Horsepower ratings

Just wondering about some rough and dirty horsepower figures. I know from reading different posts you can expect roughly a 25-40% horsepower drop when running Woodgas compared to gasoline. I was curious though is that figure the same for charcoal? Would the horsepower from charcoal gas be less, the same or more than wood gas? Also how would a water drip system effect this number?

Even if someone with some experience had a good educated guess with rough and dirty numbers I think that would be neat to see, for example gasoline horsepower being 100%, Woodgas 65%, charcoal gas 50%, charcoal with water drip 60%, I know those numbers are probably way off but I think it would be interesting if anyone had a good educated guess, thanks :slight_smile:


Check out this thread:


Hi Chris, interesting read for sure but not quite what I’m looking for. Neat to see how you can rate the horsepower (btu/hr or kw/hr) of the gasifier unit itself. What I’m asking about is more in relation to the engine itself. So theoretically if one was a master builder and built a gasifier unit perfectly sized for the engine in use I’m wondering what the horsepower drop of the engine will be.

If one had an absolute abundance of high grade wood gas stored in a tank or something (I know to never do this it is a very bad idea, just speaking hypothetically) and you feed an engine with it we know that we will never achieve the horsepower achievable with gasoline. I’m simply curious if anyone knows the difference in power between Woodgas and chargas, if there even is a difference at all.

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I’ve seen people mention that charcoal has high energy density but I’m curious if in the real world that translates to high engine horsepower, or maybe not? Maybe the chargas will make less horsepower than wood gas, but maybe with a water drip added it might bring the two closer to the same? Maybe somebody on the thread has done enough tinkering with all the different systems that they have a good guess on the matter.

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I can only speak for the charcoal gasifiers that i have built and used and run stationary generator engines with , but a stock engine with no timing advance and no indexing of spark plug or any other mod , running on a charcoal gasifier with no egr or water drip then expect to see somewhere around the 40% of the full output compared to petrol , once you start tweaking you can improve that with ignition advance and water drip , indexing spark plug and increasing compression .


That 25-40% power drop figure is a bit deceaveing. Engines are rated on max rpm so if a engine has 100hp on 7000rpm it is insane to belive it can produce 75hp on woodgas just because with woodgas its max power will be (depending on the engine) at about half the max rpm so say 3500 on the same engine. Even thugh woodgas does burn more efficiently thain petrol btu per btu you still expect at least a 50% power drop just based on crude math! Then we come to the fact woodgas is less energy dense and the figure just dives.

But those numbers are irelevant! You never drive on 7000rpm on petrol and you never use all 100hp anyway. In reality you usualy drive with about quarter throttle on petrol and you allso use about the same amout of hp on petrol and woodgas WILL give you a 25-40% power drop of THAT. Its just reality, woodgas trucks arent racecars.

Dave is being honest. Achiveing 50% of petrol power on a stationary engine with stable rpm and ideal conditions for woodgas, unless you go deep in engine modifying, is a goodresault.

But like l sayd, numbers dont matter much!

So, you see unfortunaly it isnt possible to give you exact percentiges of power loss you ask for. But l can tell you a badly operating wood gasifier is the worse powerwise. A pure charcoal gasifier is next, followed with a good operating wood gasifier. Finaly, the best of them all is a water drip charcoal gasifier, prefferably a downdraft. If you look for power, the later is the best way to go realy, because squeezeing power out of a gasifier means over drawing it. A wood gasifier quickly burns out itscharcoal reserve and nasty things haplen. A charcoal gasifier is way less prone to this as it hasnt got to make charcoal by its self in the first place.

Hope this helps and doesent turn you off off woodgas.


What Kristijan said.
I just want to add that the power loss has a lot to do with what type of engine you’re using.
The geometry of the combustion chambers, intake manifold and compression ratio are important factors. Old low compression flat heads and side valve motors are probably the worst. Modern mpfi engines seems to accept woodgas fairly well.

Also, keep in mind power has a lot to do with what amount of oxygen is present during combustion. When running gasoline only a microscopic amount of fuel occupies the cylinder - the rest is air. Woodgas, on the other hand, takes up half that space. Also, pulling hard on a gasifier makes for even less cylinder filling.

I’m actually surpriced we get the results we do. Adding less than half the fuel, less energy denst and slow burning, drawn in under high vacuum and with the extra weight of a gasifier, it’s a miracle we can keep up with traffic :smile:


They tested coal briquettes during the war, and the results were almost as good as with gasoline, according to the book.
They could go twice as far as with firewood as well, was a little worse to light.
Has anyone tested it?


