Hello Nel, let me share some of my experiences with increasing the compression ratio on my engines. Why a higher compression ratio? Physics “says” that combustion efficiency depends on the highest temperature (pressure) in this stroke, against the temperature (pressure) when the exhaust valve opens. This actually happens, I have witnessed it in all conversions, I can best describe it on the example of my Subaru, where I raised the CR to 1:13. The torque has grown significantly and so has the final power, it overcomes road gradients in one gear higher, fuel consumption is reduced by approx. 10%. I should add that high compression requires good sealing of the valves and piston rings, otherwise there is no progress, so it is good to add a little lubricating oil to the intake manifold, especially if you use propane (like me). The bottom line is that you mostly drive with less than half of the available power, so in this case the CR is much less than 1:13, maybe 1:8, but much higher than with the factory engine
Hello Tone, Thankyou for your comments. So what do you have to do to a Subaru to get it up to 13:1? It was quite a challenge on the ones I did. My experience was almost the opposite to what you described. My vehicle lost heaps of torque, driving into a carpark became a pain shuffling around at idle, my fuel economy dropped a good 10% and highway power at 3000 rpm was noticeably less. Did you do any other modifications at the same time? It seems strange, i have known people who fall in love with “crate Motors” after trying high compression, I owned a dedicated propane Ford for a while and got lots of feedback from other unhappy owners compared to those who were very happy doing propane on the standard lower compression unleaded motors and I got feedback from another two guys who “de-compressed” a GM V8 engine and a motorbike, both said lowering compression had been a great thing.
I certainly acknowledge that the normal thinking is your experience would be the expected outcome. No arguments there! It just is not my experience.
Yeah G’day Tom, I wish I knew a way attach the excel spreadsheet I mentioned. It is the 250 cubic inch ford motor from 1970 to 2013 that I was referring to a few posts ago!! ! They termed it the Barra in i think 2011! 43 years of basically the same motor…(although the stroke is slightly shorter on the latest motors). Not to denigrate the Barra at all my point was that they only got more power out of it by recording power at a higher RPM each model. Kinda funny to see it on a spreadsheet. I think i’m getting a bit deep on this subject and its going to just end with “agree to disagree”. A 1970 motor is such a pre-historic thing compared to the Barra and if they had to compare power at a lower speed there is not much improvement over 43 years. I have been disapointed so many times by believing I can add more power by all these different ideas. If 43 years doesn’t gain heaps of power then Im just saying don’t get excited by what a new exhaust will do! I am a slow learner cos I kept trying all these things.
Oh my…
My favorite subject…
Why and when higher CR would be better…
2 cents: reverse engineering, what mixture do you have/give into your engine ?
Easy tweak: camshaft overlap.
Depending your fuel / mixture, flame speed… you might need more overlap at higher CR with woodgas…
Youtube might be your friend
another 2 cents: the difference in woodgas mixtures, from one setup to another, might be as big as between petrol and gas…
Go with a WK design and a larger volume engine, never a bad choice…
With smaller engines, go with charcoal ( Gary Gilmore style )and liquid injection ( nozzle) , making an easy to tweak gas mixture…
If you want to build an engine, what are the specs of you fuel is the question…
3 best way’s into gasification: Wayne Keith, Gary Gilmore and listening to Steve U…
And of course, reading, listening to the experiences of the did / do builders…
Neil, was this the OHC version of the Ford inline six?
Did you account for the timing belt being out of sync when the head was shaved down?
Neil, I still drive this Subaru Forester 1999, it has an EJ20 engine. The factory cylinder head gaskets are 1.6 mm thick, I replaced them with metal ones of 0.6 mm and installed the heads from the EJ18 engine, which have a smaller combustion chamber, the math shows a CR of 1:13. Of course, I adjusted the tensioners of the toothed belt, so that both heads (box motor) are in phase alignment and the opening of the valves happens a few degrees later.
There is something in the connection that allows any engine to work well regardless of CR, that is a well-prepared mixture of fuel and air and, of course, a quality spark plug, such as NKG LPG1
Hi,
I want post up a brand new engines information video.
First though let me say I owned and operated for years both FORD I-6’s in 240 cid and 300 cid.
Operated different cars with the Chevrolet 250 cid I-6’s. But eight years longest heavy loaded operated the Chevrolet 292 I-6.
