Small Engines to Woodgas Run

Hi All
I wanted to have a place to share some of the “small” engines we have seen and experienced successfully woodgas ran.

Whole bunch of people now woodgas ran the years produced 1976 to early-2000’s Single Overhead cam Ford I-4’s in their different ignition 2300 and 2500 cc configurations. Works well. Ever wonder how much actual power potential these have as a stationary 1800 RPM gen-set?
Gasoline 36 shaft horsepower (27 kW) mechanical
Natural gas 33 hp (25 kW)
Propane 38 hp (28 kW)
These are Ford factory ratings on thier LRG-425 LP engine used in a certified 20 kWel Telecom system. Full data at 3600 RPM with pictures was put up here:

Both APL/GEK and Victory Shop have evolved to the Kubota DG 972 3 cyclinder natural gas engines. Why? They work very well and Kubota wanted this usage to be developed and publicized. But yeah, couple of three thousand dollars a unit new.
Hey Chris/kymetro! Wanna read about a fellow took one of your Geo Metro engines, made a 4 kW home gen-set (propane fueled), a made a home built electronic govenor system?
Starts at Relpy #10 and goes on from there. Fellow who built this put it up as a $2000. COMPLETE system challenge point.
He is now here a member here wanting to learn how to woodgas fuel it.

Then there is Daniel/foxridgecampground with his 22R SOHC Toyota gen-set. Matches Bruce’s in Iraq Toyota PU and the International Geographic/JohanL. built Toyota pickup.

I personally do like a pushrod overhead valve operated engines much better for the “weak link” of a bent pushrod when a stuck valve incident may occur. V-twins are my favorite smallest engines in these. Experience now with Kohlers and Genracs V-Twins. APL/GEK has now logged many hours on V-twin Hondas and Kohlers.

In my opinion now best to 2-3X oversize the engine versus when on gasoline or propane;
Down speed operate it below 3000 RPM just like Wayne and others overdrive and down speeds their vehicle engines on slow combustion woodgas;
Stick with multi-cylinder engines to help even out the intake pulsation’s. The woodgas gets easily push around in waves screwing up even delivered air/fuel ratios;
And MUST have electric starting!! This frees you up to fiddle with the gasifier/mixture stuff without huff and puff hand pulling/cranking passing out. Allows you to build useable woman, older responsible child capable system from the get-go.

I could go on and on but enough for now from me.
Others experiences?

Steve Unruh

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Steve, you deserve your own section of the forum. Every time I read one of your posts I learn something new.

I’m moving this to the brand new forum area - Steve’s Corner: Small engines and generating power with stationary gasification.

Don’t feel obligated to maintain it - it’s simply named in your honor and ready for your wisdom should you decide to post it.


Oh, and you can tell your Geo Metro friend that if he decides to go with woodgas, the compression ratio can be raised to 12:1 or even higher without issue, these are non-interference engines and there’s metal to be shaved. Here’s a thread on the Geo Metro Forum about a successful 12:1 engine: [start at post #187]

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Hey Steve great to see some posts about power generation. Whats everyones thoughts on a scaled down Keith style build for smaller less heavily loaded engines. I`m thinking about a 20hp twin Briggs off of a lawn tractor.
Best regards, David Baillie

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Not to bomabard you from all directions Steve, but how about a 15HP thumper with hydrostatic drive… think there would be enough rear wheel power to make a wood chunker ? I have no idea of the specifications for the hydrostatic pump or how the rear wheel torque or PSI is rated, but I want to make a chunker similar to WK’s, but using this small tractor if possible. This one has electric start, a 12v electrical system and output shaft on the front that could drive a generator too. It has points style ignition though… would I need to convert to an electronic trigger off the front shaft? This would probably be my first engine to try to run on woodgas since the mower deck is shot and I have been keeping the tractor for a R&D project like this…

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Gee Chris Saenz I am flattered and a-l-m-o-s-t speechless you would do this.
Thanks for keeping this out front in the general read section. Could you please work “Small Engine” into the title too please.

DavidB. yes I think Waynes “Keith System” can be down sized to gasoline/propane rated +/- 20 horsepower spark ignition engine ranges. Same system size probably able to go up to an actual 40 horsepower on woodgas capable putting it into 3 and 4 cyclinder 1800 ROM engine range. Call this a Small system. Smaller than this is really a Micro as in Dutch John’s; rhe smallest choke plate Victory Hottwatt; the smallest restriction GEK configurations. Fuels sizing becomes a PITA with the really small 3-12 hp engines. As I recall the rated CFM on a ~5hp gasoline engine is only ~15-32 cubic feet flow per minute Not much draw foe any gasifier. Just look at the tiny carb and exhaust holes, and tiny small valves when you go this small. The three builders I quoted recommend and/or do use more and more internal/external insulations and then SS or ceramic guts to withstand this then held inside heat. Waynes as carbon steel needs to shed out some core heat.