Yes JanA,
Modern era it is Francois Pal in France.
His Carbonite fuels.

Read down through at least post #10.
Steve Unruh


Hello JustinH.
It is the many Depends, Depends, Depends that all have been pointing out.

Horsepower ratings are very mathematical precise; and deceptive.
kW power ratings are just as deceptively bad.

I was thinking how to respond to your request.
And realized I have; have had, quite a few 7, 7.5 horsepower rated working engines.
At the top screamer RPM use range in my Stihl MS440 chainsaw.
At the other extreme in a 950 pound 1400cc 1000 RPM single cylinder made in India CS Lister clone engine.
In between much more practical a Kohler “K” flat head on a 70’s Troybuilt garden tiller. Operated 2500-3000 RPM.
A Chinese Jang Dong 250 pound 400cc single cylinder 2600 RPM diesel.
And a thourghly modern Briggs and Stratton OHV slant cylinder engine on the replacement garden tiller for the Troybuilt.
All have-been/could-have been, fueled on propane. With varying %'s of power-use set backs.
Have could-be fueled on wood or char gasses.
Giving completely different revised power usages versus their original designed-best-use fuel.

So . . . . 50% plus minus another 20%. Depends. Depends. Depends.
And that 50% + 20% will be gotten by an real working Operator-User.
Never by a math’s Johnny.
Steve Unruh


Hey Steve, thanks for the reply. Yeah I definitely understand how different engine setups, gasifier setups and operator habits can have huge effects. Looking back now I think I over complicated my original question a bit too much. I was really wondering which has more energy wood gas or char gas, but doing a bit more reading it’s obvious a good quality wood gas will have more power than a good quality char gas due to more volatiles being present.

However does using a water drip system improve the energy output of a charcoal gasifier quite noticeably? Will it also have an effect on charcoal consumption?

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KristijanL answered this from his own users experiences in his post.

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Oh geez, it’s 4 in the morning here and I just realized I missed about 3 replies! Sorry Steve


I’m piling on to Kristijan’s explanation. It depends on what you expect the engine to accomplish. The actual work being done by a engine is accomplished by rotating a shaft. This is torque. Maximum torque is always accomplished at about half of maximum horsepower. If you look at a dyno read out, the strongest engine is going to produce about as much torque as horsepower and it will do it at a much lower RPM. Horsepower will rise with RPM but it’s main function at least in my way of thinking, is to maintain a flat line torque output despite increasing losses due to friction and losses in the valve train. When you talk about power in say a tractor engine, gas or diesel, the actual horsepower is no measure of the ability for the machine to perform. That is strictly a result of torque. The question is always what specifically do you want an engine to do.


Not at all. Gas composition of a good wood gasifier operating perfectly and a good charcoal gasifier with water reducing ability (water injection) will be roughly the same. As will be the caloric value! BUT! the catch with wood is you never know what you got in your woodpile. Size, fractures, moisture… Not 2 bags of wood are the same, the wood doesent char the same in a wood gasifier every second… But charcoal is preety much the same all around the world. If a certain amount of water is found to be ideal for a ceetain gasifier, it will run perfectly every time and without fail, as long as prortional amount of water to charcoal is metered. Not hard to do on a downdraft charcoal gasifier.

In adition, the wood gasifier is usualy more restrictive. You got a restriction, restrictive air jets, grate… So, if you got a wood gasifier and a char gasifier both making identical gas, acharcoal gasifier will generaly give you better performance.


Wheew!, that would be a lot of work. I would imagine that a team of 6 smart, energetic, young people might be able to do something like that in 5 years. I don’t think such an effort has ever been made.

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Koen Van Looken has a video on here. He has a charcoal gasifier running and sprays a water hose near the intake. it draws a little mist into the gasifier. You can hear the engine rev up and start running smoother. Sorry I didn’t have enough time to find the video, but it’s a good visual. Edit here is a link to the video…


Ive built direct raw fuel machines professionally for nearly a decade and have fully switch to charcoal system.

A down draft charcoal gasifier with water drip and everything running at optimum will produce more power than a direct wood gasifier. However, you still need to factor 50% de rating as wood gas in any configuration will never ever be a static output. You need to factor in oscillating flows and energy density.


Thanks for the replies everyone!

