High performance piston options for the O-200

[JimC]

I typically prop my O-200 to static about 2550-2625, and climb out at about 2640. If I want more power in climb, I just shove the throttle forward.

Near sea level, static pull with the Mac 7440 and 7535 crosses over at 510 pounds and about 2750 rpm. Below that rpm, the 7440 static pull exceeds the 7535. Both will give you good acceleration out of the hole.

Which 90 cam are you running? The 788?

At 2625, you are already past the torque peak, though power is still increasing with rpm.
Personally, I'm not a fan of the 90 cams unless you spend most of your time above 9000-9500 DA. At lower altitudes, I'd rather run the 85 or O-200 cams and jack the rpm up with a flat prop.

Re baffling, if you are running an open cowl leave the intercylinder baffling off.
If running a pressure cowl, install it.

[JimC]

BTW, LyCon is still producing the 0.015" oversize 9.5 pistons. About $156 each.

At typical climb rpm, the 15 over is worth about one hp.

[PA1195]

Cam - not sure. Possibly the 35* 530788 but more than likely the 24* 531076. We found one at LYCON and that was the only source in 2015 with a reconditioned C-90 bump stick. I elected for new lifter bodies and lifters. The case had been to DIVCO for the front O-200 seal and lifter body mods plus case stud improvement over the middle bearing area. An experienced shop that builds power handled it for me and I paid them for those parts plus the new stroker kit and incorporated SB M47-16 Supp. No. 1 1960.

The nominal published I/E O/C timing of the C-85 and C-90 cams are within 1* but the lift exceeds the C-85 (0.382) and matches the O-200 at 0.410. Regardless of the specs and parts I'm enjoying the substantially improved static rpm and climb performance noted above, especially on floats where it matters.

Gary

[JimC]

Why did you choose the 90 cam?
Are you spending much time above 9500 DA?

"but the lift exceeds the C-85 (0.382) and matches the O-200 at 0.410".

Those are the published Continental numbers, but all three are wrong.
And the 90 lift is not the same as the O-200 even though published data indicates that it is. I don't know why Continental chose to do that.

[PA1195]

The goal was torque and the C-90 was better for that in my experience on floats where overcoming low speed drag when being loaded counts. Especially with a puny 4-cyl Continental to begin with while trying to stay airworthy. I had Continental's data and approval for a conversion that overlapped with the stroker STC process.

Most of my flying has been in far larger aircraft and engines with adequate flotation. Taylorcraft and small Pipers are not as endowed despite some owner's claim. Throw two or three Taylorcrafts or Pipers in a C-185 or Beaver and that's where I've been.

Have you profiled the new factory cam timing and lift for the C-85-90 and O-200 and can offer that here? I'm not looking for a custom grind which we know is possible from various sources. Might be revealing and informative as I have an open mind Jim.

The big problem I've come across with any of these engines is the propeller and its ability to convert power to thrust. Not many that do that are available and still legal. Today that's a concern and I have the paperwork if asked.

Oh, and for winter ops heat is required so the Luscombe setup noted in #52 below is not for me. The C-150 exhaust is.

Gary

[N96337]

Excellent and timely discussion guys!! Was just talking about the 7535 prop today. Thanks!!!
John

[PA1195]

JimC has fussed with one more than I. Local Taylorcrafter with older tapered shaft C-85 is trying one. Stock Marvel carb, Luscombe exhaust for power, Donaldson air filter, 1A90 CF 7538 just recertified turns 2350 static on my optical tach on a standard day. He cruises slower but the float and ski performance was a "WOW" over the 71?? he used before. I didn't try it on mine.

Gary

[PA1195]

I'll explore some camshaft-power-prop reading material to discuss. Will add as time goes by:

http://www.supercub.org/forum/showth...e11b7ab72be70a
http://www.supercub.org/forum/showth...Experts-Needed

http://www.supercub.org/forum/showthread.php?34104-Don-s-Dream-Machine-C-85-performance-questions

Gary

[JimC]

"The goal was torque and the C-90 was better for that in my experience"

Interesting. According to Continental, when near sea level the O-200 produces more torque than the 90's PEAK torque anytime the O-200's rpm is between 2125 rpm and 2875 rpm. Do you think maybe Continental was wrong about that?

Note though, that as altitude increases and manifold pressure declines, the 90 will overtake and produce more torque than the O-200. From memory, at 2750 rpm this occurs at a manifold pressure of 21"Hg or a density altitude of about 9500 feet. I repeat, that's from memory, so please don't hold me to the exact numbers.

I don't like the 7535 for this reason -- You pretty much can't loan the plane out with that prop on it because the risk is too great that they will overspeed the engine to the point that disassembly and internal examination is mandatory. I do like the 7440 and under most circumstances it will out pull the 7535 anyway.

in your first link, the lifts quoted by Nathan (0.382 & 0.410) are wrong. I don't know why Continental did that.

