Turbo Corvair Conversion ..........Hypothetical

Discussion in 'Corvair' started by ekimneirbo, Jun 17, 2015.

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  1. Jun 17, 2015 #1

    ekimneirbo

    ekimneirbo

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    Lately my mind has been reconsidering engine options. Turbo engines seem to have a lot to offer if set up correctly.

    The things buzzing around in my head (maybe I should have said rattling around :) ) are;

    1. In a STOL aircraft configuretion, would it be best to set one up to add power for take off and
    then have minimal or no boost at cruise to avoid high head temps for extended flying times.

    2. Would it be better to use a smaller turbo or a medium sized turbo? Its my understanding that
    the medium turbo would work fine in a range from 2500/3500 rpms and provide almost no boost
    below that rpm. I also am given to understand that a larger turbo heats the intake air less than
    a smaller turbo and helps alleviate the need for an intercooler.

    3. Further I'm given to understand that a simple turbo system can be fabricated without the need for
    a BOV or intercooler if someone is not attempting to make major power boosts. I think having
    something like 180 hp from a 3000 cc Corvair stroker with some 140 hp heads would be my target.

    What do all of you think and where am I going wrong............... :ermm:
     
  2. Jun 17, 2015 #2

    Vision_2012

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    Definition of Stroker: A Stroker kit is an aftermarket assembly that increases the displacement of a reciprocating engine by increasing the travel of the piston (that is, the piston moves further up and/or down in the cylinder). Wikipedia.
    A 3000 cu in Corvair can be obtained by increasing cylinder diameter to 92mm using off the shelf VW pistons and cylinders, the stroke used is still standard Corvair pison rod and rocker pushrods, with the piston rod bored out to receive the VW piston pin.

    140 Hp heads have been found not to have the correct combustion chamber profile and are prone to pre-detonation. I don't know why this doesn't happen in cars but the Corvair air conversions don't use these heads.

    Corvair conversions have been using direct drive to get max power at 3100-3200 RPM; to get more power, like 180 HP, I think you would need a PSRU to use more RPM while keeping the tip speed of the prop down.

    I recommend William Wynne's Conversion manual to base oneself on what has been done before. I think he has turbo-normalizing scoped out, but not turbocharging. I would love to turbo-normalize my Corvair 3000, but I would not be interested in turbocharging. But first I need to finish my plane. Keep up the experimenting.
     
  3. Jun 17, 2015 #3

    rv6ejguy

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    I've run a number of turbocharged Corvair engines in years past in cars.

    You need a wastegate and a properly sized turbo to give you good boost control and efficiency across the operating range.

    Compressor must be matched to your needs, it will be relatively small in this hp range. Proper matching is the key to lowest compressor discharge temps, not necessarily size.

    We use much larger turbine wheel and turbine wheels for aviation than we normally do on auto applications.

    If you keep boost and altitude low, you MIGHT get away without an intercooler if you keep the CR low enough. Custom forged pistons would be required to get the CR down to a workable limit if running 91 unleaded.

    You don't need a BOV on an aircraft- or a car for that matter. Just a money grab.

    180hp on a slow aircraft in the climb might have marginal cooling.

    140 heads would ok, make sure the valve seats are in there tight and keep the CHTs down to reasonable levels.
     
    Last edited: Jun 17, 2015
  4. Jun 17, 2015 #4

    rv6ejguy

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    140 heads work fine if you get the squish height down below .030. This involves milling the "step" out of the chambers. Unfortunately, this raises the CR substantially so somethink must be done with pistons to correct this for a turbo if running mogas.

    There is no such thing as pre-detonation. There is detonation and pre-ignition, 2 different things altogether.
     
    Last edited: Jun 17, 2015
  5. Jun 17, 2015 #5

    Vision_2012

    Vision_2012

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    Thanks for correcting my pre-ignition/detonation contraction.

    Who has flown 140 Heads?
     
  6. Jun 18, 2015 #6

    mcrae0104

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  7. Jun 18, 2015 #7

    TFF

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    BOVs are not great in aircraft. Nothing like needing all the power you can get and have it pop open. And to get it to close you will have to throttle back. Great for flying straight into the trees you are trying to clear.
     
  8. Jun 18, 2015 #8

    ekimneirbo

    ekimneirbo

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    I have WWs newest Corvair manual and I respect his knowledge of Corvairs. One place where he and I differ is that he wants to provide an easily buildable and maintainable
    conversion that is extremely reliable......and he makes his living doing so. Kudos to him and all the effort he has put forth. On the other hand, I like to think for myself ....but am glad to gain knowledge from
    people like WW. This is in no way a knock on him....only a statement that I would like to build something similar but not the same. I felt that if one committed to a turbo, then the use of the big valve heads
    would lend allow the turbo to be more efficient. No need to restrict the air passage with small vale heads. In a non-turbo setup I can see where the smaller heads would be fine.

    Appreciate your comments. Any pics of your engine? :)
     
  9. Jun 18, 2015 #9

    ekimneirbo

    ekimneirbo

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    RV6EJGUY: I've run a number of turbocharged Corvair engines in years past in cars.

    You need a wastegate and a properly sized turbo to give you good boost control and efficiency across the operating range.

    Reply: Any suggestions for a starting point on a turbo and wastegate?

    Compressor must be matched to your needs, it will be relatively small in this hp range. Proper matching is the key to lowest compressor discharge temps, not necessarily size.

    Reply: Again, any suggestions ?

    We use much larger turbine wheel and turbine wheels for aviation than we normally do on auto applications.

    If you keep boost and altitude low, you MIGHT get away without an intercooler if you keep the CR low enough. Custom forged pistons would be required to get the CR down to a workable limit if running 91 unleaded.

