# After market liquid cylinders for Lycoming engines

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#### Andy_RR

##### Well-Known Member
Interesting that AC Aero's ealier AX40 and AX50 air-cooled cylinders are no longer available and there's a SB that pretty much takes them out of service...

#### Toobuilder

HBA Supporter
Log Member
What is the nature of the SB? I was interested in the original air cooled versions for a while, but then I saw how "slow" Relentless was while running a set on the IO-720. It seems the "modern" port configuration didn't help the Lycoming all that much. That, and the set of cylinders for my Rocket was going to cost $8k. Not sure if the liquid cooled versions have the same ports, but if so, I don't see the benefit unless it's for a pusher or some other "hard to cool" application. Since the Lycoming case is the LIMFAC in high HP applications, I think having beefy, liquid cooled cylinders is a solution in search of a problem. #### galapoola ##### Well-Known Member I suspect that ac-aero do not anticipate that their cylinders for the 4 and 6 cylinder Lycomings will be used in combat. BJC Touche, but the point I was making is that one dead jug on an air cooled engine means less power but a good chance you still have power albeit reduced. Contrast that with a liquid cooled engine with one leak. The coolant level becomes critical and your engine seizes and you have no power. I like liquid cooled engines. They have so many redeeming qualities. Air cooled seems to be more robust. BJC #### aeromomentum ##### Well-Known Member From what we have seen and read, cooler heads and cooler intake air reduced knock when operated at the same power. This added knock margin allows a liquid cooled engine to produce more power for the same amount of fuel or burn less fuel for the same amount of power via leaner mixture, more spark advance and/or higher compression. Smaller combustion chambers also have more turbulence of the correct scale, everything else being equal, and this allows for more knock margin. Of course smaller combustion chambers can have lower thermodynamic efficiency. The sweet spot seems to be about 0.5L per cylinder. This is one of the reasons that 2L 4 cylinder engines are common. Most modern liquid cooled engines can run about 10+:1 compression, lean mixture and about 34 degrees advance timing on just 89 octane AKI without knock. An air cooled Lycoming runs about 24 degrees advance with just 8:1 compression and rich mixture on 100LL (about 95 octane AKI). This difference is huge but not all of it is due to liquid cooling. #### hangarrat101 ##### Member Strangely I was looking at these engines today! There doesn't seem to be much on the website in terms of concrete info beyond power and the fact they are "lighter." Although the 2020 Kitplanes engine buyer's guide does have a little bit more info on them. Someone posted a while back asking if the figures for the Voyager engines were ever made public? Yes they were, there was an SAE paper written on them. You can get it there, or there's somewhere you can download it for free, although i can't remember off-hand where I got mine. They gave BSFCs better than .37 lbs/hp/hr for the Voyager 200. #### Andreas K ##### Member Thanks for sharing, Andi. What is an AFM 300? Do you have electronic ignition? Thanks, BJC Hi, AFM 300 is a throttle manifold/fuel control unit manufactured by Airflow Performance. I use 2 mags. Another idea would be to extend oil cooling and have an air/oil cooled cylinder/head. So basically a larger oil cooler and some oil cooling in the heads. The cooling lines should run internally in the engine. No new medium added to the engine. You could balance the cylinders for equal and lower temperature. Just a thought. I am not an engineer. BJC #### BJC ##### Well-Known Member HBA Supporter Hi, AFM 300 is a throttle manifold/fuel control unit manufactured by Airflow Performance. I use 2 mags. Another idea would be to extend oil cooling and have an air/oil cooled cylinder/head. So basically a larger oil cooler and some oil cooling in the heads. The cooling lines should run internally in the engine. No new medium added to the engine. You could balance the cylinders for equal and lower temperature. Just a thought. I am not an engineer. Thanks. What are your thoughts about the benefits of electronic ignition with your engine? BJC #### Dan Thomas ##### Well-Known Member Another idea would be to extend oil cooling and have an air/oil cooled cylinder/head. So basically a larger oil cooler and some oil cooling in the heads. The cooling lines should run internally in the engine. No new medium added to the engine. You