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Thread: BiFuel: Petrol + LPG

  1. #1
    Join Date
    Jul 2016
    Kyiv, Ukraine
    My Cars
    `88 535iA Stanced

    Thumbs up BiFuel: Petrol + LPG

    In Europe it`s popular decision to spend less money. At first it concerns to old cars with big engines.

    If you have, for example, e34 535iA. You want to use this youngtimer everyday and you don`t want to pay for 18-20liters/100km - LPG it`s good choice to pay less. 1 liter LPG usually costs 30-45% from Petrol price (1 liter).

    Engine starts on petrol and after heating runs on LPG.

    End else - LPG is more ecological friendly

    P.S. LPG = Liquefied Petroleum Gas

    Let`s talk about this alternative fuel! ;-)

  2. #2
    Join Date
    Mar 2017
    Vancouver, Canada
    My Cars
    1998 BMW M3 Coupe
    It's still fossil fuel. Have you heard of what they are doing in Brazil with ethanol and plant based fuels? Dramatic reduction in pollution and dependence on foreign oil. Get a conversion done bud. I hope Europe follows in the same direction as Brazil and hopefully North America too.

  3. #3
    Join Date
    May 2016
    Calgary, Alberta, Canada
    My Cars
    1998 BMW 740i Stock
    Hi Yura, I cannot say how propane would work on a BMW engine but I have used it a lot on north american cars a lot. I live in western Canada in a province callee Alberta which to my American friends is right above Montana. I am in Montana a lot. Up here it is very common to find propane at the gas stations and fleet vehicles also use natural gas. I originally bought a $500 duel fuel (petrol/Propane) Ford car to run from my hobbie farm to work each day. Prices at that time were around $0.08 per litre. I think that was in around 1985. Even now propane varies in price from $0.42 to $0.73 per litre (multiply by 2.7 for US gallon and current US/CDN currency rate). Yes that is as low as $1.13 per US gallon).

    I ran it for over 15 years and if done properly is a great fuel to use. Most of the information out there was horribly wrong at the time with claims of significant lost power, bad gas mileage, hard on engines etc. Nothing could be further from the truth. To explain this in simple terms, would you put diesel in your petrol car. That answer is simple. So then why do people put propane in a motor designed to run on gas. It is a different fuel with different properties and does not run properly in a gas motor. The good news is that most gas motors can be changed fairly easily to run on propane if you make some simple changes.

    Back when I was running the FORD (factory conversion) car I could not believe how weak the car was when I was on propane and I thought it must have been in bad tune or something wrong with the motor. Yes, I was down at least 15-20% in power, mileage and everything. I am one of those people that has to tear into anything to see how it works and how I can make it work better. many a watch was torn down when I was 10 years old but that is another story. After some investigation I realised that the real problem in the case was that people were trying to make petrol run under gas conditions. Unfortunately at the time there was little that could be done so I built my own engine from scratch and did it right. When it was finished I had probably gained 25% power over the factory settings and gained mileage to boot. At no time did I ever burn out an engine even though I can be hard on them and in fact over 100K miles I could hardly notice any wear on the engine at all. Oil changes were like adding new oil to new oil. The oil never turned black like it did in a gas motor. To get the best power out of the engine I did build my own carb. from stock aluminum pieces which was relatively simple. Here are a few tips I learned along the way.

    Propane needs compression the same way diesel does. My truck motor ended up 12:1 compression. That was a 351 v-8 modified.
    I changed 2 spark plug ranges colder, ie B8ES NGK became B6ES (these are motorbike plugs. I cannot remember the real plug numbers). Heat is a real problem in propane motors.
    I changed the thermostat from a 195F to 185F thermostat but I also went with a special high flow volume thermostat from some motorhome. You have to be able to get the heat out of the engine when it spikes up.
    I changed the initial and total timing in the engine from 36 degrees to 51 degrees total. Initial went from 6-8? to 12-14 timing. I am up at 1200 Meters altitude which may mean increasing a couple degrees over sea level.
    I made sure the water pump was a high volume pump but I am not sure that was necessary.
    Propane has a narrower air mixture range than propane so I installed a gauge to watch the air/fuel mixture. In winter/Summer I changed a jet on the mixer because with the cold vs hot air it would get outside of the best air/fuel mixture range.

