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Webra 40Q with Nelson ultrathrust short pipe

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Old 10-30-2007, 12:17 PM
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hydro182
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Default Webra 40Q with Nelson ultrathrust short pipe

I have a Webra 40Q with the dynamix carb and larger stock muffler it turns an apc 9x6 17.5k to 18k. My question is, how much differance will a nelson ultra thrust short pipe make on this setup?
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Old 10-31-2007, 12:53 PM
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Default RE: Webra 40Q with Nelson ultrathrust short pipe

Figure on targeting the same rpm range, but with a 9x7 or 9x8 prop.

Look toward a the APC 8.75x8W for a real good baseline.
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Old 10-31-2007, 08:27 PM
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Default RE: Webra 40Q with Nelson ultrathrust short pipe

Thanks Bob that is what I was hoping for, I'm waiting on an apc 8.5x7 and an 8.5x7.5 that I ordered with the muffler,this engine is currently on a scatcat 500 and seems to be a pretty good match as far as speed goes.
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Old 11-01-2007, 07:59 AM
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Default RE: Webra 40Q with Nelson ultrathrust short pipe

We raced the Webra q-500 engine for a few years down south with SEMPRA. Good engine. Stock mini-pipe was not much to speak of, and a regular webra muffler choked it a bit. SEMPRA rules permitted pipes and replacement mufflers.

For that engine, the Nelson and Jett racing mufflers proved to be perfect, and were a bit less hassle than the pipes we were running (Macs 3.5cc pipe and special headers).

Try those props, but the 8.5" diamter props tend to be a bit light for the Webra/Muffler. For just sport flying... you are ok. They will work.

But you will be better off in the long run with 8.75x7.75 or 8W. The 8.8x8.5 will work well too.
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Old 11-02-2007, 08:50 PM
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Default RE: Webra 40Q with Nelson ultrathrust short pipe

Bob, I ran the engine today with the new muffler,it turned 18,000 with the 8.75x7.5 and 19,000 with the 8.5x7. The plane is quite a bit faster with either prop,I'm guessing around 120. I plan to experiment with more props, do you think the 8.75x8 or 8.5 will get me faster with the scatcat.
Donnie
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Old 11-03-2007, 09:38 AM
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Default RE: Webra 40Q with Nelson ultrathrust short pipe


ORIGINAL: hydro182

Bob, I ran the engine today with the new muffler,it turned 18,000 with the 8.75x7.5 and 19,000 with the 8.5x7. The plane is quite a bit faster with either prop,I'm guessing around 120. I plan to experiment with more props, do you think the 8.75x8 or 8.5 will get me faster with the scatcat.
Donnie
Yeah, you can probably get a bit more speed with the 8.75x8W

RPM is too high with the 8.5" prop..... skip that one.
8.75x7.5 is good...... 18K rpm is a good number... the high side of what you want to prop for.

The 8.75x8W will put you at around 17,000 - 17,500 ground peak.... back off 500 rpm for launch.. and it will jump on the muffler once in the air.
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