Cooling rail sizing

Good info on the vertical cooling rack Max. I am convinced this is the way I need to go in my climate {zone 3a}. My question is is there a minimum height of the cooler tubes you recommend? I have a cooler I built from what I had at the time not having an application. I am thinking of cutting it in half height ways. This would leave me with 2’ tubes and a 5" header both top and bottom. Would this be tall enough to condense well?

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The motor tells how much cooling area it needs.

You have to calculate the internal flowing area big enough to keep the gasflow from ripping condense drops upward. This way the condense lands in the bottom part and can be collected successfully.

The gasflow is = L X n X 3 liters per second, if the motor’s displacement is given in liters.

If the flow velocity is kept below ~3m/s it will not rip the condense upward.

1m/s = 3,28084’/s



Thanks Max not sure I am understanding ,in your formula “Lx Nx3l/s” does N =RPM x.5? I am Looking at a 7.4 liter engine running at up to 2500 rpm’s if I use this cooler I will have 18 2"verticle risers. This will be my primary cooler. During the summer months I will add more cooling modules as needed and a below bed condensate tank Not meaning to jack Andy’s thread but since coolers was the topic here it looked like a good place to ask.

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OK, Jim!
My bad writing generated a misinterpretation:
Fundamentally … L X n X 3 … is the formula for gas consumption expressed as l/s, when you know the motor’s displacement in liters and working RPM with WOT (wide open throttle) under load.
The RPM is written into the formula as a count of thousands RPM! (1000 RPM = 1) (2000 RPM = 2, etc)

L = liters displacement
n = thousands of RPM
3 = the aritmethical sum of all nonchangeing factors

L X n X 0,5 = gives cooler area in square meters.

7,4 X 2,5 X 3 = 55,5 liter/s net gas

7,4 X 2,5 X 0,5 m2 = 9,25 m2 (grand!)

Preferably you start an own “page” so Andy can use his page for his purposes?

If you follow Marvin, you put the condens bucket near the gasifier to keep it from freezing (on the flatbed).

Hopefully Chris can assist?

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Ok Max I guess maybe I am also way off base on my rpms as well. I am guessing that I will have a cruise RPM not to exceed 2500 rpm. I have no idea of WOT under load. I would like to think I will never need to go WOT. MY engine and trans were harvested from a 20,000 lb plus motorhome and planted in a truck with a max GVW of 8,000 lbs. It has 4.1 to 1 final drive ratio and a nearly 30% OD, so a similar truck to Mr Wayne’s v10 but probably 1,000 pounds or more less than his. If I am able to use OD it will run less than 2000 rpms at highway speeds. I seldom drive on highways if there is another route. I was thinking it may be beneficial to build the cooler in modules to be added and removed depending on season. Our temps here range from -40-100F. I will try to get some updated pics up on my thread titled Jim’s junk. Thank you for your help.

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Think of this: The gasoline line on a gasoline driven vehicle is not discriminating flow above cruising needs!
How would that feel???

Why should you start discriminating the flow for acceleration, hill climbing, load hauling on bad terrain, etc…

When preparing for the maximum need, then you have it when needed. Especially, when the woodgas is already cutting ~40% of what would be awailable with gasoline (unrestricted).

In winter, when day-frost prevails, ~1/3 of the summer cooling area can be enough for satisfying operation. With deep frost, even this may need a “draft restricting tarp” over it for regulating the cooling effect as needed.

1/3 can be arranged between the cabin and the “gasification barrels”, and the rest 2/3 on the sides of the flatbed in the summer, or when day-frost is gone.

Now this third (1/3), operated in winter circumstancies, needs to have counterflow for the condense.
You put the condense cistern directly after the heatexchanger near the side of the gasifier.
Here it can stay warm. It will get enough cooling from the backflowing cool condensate constantly flowing down from the cooler.

The gas from the cistern enters the bottom of the cooler. From the top of the cooler it goes to the bottom of the (hay)filter.
Then, as wet it is for a drying mantel on the heatexchanger, then it can be delivered to the motor warm and DRY!

In the summer, the sides (each 1/3) are attached to the center part of the cooler, parallelling upper, respectively the lower parts. See to it, that the lower collectors have downflow to the center low part!

PS: Thank you Chris!


Max I,m not looking to discriminate fuel flow. I was just stating that I don’t think I will be driving at WOT for any period of time, Maybe I am wrong. Is it common to drive at WOT while driving on wood? I have never driven on wood other than my riding lawnmower and yes that was at WOT just like on gasoline. Much equipment dose , pickups I don’t think. Please don’t think I want to cut corners I do not by any means.