    For the car I built a simple venturi mixing system. I would have to explain how I built the carb but in simple terms I took the throttle body off the bottom of an 1850?? Holley carb so I would have primary and secondary throttle plates to open/close the carb. There was a mixing area above the Holley base and above that were 4 small venturies fed by a propane mixer, like this one. I really do not remember the brand. The feed to the carb was the simple outlet from the mixer to the car in about a 1" hose. Vapor pressure was almost 0 psi, relying on the suction from the manifold to draw the propane out. Between the mixer and the carb I had a 1" tube with a screw assembly so that as the temperature changed radically I could easily tighten the screw to achieve a better air/fuel ratio via the air mixture gauge I installed under the dash. I would only have to adjust this 1-2 times a year and it was normally just a turn or two up or down and I was set again for a long time. Keep in mind that my location the temps can range from the 30c to -30c and keeping the mixture in the right range really helped the propane start in the winter and summer. With those temps the air density can change a lot. If the mixture range gets too far out of ideal you start to risk running the motor to hot, pre-ignition and hard starts. I also had a secondary line going to the carb used only for idle conditions where the pressure was more along 5 psi with again a limit screw to get it into the right range.
    I have always used synthetic motor oils all my life and I think with the potential for high heat conditions it may be a better option for propane motors too.

    People forget that propane is a liquid under pressures of about 150 PSI or higher. As the propane goes from liquid to gas it cools the air flow down a lot so you are getting an air/fuel mixture into the motor that is very cold and that can be great for horsepower and mileage. You only need to manage the heat so you do not have a BBQ on wheels. Most gas motors of the time were in the 8.5:1 compression range so that was one big reason they lost power when converted to propane. Also not much was done for most conversions in the way of dealing with the heat such as the spark plugs, changed timing, high flow thermostat etc.

    When finished my truck died from rust before the engine ever died. WHen I broke my back I could no longer get up into the cab so I sold it to my brother in law that was still driving on the same motor up until a year or two ago when it effectively rusted to death. The motor was still going without any changes or major work on it. Maybe 25 years on the motor I built? I have no idea of the miles on the motor.

    I also built a 455 (7.5 litre??) motor to put into my front wheel drive 1973 Olds Tornado. Even with all that weight over the drive tires I could smoke them off the line and got 21.5 MPG (CDN gallon) on a 5000?? pound car. The gearing in the cars was very low though which helped with that. This thing was a ocean liner on wheels.

    Overall I have nothing but good things to say about propane conversion. I never had any hard starting problems in the cold even down to -35. I think a lot of that problem was probably because conversions at that time had no way to adjust for changing air/fuel ratios which are typically set in a heated garage and by the time you shift that temp 40-50c it is way too lean to start or run well. With synthetic oil I never plugged it in and never used any engine heaters to get it to start. It often sat in the univeristy parking lot for 12 hours at some evilly cold temperatures and still started well. Easier than gas motors of the time.

    It really did not take much to convert a motor that any home hobby person could not do. I have to assume there is something on the market for carbs so you did not have to build one like me. Mixers were easy to find by googling them. You can often change compression ratios like in the past by changing either cams or heads to effect the necessary compression. I am only starting to play with my BMW so I could not say what you would have to do to bump compression up to at least 10:1 or more but that is where a lot of the power is going to come from. Altering the ignition may take a tuning shop with a dyno to run the engine and watching for problems while adjusting the timing at each point. maybe DUDMD could answer your questions on what vehicles could have this changed.

    My experiences might be a bit before modern times but I don't see that properties of propane would have changed any over time. Only how to achieve similar effects on heat, timing, air:fuel is all I think you need to do.

  4. #4
    Join Date
    Jan 2018
    My Cars
    1991 520e34,1998 528 e39
    I'm not trying to bring thread from ashes ...but im converting Cars to lpg about 18 years ....I can say for sure that its most reliable fuel injection system ....
    conversion system contains vaporiser ,injectors ,LPG ecu ,temp and pressure sensor,wiring,hoses "steals" signal from petrol injectors and needs to be calibrated for the car to work properly.
    Currently converted my e39 528 and works fine ,last fall sold my e34 520 24v - old fart made nearly 100000km on lpg , wifes vw passat 3b3 2,3l engine runing for about 8-9 years on LPG
    Its popular in whole europe and bmws are handling conversion very well .
    its mixture of propane and butane which is byproduct during fuel producing process....mixture differs during summer and winter ...basically we are driving on purified garbage ...if thats not eco friendly ...I dont know what is .
    costs half price of petrol im driving 528 e39 ...but driving costs like im driving for example vw polo.
    Last edited by PYRUSS; 01-26-2018 at 01:31 PM.

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