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SJ 50 vs Cast Q500 AAC

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Old 01-15-2011, 11:08 PM
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still4given
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Default SJ 50 vs Cast Q500 AAC

How close is the SJ 50 to the Q 500 engine.

I presently fly a racing cub in our Warbird racing. It has a Nelson Q500 SS. It has seen better days and I wondered if the SJ 50 can be made to run like the Q500 engines. I have a SJ 50 that I am not using because in stock form it just doesn't get me to the right speed to be useful for my purposes. Are there mods that will get the SJ 50 up to the rpm's that the Q 500 will turn?

Also, I look on the Jett website and all I see are one set of prices for the Q 500 and Q 40 engines of $325 and $375 for BSE. Are these the long strokes? Are these prices even accurate?

Thanks, Terry
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Old 01-16-2011, 10:51 AM
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Default RE: SJ 50 vs Cast Q500 AAC

Terry, I've had my SJ.50 on a Predator in the past and it was no where near as fast as a BSE SS Q500 motor. I use it in my Magnum which is a pretty slick plane too and only get around 160+ with it.
If you go back and look up the Carolina Speed Rally you can see data from different engines and airframes.
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Old 01-16-2011, 05:51 PM
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Default RE: SJ 50 vs Cast Q500 AAC

Thanks Vic,

I got a chance to run the SJ 50 today. I hurt it a little last year when I ran it on 60% by mistake. I haven't run it much since so I am hoping it will come back some after a few tanks. That said, I was only able to get 19,000 on an APC 9x6 today running the Black Jett Muffler. The Nelson turns an APC 9x7 at 19,000.

Thanks, Terry
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Old 01-17-2011, 05:13 PM
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Default RE: SJ 50 vs Cast Q500 AAC

Mine is pretty old and clapped out but I see 18+ on a 9X8 about half turn off lean.
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Old 01-17-2011, 06:33 PM
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Default RE: SJ 50 vs Cast Q500 AAC

That's pretty good. I didn't try a 9x8 because of the black pipe. I wasn't sure it would stage. I have a gold pipe and a red one. I need to get it mounted in a plane and run it for a while to see if the fit will return.

I'm still wondering if there is a way to get it to run with the Q 500 engine. Maybe Bob will chime in when he gets a chance.

Blessings, Terry
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Old 01-17-2011, 07:16 PM
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Default RE: SJ 50 vs Cast Q500 AAC

I have the red pipe on mine.
The two engines are in a different class to each other and run totally different.
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Old 01-18-2011, 08:57 AM
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Default RE: SJ 50 vs Cast Q500 AAC

Thank Vic,

Even when mine was new, it wouldn't turn a 9x8 at 18K. I was under the impression that the cases and cranks were similar between the SJ 50 and QJ 40 so I was hoping that there was a way to get the 50 to turn up like the QJ. I don't need the engine to idle since it will be used for racing. Maybe I should give Dub a call and see if he can give me the best case scenario.

Thank again, Terry
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Old 01-18-2011, 05:58 PM
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Default RE: SJ 50 vs Cast Q500 AAC

I got a chance to speak with Dub today.

He said it is not worth the money it would take to convert the 50 to turn the rpm's the Q motor will turn. He said it sounds like I need a new piston for my 50 though. Guess I'll be sending it in. I'll just have to find another use for the 50.

Thanks for all the help.

Blessings, Terry
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Old 01-28-2011, 01:24 PM
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Default RE: SJ 50 vs Cast Q500 AAC

Sorry Terry... was out of pocket for a while there.... missed your post.

Let me know how things go with the engine.

Also keep in mind ... some of the RPM numbers you see in the high desert are different than down at sea level.

One of the differences that really change on the SJ-50 to get to the racing engines is the crankshaft. Piston sleeve timing is one thing, but the crank timing is different too. The sport engine is set up for performance, and fuel draw/throttle response. Racing engines rely entirely on the muffler pressure for fuel draw, so you can compromise on the other aspects.
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Old 02-05-2011, 05:18 PM
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Default RE: SJ 50 vs Cast Q500 AAC

Thanks Bob,

Are the cases the same size on the SJ 50 and the QM2? I am building a new cub, and if they are the same size, I can use the SJ50 to get everything lined up while I am waiting for the QM2.

Thanks, Terry
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