Tom, I definitely see what you are saying there, but I have to point out my one disagreement. I’m a heavy equipment mechanic by trade so we actually had to learn about this when I went to school. You said horsepower is not a measure of a machines ability to do work, this is not right, that is exactly what horsepower is. Horsepower is a calculation of work completed in a specific time. There is actually a formula for it, torque x rpm / 5252. Now we actually know that one horsepower is not actually equivalent to the power of one horse, but rather it was there best guess at the time. It’s measured by the ability for a (engine, person, motor, water wheel) to move 550lbs one foot in one second, and any variant thereof (more weight, faster speed, farther distance) will have an effect on that number.

Like you said most engines will produce full torque around half rpm rating, the actually reason for this is because at half rpm the engine is actually at its best “breathing” speed. The faster you rev an engine after the full torque speed, the engine cannot actually suck in the equivalent amount of air, sure it may be close, but at that specific rpm because of aerodynamics within the engine, drags and a bunch of other things some very smart people figured out, that max torque rpm actually gets more air in the cylinder per cycle or revolution than at a higher rpm. It also has to do with how quickly and effectively the combustion and expansion of the gases can take place. The engine needs adequate time for that expansion to take place to extract a good working pressure during the power stroke, and that expansion we want captured between 0 and 90 degrees crank throw, which is where the greatest force will be able to be properly utilized. As engine speed increases after the full torque speed it loses its ability to extract the most potential from the combustion process due to the shorter period of time given to do that at a higher speed, which will result in a lower torque figure. Remember torque is just a pushing or pulling force on a rotating lever.

As you pointed out also, your horsepower as viewed on a dyno graph will continue to climb, and especially for a gas engine the max hp rating will usually fall somewhere in the top of its rpm limit. Now because horsepower is a measure of work done within a specific time, our torque may drop, but as rpm increases we can still in fact achieve more work completed due to the rise in rotational speed. Eventually as you will see in the same dyno graphs the horsepower will once again begin to fall off if engine speed increases from there, because at a certain point that continuing drop in torque is going to have an affect on how much work we can complete.

Horsepower may seem like a very abstract idea, but it is very much in fact measurable. The one thing I found interesting when I was completing my schooling is when we learned that horsepower cannot be changed by means of gearing, pulleys, or multipliers. That’s because total work done will always remain the same (assuming constant horsepower output, better example of this would be an electric motor). Torque and speed can be changed with gears, but at the end of the day those have to change together, torque down equals speed up, and vice versa. So no matter what you do with transmissions and gearboxes those two numbers in our equation will not differ. We either produce ample torque at a slow speed, or little torque at a high speed, but the amount of work completed will be equivalent. If you have the right gearing system you could make a 500hp engine have so little torque that it couldn’t turn a door handle, but with no load the end shaft would be turning millions of rpms. This is the same way you could stack up enough gears to make a 5hp Honda put out 500,000 lb/ft of torque, but the end shaft will take 9.5 million years to make one revolution, so at the end of the day even though you’ve made 500,000 lb/ft of torque you still only have 5hp, that number cannot be changed. What’s that old saying, give me a long enough lever and I could turn the earth itself?

One of my instructors actually put it very well, he said imagine you have 6 foot wrench, you can put it on a bolt and put as much effort as you want to pull on that wrench. You could pull on it, putting 500 lb/ft of torque on the bolt, but if that bolt doesn’t move, you didn’t put out any horsepower. If it moves slightly, you put out horsepower, you have done work. That’s because in our formula, anything multiplied by or divided by 0, is zero. So zero turning speed means 0 horsepower. In the same way, if a hydraulic motor is stalled so it won’t turn, sure it’s putting out mountains of torque, but it’s jot putting out any horsepower because it isn’t accomplishing any work.

On but off topic, I’ve worked on diesel electric mining dump trucks that, in a manner of speaking, have an onboard dyno. At a standstill you can press a button and tell the truck to load up the generator with the resistor grids used for dynamic braking, and at rated speed the computer will calculate the rpm, current and voltage and give you a live reading of how much horsepower the engine is putting out. It’s very cool and makes trouble shooting a low power engine much easier. It’s also cool to see how much power a Diesel engine makes when it’s cold vs operating temp. From a cold run you can actually lose (on those big engines) up to 500 hp just by the engine being cold, and as it warms up you can see the hp slowly increasing until it eventually reaches its rated output.

Anyhow sorry for the long rant, but I absolutely love this kind of stuff and find it fascinating so I tend to go a little overboard.


I’m trying to compare this to electric in some ways it makes sense to me in others I’m going to have to think some more. 6 foot wrench equals a gearbox on a electric motor so torgue equals max amps until magic smoke gets out of motor??

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