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If a C85-8 engine has an O-200 crank in it, does it still only produce 85HP. I recall reading somewhere the O-200 crank changes the stroke and increases the horsepower to 100.
Danny Deger
Danny Deger
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Re: 0-200 crank in C85-8 engine
I've got a Don's Dream Machine C-85-12 w/0-200 crank... with just run in time for sale(0smoh). Static test is 93-94 horsepower. Dynamic is suppose to be 97-98 Horsepower. Email me if you'd like, via private mail. SEE Members list.
With regards; ED OBRIEN -
Re: 0-200 crank in C85-8 engine
Legally the horsepower doesn't change or the STC would never hav happened. Buuuut, when you increase the stroke of any motor and change the displacement, horsepower will change. 90-95 is about right and would probably make 100 hp if you wrapped it up to 2700 rpm like an o-200. Unless you installed O-200 valve springs, you might run into valve float at that rpm though.
MikeComment
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Re: 0-200 crank in C85-8 engine
There are a lot of issues at play here. What an engine will do on a dyno stand compared with what it will do strapped to an airframe with a fixed pitch prop are two completely diffferent things. For example, if you have a prop that allows your C85 to turn up to exactly 2575 in level flight at full throttle at sea level, it doesn't matter if you replace the C85 with a 2700 hp engine, if you only turn it up to 2575 it's only making 85 hp. (Drag and weight considerations ignored.)
If you have the same prop and C85 under climb conditions, it will turn something less than 2575 and hence make something less than 85 hp.
If you put an O200 crank in a C85, what you can be assured of is it will make a greater portion of that 85 hp under most circumstances.
That's my story and I'm sticking to it...Comment
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Re: 0-200 crank in C85-8 engine
John,Sounds logical to me.Kevin Mays
West Liberty,KyComment
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Re: 0-200 crank in C85-8 engine
But due to the higher displacement and compression ratio of having the O-200 crank in it, wouldn't the C85 with the O-200 crank have higher torque at 2575, thus have more horsepower? I am a retired aerospace engineer, but have never worked on a piston airplane, so my knowledge is no greater than any other lay person on piston airplanes.Originally posted by NY86 View Post
Danny DegerComment
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Re: 0-200 crank in C85-8 engine
Don Swords, one of the STC originators claims that the dyno showed the O-200 crank with no other changes upped the output by about 8 HP (93). While the crank stroke is increased about 1/4", the piston is shortened to retain the same compression ratio, and the RPM is limited as before, but obviously the torque will be slightly greater at the same RPM.
The FAA limit on such mods with minimal testing is 10%. above the 10% gets into the many-hours-and-tear-down mode + proof data.
It does add noticeable Ooompff to climb in the several airplanes I've flown.Comment
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Re: 0-200 crank in C85-8 engine
Stroke is increased from 3 5/8" to 3 7/8".
Compression is increased from 6.3:1 to 7.0:1
Displacement is increased from 188 cubic inches to 201 cubic inches.
Power / torque curves of the C85 cam are likely similar to the C90 cam (531076) since they have the same overlap and almost exactly the same valve timing.
Lift of C85 cam is 0.382 while the C90 cam has a lift of 0.41. This may or may not give an edge to the C90 cam.
C85 cam develops more power / torque than O200 cam at a given RPM (according to various tests that have been done by STC holders and others).
Given the above, the C85 with O200 crank, rods and pistons should perform very close to a C90 with the 531076 camshaft.Comment
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Re: 0-200 crank in C85-8 engine
What was the RPMS at that rated Horsepower ...intheair2Comment
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