I think power gain is small from bone dry wood and preheat. In theory we should be able to maybe increase H2 some and step up a notch on the restriction, but probably not much extra power.
The big advantage would be turndown ratio and less risk of tar making.
For more power remains probably only a free flowing system and a big engine, unless you’re willing to experiment with higher compression or positive system pressure (turbo).
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I found that too, what JO sayd.
Modifications like air preheat, hearth geometry optimisation etc do help power some, but mainly they help idling, takeoff ability, startup time, tar safety, fuel economy…
If you want to increase power, first step is increase compression ratio. This is about the only thing that realy does make a difference. Its not a step, its a huge jump in performance, but not many want to get to that kinda project…
When l ground down my Škodas head down from l think 8.5/1 to about close to 12/1, the max speed on woodgas went from 70 to 90km/h. Since the power/speed graph is not linear, this means l probably gained close to 40% power, same gasifier, same engine…
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Yes if I pull to hard I can tell I am going to have to fill up on wood a lot sooner. My Charcoal reserve ends up in the bottom of the gasifier and is replced quickly. It is somestimes better to just blend in some gasoline to save on wood. But I usually don’t. As long as I keep my temperatures in the operating range zone. I go for it and try to drive only on wood. I always try to keep up with the highway speeds.
Here is what I did in rebuilding the gasifier is this I built it for a larger engine in design and then restricted down to my engine size in the firetube restriction area. What really keeps it from over pulling is at the auto mixer is the intake gas opening is 1 7/8" this limits the amount of gases that can be pull into the intake. I have now added a manual extra gas intake pipe into the mixer. When open this a lot more wood gas is now entering into the engine and more power. I have noticed a increase in temperature at the grate. So over building the gasifier to me is better to a point.
Bob
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I will slightly complicate this discussion, if we were able to preheat the fresh air to a temperature of 700°C before the hollow part of the fire tube enters, it would minimally take away energy from the hot zone, if the remaining energy of the output gas was used to heat the pyrolysis gases and water vapor, which enters the hot zone and finally, if the rest of the energy were used to dry the wood, we would get a very strong gas, think about it, very little coal would be used to maintain a high temperature and this energy would break water vapor into hydrogen and form methane from tar gases. When I compare an engine with a low compression and an engine with a high one, there is an obvious difference in the temperature of the exhaust gases, the engine with a high compression has a significantly cooler exhaust, because it redirects the energy to work and thus develops more power, well, it is similar with the gasifier, if we manage to remove the heat from return the resulting gas to the process, the gas will be cold and strong.
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Hi Cody, i just saw you mentioned my truck: it runs pretty good uphill, with good wood 60-70% birch, the rest conifer, it takes most hills around 100km/h which is pretty much the best cruising speed, can go faster on plane road, but burns out the charbed.
I haven’t tried it on Jan’s and Jo’s Dalarna-hills though 
(my Volvo climbed some of them hills in only 55-60 km/h, when driving to Swedish woodgas meet)
The truck i let “rest” some when lot’s of hills, due to it’s tendencies to burn out the charbed after restriction.
I believe this results are much due to the big 400cui engine, strong, much low end torque, the truck actually runs better on wood than with the original engine 6,2liter diesel.
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This is why you want the hot incoming air through the nozzles as it hits the Charcoal the heat is directed upwards too into the hopper for better pyrolysis of the wood and froming moisture and tars.
This is why some gasifiers have the nozzles angled pointing slightly upwards to cause more heat into the hopper.
Bob
Thank you Göran, then I know it is possible, must try to understand what you have done.
Can’t you @JO_Olsson , @Bobmac, @JocundJake and @Wayne drive 60 mph on the hills with your cars?
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Normally a tricky question Jan, since we have no idea what hill you’re talking about. But in this case it’s an easy one for me, because 60 is not far from my flat road top speed at 65-70 I doubt the Volvo would even manage 60 on 100% gasoline up the hill towards Falun
Edit: Yeah, -20 here also. No playing but indoors today.
