Engine basics
Before we can recommend engines well suited to the Off Gridder, let’s first take a look at engines to avoid and why they don’t make sense for any self respecting Off Grid power system. 
Emergency backup generators
Every big box retailer has them. Aluminum generators ranging from $500 to $5000. They are good for occasional use on gasoline and that’s all they are good for. Their ratings are generally way too optimistic on both their power production and expected life. Here are reasons to avoid them.
Life Expectancy- These engines are good for about 500-1000 usable hours of life. If you run 3 hours a day, every day, then in one year you need to start shopping for a replacement. Why is this? These engine rotate at a whopping 3600 rpm to get the power they need. Also, those light aluminum blocks do a great job or passing the heat from the cylinders outward for cooling, but also inward where it breaks down the oil.
Noise- Just listen to a generator screaming along at 3600 rpm every day and by week 2 you will want to kill someone. Your neighbors won’t appreciate it either.
Sizing- Many of these generators are too small in size to produce the suction needed to make a gasifier hot enough inside to run cleanly.
Configuration- There is no place to attach pulleys and auxiliary generators and pumps.
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Ideal Attributes of a Woodgas Engine
Engines best suited for pairing with the Off Gridder are:
- Cast iron construction for long life
- Water cooled
- Slow speed. 1800 rpm
- Simple construction
- Large intake manifold
- Displacement from 2-5 liters
- Pulleys or power take-off points
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Engine Ideas. What’s Your Budget?
Do You Want to Make AC or DC Power? Here are some engine/ power system recommendations for every budget.
3 Cylinder Auto Motor- Peruse Craigslist or your local junkyard and you might be able to find a good running 3 cylinder engine. With the addition of a high amperage truck alternator or two you will have a low cost DC power producer for charging batteries.
4 Cylinder Genset/ Auto Motor- Gasoline gensets by Westerbeke are rugged, slow speed generators that are built to last. Westerbeke’s operate at only part throttle on gasoline, so they have some throttle left when the less potent woodgas is used. This means that you can get near the rated performance on woodgas. Ford has a 27 kw natural gas genset that will get you about 15 + kw on woodgas at a nice price. For a very powerful yet simple engine that is ideally suited for woodgas consider the 3.0 GM marine engine available as a brand new longblock. With a custom manifold this is the ideal choice for a purpose built AC/DC generator set. 4 cylinder engines offer a perfect blend of power, suction, and fuel (wood) economy.
6 Cylinder Genset/ Auto Motor- Cummins Onan used natural gas gensets are available on Ebay for next to nothing with very low hours. Many offer 3 phase power which you can use for industrial tools and greenhouse lights. Any inline 6 or V6 automotive engine will work too.
8 Cylinder/ Auto Motor- The standard Off Gridder will run 5.0 liter engines, but the run time will be reduced from the added fuel consumption of a larger engine.
Diesel engines- Diesel engines can run on woodgas, but they require about 20% diesel fuel to enable combustion. The alternative is to add spark plugs and use only woodgas.
