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Thread: Experimental PA-11 engine Options

  1. #1

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    Experimental PA-11 engine Options

    Me and my dad are currently working on a couple of experimental projects at this time, one of them being a wag aero sport trainer. We plan to build it light, no electrics, but include standard flaps. I know we may take some criticism for the flaps, but different strokes for different folks. One option we are debating on now is engine choice. Seems to me that some folks have said that a C-85 with a 0-200 crank is the hot ticket. Is this the case and what is it that makes this engine so good?? We have considered the standard 0-200, but some most will say it doesn't have the torque which leads you to using a very flat prop. Is the modified C-85 better than your common stock C-90?? Those of you that are experts on these small continentals please chime in. We want to stay with a small continental for low fuel burn and light weight. We currently fly a wag aero 2+2 with an 0-360 and want to downsize.

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    R. JOHNSON's Avatar
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    I've got a PA-11/early PA-18 style Cub with a C90-8 and the old Continental P/N 530788 cam that increases valve overlap. And at the recommendation of many we're running 2 to 1 exhaust w/ no muffler. I'm VERY please with the takeoff and climb performance with this engine. I would like to use C85 pistons which are taller than the C90 and would increase the compression ratio.

    The C90-8 came with the project and finding another one today along with the old cam is not very easy.

    I'd say you're best bet would be either the C85 stroker (0-200 crank and rods) in which your case, experimental, you could stay with the 85 pistons. Or maybe just build an experimental 0-200 and use high compression pistons like the C85, Lycon or Lightspeed.

    Sometime in the future I'd like to switch to one of the above mentioned high comp. pistons and have the cylinders flow matched and have intake system polished by Don Swords of Don's Dream Machines.

  3. #3

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    R.jOHNSON,
    I have a c90-12 w/aeromatic prop and it performs great but always looking for a little more power so could you tell me more about any performance benefits that you gained from your 2 to 1 exhaust versus the standard exhaust?

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    R. JOHNSON's Avatar
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    Hi Gary, I've never flown the C90 with the stock exhaust. It was just recommended by Don Swords and others to run an unrestricted exhaust with the older cam. The only downside I can see is it's a little noisy but not really a big deal with decent headsets.

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    Experimental PA-11 engine Options

    If you are going experimental I would build the 0-200.It is current production and plenty of parts.I spoke with Lycon a while back and there is plenty of power to be had.They do some pretty extensive head mods to get good flow besides blueprinting,balancing,hi compression pistons etc.I know of one cub 0-200 that makes over 130 hp on the dyno.
    A good exhaust will help a lot.Stock cub exhaust is beyond terrible.There is a cub exhaust here http://www.aircraftexhaust.net/exhau...to_album2.html for 0-200.
    I would also run a seaplane prop like a Mac 75/38 or Sensenich 76AK40-2.
    Be aware that if you do hotrod one that it will make enough power to run past redline without a real load on it.
    I highly recommend that you have the rotating components balanced(crank,rods,pistons) if you do nothing else.It is inexpensive to do and makes a big difference in harmful vibration.

    Bill

  6. #6
    behindpropellers's Avatar
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    I suggest getting the Continental parts interchange manual.

    If I were trying to build up a hopped up engine I would buy an 0-300 for parts and then get a C series case and 0-200 crank. FYI. I got lucky and scored 2 C-90s for $2500 a few years ago.

    Tim

  7. #7
    cubdriver2's Avatar
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    The C90/0200 cases are a bit stronger, because they have the threw bolts, But if you are starting from scratch, with a C85 case I think Divco can do the threw bolt mod when they overhaul the case. If so, 0200, crank and rod kit, C90 cam and tappets, three valve springs per, C85 pistons"you have to bevel cut the top of the piston, or radius grind the spark plug bronze insert where it interferes with the top of the piston. Check JimCs post about compression ratio and HP.

    Glenn

    P.S. smile increases with forward throttle movement.

  8. #8
    behindpropellers's Avatar
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    I think I need to get back to working on the J-5.....

    Here is the info on the cases:


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    Beware the "530788 cam equals higher low-RPM torque" theory.

