Just correcting myself before someone else does. CNG doesnt run at very high pressure, it is contained at very high pressure so different tank and lines. Stainless tube compared to propanes hoses. CNG also must have a much larger tank than propane because its not liquified. CNG tanks must be inspected and recertified regularly..........If anyone cares

 

Back when I was a mechanic I was certified to install propane systems on vehicles. It doesn't run as clean as you might think. When i would tear the engines down there would be these big lumps of crud around the intake valve stems that would eventually cut off airflow. We had an old Ford F100 to chase parts, it had a 240 in it and it ran like crap on propane not to mention the wire to the fuel solenoid would fall off only when you were in the left lane on the freeway. Propane is a little cheaper than gas, about $2.09 a gallon. It's made from oil so it goes up when gas goes up.

 

I change my 95`f150 4x4 5.8 to lpg with an old but cheep landirenzo LCS2 venturi system 20.000 mls ago because lpg cost half so mutch as gasoline in germany - and i can`t understand the rumors about lpg. My truck runs with lpg better then with gas and I need not more lpg als gas, maybe 10-15%. No leak of power. Normal i start also with lpg;1 only if the temperature goes down below 5°C I start with gas and worm up - at 30°C temperatur of the coolwater it switch automaicly to lpg - no problems.
But I dont know witch Brands of LPG - System you use in US. Mine has an seperate Computer who use the tps-, O2- and rpm signal as input and controls the gas flow with two actuators. On LPG runnig the gas-injectors are cutted of by a emulator. The only problem i found are the fuelpump because they take the power from the car computer and runs against full pressure, but i set a relays in the fuelpump cirkel steared by the emulator and cut them off at lpg.
A friend of mine runs in a 5.7 chevy a modern lpg-Injection, controled from the car computer - it works also very well and he has no differend in milage betwin lpg and gas (but he loose power).

For a better understanding: in the lower RPM- Range up to 2500 RPM LPG give more power than Gas!!! But above this RPM it change. So if you burn out everytime with more than 3000RPM you need more LPG .

 

I'm not saying LPG is all bad. The biggest problems with it now are its usually not tuned well or used to its potential. When they were trying to push its popularity in north america many years ago, compression ratios were at an all time low and fuel managment systems were not that great. Dissapointing many people and giving it a bad name. Now it can be optimized better. Sounds like nobleboy has got his system working well. As for quality of LPG, I know some propane has different quantitys of butane and possibly effecting performance? Who knows what crap is in most fuels here, gasoline or propane. Ive never heard or seen it being tested at the pumps. But supposedly it is done.

 

The only thing i have to say is when I was in highschool a long time ago. My friends grandfather owned a propane company, and a wrecking yard. So we built a 69 chevelle with 327/390hp it was ran directly off propane. Man did it scream. We also made the 72 chev into a hunting truck and it ran duel fuel. The problem most people have his grandfather said was not knowing how to proerly installl and set it up to run duel or only propane. The only draw back was on cold winter morning in utah propane doesnt like to start.

 

I've read that the optimum compression ratio is around 11:1 for propane, but you can also crank timing to help compensate for it's higher octane/slower burning characteristics. From what I've heard people that get a well tuned setup is actually alot more torque(imagine how cold your intake gets) but a loss of top end power due to the increased volume of the propane/air mix compared to gas.