, and the differential remains, no matter how much juggling is done with A/F ratios, compression, ignition types or what have you. I don't want it to be true either, but it is what it is.

[Bluegrass]

Just about every propane dealer I know of that has been in the biz long enough runs there trucks on propane. Why is simple, it is right there to use without dependence on gas or diesel fuel reguardless of the draw backs.
Ford has hydrogen powered trucks and has to super charge them in the bigger trucks to get the power requied to do the work compaired to diesel power. Because if that fact alone they are not marketable.
This is the hangup, the practical applications drawbacks have not been overcome in a cost effective manner.
I could care less about a fuel that gets huge milages or power if it's availability and cost are still too high.
There's no gain in the end result when money drives all these things.
When the larger masses can't afford the gas and the supply is no longer there, then we are all in the same boat.
Only then will things really change. ;)

[MichiganTeddyBear]

After reading what has been posted previously, and being not well informed from any other source (I am in the dark so to speak), it does appear to me that propane has the Potential to provide better mileage and definately lower emissions (there is a reason they used propane powered lift trucks in the factories I worked in).

Since propane appears to have a higher octane rating (posted previously), an internal combustion engine could make use of that higher octane rating to provide more power (via higher compression ratio or other method of increasing cylinder pressures). It seems to me that ONLY if the engine can develop the higher cylinder pressures, can propane be used to its fullest potential. an automotive engine that was designed to run at 8 to 1 compression ratio, will not make nearly the same amount of power as same displacement engine with a higher (say 12 or 14 to one) compression ratio.

Again, I may just be blowin smoke, but thats what I have interpreted from what I have read here.


Also, I know from experience that in household use (heating, cooking, and water heat), that propane is less effecient than natural gas. I live in the boonies and use propane for all of that, and had to convert my appliances to propane when I moved from the big city. The conversion consisted of smaller diameter jetting, and resetting any safety devices in the gas line to handle higher pressures (in the house, propane runs around 14 psi, natural gas around 2-4 psi). Remember, smaller jet installed, but I have MUCH higher gas pressure to push it thru the smaller hole!

[M-317]

things will eventually change but a major reason no one wants to change is because they think that with propane and hydrogen in their cars that they are driving in a potential bomb which is true to an extent but what the avrg person fails to see is that gasoline is cumbustible also (with the right air fuel mixture) but even without that if the gas tank is punctured which is not hard to do seeing is how our tanks are nothing but 20 gauge steel with plastic covers and no blatter, we will still get a fire. What needs to be done is America needs to educate it's people on alternatives b/c the majority of people out there are so ignorant about cars. Hell i asked my sis if she needed her oil to be changed and she told me no b/c her oil light hadn't come on. AND DO CHECK OUT SOME OF THE LINKS THAT ARE POSTED ON THIS PARTICULAR FORUM POST.

[ekooke]

MichiganTeddyBear,
Factories use LP-powered forklifts for safety to humans, since the unburned LP hydrocarbons (CO) are much lower than with gasoline.

If you're just talking about heat per gallon of propane vs. heat per gallon of NG, the propane is the clear winner. It's just that the NG costs way less per unit, so it's the economic winner.

[pro-five-oh]

quote:Originally posted by 88LSCinSW-FL:
http://franzh.home.texas.net/lpinfo/index.htm

LOL, I worked with that guy during my stint making propane vehicles with UT Austin's SAE student organization. smile.gif

Here's the thing: Injectors, fuel rails, tank, pump, and computer would be changed to accurately measure out LPG. LPG runs at 110-130psi, which would blow up every part of the stock fuel system. And since its burn characteristics are quite different, tuning will be a NIGHTMARE. Even installing the tanks is a pain, unless you want to fill your trunk up with them...and make the car into a rolling A-bomb. And the car will never pass TX emissions.

So for the cost of new tanks, lines, injectors, computer, and all the user interfaces to make it easy to use, you're out a lot of money and a lot of spare time.

I'm not saying its not worth it, I'm just saying the Ford Focus is a good used car value and cheap to own. smile.gif

[MichiganTeddyBear]

One thing to remember, propane is typically shipped and stored in liquid form, and used (burned) in gas form. whereas NG is typically shipped and used in gas form . A gallon of liquid propane produces a lot more than a gallon of gaseous propane.

Yea, I agree with the safety factor and reduced emmissions from propane powered vehicles.