    Data I've seen from both Lycon and an independent cam shop show that the newer C90 camshaft (531076) and the C85 camshaft (40584) will produce more low end torque than the 530788 camshaft.

    This data aligns with the rule of thumb that says high overlap increases high RPM torque/power but decreases low RPM torque/power.

    The 530788 may produce more torque than the other camshafts but this would occur in the higher RPM range. If I remember right you don't see the benefits of the 530788 cam until around the 2550 RPM area.

    I don't understand why this obsession with the 530788 cam exists. Maybe someone can enlighten me?

  10. #10

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    Experimental PA-11 engine Options

    I don't know how it got started either.It usually starts with"a guy knows a guy who says this cam is the one to use".Of course no one has any data because that would be way too much work.I would need to hear it from someone who could back it with real data before I accepted it.It may be a great cam when used in the right application.Without a real test program it is just hotrodder BS.

    Bill

  11. #11
    R. JOHNSON's Avatar
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    Your right guys, I don't have any hard data to compare it to, I just always thought this was the most desirable cam from what I've read on here and just thought I lucked out when this engine came with the project.

    I'm really happy with the way it performs but I'm not saying it has any more power than a stock 0-200, modified 0-200 , C-85, C-85/0-200 etc. with a different cam, sorry if that's how it sounded.

    Bill and gcgilpen what is your opinion of the best set up? Bill, from your above post you seem to be in favor of the 0-200, what exactly was done to the engine you seen dyno at 130hp, sounds like a real hot rod.


    EDIT: I'm not having any luck posting the link but one of the threads that turned me on to the 788 cam is titled "C-90 experts needed" where some folks weigh in on it.

    You can see pics of the exhaust we're running by clicking on the"www" icon at the end of my post, they're in the PA-11 gallery.

  12. #12

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    R Johnson... wasn't intending to slam your post (I also run the 788 cam... and yes it does work well).

    Just wanted to point out out that the idea of 530788 being the best low-end torque producer doesn't jive with general rules of thumb or theoretical calculations.

    I'd like to see some real empirical tests done on a dyno to sort this out.

  13. #13

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    Experimental PA-11 engine Options

    R.Johnson
    I was not being critical of your post I apologize if you took it that way.
    I would like to compliment you on your cub it looks really great.Workmanship looks show quality.

    The 0-200 I spoke of was built for an experimental cub.I was told it had hi-compression pistons,extensive head work,lightspeed ignition and a cam which I was not able to get the specs for.It actually made 138hp.This from someone directly involved.

    gcgilpin you are absolutely correct in regards to the 788 cam specs.

    Lots of cub guys seem to have a thing for running these small Continentals at low rpm.Mine will turn 2600 with the brakes locked and 2750 Vy.Normal cruise 2550,that is about 3/4 throttle.

  14. #14
    Roger Peterson's Avatar
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    I don't know why you are concerned with red line if you are running a fully balanced engined. I have flown mine at WOT which is about 3100 with a 76 A2 42 for over 2 hr at a stretch to break it in and no problems at all. I am running the 788 cam and the reason it didn't work too good in the C90 was because of the exhaust system. Has to be run with straight pipes. I get more out of mine using the 788 than the stock cam.
    Google: service bulletin m49-17

  15. #15
    Roger Peterson's Avatar
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    May also want to Google:

    Continental A&C-Series Aircraft Engines Parts Interchangeability Catalogue

    Make sure you have the right lifters.

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    Experimental PA-11 engine Options

    Hi Roger
    I figured you might chime in here.If you are referring to the mention of redline in my post I only brought it up because some folks have never seen that happen.Me,I don't worry at all

    By the way in a previous thread did you mention having put that 788 on a cam doctor?

    Bill

  17. #17
    Roger Peterson's Avatar
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    The guy I use to make my cams does not have a cam doctor, but I have a new one I could send to someone if they would do it.

  18. #18

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    Experimental PA-11 engine Options

    Roger I would like to do that.I will pm you next week.

