Robinson V8 conversions

Discussion in 'Chevy' started by cheapracer, Sep 2, 2017.

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  1. Sep 5, 2017 #21

    TXFlyGuy

    TXFlyGuy

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    Having read many comments on engine operation by R.F., I'm confident that running an LS3 at 3600-3900 rpm is not going to hurt it one bit. The redline is north of 6200 rpm. So cruising at 3800 rpm would only be about 60% of the engines operating range. Robinson said to run it at 4000 rpm in cruise. And that may be where the 18 gph is.

    I am a believer in running engines as they were designed to be run. But I will not shove the throttle wide open, rather, a slow continuous push to the desired power setting will be employed. This is inflight, and on the ground for takeoff. The big 94" prop has a big arm moment.

    Just got off the phone with the folks at Supermarine Spitfire. They have been running LS2's / LS3's in their Spits.
    At high cruise, 3600 rpm, they claim a fuel flow of 14 gph. And a corresponding airspeed of 193 knots.
     
    Last edited: Sep 6, 2017
  2. Sep 6, 2017 #22

    pictsidhe

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    My 4.3 3/4 SBC will clog up if it doesn't get any hard running like a prolonged blast on an interstate. It does use a lot of oil, though.
     
  3. Sep 6, 2017 #23

    cheapracer

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    3800 rpm is a stress factor of around 30% of 6200 rpm, so should be plenty easy on it.

    18 gph might be that they are running them in SeeBees?
     
  4. Sep 6, 2017 #24

    Winginit

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    In an earlier post you mentioned they were trying to run in closed loop at higher than factory power ratings which would require the use of O2 sensors. Were they just experimenting to see which way might be the best solution ? The factory ecms are very reliable units and reasonably inexpensive. Today there are hundreds if not thousands of people reprogramming them. TxFlyGuy asked where the problem was when using these units. My opinion is the units are fine, and reasonably easy to make changes when using some of the better known programming tools. The problem lies with the person doing the programming. There are many ways to make things work, and each expert has their own ideas. Results will vary depending on the choice of someone to do the programming.
     
  5. Sep 7, 2017 #25

    TXFlyGuy

    TXFlyGuy

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    Robinson told me that 4000 rpm was a very doable cruise power setting, adding the 18 gph number.

    I called Supermarine Spitfire, who installs LS3's in their replica warbirds. They claim a FF of 14 gph at 3600 rpm.
     
  6. Sep 7, 2017 #26

    Voidhawk9

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    Assuming that they are getting 250hp at 3600rpm (a little less than shown on the official GM chart), that is an SFC of .34!
     
  7. Sep 7, 2017 #27

    TXFlyGuy

    TXFlyGuy

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    They also claim a cruise of 193 knots / 223 mph at 3600 rpm. Not bad!

    They are in NZ. Contact Ivan Campbell.
     
  8. Sep 7, 2017 #28

    Voidhawk9

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    He's based only 2.5 hours drive from here, I'm planning to arrnge to visit sometime soon!
     
  9. Sep 7, 2017 #29

    rv6ejguy

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    You have to know what MAP and RPM people are running to have an educated guess of hp and BSFC figures. Doubt if this is at 30 inches.
     
    Jeffd likes this.
  10. Sep 7, 2017 #30

    TXFlyGuy

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  11. Sep 7, 2017 #31

    Toobuilder

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    That chart is for sea level.
     
  12. Sep 7, 2017 #32

    Winginit

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    I don't think the actual operation of the engine at slow speed would normally have a detrimental effect. Remember that in their original designed purpose they are usually operated at even lower rpms for extended periods when cruising down a highway. Once you adapt it to a redrive with a propeller, you change the forces that the engine is dealing with. Each of the conversions brings it's own set of circumstances due to variations in gearing, tolerances,prop weight,size,and configuretion. It's possible that both are correct when dealing with different airplanes.
     
  13. Sep 7, 2017 #33

    TXFlyGuy

    TXFlyGuy

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    Apples and oranges? A Mustang and a Seabee? Two different drives and props, for sure.

    Chain versus geared. Note that the Spitfire uses a belt driven PSRU.
     
  14. Sep 7, 2017 #34

    Voidhawk9

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    Oh yes, of course -duh me. :eek:
     

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