Does anyone have degrees of exhaust duration on a known good stunt engine with a baffle piston like a SuperTiger 46?

What are some good numbers, maybe I should measure a Fox 35 to compare?

I have a couple of nice Webra Silverline 40's I want to use but not sure they would give me a good stunt run.

Thanks,
MM

  Other things matter too, but 140-145 degrees is about the right answer. Thats the RO-Jett 61 "Brett" version and the the 40/46VF.

      Brett
   

These engines are like a K&B 4011 with the square windows but a smaller single bypass and smaller crank. I think they're some kind of Webra Sport series. here's a pic of one on ebay:

http://www.ebay.com/itm/Webra-40-RC-GMBH-8581-Weidenberg-engine-power-airplane-model-speed-flying-/221824522610?hash=item33a5c59972


MM  

Just put the degree wheel on it, 130 exhaust. I want to put this on a Yates Dragon for old time stunt. What would be a better engine for old time?

MM

I have tested the same engine with 136, 140, and 145 degree exhaust durations. As the duration got longer, the engine ran with progressively less boost and brake. The RO-Jett 61 with 136 degree exhaust like the PA had the same run characteristics as the PA, with very abrupt and strong boost, particilarly. 140 was smoother, 145 was smoother still - just like the 143-146 degree OS 40VF. This seems to be an intrinsic property.

   The reason I have RO-Jetts (and the "Brett" version that is 145, although it should probably be called the Jim Tichy version) is that they don't have the abrupt hard boost/brake of the PA. We were never entirely able to remove that with the PA61, without also killing all the power. David solved that problem by going to the PA75, and then the detuning to soften it up still yielded sufficient power. That was not an accident, he more-or-less set out to replicate the Jett 61 run with a PA.

  There are certainly a lot more things to it than just the exhaust duration (like the *other* major difference between the RO-Jett and the PA, leading to the difference in inside/outside speed symmetry), but I think my experiment is about as controlled as they come in stunt, and the results are clear.

     Brett

Brett did you ever try the PA-65?

For me, the 61 and the 65 are not even in same family.  They may look the same but that is about it....   That's just my .02.

Other than the larger bore  everything is exactly the same, timing and all. I can make the 51 61 and 65 all fly the exact same plane extremely well, and have done this numerous times.
Right now I am using a PA 51 in a KATANA, although the 61 and 65 have been there and also fly the plane very well.

Randy

Oh, there is no doubt they can all be made to run and fly the same plane very well and have done so on 1000s of occasions all over the world.  But as far as I am concerned the 65 has just enough extra displacement over the 61 to make it a VERY VERY VERY strong yet docile motor. But not too much extra to where you might have to change the way you run it.  This is just my very worthless opinion, but it really is the best of both worlds.  I will be hoarding my one and only 65 until the end of time.

 

or a reason to try to again, bash PA engines, or pump the RJ mistake version,

   Since I was doing neither, I don't know why you said that. Comparing and contrasting the two, or daring to speak aloud in less than effusive praise, is not "bashing". This is your issue, not mine.

    I am relaying the *objective* experiences several of us have had with the PA that doesn't happen on the VF or "accidental" RO-Jett 61 version and the fact that the difference appears to be at least partially a function of the exhaust duration.

    Brett