Pistons in the o300

How to keep the Cessna 170 flying and airworthy.

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abushey123
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Joined: Tue Mar 01, 2022 3:26 pm

Pistons in the o300

Post by abushey123 »

Hey guys. I have hung low time o300d on my 170 which has new millennium cylinder. At the moment I am looking to get a few more ponies out of it. I understand the risk of pushing more than rated power out of anything but am curious if anyone has any experience with the combustion technologies ASC539021 pistons. They claim a 9:1 compression which is a nice bump from the stock and just a hair more than the c85. I am planning on pulling timing back to avoid any ignition knock but am curious if anyone has ever tired these and have anything to say about them. :twisted: :twisted:
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GAHorn
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Re: Pistons in the o300

Post by GAHorn »

No I’ve not tried them…because I only use engine components which can be installed in a legal certified engine.

Also, you might keep in mind this C145/O300 engine ONLY “makes” 145 HP when it turns 2700 RPM. While different pistons might raise the compression-ratio…that would only affect efficiency….and no actual HP increase would occur unless there was a commensurate RPM increase…and you’d likely not accomplish that because you’re planning to retard the ignition-timing.

I believe your plan would not only be a waste of time and money it’d also make your engine illegal and may conflict with any insurance coverage you may have.

Here’s what Combustion Technologies state: The Oil Scraper Ring is not used on this piston - top 3 rings only!
This Piston is not FAA-PMA approved and is for experimental or ground use only!

Notice that their piston charts do not even provide the actual data on the AC539021 pistons: https://combustech.com/pages/piston-specs

And notice that since the piston you are considering does NOT have provision for the standard Oil Control / Scraper ring….it will only accept the top 3 compression rings. I suspect you’ll be burning more oil and running higher Cylinder Head Temps.

If you do this, to remain legal, you should re-classify your airplane into the Experimental Category. After you do that, you will find all kinds of new restrictions apply….and it’ll be unlikely you will be able to return the aircraft OR engine to the standard category without considerable money.

Sorry not to have happier response for you.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
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abushey123
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Re: Pistons in the o300

Post by abushey123 »

I’d have to disagree with the compression ratio increasing power output. If the compression ratio increases the amount of air that is in the cylinder gets compressed more increasing the amount of pressure pushing on the piston. If the cylinder at bottom dead center accounts for no compression at by the time it gets to the top of the stoke it’s at 9.1 times what I was at the bottom that means when a combustion event occurs the cylinder pressures will be higher and there is more work that can be done on the piston. I understand cars are different then airplanes but the concept of a four stroke gas engine remains the same. Motor trend did a really nice write up on why static and dynamic compression ratio increase hp. I have attached the link.
As far as the oil scraper rings I think it has one seeing compression rings don’t normally have holes behind them. Looking at the picture the bottom most rings has holes suggesting it has one oil control ring. It likely doesn’t have the oil scrapper at the bottom of the piston.

https://www.motortrend.com/how-to/compr ... ore-power/
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