High performance piston options for the O-200

[astjp2]

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

Gary, there is an aeronca sea plane that is certified for a 74" prop on an 85...I posted about it before...even if Mac didnt approve it, Aeronca did.

[PA1195]

Have you tried prop vibration analysis and balancing? I've had positive results on several airplanes and engines. The latest equipment is better than the early Chadwick units made for copter blades and rotors I'm told in that it can give harmonic data. I pay and fly - they fix so that's what I've experienced. Even flew a C-185 with one mounted and the meter in the cockpit. Every rpm or power setting changed the values. Fixed pitch might be better suited.

Gary

[PA1195]

Gary, there is an aeronca sea plane that is certified for a 74" prop on an 85...I posted about it before...even if Mac didnt approve it, Aeronca did.

Sorry Tim I forgot that but now recall your post. Maybe Terry can offer us some options via DER? With the new balancers available checking out the vibes should be easier. I saw Mac here last year doing a test on a Cessna with one of their scimitar props. Had probes all over the blade and airframe.

Tim...what's your goal for performance? You started this thread and I hope it hasn't gone too far afield.

Gary

[astjp2]

It is just a posting about data, people claim that the 85 piston was blah blah blah and when you looked at the numbers, it was more realistic to use aftermarket pistons if you want real performance. I have the o-200D manuals and if you compare them to the A manual, the inspection criteria was WAY more critical. I still want to flow a cylinder with different intake elbows. That way I can have some real data to post.

[JimC]

I'd really like to see some decent intake elbows. Keep us posted on that.

[PA1195]

I'll throw this info below in for the record. It's a post I made on Supercub.org regarding air filters 11/16. I've said up to +50 static but was wrong after reviewing my logs and the later post below. JimC and I had a discussion like here sharing info.

"On pretty much a standard August day at 425' MSL, 72F, 29.85" Hg from set to 0' on altimeter...MP gauge read 30.10" Hg. Nosed into the bank on floats...fresh C-90 in a PA-11. Prop Sen 76AK-2-40. Used digital remote sensing Proptach sitting on panel. Here's the WFO static data I recorded with a new Brackett filter element and new Donaldson P10-7150:

Brackett 28.5" 2300 rpm
No air filter 29" 2325 rpm
Donaldson filter 28.9" 2320 rpm

Every little bit helps.

Gary"

This summer under similar weather conditions and elevation (425 MSL) with the low time C-85 Stroker, same propeller and pitch, C-150 exhaust, some cylinder passage work, same airbox design (both recent rebuild), same compression 7:1, and same Donaldson P10-7150 air filter. The Taylorcraft turned 2440 static on two different types of external meters but same number on both. The MP was same as above about 1" Hg lower than before startup. Essentially the same innards as a C-90 but probably better flowing exhaust and C-85 mag timing 28R/30L. Engine does 2625 at 1500 MSl wide open which is the 5 minute rated max for a C-90.

Gary

[JimC]

I've tried Total Seal rings in a 9.5:1 O-200.
It was a no-go. They sucked too much oil in through the valve guides, and I was never able to seal the guides well enough to stop it. Gave a puff of blue smoke every time you cobbed the throttle, and fouled the plugs in short order.

If I remember correctly, Performance Engines has roller rockers available for the O-200, and is working on titanium rods.

As an aside, Continental's published lift of 0.382" for the C85 and 0.410" for the C90 and O-200 is wrong.

The 1.2 rocker ratio can be adjusted by using offset rocker bushings.

C85 pistons in an 85 Stroker, C90, or O-200 give 8.68:1 compression ratio.

"Every little bit helps".
Gary, you got that right.

My 9.5 O-200 with Brackett filter, stock J3 exhaust, and McCauley 1B90 CM 7142 statics about 2525-2550 rpm.
With a 7441, about 25 rpm more (maybe 50, if you twitch your nose just right :-)
From memory, about 2650 with a 7535.
On a J3 landplane in WOT level flight, most I've turned it with the 7142 is 2950 rpm (118mph). With a 7535, 3150 rpm (115 mph).