    Reply: My thoughts are not for any high altitude flying...just mostly cruising and exploring at reasonably low altitudes. We are 600 ft above sea level locally, but I guess its possible that
    some higher altitudes might ocassionally be ne
    eded.


    You don't need a BOV on an aircraft- or a car for that matter. Just a money grab.

    180hp on a slow aircraft in the climb might have marginal cooling.

    140 heads would ok, make sure the valve seats are in there tight and keep the CHTs down to reasonable levels.
     
  10. Jun 18, 2015 #10

    TFF

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    I would have a manual waste gate. You need to experiment on procedure, but then you can maximize what you want. The only problem with turbos in airplanes is they can be slow to spin up. You will have to hold and throttle up and get your boost then go. For as slow as a direct drive airplane engine spins, any of the ports would be ok wirh a turbo.
     
  11. Jun 18, 2015 #11

    akwrencher

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    I got a book recently called Turbochargers by Hugh MacInnnes. Found it on Amazon. It's a good read and might help with a better understanding of the issues involved in sizing a turbo. I got it because I've always wanted to learn more about the subject. At the very least, might help with knowing what questions to ask for sizing, etc. There's probably other similar books as well, it's just the one I ended up with.
     
  12. Jun 19, 2015 #12

    Bill Clapp

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    We are currently working on a turbo setup for our engines. I have flown behind many turbo'd engines - one being the VW Revemaster2180D - no wastegate but a Maloof constant speed prop. We dumped the prop after a few hundred hours and installed a wooded prop with fairly high pitch. I used the MAP gauge to watch boost (take it easy) and use slight boost at low altittudes and then increase once higher. For our Corvair conversion we are having a custom made prop fabricated that will give us in-flight control to take better advantage of the turbo. we will probably use a Garrett with eith vane control or wastgate...Havent fully made up my mind yet. I did the test flying for WW on the turbo engine - have my own feelings about that. I will post more later on this design and installation.....call me if you want more :)
     
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  13. Jun 19, 2015 #13

    ekimneirbo

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    I'm looking forward to more from you on the project. Right now I have some basic understanding of turbos and have several books on the subject. The problem is getting and deciding on specifics ...so I'm trying to learn more before plunking down any cash. I have several Corvair cores in my shed and am fairly handy at fabricating things I need (want ?). What I'd really like to build is a
    fuel injected turbo Corvair. Most info I have found on the subject seems to lean toward extracting maximum power with a turbo. One of the books discusses how many OEM automotive turbos were originally set up with a smaller turbo to give that
    initial burst of power but then quickly tapered off and didn't provide much on top end. Then they proceed to maximize power output. Since I want to work in the 2000-3500 rpm range, the knowledge I'm looking for seems harder to come by. I also want
    to stay lightweight and use as few parts as needed.......key word being "needed". If the system needs a certain part then I won'r sacrifice safety or reliabilty for a few more lbs. A BOV is an example of a possibly unnecessary part in an aero set up that
    is using a turbo that doesn't get near its maximum output. But I want other opinions.....maybe I'm not considering or analyzing things correctly. The operating parameters for what I want to do seem to be diametrically opposed to the type of buildup
    most people are looking at...........so I have to glean what I can by reading between the lines about what the effects of turbos are at lower rpm levels. :) I appreciate EVERYTHING anyone has to say on this subject. I realize sometimes comments are
    going to be contradictary to each other, but I still learn something from every comment.
     
  14. Jun 19, 2015 #14

    akwrencher

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    I hear ya, and that book is geared more to automotive type setups, but does have allot of info in it about how to read compressor maps and such, and what the numbers mean and what effects they have. Worth the few bucks for sure. Anyway, good luck with your project and keep us informed :)
     
  15. Jun 20, 2015 #15

    rv6ejguy

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    Best book on turbos ever written. The theory still holds true but most of the turbos in the book are obsolete these days.
     
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  16. Jun 20, 2015 #16

    rv6ejguy

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    BOVs are unnecessary on almost all applications but especially so on aircraft. People who don't know better usually insist they are, failing to notice that few professionally built race cars or aircraft use them (outside of overboost protection, which you can do with EFI easier).

    I could help you match a Garrett turbo if I knew hp, power setting for cruise and typical cruise altitudes. Be aware that matching for low boost/ low pressure ratios and/or normalizing usually results in relatively low compressor efficiency since most turbos are simply not designed for that range. You may need an intercooler to keep induction temps down to safe levels.
     
  17. Sep 15, 2015 #17

    slevair

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    I have a lot of experience on earthbound Corvair turbos, and high output with 140 heads won't play nice. Look at the factory set up. My unscientific observation is that the larger valve seats expand more with the load and extreme heat of the turbo and fall out at a greater rate. I also agree with Ross that the combustion chamber shape is not ideal. Heat rejection/soak is a huge problem on Corvairs at higher load/power settings. It was designed in the 1950's for about 95 hp with a bit of room to grow. I grew up racing these motors and love them, but I understand the design limits.
     
  18. Sep 15, 2015 #18

    ekimneirbo

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    In your experience, I would guess that you were attempting to gain the most hp possible (within reason)
    from the engines you built. These engines would operate at a higher rpm than on a direct drive airplane setup. What do you think about a setup operating at maybe 3000 rpms and wanting to add just 30/40 hp? It would seem that pushing the engine to higher outputs at higher rpms would produce a different result than a moderate boost at lower rpms using the same components. (I realize the turbo choice would be different) What are your thoughts on a combination like that?
     
  19. Sep 15, 2015 #19

    Bill Clapp

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    Working on one now for the Saberwing - bolt on kit for our 100 and 120 HP engine kits.....Skunkworks :)
     
  20. Sep 16, 2015 #20

    don january

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    Bill has there been a fuel injection set up made for the corvair?
     

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