If you were going to choose between a ROJett .67 LS and a ROJett .76 (both rear exhaust) which would you choose and why?

Thanks,
Jim

     I (obviously) took a third option, but, given those two choices, I would probably get the 67LS. Paul tells me that the 76 really only works with giant props, and if you run normal-size props, it's no more powerful than the 61.  I know Richard and Dub think the 67LS is the best of the bunch, but Richard runs a lot slower than I would want.

   I don't have enough experience with the 67 to make any good prop recommendations, but most of the current 67 runners use a lot more pitch than I feel comfortable with. I don't know what pipe to use or what length.

  As always, it is not about getting enough power, it's about getting the optimum power delivery.
 
   Brett

Bret,

Thanks for your insight.

I have a friend who has a near new .76 that I can get at a good price.  What prop should I start with?

Jim

   It depends on what airplane it is for, and what the other parameters might be (particularly which pipe and what length). My best guess is that you will come to grief with any of the smaller airplanes (Thundergazer, etc) or less-that-max passive yaw stability. For a reference, the current version of the Infinity is probably the king of passive stability and was intended to deal woth larger props - and I don't care for it even with a pretty light 13-3.75 3-blade. The engine would handle *much more*, but 12.5 is about all I want to deak with. So, while a reasonable prop for the engine, not pushing anything, might be a 14-4 3-blade (with maybe a 17.75-18" pipe), I would expect that to be a difficult trim issue even on an Infinity or Impact.

   All this is merely speculation, I have not run the 76 and only seen a few of them, those on mufflers, so that was a whole different set of issue  difficult to deal with, not because engine is particulalrly touchy, just because these mega-motors are such overkill that even a slight power variation is far too much to handle with just a needle valve. Windy found that one out the hard way with the 90 (or 88, or whatever it was).

   Brett

   

I've used the .76 exclusively for about a decade.  I used the .61s before that.  I have a new .67 that hasn't seen an airplane yet.  My preferred props are of my own making and are 12.5 x 6+ pitch 3 blade.  They are very close to the old Mejlick 12.5 x 4.6 which are not available any longer. 
It delivers a great deal of power and seldom needs to break into a two cycle, depending upon particular prop and rpm.  My 61's are also great but will need to break more often in the pattern.  I use the same props on both.  These are turning pretty slow compared to others-8000-to 8600 again depending upon exact prop and obviously quite long pipe length-near 22".  The .61 pipe is exactly 2" shorter.  The way I run these they have very little tendency to speed up in the wind so act to keep speed down which is also what the pipe is trying to do.  Just my personal thoughts;  I think the .76 has gotten a bit of a bad rap because those who tried it didn't find the best way to run it,  making assumptions that pertain to other power plants they were familiar with that didn't adapt well to this engine.  It uses less fuel than the PA .75 (also a very fine engine), pulls more and is readily available as is service and parts.  The most difficult part these days is obtaining the larger pipes and headers for them..that will be the same problem with either engine.  They ALL are drop in fits in the same airplane.  The larger engines have a little taller, larger heads.

I have no experience with any of the Ro Jett engines mentioned. I do have an observation from the peanut gallery about the 67L . A few years ago I went to the Bill Rutherford Memorial contest in Houston. Richard Oliver was using the 67L side exhaust on a large profile. I believe it was a profile of his Maverick design.
 I usually fly by myself and wasn't quite sure about maneuver sizes and where 45 degrees is on the "dome". I wanted to watch real stunt pilots fly the pattern. I watched Joe Gilbert and Richard Oliver, the then current F2B Team Members, from the Judges area. What blew me away and I found amazing was the absolute constant speed of Richard's 67L powered plane. Through each maneuver whether inside or outside squares, square 8 even the hourglass the plane maintained a constant speed. It was eye opening. I wasn't smart enough to order a Ro Jett right then and there. Since then, I've come across good deals on a Ro Jett 40 BSE RE and a OS 40 VF both with header and pipe. I hope to have them in planes by the end of the year.

David

I spoke with Paul the day he tested a loaner RO-Jett .76. He said it needed a lot of load, meaning big prop. I know he's not a fan of large diameters, but it would seem to me that more blades could solve that. Then, I read Matt Colan's recent comments about how changing from a 4 blade to a 3 blade improved his corners (PA .75). Mystery! Steve