[PA1195]

The critical point for me about power and props is on floats when going from a step-plow to planing and then accelerating to takeoff speed. There's lots of water drag to overcome unlike on wheels. I'd have to guess that's 15-40 mph but so far never tried a GPS to pin that down better. It would take an onboard camera looking at or integrating the GPS' speed/time readout and plane's attitude out the windshield.

Taxiing slightly nose up, then the bow rise to plowing under power followed by nose down as the floats climb up to a planing attitude just like a boat. Light that's a quick event but heavy it can take several long seconds if it ever happens. Sometimes weight reduction is the only way to get on step.

On skis takeoff distance can be measured via tracks in the snow. That would be another way to compare propeller and power performance especially if the snow were deep.

With the right diameter and pitch the "air traction" can be felt especially with puny power from these small Continentals. The plane suddenly accelerates at some forward speed after power application. When that surge happens during takeoff can be adjusted via propeller pitch at a fixed prop diameter, and probably between propellers of the same diameter and pitch configuration between manufacturers (the prop's airfoils, shape, and chord vary).

Doing a static pull at 0 forward speed is a crude way to determine performance with my high drag criteria.

Gary

[JimC]

"Doing a static pull at 0 forward speed is a crude way to determine performance "

Indeed so, but it is about the only practical way to get an approximate comparison.
BTW, if you have an android phone, there are apps that will record your acceleration variation with time.

[PA1195]

Thanks Jim for the tip. I had heard from a friend that likes hot road rigs he had some way of measuring the power changes in his coal burning diesel truck. Maybe that's what.

Have you tried that app yet? Might be a good topic for the curious and power modders that fly.

I don't do personal assistants but my wife has several. It sounds like feeding time at the zoo who they all light off with calls and text messages.

Gary

[astjp2]

C85 pistons in an 85 Stroker, C90, or O-200 give 8.68:1 compression ratio.
.

Jim, considering the 8.5 to 1 piston has a taller deck height, how can a shorter c-85 piston give more compression? Tim
C-85.......1.698-1.708......????
O-200D...1.745-1.750......8.5-1 compression
Performance Aero pistion is 1.870 ....... 9.0-1 compression

[JimC]

I haven't looked at the 8.5 piston. Rod length?
In the visual description below, pretend the cylinders are vertical.
The C85 piston is tall enough that the top perimeter has to be chamfered to clear the head. That would seem to be about as tall as you can make a flat top piston. And on some assemblies, others have reported that the bottom of the top ring can get high enough to hang on the top of the steel cylinder barrel. I hear it is a bit of a struggle to get everything back apart when that happens (I've.not confirmed this for myself).

[PA1195]

Briefly my wife consented to download an acceleration app from Apple to her I-Phone. Three axis X-Y-Z planes with + and - G values ref to phone position. Start run and stop run plots a stream of 3-axis data. Others offer plotting software to export and plot the results. Will cost me a dinner for two her choice.

https://itunes.apple.com/us/app/accelerometer/id499629589?mt=8

JimC have you experimented with this tech? It's like ...why is this news? I would have thought the builders and modders would have figured a way to apply this to their alterations by now and discussed it.

Gary

[astjp2]

I haven't looked at the 8.5 piston. Rod length?
In the visual description below, pretend the cylinders are vertical.
The C85 piston is tall enough that the top perimeter has to be chamfered to clear the head. That would seem to be about as tall as you can make a flat top piston. And on some assemblies, others have reported that the bottom of the top ring can get high enough to hang on the top of the steel cylinder barrel. I hear it is a bit of a struggle to get everything back apart when that happens (I've.not confirmed this for myself).

Rod length is the same for all of the engines that we deal with. I would love to get some measurements on the Lycon pistons along with some weights.

Also a real dynometer would really give true numbers, but most of us cannot afford to start doing mods, run on a dyno then do some more and get more numbers. I would be happy with flow numbers on carbs and intake configurations with some porting, polishing, and gasket matching mixed in.

[PA1195]

I think plumbing a manifold pressure gauge into the induction should reflect incremental improvements. The closer the WFO value is to the reading prior to start the lower the induction system loss. Not sure where to plumb. Mine is at the induction spider but cylinders typically have a tap over the intake port.

Continental offers a range of expected values at full throttle in their Testing After Overhaul section late in the O/H Manual. I assume a lower vacuum/higher manifold pressure reading is better.

Gary