As far as effeciency is concerned, I know it takes a little more (not incredibly), time and effort just to boil water with propane than it did with NG. Same goes for my gas dryer, it does not seem do quite as well. The conversions I got were directly from the respective units manufs. (I know this paragraph is WAAAYYY off topic, but its my personal experience, and may shed a little light (or darkness) on the relavent topic).

[Desert Stallion]

Ya' know, I tossed this around a little at one point, but one thing stopped me from going any further...

One morning my step dad got into his company Yukon which had a propane conversion done (part of the blue-plate tax write-off deal we had a couple years back for alternative fuel vehicles), cranked it over a few times, and the resounding 'boom' woke up the neighborhood.

Aparently the propane system had failed overnight and propane pooled in the intake/heads and ignited all at once. Blew the intake apart, cracked the air cleaner, destroyed the MAF, etc. Pretty cool lookin' aftermath. :eek:

This conversion was professionally done by whoever the dealership had doing conversions for them, not a home made setup, and worked for a couple years anyway. The truck wasn't really down on power when the system was used. Just comes down to whether or not finding propane filling stations is worth the hassle to some people.

[cason1]

It seems this is turning into a rather interesting discussion so let me throw a few more ideas out here. Search for the compressed air engine on Google. Basically they have big air tanks under the car and they are used to keep pressure on the system. Couldn't find exactly how it works but I have ideas that I want to try out if/when I get any money.

[pro-five-oh]

quote:Originally posted by Desert Stallion:
One morning my step dad got into his company Yukon which had a propane conversion done (part of the blue-plate tax write-off deal we had a couple years back for alternative fuel vehicles), cranked it over a few times, and the resounding 'boom' woke up the neighborhood.

Hey DS, what that a LPG or gaseous Propane conversion?

[gadget73]

essentially air powered cars use a big version of whats in any air powered tool to function. Kind of interesting but it requires a lot of filling up with compressed air.

[cason1]

That's what I am trying to deal with. I have a basic idea that might allow me to basically convert a standard engine to air. It is very complicated to explain but it works in my mind so far. Hopefully my dad and I can get a block and the supplies and work on it this winter.

[Steve Moran]

This whole engine discussion on what an engine needs to be set up like can be answered by saying that you need a (diesel like) setup.
The compression, timing, camshaft and whatnot are ideal for LPG.
To build an engine to run on it efficiently would be tuff but I think would be a fun thing to give a shot. I know back in 77/84 a family near where I lived used 400 cid engines with dome pistons, and high lift RV Type Camshafts in their LPG engines and they pulled fairly large horse trailers, they did remove the gasoline tanks eventually and never converted back.
I moved away so I don’t have an answer as to if they still do it. But to my last thought on it he didn’t look as if he would.

I am the kind of person to give it a shot nomatter how unfeasable it sounded I would try it just to say "I did it!"

[pro-five-oh]

quote:Originally posted by Steve Moran:
The compression, timing, camshaft and whatnot are ideal for LPG.

Nah, I think most modern cars (ones built after 1990 or so) have enough compression and aggressive cam timing to make LPG work. More compression would be ideal, 9:1 on the Mark isn't that bad and I expect that's what our Chrysler Minivan had when we converted.
http://www.me.utexas.edu/~sae/picdatabase/1996-97/propvan/propvan.html

LPG is actually pretty good to work with, since it creates a cooling charge like Nitrous when injected into the motor. LPG turns into a gas and cools the intake charge in the same process. Cooler air = more power, power with similar levels of acceleration to a gas vehicle.

Of course our Minivan was a gift from Chrysler, had about $10,000 worth of hardware, and a team of graduate students trained to monitor the engine vitals. Your experiences may vary. smile.gif

[ August 20, 2005: Message edited by: pro-five-oh ]

[john's 88 LSC]

In the long run, running Propane, LPG, NG, or any of it's derivatives, still has the same problem, it a fossil fuel that comes from oil wells.

If the use of Propane and LPG caught on, it would cost just as much or more than gas in no time at all (it's called greed). Look at diesel, in the matter of one week it went from costing about the same as regular gas to more than premium (almost a 40 cent increase in one weekend here). The excuse was a refinary 'fire' that only affected diesel production, not gas. There always seems to be a 'fire' or other problem that causes the prices to go up, but when it is fixed, gee, the prices don't come down anymore than a cent or two.

The big oil companies posted the largest profit increase of any company in the history of the United State last year. They are not hurting one bit.

