In the 1970s there were several documented cases of a device known as a “vapor carburetor” that vaporized the gas before injection into the piston thereby increasing the gas mileage to well over 100 miles per gallon. What happened to this invention?


In fact in the late 70’s I installed dozens of Vapor Carburetors so let me give you the unvarnished scoop. During this time Canada gave a $400.00 incentive to install these devices as a clean burning fuel system. A complete system could run from as little as $1200.00 to $2500.00. It never gave over 100 miles per gallon but it could reduce your fuel costs by 50% and provided cleaner combustion. It sold like Hotcakes to gas guzzling pickups because they were easiest to convert and used the most fuel.

In fact the technology is still around today, I will give you a link at the bottom. So what was this marvelous technology that converted a liquid fuel to a vapour and then fed it into your favorite Ford, Chevrolet , Dodge truck or even standby power generator ?- a hint there

1st lets look at fuel, the heavier it is per gallon the more heat energy it contains, although octane can make a difference as well. So starting with something we are reasonably familiar with we have non fuel water at 10 lbs per Imperial Gallon or 8.34lbs per US Gallon. Then Fuels like Diesel at close to 7 lbs per US gallon, Gasoline at a bit over 6 lbs per U.S. Gallon and Propane at 4.2 lbs per US Gallon in fact it has to be compressed about 160 psi to carry around as a liquid at room temperatures. Though at -40 you can carry it around in a bucket.

So its pretty straightforward to see why Diesel gets better mileage than gasoline, add into the equation that its directly injected into the cylinder and uses much higher compression which also comes back provides more power. By weight alone it should get at least 10% better than gas.

Now compare gasoline to propane and diesel by U.S. gallon looking up on Google

Energy Source Unit

Energy Content (Btu)

Diesel 139,000

Gasoline 124,000

Propane BTU 91,600

Gas being 25% more BTU’s more than propane should get about that much better gas mileage.

Propane is also a high-octane fuel with a pump octane rating of 104. Propane typically works best with a static compression ratio of around 10- to 10.5-to-1.May 15, 2015

CNG and Propane Engine Builds – Engine Builder Magazine…

Now I went through all this so I could tell you the popular vapour carburetor I installed were for Propane made by IMPCO
the fuel was 1st vaporized by running through a device called aptly enough, a Vaporizer which use the antifreeze lines off the water pump and headed towards heater with Y fittings cut in.

Other brands also came on the market including italian Viale and OHG.

Now because we were not increasing compression ratios of vehicles our findings were we could provide ….drumroll please ….the same power as gasoline, often we could get the same mileage in spite of the 25% less BTU’s, especially on a V8 in need of a tuneup but on a new efficient 6 cylinder gas unit we would end up with 25% less miles per gallon. The selling point was we were 30 miles from the refinery and the company Joy Propane, sold propane for about 1/3 of Gasoline prices.

Tuneups were integral to the conversion as we did install different distributor weight springs to better match the power curve for propane. On one custom bodied panel laundry truck I had a delima as I could not view the timing marks with engine running. It turned out mechanics before had the same issue as I finally found a method using a mirror and the settings for gas were too retarded and the vehicle had 30,000 miles or so already. That one got a serious boost in power and mileage when converted to Propane and fuel at 1/3 the price of gasoline once I introduced the correct timing for propane. Of course a properly timed engine would have provided equal power and at least equal fuel mileage on Gasoline had it been done.

So why did Propane not take over. 1. Many places propane sells for more than Gasoline. 2. The government pulled the grant. 3. Most important – Fuel injection of Gasoline reduced the pollutants from gasoline to that or better of the vapourized propane mixer also known as carburetor and this guaranteed the miles per gallon or more accurately per BTU’s supplied were as good as achieved with propane. 4. Propane Tanks are heavy and less weight provides better mileage . Propane did come along with direct liquid injection but now you were looking at a $4000.00 bill and could only run propane maybe at a fraction of a percent better than gasoline, still no 100+ miles per gallon and all this on highly engineered systems, not some guy wrapping a stainless steel gas line around his exhaust in an effort to blow himself up on You Tube. If you want to try for yourself buy any of the small electric Generators on the market that say they run on Gasoline, Propane, or Natural Gas. They don’t promise extra run time on the vapor fed fuels either. There was the hint I mentioned above.

For a while there was a big push on Natural Gas for vehicles using direct injection. Unfortunately the tanks need to store cooled product or only run compressed natural gas. Propane was a better option as it was a liquid without cooling and thus had a better range before refueling was required. I suspect it would be cheaper to refine Natural Gas ch4 to Propane c3h8 and use the extra 4 hydrogen atoms to make something like Ammonia for fertilizer NH3 pulling the nitrogen out of the air.

In Canada we have a big push on to export the natural gas, yet the most recent export increase I recall was for … propane. Takes up 1/150 of space transporting as a liquid in a pipeline. Has more BTU’s so transport by ship is also more efficient . Would not need a hydroelectric dam to cool the Natural Gas for export. We could use the dam to run all those electric cars instead.

Credit: Ken Graham

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