Determining compression ratio on O-360

[Sunriver Ken]

I have an Rv-9A that I bought from the original owner who is now deceased (hopefully there is no coorelation there). He installed a new Superior O-360 in 2002. He had a nose wheel issue/prop strike and sent the engine to Lycon for checking and fix. While there Lycon did the performance improvements such as port and polish and balance but they say they did not change to a higher compression piston. The engine dyno'd at 214HP at 2,700 RPM which seems high to me for an engine with stock compression ratio pistons.

I have talked with Superior and their records show the engine to be a stock 180HP engine. The engine has Lazar electronic ignition.

I would like to run premium mogas with no ethynol but am hesitant as I do not want pre-ignition/detonation. The conbination of dyno'd horespower and electronic ignition has me a little scared to use anything except 100LL.

Any idea how I could determine the type /compression of the pistons without maybe a borescope?

[sailvi767]

Originally Posted by Sunriver Ken

I have an Rv-9A that I bought from the original owner who is now deceased (hopefully there is no coorelation there). He installed a new Superior O-360 in 2002. He had a nose wheel issue/prop strike and sent the engine to Lycon for checking and fix. While there Lycon did the performance improvements such as port and polish and balance but they say they did not change to a higher compression piston. The engine dyno'd at 214HP at 2,700 RPM which seems high to me for an engine with stock compression ratio pistons.

I have talked with Superior and their records show the engine to be a stock 180HP engine. The engine has Lazar electronic ignition.

I would like to run premium mogas with no ethynol but am hesitant as I do not want pre-ignition/detonation. The conbination of dyno'd horespower and electronic ignition has me a little scared to use anything except 100LL.

Any idea how I could determine the type /compression of the pistons without maybe a borescope?

Perhaps Lycon can send you a copy of the work order for the engine. The HP figure sounds very high. I am told my engine is around 205 to 210 with the work you mentioned from Lycon and 10 to 1 pistions. It has dual electronic ignitions also. I am still afraid to run LOP let alone burn auto gas. I am not sure I would run auto gas even with 8.5 to one pistons because of flash point concerns and the lack of dye for leak detection. I have seen a few troublesome reports about fires in aircraft fueled with auto gas. I might however just be over cautious however reading about the huge swings you can encounter in pump gas quality from week to week at the same station is a bit scary.

George

[Sunriver Ken]

Everything you said is valid and that is why I was wondering about the compression ratio. I am not as leary of auto fuel as you as I ran it for three years in a 160HP Glastar and never had a problem. But I did not have electronic ignition and I new what the pistons were. Regarding quality of mogas, I think I have had bad 100LL a few times but never any with MOGAS (that I know of).

[Kinnerhatz]

Just brainstorming, but could you put one piston at top-dead-center with the valves closed and fill the cylinder with oil through the spark plug hole? If you measured the oil going in, you could calculate the compressed volume of the cylinder. You might have to tilt the airplane so that the spark plug hole is at the highest point.

[jrs14855]

Here we go again. Lycons horsepower numbers have absolutely no credibility. Talk to other shops such as Barrett for some real world horsepower numbers.