could balance the cylinders for equal and lower temperature. The SMA305-230 diesel engine does exactly that. The oil comes up the cylinder wall from the case though channels and into/out of the head. The head is a removable part, so there's a head gasket, and the early engines leaked at that spot. We did a bunch of work on one of them. A large oil cooler is part of the system. #### Marc Bourget ##### Well-Known Member Don't remember the exact source or the specifics but my memory trigger reminds me that the extended low power settings were the reason for the liquid cooled head in Rutan's design. Take with the usual oz of salt! :^) #### Niels ##### Well-Known Member Someone posted a while back asking if the figures for the Voyager engines were ever made public? Yes they were, there was an SAE paper written on them. You can get it there, or there's somewhere you can download it for free, although i can't remember off-hand where I got mine. They gave BSFCs better than .37 lbs/hp/hr for the Voyager 200. Thank You for leading me to SAE paper 871042. 0.37lbs per hph is 170 gram per hph or sligthly more than what Hirth found in laboratory testing some 1950 really direct petrol injection on a two stroke,spark ignited engine. What is the BSFC for a standard O-200 leaned to limit and on leaded fuel? #### Andy_RR ##### Well-Known Member With decent mixturedistribution and a good ignition system you could achieve 0.37 on an air-cooled O-200 or an O-520/550 or just about any other engine. It's the inaccuracy of fuelling and ignition that impairs the fuel consumption potential of most aero engines. It's the price you pay for simplicity and (alleged) reliability #### Brünner ##### Well-Known Member HBA Supporter All assets are for sale. #### Dan Thomas ##### Well-Known Member All assets are for sale. Not surprising. Back in post #27 I said this: These liquid-cooled cylinders could easily sell well if the conversion costs were reasonable and the loss of useful load wasn't too bad. And even more so if the price of avgas goes way up again. But keeping costs within reason is difficult, as we've seen in so many instances in aviation. Jut try counting the number of startup aviation companies that have miscalculated the costs and complexities of improving on existing technology. The world today is not the world of 50 to 80 years ago when so much of our engine technology was developed. Standards of living are higher, demanding bigger wages and salaries and benefits. Taxes are far higher. Engineering education costs a lot more. Regulations have multiplied like rabbits. Acceptance of personal responsibility has given way to suing anyone who makes any product involved in your injuries incurred by your own stupidity. General aviation is shrinking at least as a precentage of the population's participation and probably shrinking overall. The cost of anything anyone develops has to be amortized over a tiny number of units produced and sold. It's not just aviation. Just look at the costs of building or replacing highways and bridges and dams now, things that were built with little difficulty or opposition in great numbers 50 to 80 years ago. It's a different world now. #### Sockmonkey ##### Well-Known Member From what everyone is saying in this thread, it seems like aftermarket liquid-cooled cylinder heads would be the most marketable option rather than full cylinders. #### Brünner ##### Well-Known Member HBA Supporter From what everyone is saying in this thread, it seems like aftermarket liquid-cooled cylinder heads would be the most marketable option rather than full cylinders. For Lycos and Contis? Probably. Rotax showed that liquid cooling is not necessary for the cylinders. It would be interesting to try it on the old VW engines as well... #### cheapracer ##### Well-Known Member Log Member Does anyone have experience with aftermarket, liquid cooled, cylinders from ac-aero? See Gladiator - AC Aero Engines Sheez, only$20K hey?

... bargain.

For Lycos and Contis? Probably. Rotax showed that liquid cooling is not necessary for the cylinders.
It would be interesting to try it on the old VW engines as well...
Porsche ran water cooled heads only for a while when they had to start leaning out to meet emission and mpg standards. Now fully water cooled.

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#### TFF

##### Well-Known Member
Rotax is also geared. That in itself doesn’t matter. What it is is small. It’s at a sweet spot where you can get away with air cooling a cylinder in combination with a water cooled heads. Move to a bigger platform and it’s not going to work.

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