    Bill

  19. #19
    centmont's Avatar
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    CubCrafters 4 in to none exhaust is a great improvement .... worth a look. Ralph
    "Entropy just isn't the same anymore"
    www.TheCubWorks.com

  20. #20
    cubdriver2's Avatar
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    At one time, I owned a C90-8 pa11S and a C90-8 Champ at the same time, the 11s C90 had been built up 20 years ago and they put the 0200 cam in it, with 0200 timing, a mac 69/48 prop. On a 70* day it would turn 2700 rpm on take off. the champ had a mac 73/41 and I could get 2450 rpm on take off, and flat out to 2575 level flight. I put the 73/41 on my pa11 and it would only turn it 2250 full throttle level flight, if I dove it a little it would go to 2300 but would drop to 2250 in level flight again. In my opinion the 0200 cam didn't have the balls to turn the bigger prop, that the stock C90 had no problem with. I never was good at math, but the seat of my pants science has YET to let me down. But than, I tend to only remember the good stuff.

    Glenn

    P.S. please don't ask me to compare cub verses champ.

  21. #21
    Tim's Avatar
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    Glen, what happened to that nice PA-11, I heard it was a nice ride

  22. #22
    R. JOHNSON's Avatar
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    Flew the plane today and came up with the following:

    32* F, 10kts on the nose, empty weight 860lbs, 175lb pilot, roughly 18 gals on board. Mac. CM71x46 prop.

    Three take offs, shortest 125' to 155', longest 180'.

    Take off RPM: 2450

    Vertical speed: 900 to 950 fpm (according to GPS)

    Average of 2300 RPM cruise speed (north, south, east and west) came out to be about 78 kts.

    I'd like to try a "flatter" prop like the 75/38 that Bill recomended.

    Ryan

  23. #23

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    Experimental PA-11 engine Options

    R.JOHNSON
    The Mac is not certified on the 90 so the Sensenich 76AK##-2 would be the one to try.I know roger really likes that prop.

    Bill

  24. #24
    R. JOHNSON's Avatar
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    Hi Bill, we're experimental so the prop I've really got my eye on is the Sensenich ground adjustable.

    Has anyone heard the latest on there bolt failure issue, where I (think) they had a SB out to replace the hub bolts every so often, don't really want to spend that kind of money until they've got that remedied.

    Ryan

  25. #25

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    Experimental PA-11 engine Options

    R,Johnson
    I talked to Ed Zercher at Sensenich about a week ago.They have re-designed the hub and were shipping the first last week.Current owners will get a new hub at no charge.I am holding off til the 76" blades are available which won't be until summer.They are going to make pitch cartridges in flatter pitch also.Those blades are really light like 1-1/2lbs each.Don't know how durable they will be.

    Bill

  26. #26

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    R. johnson,
    You might want to look at the newly manufactured aeromatic prop for your c90. I put one on my pa18-95 w/c90-12 and it made a world of difference. I removed mac 7147 and form my short time with the aeromatic i would say that it gives me about 7140-7147 range automatically. Takeoff now comes before i'm ready, no need to raise the tail.
    www.aeromatic.com

  27. #27

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    Quote Originally Posted by R. JOHNSON
    ...
    Take off RPM: 2450
    ..
    Ryan your take-off RPM sounds good for a 7146. I get about 2475 with a 7440 McCauley.

  28. #28

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    .......The 530788 may produce more torque than the other camshafts but this would occur in the higher RPM range. If I remember right you don't see the benefits of the 530788 cam until around the 2550 RPM area.

    We don't really care which cam produces more torque in the low rpm range. 2550 is right where you want to see the cam kick in, since that is about the static rpm you want to shoot for.

    I fly an O-200 J3. A friend flys an 85 stroker J3. I outclimb and out cruise him. I'm running a 7142, staticing about 2525 to 2550 depending upon density altitude. I climb it out at 2640 rpm by choking it down by means of climb angle. When running a 7535, I static about 2750 and climb out at about 2850 rpm. When running a 7441, I static about 2500-2525.

    The urban legend that the C90 has more torque than the O-200 is due to a drafting misplot on the O-200 power curves for 2550 rpm above 26" manifold pressure. Correct that mistake in the charts, and the O-200 develops slightly more hp and torque than the C90 throughout the mid to high rpm band. Again, who cares which engine develops more power and torque when the throttle is at idle ?

