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Author Topic: Venturi size for ST G20/.23 glow engine?  (Read 860 times)

Offline frank mccune

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Venturi size for ST G20/.23 glow engine?
« on: March 31, 2019, 12:03:19 PM »
       Hi All:

       What would be a good venturi diameter for a ST sprinkler style to use for a ST G20/ .23 glow to be used for Sport flying?

                                                                                                                                                     TIA
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Offline Carl Cisneros

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Re: Venturi size for ST G20/.23 glow engine?
« Reply #1 on: March 31, 2019, 08:24:10 PM »
Frank

check with james at Lee Machine Shop

can't go wrong there.

http://leemachineshop.com/Ordering/Order.php

Carl
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Carl R Cisneros, Dist IV
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Offline RandySmith

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Re: Venturi size for ST G20/.23 glow engine?
« Reply #2 on: April 01, 2019, 03:46:31 PM »
Quote from: frank mccune on March 31, 2019, 12:03:19 PM
       Hi All:

       What would be a good venturi diameter for a ST sprinkler style to use for a ST G20/ .23 glow to be used for Sport flying?

                                                                                                                                                     TIA

Use a number  21  drill bit for it, if your  making a venturi  and  not a  restrictor

Randy
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Offline frank mccune

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Re: Venturi size for ST G20/.23 glow engine?
« Reply #3 on: April 03, 2019, 04:40:23 PM »
      Hi Guys:

      Thanks for the replies.  My friend has a venturi that was made for the G20-.15 Diesel.  It is about 1/8" in dia. and does not deliver the power that he needs for his plane.

      When I compared my G20 /.23 with My Brodak .25,. I found that the .23 out powered the Brodak engine.  Perhaps I need a larger venturi than the stock one that came with the engine.  Sombody suggested to replace the .25 venturi with the one that is shipped with the Brodak .40 for more power from the .25.  Any thoughts re. this swap?

                                                                                                                                                                           Be well,


                                                                                                                                                                            Frank
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Offline Steve Helmick

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Re: Venturi size for ST G20/.23 glow engine?
« Reply #4 on: April 04, 2019, 04:47:20 PM »
I don't know anything about the B.25, but the early B.40's came with a .305"-ish venturi bore....way too big for a .25. Locals who have tried the B.25 were not impressed with the power compared to the OS .25LA. IF the spraybar goes straight through the center of the venturi bore and the spraybar is the usual 4mm/.156" diameter, I'd expect something around .257" > .272" bore would work ok. Use a layer or two of pantyhose mesh over to fine tune. I would not be surprised if the B.25 has quite low compression, so I'd look at head clearance and volume, and compare it to the OS. I believe B.25 also comes in a racing version with higher compression and timing...might look into that and trying the racing head? :!  Steve 
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Offline Brett Buck

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Re: Venturi size for ST G20/.23 glow engine?
« Reply #5 on: April 04, 2019, 10:40:14 PM »
Quote from: frank mccune on April 03, 2019, 04:40:23 PM
      Hi Guys:

      Thanks for the replies.  My friend has a venturi that was made for the G20-.15 Diesel.  It is about 1/8" in dia. and does not deliver the power that he needs for his plane.

      When I compared my G20 /.23 with My Brodak .25,. I found that the .23 out powered the Brodak engine.  Perhaps I need a larger venturi than the stock one that came with the engine.  Sombody suggested to replace the .25 venturi with the one that is shipped with the Brodak .40 for more power from the .25.  Any thoughts re. this swap

   At least some of the Brodak 40 venturis are far too big for a 40, much less a 25. Some one mentioned that their 40 had a *.308* (presumably 7.7 or 7.75 mm) - which with the typical spraybar is FAR, FAR more choke area than David Fitzgerald ran on the PA75 when he won the WC.

     You aren't going to make a silk purse from a sow's ear, and it doesn't surprise me that the G21/.23, the big brother to one of the better  performance engines of the 60's (the G20/15), is able to beat an iron curtain "retro" engine that was  intended to be a chugger for an ancient approach to stunt. I would certainly start with Randy's recommendation,  then adjust from there.

    My first "big" airplane was a Ringmaster Jr. with a G21/23. It was, not surprisingly, way, way, too fast and I don't think I ever got a flight out of it where something didn't fall off or break. The engine would fly a S-1 Ringmaster perfectly well.

     Brett
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