High performance piston options for the O-200

[N96337]

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

[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

[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]

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]

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.

[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.

[PA1195]

"Gary, what engine are you currently running and which prop do you prefer?" I have a new C-85 Stroker w/C-90 cam in my Taylorcraft. The Sen M76AK-2-40 was transferred from my PA-11 that had a fresh overhaul on a C-90-8 in 2003. No longer owned. The current engine with C-150 exhaust, Donaldson air filter (+35-50 static over Brackett), 7:1 flowed cylinders, and C-85 timing does 100-115 more static on the same outboard optical tach (2440). More than Taylorcraft allows so I can pull it back some but cruise at 2350 is in the low 90's on floats. It turns 2625 redline an ok figure for a C-90 equivalent for 5 minutes. I've not tried other props with this engine as there's nothing as long approved on the C-85, just O-200 F-19 Taylorcraft and C-150 seaplane. But 44-45 years ago I tried a 7535-38 and 7440 on another Taylorcraft C-85 and they both pulled well but saw slower cruise on floats. I've no doubt a Mac 7440 would be good same for a Catto.

"I find that interesting." Not my personal experience just ramp chatter from those that have. Heat and wear were comments I heard but performance was better over 8.5. Makes sense but who knows what cylinders were reused or what fuel flow was available via jetting if volumetric efficiency was improved. Then there's engine baffling and flat props that can create heat where it shouldn't. Don't know but as you mention if there's a progressive overhaul then things can be monitored for change.

Edit: I had the Sen prop overhauled recently to confirm the pitch and quality plus a dynamic balance done after the installation. On floats it starts up on step well then at about 20-30 mph it starts to pull hard into a takeoff and climb. If I wanted better climb I'd go to a 42" pitch to stay on top of the torque curve I think. I need to monitor rpm with the digital reach onboard better and see where and when it pulls the best. Maybe 2500 is a good rpm to shoot for during takeoff?

Gary

[JimC]

"Locally experiments I'm aware of with compression over 8.5:1 have not always gone well".

I find that interesting.

[JimC]

Gary, what engine are you currently running and which prop do you prefer?

[JimC]

Old Continental cylinders tend to crack no matter what compression or fuel you are running.
I always keep a couple of extras on hand so I can be up and running again in an afternoon.

In the oops department, I wondered why valves were mentioned in conjunction with 100LL.
So I went back and looked at my post. Fumble fingered me wrote valves when I meant to write sparkplugs (those pesky lead balls - Wish I had said more so I could take that back too :-)

Another aside. Back in my J3 Search & Rescue days in the late 60's, I used to run a Mac 7438 on my C85-12F. I loved that prop, but it sure was hard on cylinder base studs.

I got my O-200 in 1969. It's still hanging in there in sort of a continually progressive overhaul. Crank and cam are still in OK shape. I think it's gonna outlast me.

[Hank Jarrett]

If you are having trouble finding no alcohol fuel try your local marinas. Lots of outboard motors can't take alcohol either. Another place is to talk to the guys at local race tracks. The bike and car racers know where to get the "off road" fuel, some of which still may even have lead. Excess lead DOES NOT INCREASE POWER!!!! It allows you to pack more fuel air charge into the engine at higher compression ratios. THAT makes more power with a LOSS of HP/# of fuel. You just more than make up for it in the number of # of fuel you can use per hour. Our old engines were designed to run on the "normal" fuel of the 1920s and 1930s. That was down around 66 octane! The timing is advanced from back then to take advantage of the "high octane" fuel that was WAY UP THERE at 80/87 from around WW-II. The Battle of Britain was fought with 87 octane fuel. The 115/145 fuel from later in the war worked by running very high compression ratios. One of the big false information wins from the US in WW-II was to convince the Germans there was so much Lead compounds in our fuel because we had poor refineries. They didn't figure it out until the war was almost over.

Hank

[PA1195]

JimC I pirated and posted those graphs you developed from other Forums. Your experiments and comments regarding performance have been very worthwhile and informative. Locally experiments I'm aware of with compression over 8.5:1 have not always gone well. Despite using 100LL there have been issues with increased CHT and in once case cylinder failure and precautionary landing. Things break for various reasons of course and tying issues to a single cause without complete engine monitoring (CHT-EGT) plus uniform parts quality begs the question as to source.

I agree on your prop assessment and have flown both the 7535-38, 7440, and now a Sen 76AK-2-40. The Sen is field approved on my T while the others and Catto fly at night and on weekends.

Gary

[JimC]

"Just because you got away with it does not mean it is good".

I totally agree. I don't run the alcohol for any performance benefit; I do it because it is what is available at the pump, and I was curious about what it would do to the engine. I am aware of both the benefits and downside of lead. There are no aluminum fittings in my fuel system. And of course, the alcohol will corrode the carburetor itself in the same way that it corrodes the carburetors in our cars. Though I fully expect to die of old age before it does so (as I mentioned, I'm a bit long in the tooth).

The reason I posted this was because someone had previously posted my two graphs of Continental's power and torque curves for their small engines (plus a couple of curves for the thermodynamic effect of increased compression), and I was responding to those previous posts.

I'm not encouraging or suggesting that everyone should run out and install 9.5 or 10.0 pistons in their small Continentals. Just posting what I observed after I did 0.015" oversize 9.5 pistons in an experimental O-200. BTW, I usually cruise it at 2250-2300rpm (avg fuel burn 4.3 gph including one climb to altitude) and climb out at 2640 rpm (most rpm I've turned in a J3 55mph climb was 2850rpm with a Cessna 150 seaplane prop - a Mac 1B90 CM7535). As an aside, I don't like that prop - I prefer a 7440. Also, I make it a point never to turn it faster than 3150 rpm, and I've only done that twice, as a test.

Again, just posting results, not suggestions.

I may have some measurements of the LyCon pistons, I'll fish around in my files and look.
If not, I'll measure them next time I open the engine up to look at the condition of the insides (since it is an experimental test engine, I do that fairly often).

[Ragwing nut]

Where do you live? and lead is SUPPOSED to be there to cushion the valve seats in older designed engine. The alcohol can kill you, it will corrode any aluminum fittings, gascolator and inside the carb. Just because you got away with it does not mean it is good. Oh and unless you are running e-85, the alcohol is a dead filler that lowers the octane...

Oh do you have any measurements on those lycon pistons?

what he said^^^^^

[astjp2]

True, but it is what is easily available at the service station.
I've been using it since about 2007 (the year it was mandated in automotive fuel).
I watch it pretty closely - No detectable damage in the last twelve years, but it will likely get me eventually, if I live that long.
I probably won't - I'm getting a bit long in the tooth.
I'm leery of running no-alcohol regular at 9.5:1 and 28° BTDC, and 100LL is both expensive and potentially a bit hard on the valves. I do use a steel needle and seat.
So in short, I just go with the flow and luckily, haven't had any corrosion.
I consider engines to be consumables anyway :-)

Where do you live? and lead is SUPPOSED to be there to cushion the valve seats in older designed engine. The alcohol can kill you, it will corrode any aluminum fittings, gascolator and inside the carb. Just because you got away with it does not mean it is good. Oh and unless you are running e-85, the alcohol is a dead filler that lowers the octane...

Oh do you have any measurements on those lycon pistons?