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6930 wrote: ↑Tue Aug 30, 2022 9:30 am
Did my engine with the O-200 crank in 2011 including 4 new ECI nickel carbide cylinders. It was a great investment and I’m glad I did it.
Definite HP increase. Judging by before and after static run up RPM, I estimate 14 HP total increase using the power curves for the C-85 with some of that (guessing 4 or 5?) from having new cylinders, the rest from higher compression and increased displacement with the O-200 pistons and crank.
Over 1,000 hours since the overhaul and I’m climbing at 2425 RPM, fully loaded at 70 MPH.
Does the STC permit using the O-200 pistons as implied above? Believe it's supposed to use the original C-85 pistons, hence the other posting about having to possibly eat them if buying assemblies. Some places would do the swap in the assembly in the past however.
For what it's worth, your numbers are similar to mine - about 2400 rpm at 70-72 mph and generally 500 fpm climb even when very hot in summer. Have the conversion from 1999 overhaul and swinging a 71/48 prop. Got to 6500 feet leaving from sea level at 90 F in 15 minutes the other day. In my opinion outperforms stock and a full O-200 conversion having flown both.
To use the O-200 crank with its longer throw, you have to use the O-200 rods and pistons. Otherwise, the pistons will hit the cylinder heads at the top of the stroke...
I recall it is possible to use O-200 rods and C85 pistons, but it puts the compression ratio way too high, and may require other modifications. Experimental only...
I recall it is possible to use O-200 rods and C85 pistons, but it puts the compression ratio way too high, and may require other modifications. Experimental only...
Thanks John. That's how mine is set up (and how I ordered new assemblies for the upcoming top)
Definite HP increase. Judging by before and after static run up RPM, I estimate 14 HP total increase using the power curves for the C-85 with some of that (guessing 4 or 5?) from having new cylinders, the rest from higher compression and increased displacement with the O-200 pistons and crank.
Based on the stroke change alone, I estimated 6-7 hp with the conversion, suggesting any additional extrapolated hp is from higher compression by virtue of also using the O-200 cylinders. Believe that new cylinders don't change the power, just reliability and safety since Continental has run engines with zero compression (static) and still showed rated hp was made (so have been told).
Any way you slice it, the conversion seems to be the sweet spot for the 120/140.
The only functional differences between C85 cylinders and O-200 cylinders is the valve springs and the pistons. You will have the same compression ratio with a C85/O-200 crank STC, a C90, or an O-200.