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Oh, I tried to explain it before, taking it again
Several questions (bored when it’s so cold) can you maintain 60mph on a 3-4% uphill which is around 0.15miles on just wood gas?
No, I can not. Probably down to 50 mph.
60 mph is probably a little higher than what I will be able to do on basic rolling hills. and obviously much slower on the mountains. I would say on most of my area I run about 50-55. but I also tend to be a purest. I have a really hard time turning on gasoline even on the big long hills. Also a lot of my driving is hauling loads so that slows me down some.
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Good morning Jan .
Like the others have said . Depends on how steep the hill is.
Often we drive to Argos Indiana which is 600 miles and we make the trip in 12 hours . This includes rest stops , meals ,refueling and pulling a small trailer.
Below is Bobmac truck over our local mountain .
On upgrade it held 60+ and went to 90 on the down grade .
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Driving 60 mph on a hill? 6% grade more like 55 mph on a long drive up the hill. With a full load of bagged wood in back. No hybred or gasoline mixed in. A 4% grade yes 60 mph wood only. But burning lots of wood and slipping lots of charcoal because of the high vaccum pull 30 plus or more on the gasifier grate area. On a 2% grade hill 65 mph. High vacuum pulling on the gasifier. On the flat land 70 mph plus. Remember we are using V-8 engines with more horsepower. With our advancing on the timing to around 38°.
Bob
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hey Bob did you and Jacob run over Vantage on your way through to Idaho? If so how was that on wood power that’s a hell of a long knarly grade. I have been in a half ton v8 dodge that took out a transmission on that grade pulling a car trailer loaded with fire wood, a 4 cylinder Honda that popped a head gasket, and a 32" U-Haul diesel with a bad turbo boot with the contents of a entire house in it. That was a long haul 15mph up that hill with the flashers on
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Thanks for all the replies, it was very interesting to hear how your cars actually do on the slopes.
I have one more question for @JocundJake , how much restriction do you have in your car?
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Goran, this is an interesting statement, well, let me give some data about the characteristics of a diesel engine, an average diesel engine achieves a torque of approx. 50Nm per liter of working volume and thus develops 10 kW of power at 2000 revolutions/minute. Can we achieve this with the same size wood gas engine? In order to be able to answer this, it is necessary to look at the chemical composition of oil (C12 H23) and wood gas (CO, H2, CH4, N2). Hmm, it will be difficult, because nitrogen must be reduced to a minimum, and the proportion of H2 and CH4 should be increased a lot. Some time ago I announced that I would do a load test with the generator on the Bertolini lawnmower, but there was no time for that yet (engine 490 cc, power at 2000 rpm ???).
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I think I am running a 7.5 inch but it might be 8 inch. I haven’t had it out since I built it so I don’t remember for sure. I am running a V8 like Wayne.
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Hi Tone, i probably did a bad comparison, my truck had a 6.2 liter diesel v8 when i got it, i changed that out for the 6.6 liter gasoline v8,
The original diesel had 135hp, and are no speed-demon, can be experienced as somewhat “sluggish”, i put in the 6.6liter v8, 260hp on gasoline, it feels to really like woodgas, probably therefore i experience it more “lively”. 
At the time i changed engine i was a little lazy, seemed to be much work to adapt the diesel for woodgas, today i maybe had tried.
Interesting fact: GM made a 5.7 liter diesel (Oldsmobile) that was no wonder of reliability, got a very bad reputation. It was somewhat based on a gasoline engine, the Finn’s has managed to adapt the heads from Oldsmobile 350 (gasoline, “sister engine”) with double headgaskets it becomes a 14,5:1 compression, very sturdy woodgas engine. As i understand it the diesel has a vacuum pump where distributor normally goes, no trouble to “put back” a distributor. This is something i should want to learn more about (i even has spotted a used 5.7 diesel, maybe for sale)
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No we went over Blewett pass way. Yes the Vantage grade 9 miles to the top, and climbing up all the way 6% more grade.
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