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What RPM does a Magnum 91 4-Stroke turn an APC 14x6? Please give flight RPM, peak RPM and Nitro content.


Thanks,

Scott "Nobody" Allison
Louisville, Kentucky

Ed_Moorman

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I'm going to answer even though I don't normally take rpm readings. I've been flying powered model airplanes since 1950 and I still have no idea why people are so enamored with rpm. You can't compare anyone else's rpm to yours. The temperature, humidity, engine condition, fuel and various other things can affect the result. What you need to now is how it pulls your plane. I have owned a tach for years and, to tell the truth, the only time I use it is during break-in to keep the rpm in the 4000-5000 rpm range for the first 2 tanks on ringed engines. I also checked to see how much I gained on a Performance Specialties Ultra Thrust muffler. (800 rpm on a 14-6, OS .91FX)

I have a new Magnum .91RFS. It has had a half gallon of 20% oil, break-in fuel run through it on the bench. The fuel is regular Omega with extra castor to bring it up to 20% oil. In this case, I added 6 ounces of castor to a half gallon of fuel. During the bench run, the compression came up very well. As a matter of fact, the compression seems as good as the 2 Saito .91s I have, and they have excellent compression seals. The Mag .91 now has "snappy" compression so you have to hold the plane to turn the engine over. I attribute this to the half gallon of slobbering rich running to let the ring seat well. A proper break-in pays off. I did check and set the valve gap after the bench run.

I installed the Mag in my old Joss Stick, which is my .91-1.20 engine test and run-in plane. I'm running a Master Airscrew 14-6 at this time to see how it flies compared to other engines that have been in the plane(2 Saito .91s, Mag .91XLS, OS 1.08 & .91FX, TT .61). After a few more flights, I'll switch to an APC 14-6 or more probable, an APC 15-4W to get it tuned for fun fly use.

I put only one flight in today because it was cold (below 60 is cold for me). I landed and leaned it out twice during a long flight. At the end, it seemed to pull the plane vertical as well as with my Saitos, both of which have been in the Joss. After I leaned it out, I took off and pulled vertical. I remember thinking that this engine is pulling pretty darn good. I'll be out of town next weekend visiting grand kids, but I am anxious to work it out some more, even on the old Joss which weighs nearly 11 pounds. At this point, it would seem to be an excellent alternative to the more expensive Saito. It should also gain a little more power after another gallon runs through it.

RC Thumbs

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Thanks...............but I really needed the RPM numbers. I don't need any break in advice. I'm working on performance mods and was looking for base reference numbers. (Other than my own)

Thanks.

Scott "Nobody" Allison
Louisville, Kentucky

Doug D.

If you haven't done anything to the valve springs, that's as good as it gets.
My Saito .90s turn about 9,500 with a 12x7 and 15% fuel. With different props they pull very well.
You may want to switch over to the engine forum. You may get more hits there. [&:]

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Thanks..........

shford

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I have a Magnum 91 FS in my Lanier P-47. I an using a Master Airscrew 14x6 prop. Top end is around 95-9700. I usually don't let it run it that high. I usually run around 92-9300 to keep it a little rich. I am happy with the engine.
Sam

RC Thumbs

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Thanks Sam!

I was looking for a base number. This particular engine turned 9,500 in stock form (peaked) before the mods.

Thanks for the numbers..........

"Nobody"

shford

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Nobody,

shford

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I hit the enter button by mistake. You asked about nitro content. I use 15% Omega in my four strokes.
Sam