All American 1960’s originating conventional hydraulicly operated push rod two valve non-crossflow engines.
That 292 with a smaller bore than stroke, TALL high block, Long connecting rod engine would out-pull, out-work all of the others. Closest I ever got to 6=8.
But it is the bigger bore, shorted stoke, relatively short connecting rod Ford 300 cid/5.0L I-6 engine that did get hot-rodded up to 400-600 horsepower NA.
My current daily driver is a 2003 Toyota Camery 2003 2.4L 2AZ-FE engine.
Toyota’s next generation engine 2.5L was claiming 11% better efficiency, less carbons polluting by then using an offset cylinder centers to the crankshaft centers design. Ha! Yes. Minimum of three-four other changes then too.
View this listening carefully why most did go with offset cylinders by late 2000’s:
Note in particular the different piston speeds and longer time for the power stroke. That is one of the Atkinsons Cycle claims to fame.
Too many factors juggling (with irregular dumbbells) to be able to ever single factor truly isolate imho.
My four “cheats” I’ve evolved to use is really pissing off my older sister with her newer 2011 Camry that I get better milage in her old one, versus her new one.
S.U.
Thanks Koen, I am already well committed to the petersen gasifier…just spent a few hundred dollars getting the first set of plates cut. Do you have any views on the Petersen unit? The fuel mixture I used to give was easily adjustable, I used to sometimes do a run 600kms away. On this long drive I tried a few times to save fuel and leaned out the mixture (which is safe to do with vapor fuels and very, very dangerous with unleaded fuel). When it was lean I would need to use most of the throttle to do highway speed, when it was normal or rich very little throttle was required. BUT it always gave the same fuel economy…and about 10% less when running 13:1 CR. I have tried quite a few different camshafts…I have also been unimpressed and have lost any motivation for trying to achieve outcomes using camshaft variations. I would rather low compression than seek a camshaft to suit high compression. No matter what anyone says high compression COSTS power…the big question is whether extra power is made from a better combustion? Getting extra power out of a vapor fuel is a lot harder than from liquid fuels that MUST vaporise prior to combustion.
Thanks so much for the advice on vehicle choice, I am not committed to any vehicle yet and I am definitely trying to choose a vehicle with power to spare!
I feel quite uncomfortable making these comments because I am so new to woodgas, but I don’t see woodgas being any different to other fuels regarding CR. Everyone claims liquid fuel, propane, diesel and every type of fuel benefits from higher CR. Even when these are dispelled we can always wonder if woodgas is different??? we just like high CR!
Tone and SteveU’s India paper are the only two reputed cases I have heard that higher CR has worked, and I know plenty that have not worked.
I need to respond to Steve and read the document better from India, but so far the India paper mainly focusses on what ignition advance they can run at CR ratios above 10:1. Their power comparison are absent of a standard 9:1 CR motor and the power outputs given seem to be from diiferent sized engines!?
I was hoping it would be the same motor built at different CR for all to see the maximum power that can be achieved from each CR. That is what I did!
The India people put a lot of effort into establishing advance curves. In my experince this only matters when faced with pre-ignition due to high CR. A standard compression motor doesn’t get much attention to ignition for two reasons 1. Pre-ignition is far less likely 2.(The best bit is) small errors in timing make very little difference to performance. This is where lower CR might be really great with woodgas because a dose of low octance fuel won’t cause detonation and a dose of high octane fuel will still be happy.
Many thanks!!! neil
Hi Cody, No it was a version of the motor that evolved into the Barra, from 1980 to 1988, the range went to overhead camshaft about 1989. I have used a lot of camshafts, I even used a real stump puller that made a standard cam look like a racing cam, it ran out of puff at 3000rpm and gave great torque. In the last 13:1 motor I built I used a conventional mild sports cam. I actually had two of these 6 cylinder vehicles over about 15 years. I have never counted them up but pretty sure I put about 7 motors through those two machines over the years. Fuel economy was always my passion and it never really changed much despite what cam I was running.
I don’t know what 350 V8s are normal for you over there but a did a search on 1970 350 specs and I saw one that was making 375hp@ 6000rpm??? For all the messing around the manufacturers have done have they really made any improvements? And I would bet me left arm that the long runner intake manifold by itself is a 15 HP gain…so 15HP plus 375HP is 390HP@6000rpm.
