venturi???

[Bootlegger]

  This maybe should be in the engine section, I have a RO Jett 40 R/E with a # 10 venturi, on 15% nitro spinning an 11x4 APC prop at about 9500 rpm it is getting almost 7 min run time.
  I'm thinking that the venturi is too small, and it is a "true" venturi, if memory serves this is about a  .193 venturi .
  It will not run much faster than the above RPM..
  Sure could use some advice...
                         And thanks,

[Steve Helmick]

Gil...Is this on a pipe or on a muffler, or open exhaust? The #10 is .193", as you thought. Is there a spigot protruding into the bore? That needs to be corrected for, if so. According to Leonard Neuman's venturi chart, the size looks good for a .40.

I have launched Mike Haverly's Oriental Plus/RO-Jett .40 many times, and flew it once at least. His standard fuel is 10% (but it's cooler and less humid here), and the standard prop is an APC 11.5 x 4. That's on a Randy Aero pipe.

Makes me wonder. What's your head shim situation? If piped, what pipe and length?  Steve

[Brett Buck]

  This maybe should be in the engine section, I have a RO Jett 40 R/E with a # 10 venturi, on 15% nitro spinning an 11x4 APC prop at about 9500 rpm it is getting almost 7 min run time.
  I'm thinking that the venturi is too small, and it is a "true" venturi, if memory serves this is about a  .193 venturi .
  It will not run much faster than the above RPM..
  Sure could use some advice...

  What pipe length?  Sounds like you are running up against the "wall". That venturi doesn't seem small to me -  I would guess the choke area you are using is about what I am using on the 61.

   7 Minutes on how much fuel?


    Brett

[Bootlegger]

       Guy's I gotta appologize, I forgot to say that I am running a mufflet instead of pipe. I sure did think that on 15% nitro that the run would have been shorter (almost 7 min).
       The muffler that I am running is the RO header muffler that is for the engine.. Oh,The amount of fuel is 4 oz...
   Thanks for the help....

[Brett Buck]

       Guy's I gotta appologize, I forgot to say that I am running a mufflet instead of pipe. I sure did think that on 15% nitro that the run would have been shorter (almost 7 min).
       The muffler that I am running is the RO header muffler that is for the engine.. Oh,The amount of fuel is 4 oz...
   Thanks for the help....

   That doesn't sound too powerful to me. I have no experience with this combination but I would look at the exhaust end rather than the intake end of the system. Maybe run it on the bench with the muffler off and see if that picks it up. I would expect an AAC 40 to spin that prop around 12000 rpm or so if needed.

      Brett

[Bootlegger]

  Brett, I sure would have thought that it would turn higher also, with 15% nitro to boot, I have been running it on the bench as I don't have a plane for it yet, however the apc prop (11x4) does have a wide blade, I think that I might try a 10 1/2 x 4 1/2 apc next, on the bench again, and see what, if any increase I come up with.
  Thanks for the input...

  Steve, do you remember what fuel,and plug, and prop he was using and what rpm it was turning ?
  Thank you for your input also...

[Bootlegger]

   Brett and Steve, I got to looking some more, and thinking about what Brett said about checking on the exhaust end, there is a Bubro rubber deflector on the end of the muffler.
  Makes me think that this could be some of the problem, I also checked to be sure that the spray bar is open all the way thru and it is.
   What are ya'll thinking

[Mike Alimov]

Gil,
my well-worn OS 40 FP spins an APC 11.5x4.5 prop at 11000 RPM - and that's a plain bearing engine with a small venturi and old-style muffler, undrilled.  Something tells me your RO-Jett 40 should be capable of quite a bit more.
Check to see how tight glow plug is, and check the tightness of the head screws.  I had a few instances of pressure leakage through glow plug threads and/or head gaskets - a sure way to lose power.  Be careful not to over-tighten, though, as it will cause warpage.  I started a thread (a year ago?) about torques required for head screws  - see if you can dig it up through search.
Good luck.

[Mike Haverly]

I launch my RO-Jett .40 (piped 17.75") at 10,600 with a 11.5 x 4 Bolly 2 blade and use about 4.5 oz of 10% for a pattern. I can shorten the pipe and get a lot more if I want but it is like a cannon out of the corners. 15% doesn't change much on run time depending on outside temp but of course the needle changes.  It sounds me like restriction on the exhaust, like Brett said against the pipe; similar situation.  Get some ear plugs and try an open stack. 

Mike Haverly

[Bootlegger]

  Thanks for the reply's guy's, I am running the engine with a RO Jett rear muffler, trying to "sneak" up on a pipe set up...

[George Waters]

I run the header muffler like yours on that same engine with a gator 11.25x4.5 or a Bill Lee 11x4.5 3 blade with a 4.5 oz tank. I drilled my intake to.205 and it runs very well, about 630 on 4.5 oz. I didn't use the tach on it recently but it was about 9200 when i did.  George