Pet project of mine has been to take a standard rural/urban riding lawn mower, 100 amp car/PU alternator and see with the mower deck pulleys and parts just how effective of a “Nail/Stone Soup” woodgas home charging system I could cob up.
Rule of thumb using automative type DC alternators at only 40-60% efficiency is you need ~1 shaft horsepower for every 12vdc 20 amps charging. Yes, really, only ~280 usable electric watts. So yeah need to start with at least a 15 hp rated gasoline engine with woodgas AND Engine Speed Derating. Derating engine speed helps much with the scream-a-matic air cooled sound, engine life and woodgas fueled needed ignition timing advance change.
Ha! Ha! I will be able verify and qualify a Keith System able to do this by summers end. I want greenhouse heat and Lights this upcoming winter. Woodstove heating only gives me the one not the other.
Yeah, yeah MicroCoGen fellows I know be better system efficiency to go with 24 - 32 - even 48 VDC system. But since the inefficiency IS waste heat from the alt unit, pulley drive and light bulbs then as a greenhouse heater/illuminator it is all good. Sic: 1000 watts electrical out = 1000 watts heat out off an auto charging units. Why you have to spin the DC alt head at least 4000 RPM so it will self fan cool itself. Engine fan and alt fan are your air circulating sources. Use these DRY heats along with rising engine DRY exhaust heats to pre-dry my always +20% fuel wood and this moisture then humidify the greenhouse.

Hey Gary “I think” woodgased this engine would have enough power to operate a small Kieth/A.Juso style shear chunker. I do not “think” it will do it through through a belt driven Hydro trans-differential. Not geared low enough. Hydro trans “may” just just fluid coupling stall out (slip) or the unit drive belt(s) slip on this kind of load. Only way to know is to try it. Study Wayne’s and the Finn A. Juso’s (sp) videos. Build the chunker shear head and try it on full power gasoline engine power first.
If this is a Briggs, Tecumseh, or Kohler with the ignition points under the flywheel for some of these there are electronic ignition conversion kits available. Try an Internet search for this. On disassembly look also just how you could ~15 degree advance the timing from stock.

Steve Unruh

Hey Steve,
That is more or less my plan too. 20hp Lawn tractor, wood gassifier, turning an alternator, secondary battery bank in the greenhouse backcharging the house through an inverter then a 24 volt charger in the house seperate from the inverter charger setup. The charcoal 110ac I built works fine but those small fluctuations in the AC drive me mad and the ever so slight delay between load change (pump, dishwasher, fridge) can make the inverter/charger kick off. It’s one of the vestiges of inverters being derived from RV units I think. The makers seem to think that you have unlimited AC when you plug them in So you need 3 times the AC generator you otherwise would use for battery charging just to handle peaks therefor more fuel usage. I figure I can do all those conversions and still come out ahead in terms of efficiency. Off to the salt mines, David

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What forum name/sub-title sounds best to you? You name it, you got it.

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Steve’s small engine soapbox Where small is beautiful…

I forgot. If we can figure out a sizing for it I thought of building one for my real tractor. A 1951 Ford Ferguson tea20 4 cylinder 28HP with pulley at the front for turning an alternator and pto on the back. would be perfect I think; the engine is a tank and easy to work on huge air intake with easy access. Steve, what should I be reading to figure out sizing the main unit? Need some advice.
thanks, David

Ah! Ha! There you go ChrisKY. Diversity of thought, experience and especially intent is the most important thing to accommodate for small woodgas system/engine users.
I am very myopic pigheaded as both Jim Mason and Ben Peterson can attest.
So I think just simply “Small Engine Users Corner” would be just fine. Woodgas is assumed in the site name. Both stationary and small mobile could be accommodated within here. Us small fixed timing engine guys have much to learn from the small engine distributor turners. And they from our ability to cheaply compare and use side by side different valve in block with different overhead valve versus different compression ratios aircooled engines.
I would be happy with just a topic line. Those who want to continue working on the really low horsepower 1-8 stuff can feel comfortable here too on a separate topic line. DJ’s MicroGasifier info is the ticket for these. He has really defined the lower boundaries. Fellows still wanting to convert small diesels can feel comfortable here too on their own topic line. Just because I loudly say now I have lost interest in these areas my “name” out in front should not make them feel exclude out.

