Compression Ratio

Hi Guys,

I was wondering if anyone has stepped up the CR on a wood gas engine.

Peter C.

That’s my pet project, actually. I have read that it will tolerate a 17:1 ratio, and it seems like you could dual-fuel with ethanol, CNG or race fuel, especially if it were only on low RPM startups. Actually we need a good hot-rod guy like you to work out the engine performance issues. Basically our solution thus far is to add cubes - a V8 Dakota shortbed is no slouch. But hitting up the CR would add a lot, methinks. I’d really like to try it.

What do you have in mind?

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Count me out!!

I want to keep my drivers license.

For sake of discussion, let’s talk about an early stock, carburetor style GM 350 ci. engine. If the engine was at 8.5 to 1, how much timing would it tolerate on wood gas @ WOT under full load condition? (assume 5000 lb vehicle)

Wayne, in your case, never mind CR, we would have to put my hemi in your Dakota & send you back to Bonneville!! Problem is, you will need a gasser the size of your entire truck! ------------- lots of barrels


It’s hard to say for sure, but I know I usually advance the timing about one post forward, believe that’s about 22 degrees above standard? Seems to work good.

It wont knock on woodgas for a long ways, I’ve never had it high enough to knock. But the extra power you get is diminished above the 22 degree setting. And if I switch to gas I have to be sure to bring it back down or it rattles hard. With a blend of the two I can leave it up. Also it’s up far enough to make the starter bind a little, so I start it with the time down and push it up once I get it switched over. Computers take care of this automatically, although Wayne has a manual advance on his dizzy to move the range the computer will operate in. The V10 is distributorless and works very well. But it’s hard to say where the time is set on the road. Is there a scan tool that can read timing advance?

Chris, Is the power increase marginal, moderate or huge when you crank in the 22 degrees? Does the WG have an adverse effect on aluminum heads & intake manifold? What engine are you running? Do you start your engine on gasoline or WG.?

Power increase is marginal to moderate, I can tell that it helps some but it runs well at the stock timing as well. The gas is slightly acidic and will corrode aluminum over time, but this hasn’t been a big problem for Wayne yet. I’m running a 318 Dodge D250, non-Magnum. Cranks on gasoline and always has an idle feed from the carby but sees little vacuum in most conditions, so I can safely say I’m running 99.99% woodgas. Running dual throttles, one under the carb. Read all about the project here:

For the GM motor heads out there the chevy 400 cid small block, with flat top pistons and 74 cc heads will net you about 12.25 to 1 with a good cam this may get 300 plus HP on wood gas.


Sounds to me like pistons, heads, intake,ignition & cam change would prove to be an interesting experiment. I am wondering if in fact performance would improve and at the same time lower wood consumption. Would be very interesting to install a Race Pac (data acquisition system) on both engine and gasser. I am looking forward to this part of the project. I think i will have much less trouble doing this than learning gasification. Well, for now i just have to just crawl along.


In the late 80s we ran 42 degrees (btdc) full in at 5800 rpms on our sb race engines. this was at 12 to 1 comp
with 104 octane leaded gas.


In the late 60s & early 70s we ran big block Chev’s in T - buckets @ 12.5 to 1 on pump gas. (260 Sunoco) Good old days!! Not knowing anything about WG, i am trying to compare it to something i that am familiar with. From the information i have so far, it sounds like an alcohol engine with too low compression & not enough timing – lazy & down on power. Very cool to think of the possibilities if in fact WG wanted a similar tune up as alky.

That’s the way I see it. A alky motor would get the lost 25% back and maybe then some.

ya sounds like a situation similar to alcohol, also consider that alky has less btu’s than gasoline so a motor set up for alcohol might be a good starting point. was just pondering this the other day considering e85 uses 30% or so more fuel for the same HP. HMMM maybe we need to put a cam ground for alohol in some ones gasser.

hot rod power tour rolled into town today, got to watch for a few hours before trudging off to work :frowning:

From what I’ve read alcohol will tolerate a 14:1 ratio, which is close to the limit for woodgas (17:1). If you went 14:1 you should have no trouble getting “starting fluid” as E85 becomes more popular. There’s 3 stations within 30 miles of me.

As far as “optimal power” you’d have to do a lot of testing to be sure. I have heard conflicting reports on “slow burning gas” and “3,000 RPM limit”, and then Sean French takes it to 5,500 and holds it there on the highway. The hydrogen is thought to burn faster and the CO burns slower? So depending on the makeup of the gas you will get different flame qualities.

Another factor has got to be the air/fuel ratio. We are blessed to have a wide range of acceptable mixtures, and so mixing is done by hand. But if you’re optimizing already. I’d go for an O2 feedback system to automatically control the mixture. Alternatively, Dutch John has used a pressure equalizing valve to make sure the engine gets a balanced pull on the air and woodgas, he sets the mixture once and the valve takes care of the fine tuning. I don’t know if he’s running any sort of feedback though.

I have seen E85 in a few places like on a lawnmower i i just bought telling me i can’t use it… what the heck is it? fuel made from corn??

Just an fyi, I know i can spin up our little gen set to well over 4000 rpm on wood gas with out any changes to the 8hp briggs at all.


My reference to “alky” or alcohol is referring to pure methanol. E85 is ethanol & gas. E85 is not available out here, wish it was. From what i understand, drag racers are building purpose built E85 engines with outstanding results. On a methanol engine, air fuel ratio is roughly 6 to 1 — vs 12 to 1 on gasoline. (race tune up) This is why a gasoline engine will tend to go lean when ethanol is added to gas. Very noticeable in small engines, i have been told. Has anyone played with the mixing valve with the timing kicked up? Any or no difference? Any information on WG performance would be appreciated, i can see a plan coming together!!

Doc Reed talks about using several methods in his handbook for biomass engine conversions. They work very well and they aren’t expensive. There are several ways to squeeze more power out of these things.


Could you post some of these methods? Have you tried any? Would like to hear the results.