Is there any noticeable improvement from Chevvy to justify all the stuff they do?? If chevvy can’t make noticeable improvements why should we strip motors and spend money having a go?
“There’s no substitute for cubes” if you double RPM then double the work can be done and double the HP is made, but to me that is irrelevant.
Im just asking cos ive wasted a lot of time and money! In hindsight the thing that really kills me is I later drove the ealier version pre-crossflow motor over a hill I used a lot! The torque those old motors had was better than the later motors (even tho they had less HP). I wish I had known to just build a good standard CR motor of the earlier pre-crossflow version (dunno tho what fuel economy would be). Torque they had came from smaller intake valves and smaller diamter ports…in 1970 they did two versions of that motor, peak torque was delivered at 1600 and 2200 rpm, very handy!!!.. the things we learn in hindsight!!!
Neil Wiese; respectfully; I have now become confused about what were your goals previously with modifying your propane converted Ford inline six cylinder engines?
Maximum power? If so, to what purpose?
Maximum loads and towing capability? In weights moved? In varying terrains travel time?
Maximum fuel use efficiency? In energy numbers? Or in least out of pocket fuel money spent?
My 55 years driving life experiences says you can only ever have two out of these three. And whenever a fellow focused down on just one the other two will suffer greatly.
Now working forwards to driving on woodgas? Yes? Your goal?
Still these same broad three routes to pursue.
You should sign up and join the Premium DOW side here. Better DOing it stories of fellows actually driving on woodgas having to had made these choices.
Mr Wayne evolved UP from woodgasing Ford’s biggest pick up truck 460 CID V-8’s to even larger engined Dodge V-10’s to get better loads moving abilities on woodgas. And towing not-fast, or long distances.
He then chassis and engine downsized from the big Ford pickup 460 CID V-8’s to smaller Dodge mid/compact pickup with smaller 5.2L V-8’s as his on woodgas drive-around, and long-distance traveler vehicles. He drives very fast and has the tickets (certified speed trials and Police) to prove it.
Him being at heart a Ford pickup guy he says; he said it was a bit tough accepting these necessities to get the results he needed.
Honestly out here on the General Discussion side most vehicle fellows are happy if their rig with drive in any fashion, NOT slaved away to one of the Pump-gods. Fuel Freedom. A whole different goal. What your Aus. Kurt Johanneson, and the the Bates? missionary couple were after.
Regards
Steve unruh
Hi Neil,
The point where as woodgas is a “different” fuel…
The amount of Fuelgas/nitrogen entering the engine, together with the air/oxygen for combustion
Woodgas is nearly always a high amount of nitrogen with “some” fuel gasses
This nitrogen dilutes the power potential of the total gas mixture.
Me, with charcoal gasifier, compensate with adding “stuff” in mixture with the charcoal to replace the amount of nitrogen in the fuel gas = different behavior of the combustion
key = the nitrogen in the mixture prevents a “hot” combustion, allowing an increase in the CR
I do run some engines at 17/1 without cooling problems, i did ran same engine on high grade biogas and overheating all the time…
it’s not black and white… nor easy or difficult…
if you can manage making consistent gas quality, then an engine can be “prepped” to run smooth and power full…
gasmixture, compression, = combustion speed = timing…
a car-gasifier have some disadvantage for perfect prepping an engine at max performance: the gas quality fluctuates with turndown-ratio and it is basically a batch process, where as the gas in not same in the beginning as in the end of the batch…
gasifier and engine = endless fun…
Hi Steve,
I only ever tried to optimize what I was driving. It is true that normally everything is a trade-off against the other. But many vowed that to increase CR was only a gain in all areas. This universal gain was supposed to apply to diesel, unleaded fuel and Propane. Propane was supposed to be the most obvious beneficiary of increasing CR because of it octane rating being at least 100!
In reality what I got was losses in everything torque, economy and highway power.
Over the years I have found three other cases where my same experience was experienced by others…meanwhile textbooks teach that increasing CR is a universal gain…
I hope I am not frustrating anyone. I have really enjoyed hearing Tones good experience and Koen’s to! I have learned lots of things and am open to maybe try higher CR using woodgas (but not at the start). These things i will face after i have learnt a lot more. I am aware using a gasifier is going to be a big learning curve for me so I need to keep making time to be building my petersen unit.
many thanks Steve!!!