DavidB. Lot of reading to calculate this out. By horsepower/kWme in Doug Williams/GEK-APL/Tom Reeds Rossetta Stone. Dutch John’s site has his and Max Gasmans simplified practical calculator. For your specific tractor even the FEMA paper is good. It was an actual project paper to build for a tractor very similar to one of these. Waynes system is derived from a FEMA base. So leaking info out a little bit since he has evolved to a very thick well casing burn tube then I think just start with a minimum 6-8" well casing tube. And GEK/Hottwatt experience tells me you do not want to go with less than a 3" choker plate restriction at the bottom of this tube. Now how tall of tube and number and big of air nozzles?? Wayne may chime in with a guestimate but I think the whole point is for us to cut 'n fit try and then be able to experience feed back and be able to tell him and others.
Ha! Ha! Big lump of an engine be great mass of cooling off thermal if you can store it in a greenhouse end wall enclosure. I will chuckle however if you stick a valve open on this valve on block flathead and discover you have to coolant dump and remove the cylinder head in addition to the intake manifold work it loose. Pushrod over head valve is so much easier with usually just a valve cover to remove.
Steve Unruh

My experience with the small ones is that they are very picky. The small dimensions ask for very well insulation which is difficult, because the ratio radiation surface/volume is large compared to bigger gasifiers. And small wood is seldom good flowing blocky, but often flat, sharp and light. Resulting in an intermittend flow.

I did not test it yet, but using dimensions as if the engine were much bigger and putting more effort in heavy hearth insulation would be a better way to go. Heavy insulation allows a larger turndown ratio. Of course the power demand of the small engine has to fit into the ratio.


Steve U, done. Your wish is my command.

Dutch John, welcome to the site! Very glad you came by, we value your input. Yes, pictures of the new project, please!

Hi Steve, I got a used car the other day that has a cute little engine in it. EFI 1.6L DOHC . Not sure what the power rating is for this on gas, but it seems like it could make a decent, fuel efficient engine to run a genset or do some other work around the house. Of course, I cant rip it out yet. This is in my Daughters first car : (

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Love this site…have been playing with woodgas for several years…retired auto engineer…hopeing to
Attend the show in Indiana Need more information…Dave

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Sure. Sure. GaryG. These little Nissan DOHC I-4’s when running well tick over nice and smooth like fine watch.
“Small” for a woodgasifier fueled engine is really defined by the low continuous low horsepower needs. Read DJ’s Microgasifiers PDF and you will see he was fooled designing for his “Tiny” (DJ3) lawnmower application when the gas flow wants were NOT following the engine horsepower rating but the actual est. 1 horsepower his rare English power reel bladed mower needed. Less horsepower to fuel -> less woodgas needed -> less woodgas needed -> less heat generated -> less heat generated -> less heat available to drive the fuel drying/pyrolisis/oxidization/reduction conversions. Smaller the gasifier system the prortionally smaller the weight and fuel “bit” (chunk) size causing gravity fuel flowing down problems. Smaller the gasifier size as he said the smaller the hot internal space volumn mass to the outer radiating surface area. Example: same cool climate; BIG cow - short fur. Smaller the animal, the thicker the fir needed to cope with the cold. So every factor on small gasifier systems is driving you into a Humpty Dumpty, Ring Around the Rosie, we all fall down system collapse into a cool tar soot mess.

GaryG this direct cam over the valve engine is defiantly a valve will hit the piston engine with any problem. It will not just bend the valve stems, but with no where to bend aside safely will break the valve heads off imbedding them into the piston crown and often even scoring the cylinder walls in. So be sure you work through ALL of your system/operator possible tar issues on your Gosellin/Dobson/Keith hybrid design on your nice safe garden tractor engine first.
BTW second mowing of the year I went out and really stall loaded that rider of mine with the hydro trans in my pictures. Yep the single small upper pictured trans drive belt would just spring arm tensioner scream and then the belt slip. PITA to change this belt on mine.

Welcome DaveB.
THE most important woodgasifier lesson is to go somewhere and see, hear, feel and even taste one successfully fueling an IC engine under loaded power. You betcha’. Go there and get it really in your blood. You will figure out the tasting part from opening up and peeking into hoppers and whiffing the erie weird yellow hopper smoke. If you just must finger dip some hopper condensate ONLY just tiny bit to the tongue man. Takes days for that to go away. Hey! Don’t all curious inquisitive little kids do that? Thats woodgassing. Makes you feel young again when the world was simple and directy understood.
Maybe woodgasing IS the fountain of youth, eh?!


I run a DOHC engine on wood gas and never again. It runs good, but like Steve says it is too risky. Plastic intake manifolds also present a problem because they run colder than normal and they are difficult to clean out the soot after running a few thousand miles. I would recommend against this type of engine for wood gas unless it is an emergency.

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good info here… keep up the good work

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You keep up the good work too Mr Olsen.
I have been admiring much yours and TerryL’s use of StephenA’s design.
Please do put of some content of your use of it here.
Engine capable chip fuelers are rare, valuable and needed.
This Small Engine Corner is out front for public free reading for people to be able to put up results that will be seen and encourage others woodgas is real and for today.

Anytime you want some experienced confidential back and forth request into the Premium section in either the Builders Discussion or the Projects sections.
You are one of the real DOers out there in the world today making it happen.

Best Regards

Money is tight right now or I’d already be a premium member…

In the mean time I’m working on some ideas I have, with a little luck they will come to fruition

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