In the third link, I said
"The three operational 85 strokers that I'm familiar with dyno about 97 hp (one was dyno'd, the other two perform similarly). They are somewhat limited at higher rpm relative to the 90 and O-200 because of their lower valve lift. The O-200 J3 that I fly regularly outperforms them, and I have to throttle back for them to keep up with me both in climb and cruise. When running a 7142 prop, I top out at about 2950 rpm depending on density altitude, and when running a 7535 I can't apply full throttle in level flight because it substantially exceeds 3150 rpm (enough to force disassembly of the engine and stamping of the crankcase). In 55 mph climb, I turn the 7142 2640 rpm, and can turn the 7535 about 2800 to 2850 rpm -- again, depending upon density altitude".

BTW, I think we should point out that we are discussing what people have done in the field, not what is allowable per TCDS. Do not blindly emulate these choices.

[PA1195]

My experience is limited to C-85/C-85 Stroker/C-90. Last time I flew an O-200 was 1977. Maybe if I had flown yours I'd throw rocks at mine...smile.

Yes an O-200 would be a choice if I had one at the time I did the work, not the C-85...and then if a long legal prop/engine combo could be approved by a DER like Terry at CAP that owns the Gilberti/Harer C-85 SA1-210 STC. Now simply put my 1941 Taylorcraft isn't STC'd as the equivalent of an O-200 F-19 with the 7443 they approved. If it were eligible then by all means why not use what's best? Why not add a F-19 O-200 equivalent to his STC? He alludes to something like that on his webpage Blog: http://dc65stc.blogspot.com

Great discussion. Jim if you come across the correct timing and lift as I mentioned above please share.

Here's from #23 in Post 53 Link #1 above. It may be superseded:

"OK here it is right from Continental.I got a guy that really wanted to help.

The numbers posted above as far as opening and closing points are correct.

The C-90 and 0-200 both are.410"lift cams.

The C-90 is 245 degree duration on both Intake and Exhaust with a 24 degree overlap.

The 0-200 is 259 degree duration on both Intake and Exhaust with a 35 degree overlap.

The C-90 cam will produce it's peak torque at a lower rpm due to it's shorter duration and overlap.

The 0-200 cam will produce more power up top.That said ,there is no reason to run the C-90 cam in an 0-200 UNLESS you are limited to the rpm you are allowed to turn by STC .

Continental built the 0-200 for the Cessna 150.it did not have the ground clearance to run a 74" prop like a Cub or other tailwheel aircraft.The only way to get the needed thrust with a short prop was to cam it so it could be spun higher.

My 0-200 turns 2600 with the brakes locked.I cruise 2550@5gph leaned and see 92 mph.That is with a 75-35 prop.I think the 75-38 would be perfect.And a 0 thrustline works as well on an 0-200/cub as it does on a Supercub! Hope this answers your question. Bill"

Gary

[JimC]

"older tapered shaft C-85 is trying one. ........... 1A90 CF 7538 just recertified turns 2350 static"

My favorite performance prop for the stock C85 is a Mac 7438.

[PA1195]

"older tapered shaft C-85 is trying one. ........... 1A90 CF 7538 just recertified turns 2350 static"

My favorite performance prop for the stock C85 is a Mac 7438.

Yes but legally limited to 71" diameter on a C-85 according to Mac due to vibration issues per TCDS P-842 Note 9. They allow 73" on a C-90 and of course 75 on an O-200. Which is why my approval for a Sen M76AK-2-?? on my C-85 is important. Sen says it's ok in TCDS 1P2 for C-85 and C-90 but Taylorcraft never bothered to approve it. The FAA did.

Find that new cam data please.

Gary

[JimC]

I've got a spreadsheet with the various cam part numbers, cam timings, and total lifts. I'll fish them out.
I do NOT have profiles for any of them. Wish I did.

Note that some O-200s go like a striped **s ape.
Others not much better than a stock 85.
I think maybe the puny O-200s are running with retarded timing.

My take on all this has gradually evolved to:
1) run a peaky cam with good high rpm torque.
2) run a large diameter prop pitched flat enough to let you achieve that high rpm.

My favorite props are all Macs, listed in no particular order except that my all around favorite is the 7440.
7440 (on anything)
7438 (on stock C85) yes, I'm aware of the vibration issue
7142
7141

Although it can be a warhorse, I do NOT like the 7535 because of the potential for overspeed.
A 7440 will out perform the 7535 on most engines anyway because they won't turn up enough to allow the 7535 to come into its own.

As an aside, a 7535 on a high compression O-200 will climb a J3 at a steep enough deck angle to unport the fuel tank when fuel level is less than 2 or 3 gallons. Be extremely cautious at low altitude. If it unports in a maximum climb at less than 250-300 feet AGL, you won't recover.

[PA1195]

Thanks Jim I knew you'd come through with info here. Great discussion! Catto may be the answer it appears from field reports. Do you have any experience with them? I do not yet.

Gary

[JimC]

"Yes but legally limited to 71" diameter on a C-85 according to Mac due to vibration issues per TCDS P-842 Note 9".

That's true, and my 7438 was constantly breaking cylinder base studs on my C85 due to stud fatigue fractures. I loved it anyway, till my foster brother's cousin ran it over a Stearman landing gear discarded in the weeds while parking it. Rest in peace little 7438; you were great while you lasted.

The cam data I have is from way back when. I don't have anything on the O-200D.

I don't have anything on the Catto. Wish I did. Much of what I've heard is just hangar talk that sounds too much like marketing hype. I'd love to see some static pull numbers, but they are harder to come by than Trump's tax returns.