SJ 50 vs. YS 45

SJ 50 vs. YS 45
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SJ 50 vs. YS 45 - 8/17/2007 5:16:31 AM

sti warrior

Posts: 7
Joined: 7/26/2007
From: san antonio, TX, USA
Status: offline

i just purchased my first Jett SJ50 engine and i am really amazed had no trouble firing it up.
My question is i have a YS 45 engine, on the ground it turns 15200 rpm which is less than what my jett turns 16600 RPM
but still i cant catch up with it, it seem YS engines really turn up rpms on the air. What prop could i use to catch up to it, Both engines are on the same plane,
i am using a 10x6 on the Jett and a 9x8.5 on the YS. already switched props and still YS seems to be a tad faster.

< Message edited by sti warrior -- 8/17/2007 6:46:27 AM >

Post #: 1

RE: SJ 50 vs. YS 45 - 8/17/2007 6:53:26 PM

bob27s

Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline

The YS 45 is a darn good engine ..... so nothing wrong there. Ive flown a few of them over the years.

As far as speed --- a lot depends on the exhaust system you are using on the YS ... full pipe? tuned muffler? stock can muffler? Tell me a bit about the setup, pipe length, fuel, etc.

Your Jett engine will unload quite a bit in flight above its ground peak rpm. Most engines will see 500-1000 rpm more in flight. The YS is similar. So I would not expect to see the 15,200 rpm match or exceed 16,600 in flight (gain 1400 rpm) under normal conditions, and with the props you noted... but it would have to if the aircraft is traveling faster.

From my experiences, the YS45, with a full tuned pipe setup, properly tuned for use with a 10x6 will usually match what the Jett 50 is capable of (Jett rpm would be with the stock jett-stream muffler). The YS does better with bigger props, tends to have more conservative timing, and the pipe helps with torque.

Tell me about the airplane. Prop selection has to be matched to the airframe and the application, as well as matched to the engine. It also might help to have a photo of the aircraft and installation. Knowing more here, I can recommend a few props to try.

How are you compairing airspeed? Radar? Air data? or just "it looks faster" ?

RPM of 16,600 with a 10x6 on the SJ-50 is ok for the new engine. I trust you followed the break in proceedure. The rpm is still a bit lower than the baseline, but it will get up there a bit after break in, and will continue to get better over time.

If you did not break-in the engine on the bench.... please read the proceedure that came with the engine, or the one posted on the jett website.

When experiementing with prop selection on the SJ-50, try to select props that allow the engine to see between 16,500 and 17,500 peak ground rpm. For flight, find the peak rpm, and back off 500-700 rpm from that point.... that should be a solid needle setting.

Let me know on the questions above

Bob

_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to sti warrior)

Post #: 2

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