    With the 7142 on grass, about 65 degrees, 8 knot wind, empty weight about 789 pounds, pilot weight 165 pounds, fuel about 6 gallons, takeoff roll is 65 to 70 feet. Would be shorter, but the plane is running an 8" tailwheel.

    Same prop, grass, 100 degrees, no wind, full fuel, 215 pound pilot, takeoff roll is about 185-190 feet.

  29. #29
    S2D's Avatar
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    Quote Originally Posted by JimC
    -
    The urban legend that the C90 has more torque than the O-200 is due to a drafting misplot on the O-200 power curves for 2550 rpm above 26" manifold pressure. Correct that mistake in the charts, and the O-200 develops slightly more hp and torque than the C90 throughout the mid to high rpm band.
    Jim
    Would that hold true when operating at higher altitudes? I seldom see much over 26" manifold press here ( I'm at 3000'). How about posting the charts and explaining that to us
    thanks
    Brian
    I may be wrong but that probably won't stop me from arguing about it.

  30. #30

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    Interesting thread...these small continental ones always are...lots of different opinions...I have a C-85-8 powered T-Craft and a C90-12F powered T-Craft...the C90 gets off quicker...climbs better and has same cruise as the C85 powered ship...both planes are around 800 EW...the C85 has a McCauley 71-42...The C90 has a Sensenich 76AK-2-40...great off the water on floats 6-8 seconds....runs abut 2450-2460...the C85 with the McCauley 71-42 gets off in 12-14 seconds and runs about 2350-2400 Rpm...

  31. #31

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    Crap -- my response just went off into computer never-never land. Here goes again......

    The pertinent charts are Figures 15, 16, & 17 in the Operations Manual. I don't have broadband, so can't send them. You can use them to determine power both at sealevel and at altitude.

    A couple of examples of the sealevel power cross over points are:

    At 2350 rpm at sealevel, the C90 produces more power at manifold pressures below 20.8 inches; the O-200 more power at manifold pressures above 20.8 inches. At sealevel and that manifold pressure and rpm, both engines are producing 55.85 hp or thereabouts. That is 62.0% power for the C90 and 55.8% power for the O-200. Both engines will produce more power than this at sealevel, so the margin goes to the O-200.

    At 2475 rpm at sealevel (full rated rpm for the C90), the C90 produces more power at manifold pressures below 23.0 inches; the O-200 more power at manifold pressures above 23.0 inches. At sealevel and that manifold pressure and rpm, both engines are producing 57.5 hp or thereabouts. This is a rather low power setting for both engines, 75% power for the C90 and 67.5% power for the O-200. Both engines will produce more power than this at sealevel, so again the margin goes to the O-200

    You can back calculate these for 3000 feet, or other altitudes.
    JimC

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    It is an interesting thread. I run a 1B90 7142 on the O-200, and climb it out at 2640 rpm.
    JimC

  33. #33
    cubdriver2's Avatar
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    Jim, your best guess for a prop, and timing, C85, 0200 crank, rods, C90-788 cam, C85 pistons, cub on 1320s. What would give me the biggest smile

    Thanks Glenn

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    Glenn, me, I'd run the standard C90 timing and a 1B90 7440 prop. The C90 timing is slightly more conservative than the 85 timing, particularly with the 788 cam. I would not run the 85 pistons -- they give only 8.68:1 compression ratio. I'd run Lycon 9.5 pistons. They'll do fine on premium autofuel. As an aside, I tend to like the 0-200 cam, but I run a flat prop and high rpm.
    JimC

  35. #35

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    Re exhaust for C-90/0-200, installing the four pipe tuned exhaust on my 0-200 CC Sport Cub made a huge difference in power output over the standard Y exhaust. The only drawback is this exhaust is very loud. The benefit is an easy 10% increase in horsepower. Richard

  36. #36

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    Richard, that'd give you about a 14% increase in rate of climb. Is that about what you're seeing? Sounds like its well worth the doing.
    JimC

  37. #37

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    Has anyone put a modded high compression IO-240 in a PA-11 ?
    JimC

  38. #38

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    Does anyone know of an STC or previously approved 337 for mounting an O-200 on a PA-11 ?
    Thanks,
    JimC

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