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Re: could be a loop hole ??? o-200
Hi Rob,
There are two sources for the C-85/O-200 conversion STC:
STC SE02004AT Don's Dream Machines www.donsdreammachines.com/site/ in Georgia.
STC SE00979AT Aircraft Specialties www.aircraft-specialties.com/ in Oklahoma.
Aircraft Specialties lists the C-85/O-200 "kit" at $2630. They don't have a parts breakdown but I'm fairly certain that is for all the required parts (crankshaft, rods, pistons but no accessory case). There are two part numbers listed for their kits. Give them a shout (or email) to see what the applications are for the different kits.
As Tim said, the accessory case for the -8 is the same for all the engines from A-65 through C-90. Early cases were magnesium while the late cases were aluminum. But, changing a C-85-12 to a C-85-8 is much more involved than just swapping accessory cases. The main cases are different, too. Continental recommended against converting any -12 to a -8 and vice versa because of the large number of parts that must be changed out. Fortunately, (again, as Tim already mentioned) Don Swords has an STC to convert any -12 (including the O-200) to a -8. That's the way to go if you want to do that conversion.
Some random comments: The C-85/O-200 conversion does not make your C-85 into an O-200! It does give a slight increase in displacement (188 c.i. to 201 c.i.) and compression ratio (6.3:1 to 7.0:1). Most folks do report a noticeable increase in power but, the engine has a C-85 data plate, cam and C-85 operation limits. What you end up with is a strong C-85.
The C-90 cam story is really interesting. The early C-90 cams were designed for straight, free flowing exhausts. As airframe manufacturers added larger and more restrictive exhausts to meet carb heat rise requirements and cabin heat comfort requirements, performance suffered. That's when Continental changed the C-90 cam and came out with SB-M49-17. Here's a link to that SB on the PopAv website;
http://www.popav.com/docs/ContinentalSB-M49-17.pdf
The SB explains the reasoning for the change and the part numbers required. The pn 530788 C-90 cam is the hot set-up as it has 35 degrees of overlap along with a different profile. However, to see the performance increase, you need a free flowing exhaust like the Luscombe dual stack system. These old cams are getting very hard to find. And of course, they are only legal for use in a C-90.
The C-90 is rated for 90 h.p. continuous @ 2475 r.p.m. and 95 h.p. (5 minutes max although later Operations Manuals allow only 1 min) @ 2625 r.p.m. The only way to get the engine to turn up to 2625 r.p.m. is to use an adjustable pitch prop. A fixed pitch prop won't meet the static r.p.m. limits if it can turn up to 2625 r.p.m. on take off.
Dan
Hi Rob,
There are two sources for the C-85/O-200 conversion STC:
STC SE02004AT Don's Dream Machines www.donsdreammachines.com/site/ in Georgia.
STC SE00979AT Aircraft Specialties www.aircraft-specialties.com/ in Oklahoma.
Aircraft Specialties lists the C-85/O-200 "kit" at $2630. They don't have a parts breakdown but I'm fairly certain that is for all the required parts (crankshaft, rods, pistons but no accessory case). There are two part numbers listed for their kits. Give them a shout (or email) to see what the applications are for the different kits.
As Tim said, the accessory case for the -8 is the same for all the engines from A-65 through C-90. Early cases were magnesium while the late cases were aluminum. But, changing a C-85-12 to a C-85-8 is much more involved than just swapping accessory cases. The main cases are different, too. Continental recommended against converting any -12 to a -8 and vice versa because of the large number of parts that must be changed out. Fortunately, (again, as Tim already mentioned) Don Swords has an STC to convert any -12 (including the O-200) to a -8. That's the way to go if you want to do that conversion.
Some random comments: The C-85/O-200 conversion does not make your C-85 into an O-200! It does give a slight increase in displacement (188 c.i. to 201 c.i.) and compression ratio (6.3:1 to 7.0:1). Most folks do report a noticeable increase in power but, the engine has a C-85 data plate, cam and C-85 operation limits. What you end up with is a strong C-85.
The C-90 cam story is really interesting. The early C-90 cams were designed for straight, free flowing exhausts. As airframe manufacturers added larger and more restrictive exhausts to meet carb heat rise requirements and cabin heat comfort requirements, performance suffered. That's when Continental changed the C-90 cam and came out with SB-M49-17. Here's a link to that SB on the PopAv website;
http://www.popav.com/docs/ContinentalSB-M49-17.pdf
The SB explains the reasoning for the change and the part numbers required. The pn 530788 C-90 cam is the hot set-up as it has 35 degrees of overlap along with a different profile. However, to see the performance increase, you need a free flowing exhaust like the Luscombe dual stack system. These old cams are getting very hard to find. And of course, they are only legal for use in a C-90.
The C-90 is rated for 90 h.p. continuous @ 2475 r.p.m. and 95 h.p. (5 minutes max although later Operations Manuals allow only 1 min) @ 2625 r.p.m. The only way to get the engine to turn up to 2625 r.p.m. is to use an adjustable pitch prop. A fixed pitch prop won't meet the static r.p.m. limits if it can turn up to 2625 r.p.m. on take off.
Dan
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