For the record of one that has shaved the head of their cars, Joni aka Yevgen Kolyvan increased his compression ratio to a mathematically estimated 12:1 in his Opel Kadett. He had been driving it on woodgas before doing so and noticed gains.
He is in and from Ukraine so I think you’ll be hard pressed to get dyno results from him.
G’day Cody, Thanks for the additional testimony. I will definitely keep an open mind that increasing CR might be something i will do in the future (on woodgas only)!..For the record I never intended to say I knew CR increase doesn’t help with woodgas, im just sharing what happened to me…contrary to popular advice…and happy to do so the face of knowing most would say my results were unexpected, incorrect or worse. I will try to post the Ford 6 motor covering pre-emission 1970 to quite current. It is very interesting to see the power loss through the 80’s (emissions) and the recovery of performance through the nineties. And the real failure to gain much more power at comparable rpm from what was made in 1970.
Cheers, Neil
Welcome to this group of tinkerers, Neil. I agree with your dim view of unwarranted enthusiasm for ever higher compression ratios as though the law of diminishing returns does not apply to this facet of the internal combustion gem. You, Tone, Steve, Cody, etc. have an intuitive understanding of motion which most do not. It’s a gift from our Creator, like being able to play a musical instrument. You can close your eyes and see the engine running. Pick up a steam engineering textbook which was state-of-the-art 110 years ago. You will discover the “indicator card”, which mechanically recorded the instantaneous cylinder pressure through the cylinder’s stroke as a graph on a card. Like an engine EKG. We used to instrument diesel engine fuel injection lines at both ends with pressure transducers and trigger an oscilloscope from the crank to observe fuel pressure dynamically 40 years ago. If there is a transducer that can survive the conditions, a cylinder head could be instrumented this way. Those caps on Tone’s diesel would be the easy way to gain access to the combustion chamber. Anecdotal evidence shows that woodgas likes to run with plenty of advance. Obviously the ideal is to build pressure rapidly just after TDC without detonating the last pocket of the charge via spontaneous combustion ignited by heat, pressure, and hot spots. You have heard of BMEP, right? Brake (Prony brake, the old-fasioned dyno) Mean (average) Effective (the collective result of many factors in the always-changing volume) Pressure (confined gasses in the chamber). Now freeze-frame the high-speed camera’s film in your mind. See Instantaneous Effective Pressure. You can see that a very slow-burning mixture would just chase the moving piston on the power stroke, not imposing much force on it, giving poor torque. A steam engine is different - pre-pressurized gas crosses the slide valve into the chamber until it shuts, a point called steam cutoff, partially down the power stroke. Internal combustion has a batch of mixture to work with in the chamber for each cycle. The lopey idle that hot-rodders hear as BIG POWER is actually inconsistent batches caused by inconsistent charge dilution during a long valve overlap period at the exh/intake interchange at TDC. Wave action in both the intake and exhaust are only “on the pipe”, as 2-stroke tuners say, at one RPM, and this is dependent on the speed of sound, which varies with density, which varies with temperature. So the whole thing is a randomized mess. The power you feel as vehicle acceleration is the sum of thousands of batches processed. Tuning an engine to only run right at one very high RPM is only good for fun, not practical usage. Side note: We see the ram horns emblem on Dodge trucks. This evolved as a trademark. The original meaning was the ramcharger(R), long intake runners on a V-8 which had carburetters located over the opposite bank’s valve covers! These, tunnel rams, headers … all are efforts to take advantage of pipe organ theory to cause a reflected high-pressure wave (think of a Slinky(R) toy) to arrive at the intake valve just before the overlap period, giving a chamber-packing effect without paying for a supercharger. But, of course it only works at one RPM and at multiples of that RPM. So why is there an overlap period at all? To a large extent, there isn’t any in modern engines because it causes unburned hydrocarbons, …pollution. But the reason for it was to increase duration, to give more (area times time), in turn to deal with the reality of inertia in a spring-closed cam system operating the valve train at high RPM. You have to keep the follower on the cam’s return slope so the valve does not hammer the seat at closure. Ever-stronger springs cause other problems. The other end of ‘duration’ has an Atkinson effect on the