Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

speed engine- OS 91SZ-H ps-hyper ?

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Old 11-06-2008, 08:39 PM
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brjensen71
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Default speed engine- OS 91SZ-H ps-hyper ?

Just got an almost new OS 91SZ-H hyper heli engine for $143.

I seen another post about the 70 size OS heli engine working well for a speed plane. Is the 91SZ any good?

I still have to order a proper adapter, header and pipe before I can test run it.
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Old 11-10-2008, 10:15 PM
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Default RE: speed engine- OS 91SZ-H ps-hyper ?

with a GMS 76 size muffler installed and 10% nitro ( had to slot the muffler mount holes by .035") :
APC 10X10 14800
APC 11X12 12400

got a header and Pipe on order to test next.
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Old 11-10-2008, 11:29 PM
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Default RE: speed engine- OS 91SZ-H ps-hyper ?


ORIGINAL: brjensen71

with a GMS 76 size muffler installed and 10% nitro ( had to slot the muffler mount holes by .035") :
APC 10X10 14800
APC 11X12 12400

got a header and Pipe on order to test next.
Good idea. those numbers are quite low. When it's running right, that 10X10 may be too small. 11X10 or 11X9 at about 15K
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Old 11-15-2008, 05:57 PM
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Default RE: speed engine- OS 91SZ-H ps-hyper ?

got the pipe and header. had to actually lengthen the header to get on the pipe.

so far a little disappointed, with 30% nitro, an APC 10X10 I can get 15400 to 15600 rpm depending on pipe length.

I haven't tried my other props yet. I have APC 11X12, 11X11, 11X10 & 11X8 props to try.
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Old 11-15-2008, 08:24 PM
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Default RE: speed engine- OS 91SZ-H ps-hyper ?

Well that engine's peak power is at 15K. Now load it with more prop. What pipe are you running?
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Old 11-16-2008, 07:20 PM
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Default RE: speed engine- OS 91SZ-H ps-hyper ?

With a little help from the "Glow engine" forum I got the pipe set-up correct.

I was able to get 16200 RPM on 30% nitro and an APC 10X10 prop
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Old 11-16-2008, 07:29 PM
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Default RE: speed engine- OS 91SZ-H ps-hyper ?

the pipe works like a governor too. Dont forget that.

You have a baseline. Start going up in prop size. Do not change the pipe.

When you get to a point whre the needle becosme hard to set, or if the engine refuses to stage on the pipe...... the prop is too large. Back off a size and repeat the test.

On the Jett 90LX FIRE engine, a 10x10 and 11x7 turn appx the same with the same setup (around 16K). Loading down with an 11x8 put the engine on the up-side of the power curve, so when it unloads in flight....... it gets right back up to 16K in a hurry.
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Old 11-16-2008, 07:41 PM
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Default RE: speed engine- OS 91SZ-H ps-hyper ?

ORIGINAL: brjensen71

had to actually lengthen the header to get on the pipe.
Normally I need to cut off about 2" of a new Macs header (depending on the plane and engine). I never heard of lengthening a new header?
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Old 11-16-2008, 07:57 PM
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Default RE: speed engine- OS 91SZ-H ps-hyper ?

I ended up shortening the header to get to 16200. But was able to get over 15500 by lengthening it before I shortened it.
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