Here is a pic. The black on the right is the hx/ drop box. Under it you see a hole in the floor and white below. That is the summer condensate tank. The black one on the left is the winter tank which will be used year round. and drain through the summer tank. The winter tank is between the gasifire and front of box and directly below the front cooling rack, winter third yes . This brings us back to my original question, If I have 18 2"diamater risers in this section of cooler but they are only two foot high with another 8" of top and bottom headers. Do you think that that is enough height for the steam to condense back out.
I will try to get better and more pics up. I am computer and phone stupid to begin with and now both are new and don’t play well togather

If you’re trying to get anywhere… :grin:

It depends on the vehicle and the road. Any kind of a hill, likely WOT. Weak gas and trying to accelerate, WOT. And so on.

If there’s much restriction from the gasifier, it will act like a part closed throttle. So there may not be much difference in half and full throttle, under some conditions.

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Put a smile on my face… I remember in the 80’s driving the binder with the MEN gasifier. Twist grip throttle on shifter locked at WOT and just sit back a watch the scenery slowly go by. I need to find a M37 and join the Dodge family… :wink:

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I knew we would be down on power but had no idea it takes WOT to get anywhere. Wayne took me for a ride in Argos 2 years ago and his truck accelerated from 40 to 70 faster than my 69 Chevy does on gasoline . He punched i,t it droped 2 gears, tach to 4 grand and we were gone. I was impressed enough to go get me one of them little Dodges

Sure… it accelerates very well at WOT. You should see it on gasoline… :open_mouth:

Most of the time cruising you’ll be at part throttle. Hills and acceleration do need full throttle, in my experience. Again depends on the vehicle and the road.

You can simulate woodgas acceleration by putting a 2x4 under your gas pedal.


Not putting words in Max’x mouth but I believe he is saying " design for the worst situation and you will be in good shape in less than worst situation." I have a heavy truck and little engine so I run flat out ( I mean WOT) most of the time. The guys with the little trucks and big engines ---- look back at how much conversation there is about “Hybrid” driving.TomC


F150 302V8. 5000 lbs plus me and whatever fuel I throw in I’m at 3/4 to WOT 95% of the time
Your mileage may vary


I have not driven a singel meter on woodgas (yet) but I am curious if have missed something here.
What has power to do with if you are a bit low on cooling area (rails)? Would that not only mean more condensate will appear later in the system (hay filter). As long as the gas is cool and dry when it enters the engine one should be fine, right?

@JO_Olsson I’m guessing that it’s assumed that of your cooling rails are too small to give cooling, then they are too small to give flow/breathing to the gas for high-end needs (pulling a load up a hill or whatnot).

Hello JO. Long time no talk. I believe Max is talking about cooling all the way from the gasifier to the engine. Pulling hard on the engine ( WOT) creates more heat and you have to have more surface to cool it — be that surface in a traditional Imbert type cooler / filter or cooling rails, but it includes the piping to the engine and possibly the heat exchanger and hay filter— the entire system is figured in.
Yes as long as the gas is cool and dry it should be fine. BUT, I like to heat my gas back up just a little to get it to hold any moisture that I didn’t get out in the previous part of the systemTomC


Thank you, Brian and Tom !
Reading posts again, now when I’m no longer in a hurry, I realise I reacted to something that isn’t there.


Hi, Jim!
Your 18 pcs. 2" diameter, 2’ long tubes represents slightly less than 19% of the estimated summertime total cooling surface.

It might suffice in VERY cold circumstances, but the hard problems come AFTER that deep cooling; the cooling continues “without asking permission” making ice-pellets and ice-grain in the following passages.

So, before or at least after the INSULATED (hay)filter you have to reheat the gas substantially in a welded-on mantel welded on the heatexchanger!

IF you reheat the gas before the (hay)filter, you will re-boil most of the latent water bound in the filter material and on the bottom!
That is NOTHING a motor wants to start on, or run on if force-started on gasoline… and steam-bathing!

This is the only way to deliver warm and dry gas to the motor, through an INSULATED tube to the motor.



Thank you for the clarification on throttle position while driving Chris, seems the truck will outrun the gasfire . I get it, being the fuel is now a gas and rather than liquid. The passages not large enough to fill cylinders completely. Max, thank you for your help here. I will set this cooler aside for another purpose. It seems all this insulation on tanks and plumbing must be seasonal or I will need 200, of pipe. My reheat mantel, could this be on my 3 1/2 " pipe from heat exchanger to condensate tank. Probably better to make another heat exchanger here . Hot gasses to the outside ,cooled gas reheated to the center?

Hi, Jim!
Now, it is easy to give bad suggestions on wrong assumptions, before your general and detailed pictures are available…
Don’t rip off the cooler yet; at least not before photoing and allowing some tests; results are valuable now when it’s cold.
The reheating of the cooled gas may need a bigger heatexchanger area on a hotter surface… if one gets too much reheat, it is easily “diluted” with a parallel cold flow tube with a regulating flap, joining and mixing back into the hot flow after the heater.

But, pictures puts one on “safer ground” for suggestions…


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