Propane conversion ... already have aftermarket EFI

Actually custom tanks in the Factory location would be "doable" I would think....

Entex fleet trucks here have run on it for decades, I think it's just a swap of the carb system with no engine mods...not sure.

 

You may have the only LPG powered Ferrari in the world after this. A spare wheel well tank (torus) should not be too difficult to come by. At least in the EU they're plenty available in many different sizes, from 5 to 50 few gallons, even standing torus tanks.

Do a search like this one: http://www.google.nl/search?hl=nl&q=reserveradmulde+tank&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1280&bih=807&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi

 

Take a look at this document:

http://www.autopropane.com/Prins_Sequentially_Injected_System.pdf

 

search the mustang forums, i know there were a few guys running injected LPG cars there.....the most notable one i know was the 'slot cars' mustang GT

would be an intersting project to be sure....LPG has the advantage of high octane ratio, but some special equipment, and different fuel storage

 

i have been driving a 2003 Peugeot 607 V6 with 200 hp running LPG for the last 2 years and cannot feel the difference with gas.
i have also had a Range Rover V8 and an Opel running LPG in the past 15 years.
the 12 gallons tank replaces the spare tire and has a capacity of 300kms more or less, depending on how i drive.
don't know about the price but here the difference is around 50% less for a liter.
I only take my car to someone who is really specialized with LPG.
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The LPG vehicle conversion industry in the US has nearly been regulated out of existence, so anyone contemplating doing a conversion will be hardpressed to get it done "legally" unless the car is old enough, or special enough that it's exempt from various EPA/DOT/NHTSA regulations. Fleet vehicles do get special treatment, but a single end user wanting to get his own personal vehicle converted is pretty much SOL. Very unlike the situation in Canada, the UK, and Europe where automotive LPG conversion is a thriving industry.

I'm somewhat familiar with both carbed and injected gaseous fueled engines as I worked for two of the US's largest gaseous fueled engine companies for a number of years, so I'll try to answer some of the questions posed to the best of my ability:

Normal gasoline injectors will not work for a "typical" LPG vapor injection system for several reasons - they're too small, plus gaseous fuel doesn't provide enough lubrication for a gasoline injector. Gasoline injectors "might" be large enough for a liquid LPG injection system, but those systems are still few & far between. Keihin of Japan make excellent bespoke CNG and LPG injectors, and the high end LPG systems from Prins (NL) use them. The cheaper Italian systems use everything from simple solenoid valves to proper injectors, depending on the brand.

The vapor pressure in the LPG tank is usually enough to feed an injected system on a naturally aspirated car, or a very low boost turbocharged car in a hot climate. But the PVT characteristics of LPG are such that on a cold day, there may not be sufficient pressure or temperature to vaporise the LPG and start the car, so starting is almost always done on gasoline, unless supplemental electric fuel heaters have been fitted as a vaporisation assist.

Driving range on LPG is about 75% of an equivalent amount of gasoline because LPG has less energy per unit volume than gasoline. Also LPG tanks can only be filled to about 85%, and should not be fully drained, so one doesn't get the full capacity of the LPG fuel tank.

Another impediment to automotive LPG conversion in the US is the lack of suitable tanks for passenger cars. It's difficult to justify dedicating your trunk space to a large cylindrical LPG tank, and only Manchester Tank, and maybe one other North American company make them. The nice little toroidal tanks from Stako (Poland) that replace the donut spare are not yet ASME stamped (last I checked), so they "legally" cannot be used in the US, although they're certified to TUV regs and are popular in the UK, Europe, etc. Plus toroidal tanks don't have a very large capacity (50-80 litres typically), so they provide a fairly limited range for a high performance car.

As much as I like gaseous fueled engines, and would like to see more LPG fueled vehicles in the US, the driving reason to convert to LPG in most automotive applications is the cheaper cost of the fuel, and that advantage is only found outside the US. The $/BTU energy pricing model in the US makes LPG not much cheaper than other motor fuels. To be sure Agro and home heating LPG are cheaper than the motor fuel, but a reputable LPG company won't give your car a fill with these fuels, and trying to fill your car's tank from a stationary tank could turn into an exercise in self immolation unless you really know what you're doing.

So for most people, the cost and hassles involved in converting a car to LPG for higher performance reasons might be better spent on fitting a small auxiliary tank of C16.

Still and all, after pointing out all the disadvantages, I do have a complete Prins LPG vapor injection system waiting to be eventually installed on a supercharged V8 I'm playing with, if I should live so long

 

There are two LPG injection technologies - the tried & true vapor injection, which keeps the LPG liquid until it reaches the engine bay where it passes through a vaporiser/regulator, and it then goes into the fuel rail(s) and injectors as a gas.

The newest technology keeps the LPG fuel in liquid form and injects it as a liquid fuel. This technology operates at much higher pressure than the vapor, and last I knew, still wasn't quite ready for prime time, as it requires heavy insulation of the system, plus pumps to maintain the system pressure, etc.

The vapor pressure of commercial HD5 propane at 100 degF, is around 175 psig, but it drops with higher concentrations of butanes and other heavies.