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Off-road kits are the only ones generally available to the DIY mechanic because off-road vehicles are not required to meet any sort of emission regulations. Propane is especially well suited to off-road applications because of the propane fuel system's ability to run in virtually any orientation. Because of a mono-fuel conversion's effect on a vehicle's emission controls, mono-fuel conversions are the most common for off-road applications. The least expensive conversions (at least for typical North American vehicles) use Impco or OHG/Woodward carburetors and most any type of engine can be converted with these components. Impco carburetors consist of a mixer (the device that meters the correct amount of fuel to the amount of air passing through it) and a throttle body (the device with the butterfly or throttle valves). Combining the mixer with a throttle body creates a carburetor. Impco has a number of mixers in a variety of flow ranges. Because the gas valve inside the mixer reaches the top of its travel at the flow rating of mixer, it is important to correctly match the mixer to the engine. Too small a mixer will limit the maximum power of engine and too large a mixer will make for a hard starting and poor idling engine. For each size of mixer, a number of throttle bodies are available to bolt onto common 1bbl, 2bbl, and 4bbl intake manifold flanges. It is extremely easy to create a properly-sized carburetor for just about any engine. Impco and Gann at one time made adapters to mount mixers onto the throttle body of the engine's OEM carburetor but many of these adapters are already obsolete. If you're lucky, you might be able find old stock still sitting on a shelf and this will save you the cost of installing a universal throttle body. Raso Enterprises has created universal carburetor kits for a variety of engines. Once the carburetor is selected, it needs to be correctly matched to the converter. The engine's power output depends upon the vaporization capability of the converter. For engines up to 100 hp, the Model J will work fine. For all others up to 325 hp, the Model E or Model L converter will be suitable. We have created basic component kits that make an underhood conversion kit when matched with a carburetor kit:
For example, the most economical way to convert a 4bbl Chevrolet 350 engine would be to use a 425 Quadrajet Carb kit with a BCP-EE components kit. The fuel economy (read $/mile) of an open loop system is dependent upon engine temperature. Cold engines have rich fuel mixtures because the converter supplies fuel at a constant pressure to the mixer and colder water produces colder, denser fuel vapor. To ensure that the fuel mixture never becomes richer than stoichiometric (chemically ideal), we recommend the use of feedback controllers like the Dual Curve 5952 and the Technocarb Voila, even with standard and lean open-loop gas valves. For propane carburetor kits with higher flow capacity, Technocarb has the complete underhood 4bbl carburetor kits in the following sizes:
Raso Enterprises
GotPropane.com
Hendrix Industrial Gastrux
Jasper Engines
Propane Guy
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