Hi Clint,

I think I can give you a good perspective on the long vs short stroke on the Arrow. I am currently flying a MK Arrow 60 with an OS .61RF on it, APC 12x10 prop, Hatori header and Macs muffled pipe. I purchased the plane with the OS 61RF already installed. Although it flys very good with this setup, if I were to build it I would not go with the OS 61RF. I would much prefer the YS-60FR short stroke, or the Rossi or Webra short strokes.

Here's why: The problem is the pipe deck on the Arrow is not long enough to allow the long stroke 61RF to fully stage. You can measure the length of the pipe deck from the plans. From glow plug to end of pipe deck measures only 22" total, which is perfect for a short stroke, but too short for the LS engines. My header/pipe combo is absolutely maxed out and it still not long enough to come to full tune. Another 1" or so would be perfect.

If you do a search you'll see quite a few posts with this same issue if using a long stroke. The MK version of the Arrow 60 was modelled after Wolfgang's Arrow in '79. Somewhere between '81 to '83 he changed to the LS engine and lengthened the pipe deck to accommodate. But the MK plans/kit are the original SS version.

The good news is the long strokes are quite tolerant of pipe lengths and the 61RF still runs well. It's just not as fast as I'd like . So I am doing just the reverse of what you are doing, I'm taking out the 61RF for a YS-60FR, now waiting for the MK soft mount for the YS to arrive from Singapore Hobbies.

Btw, when I purchased the plane I also considered swapping out the 61RF for a new 61RF-P that I had (this was prior to realizing the pipe deck too short), but in my mock-up the pump gets awfully close to the rear firewall. After running the 61RF, it ran perfectly steady without pump pulling both inside and outside loops. So any engine without pump should work.

The plane flys awesome, smaller and more nimble than I expected. For something like this, it just feels more right to have a 15K rpm short stroke up front! If noise is not the issue, I recommend the short stroke. If you prefer LS engines, you might need to consider to lengthen the pipe deck for a perfect tune.

Matt