As far as alternatives, grain alcohol has been a viable alternative for over 50 years. For diesal applications, soy bean oil. The big oil companies have spent BILLIONS on lobbists groups in Washington to do everything they can to stop it's use. They like to promote the false belief that it takes more energy to produce grain alcohol than you get out of it, that has been proven wrong many times. The point is, it is not in the best interest of the oil companies for any of the other 'alternative' (i.e. non oil based) fuels to be used.

The change over to non fossil fuels can be, and has been done. There are some countries that after the 70's 'oil crisis' mandated that all new cars sold in their contries run on grain alcohol, and they have been for nearly 40 years now.

The technology is, and has been there. But the oil companies want us to stay dependant on them, and they will and do, spend billions of dollars to ensure federal legislation ensures we do. The spend this kind of money on lobbyists groups, and STILL post record breaking profits in the US. They don't have to sell gas at this high of a cost, they do it becuase they can and we keep buying it.

Sorry for the rant.

[Desert Stallion]

quote:Originally posted by john's 88 LSC:
The change over to non fossil fuels can be, and has been done. There are some countries that after the 70's 'oil crisis' mandated that all new cars sold in their contries run on grain alcohol, and they have been for nearly 40 years now.


Which countries, if you don't mind me asking?

[M-317]

john's 88 I'm totally with you on the the rant i believe in what u just said 100% and have been saying the exact samething for 4 years now (ever since i was mature enough to grasp it) i'm only 20. Ok lets says i don't go to propane. what else is there provided i want to keep the mark but convert the fuel. Because that is the point of my post, i want to keep the mark but run it on something else besides gas or fry grease. I have an idea for a car that uses tech that is all around us it basicly alows you to drive where ever you want and how ever long you want while only having to fuel up my once or twice a year. I have drawings and such just need the $ to make a working model. I'm going to college soon so hopfully i can get some grant money from a non gov funded agency because the last thing i want is my research confiscated because oil cos will lose bussiness. But if my plan does work i will make alot of enemies. tongue.gif

[ekooke]

Brazil runs 75~80% of its vehicles on alcohol derived from sugar cane; they have since the 1970s. Of course, not every climate will support sugar cane growth year around, and one day (probably very soon) Brazil's topsoil will be effectively gone, that biofuel supply will dry up, and vehicle owners will then get their needed fuel at gunpoint; either their own, or the military's. smile.gif

[AGE]

M317,

I am a retired engineer--worked in power and propulsion for 40 years. I worked at Ford 2 years--gas turbines; General Electric 5 years--jet engines; Westinghouse 28 years--nuclear reactors, Transnuclear 5 years--nuclear fuel shipping. Yes you can run a car on lots of stuff, even charcoal fumes with lots of smoke. Batteries, compressed air and spinning flywheels work for a short distance if fumes are unacceptable but need outside charging sources requiring energy.

However, you need to go to school before building your car. IMHO the only device that will do what you want is one of those big suction cup keys that they used to stick on the trunk of VWs.

Sorry, I couldn't hold back any longer--nothing personal.

[M-317]

so AGE are telling me that i can not do this, remember i want to know are there any conversion kits sold in america. I am fully awar of how many different ways there are run a car but i want to go to propane, or i am rather interested in going to propane. I am not building a car i am wondering if i will be able do to this once i find a conversion kit. Keep this thought I want to save money in the long run and that doesn't mean buying another car, im only 20 and in college so my budget isn't too big, at least not big enough to be fueling up 2 cars and be paying insurance on 2 cars.

[AGE]

M-317,

Yes you can run your car on propane or even natural gas. These are hydrocarbons composed of both hydrogen and carbon just like gasoline and diesel fuel. They're all a little different but work well in internal combustion engines. I'm not sure what it would take to convert a Mark VII to propane, but I'm sure it could be done and probably has been done. There are lots of propane powered vehicles out there. Ford even made a mess of Crown Victorias powered by natural gas.

Now then is this practical? Maybe or maybe not. If you have smog inspections in your area they won't pass a highly modified vehicle. That is just an immediate practical problem.

Would that conversion be economical? That depends on the price of propane vs the price of gasoline, the cost to convert, how much you drive and how long the vehicle will last. If it costs say $3000 to convert and you save 50% on fuel (just wild assumptions) you will not have a net savings unless the car lasts long enough to burn $3000 of propane (remember gasoline would cost $6000 so you saved $3000 worth of gasoline but you spent that on the conversion). If you wreck the car or it wears out (or if you get tired of it) before then you will have a loss.

Nothing is free but some choices are better than others. The best choice is what is cheapest and/or what works best. Good luck in your career.