C-85 "stroker" vs the 0200 crank/pistons/rods STC

[sbmackie]

Are these two different ways to describe the same engine mod, or is the "stroker" a different mod?

I've found the literature on the crank, pistons, and rods STC, and it says "no power increase". I'm assuming this STC is out there as parts for origianl C-85's srt becoming scarce?

Thanks
Scott

[a64pilot]

I’ve been told that there is a power increase, STC says there isn’t because if there was, then that would have required a bunch of flight testing and a whole lot more paperwork to Certify.
How much if any increase I have no idea though, it can’t be a whole lot.
It’s not an inexpensive STC, I’ve flown aircraft with it, years ago I got my seaplane rating at Brown’s like everyone else, and all their cubs engines have the STC, I assume for the power increase, but maybe because cranks are difficult to find, but as I wasn’t flying a Cub with a plain C-85 back to back I can’t say if it had more power or not.

Personally the only way I’d go down that road is if my crank was bad and I needed rods too and or a crank just couldn’t be found.

I hopefully dodged the bullet on needing a case, unfortunately it’s not hard at all, especially if your not an A&P to be faced with having to spend more money on an engine than the airplane is worth.

[8362]

I believe that they are the same thing.
I did the STC a few years ago and don’t have hard data on hp increase.
I can quantify that my fuel consumption did go up ~10% and the plane seamed to take off quicker.

[2066]

Yep, it seems that the "stroker" term may be borrowed from automotive mods(?)...it's the same. RE HP increase, Don Swords made a presentation @ our Newnan convention and discussed the STC in some detail -- of course, he had pioneered & earned the STC that was later sold to a well known vendor. As best I recall, Don suggested an increase in HP to 92 might be realistic 'though, as mentioned above, had he pursued adding that to the STC would have meant much more engineering data...time & expense. Randy and John have discussed in the past the RPMs necessary to realize any significant power increase & that detail escapes me. The fact that the longer prop that's legal on the C85 can still be utilized on the C85 with the "0200 Crank STC" seems to help. In the final "analysis" and having flown behind this STC for a few years, now, it "feels" like a bit more power on take-off/climb...however, having spent quite a few bucks for it probably influences the "feel", too . Again, as I recall, Don suggested that the declining availability of serviceable C85 cranks led him to develop the modification. Incidentally, he gifted the Association with an STC "door prize" for several of our conventions while he was still in the engine building biz as well as participating @ "maintenance forums" -- yet another of many "friends of the 120-140 family!" who have contributed & supported us over the years. Mac

[a64pilot]

Most often higher RPM is required or realize greater HP because HP is Torque x HP div by 5252.

Look at ANY dyno chart, if an engine turns over 5252 RPM, the HP and torque curves MUST cross at 5252, if they don’t, then someone has doctored that chart, and that’s not uncommon.
So if an engine can maintain the same torque, turning it faster realizes greater HP, if RPM remains constant then you have to increase torque to increase HP.

However it should be pretty easy to quantify, if you increase torque, then static RPM will increase.

An issue is that very often people will see an increase, but what they are comparing it to was an old tired, worn motor.

If it increases stroke, and if the pistons are the same as in compression, there will be an increase in compression due to the combustion chamber volume being the same, but the cylinder volume increased by the longer stroke.

Mind you I know nothing at all about the STC, but would be surprised if there wasn’t a modest increase in power.

[6643]

Due to the magic of fixed pitch props, Your new STC'd engine will put out exactly the same hp at redline in level flight as the tired old engine did. The two places you'll see an increase are in static RPM and in full throttle climb, where you're operating off propeller load and your RPM will be higher witht he new engine.

Put another way, in climb, or on a test stand, the engine will produce more power, but in cruise you're constrained by RPM, so you'll be using less throttle to attain the same RPM and the power will be exactly the same.

[sbmackie]

Reason for question is considering two, very similar in hours/looks/fabric/gizmo's, one has the STC and the other is a straight C-85. Wondering if the STC should really sway me considring I'm not buying a bush plane, but will operate in DA's of 3500 feet routinely through out the late spring to early fall.

[6643]

If the engines were the same, which one would you buy, and why?

If that's the only significant difference between the two, buy the one with the O200 crank.

[8224]

About 12 or so years ago I bought the STC kit from Aircraft Specialties in Tulsa and installed it on my Aeronca 7DC. The very nice and helpful girl at AS told me I would not find it written anywhere in the the paperwork of the STC but the engine would produce 96.5 HP at rated RPM. I don’t know if it did but I do know the takeoff performance was much better after the alteration!

[6930]

I did the upgrade to my engine 10 years ago with new ECI nickel carbide cylinders. Power increase is impossible to nail down without comparative dyno tests, but what I found was that I got a 125 RPM increase in static RPM before/after with the same prop.

Looking at the C85 power curves, the way I interpret it, that translates into a 14 HP gain. How much of that was because of a new engine I can’t say for sure....but I’ll bet 10 of it was because of the O200 STC.

I did a bunch of time to climb tests after the O/H and found Vy in my plane is now 70 MPH. As John C noted, it doesn’t do diddly for you in cruise, but the difference in climb was significant.

Mike