intake stroke and a negative effect on BMEP on the tail end of the power stroke. Add it all up and at low RPM the cammed-up Rat motor makes less low-rpm torque than the showroom floor mouse motor. So the rodder puts 4:11 or higher gears out back and burns gasoline as if he owns the oil well. And the engine is only running right when the rig is going fast enough to get a big speeding ticket. So now the MFG’s hot-rod with variable valve timing and get the strong, flat torque curve we could only dream of 40 years ago. But the price is complexity and the potential for breakdown with age, and sensitivity to proper maintenance. It all boils down to this, and I think Steve would echo this, You Can’t Have Everything. A steam engine makes mountains of torque right from zero RPM and does not even need a starter, but then there is that huge, dangerous boiler that feeds it. About compression ratio: The John Deere 2-cylinders with their 5 1/2 to one compression ratio consistently held the fuel economy title year after year in the Nebraska tractor tests back in the 30s & 40s. Compression ratio is one of many factors, it is not the sole determinant of performance. Scavenging ratio is never spoken of but is more important. Charge dilution is important. EGR is intentional charge dilution. Unavoidable nitrogen in woodgas is charge dilution. Gas mixing during valve overlap is charge dilution. The proportion of chamber volume at TDC to that at BDC is held out as a magic number OMG it’s got a 13:1 CR - what a powerful engine - hear, hear!! How simple-minded. Put a compression tester on it and give me the PSI reading. Factor in your local barometric pressure to compute the pressure in absolute PSI or megapascals. That is what counts. Of course it changes with engine speed and charge density, and that’s the point of swapping cam profiles, header and intake lengths, superchargers, intercoolers etc. That’s all harmless fun, but there is also a place for practicality, and I vote for Tone’s Fergie to be second in the future DOW Hall of Fame, right after Wayne’s V-10 hauling that long trailer full of cattle. -RedOak from the “States” Edit: I meant 4.11:1 gears. Edit#2: The Atkinson effect occurs at the beginning of the compression stroke, defeating some of the prior intake stroke at low RPM. At high RPM, moving intake air column inertial begins to counter this. Organ pipe effect can also counter this at one narrow portion of RPM range. Hello peaky torque curve! Edit 3: Sorry, I should have proof-read this, it’s NOT ‘to arrive at the intake valve just before the overlap period’, but '‘to arrive at the intake valve at the end of intake valve duration’.
Mark, nice post. Today I drove the tractor on the open road, many climbs, where full power and torque are required. I listen to the engine, I change the gas/air ratio, I change the pre-ignition, well, Cr 1:16 at full power and warm engine causes slight detonations, but the engine still pulls nicely,… You state that the ignition immediately after TDC would give the best result, I think so too. If we want to make the best use of the hot gases during the combustion of the mixture and use this to push the piston, it is good if we start the ignition as late as possible, so minimal heat losses occur and the energy goes to work, well, the condition is fast and intense combustion, which is ensured by a high CR . If we compare the heat losses (and thus the pressure drop) that occur during ignition 30° before TDC with ignition 10° after TDC (assume that the exhaust valve opens 150° after TDC), these are inappropriately larger in the first case, 30% longer they “cool down” in the engine housing,… 
Tone, That makes sense. If a charge of woodgas + air has a high “octane rating”, and a need to pack molecules closer to propagate the flame front rapidly, then it would respond differently to high compression than does a charge of gasoline + air. I did not mean that ignition should occur at 0 degrees, but that peak pressure should ideally occur close to 0 degrees, if some negative effect elsewhere does not forbid it. Engineers at the major automakers have to avoid this because of Noise, Vibration, and Harshness restrictions. Even at idle speed, gasoline engines run best with 6 to 10 degrees of spark advance, as we all know. We can’t argue with success, so if Fergie is running well on woodgas using 16:1 compression ignition with current-modulated glow plug assist, that is ‘one small step for mankind’. At least for farm tractor usage. Of course we have no idea what your engine’s actual ignition timing is now. And this wild, freebird ignition might not be so good in a pickup truck in traffic. Too much turn-down ratio. Maybe someone will try it. I’m trying to find a low-cost way to instrument your engine to map combustion chamber pressure as a function of time or crankshaft position. No success yet. -Mark