Paul,

We might be starting to loose track of your threads (at least I am, not that it matters I suppose). Just a suggestion: it might be easier to have an ongoing discussion about your Minare and the engine setup if you concentrate on a single thread. I believe there are now 4 threads with a few posts and things may be getting "lost in translation", so to speak.

Anyhow, Dick's advice offered above is always nice to have. Someone with much experience with this type of engine and this type of pattern design in particular. For reference, Dick Hanson is the designer of the venerable Tiporare - a variation on the Prettner Curare.

Getting back to your engine, I read in your other thread that you "cut your pipe". I'm not sure if this means that you actually cut the pipe inlet (presumably) or just cut the overall length of the exhaust in the header length (although in this thread you suggest that you haven't cut the header). It is always a good idea to cut the header to tune the exhaust rather than the pipe as the latter will affect the expansion chamber volume and resonance behavior of the pipe. Reducing this in an 8.5cc pipe may effectively turn it into a 6.5 or 7.5 cc pipe. I've never done that or seen others do it so I don't really know how a pipe would behave if it were cut substantially at the inlet.

Other than the good tips suggested by Dick above, I am aware of others using the Macs 8.5 QP on an OS 55 AX and commenting that while this pipe resulted in more power (higher rpm), it was less "usable" as the throttle response was rather "peaky" with a less friendly power band. Instead, the 10 cc QP was favored and resulted in the engine behaving much better. The Webra 50 is slightly smaller than the OS 55 but it may respond in a similar way and using the longer 10 cc pipe may work out better.

I've also attached a review of your engine which you may find interesting. You will note that you are getting 1300 more rpm than Clarence Lee did in his tests. This difference makes sense considering his figures are using a Webra muffler and of course your plug, prop and fuel are different. Those differences aside though his tests yielded 14,200 on a Rev-Up 11x6. Given that, it seems that you could stand to loose 300-500 rpm on a slightly longer pipe setup (either different pipe or simply longer exhaust) and have a more reliable engine. At 5 lbs, your model should still have plenty of thrust in uplines on the APC 10x7. I would also try the 11x6 although this will require a longer exhaust setup yet. You might get ~13K+ on that prop when tuned.

As a point of interest, the recommended engine for the new Austrian Curare 60 ARF is the OS 55 (not the 65). I believe that model weighs around 7 lbs all up so your Webra 50 on a 2 lb lighter (and smaller) model is surely an impressive setup!

David