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K&B 7.5 DF engine tuned pipe length

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Old 05-21-2006, 07:31 PM
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jmupilot
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Default K&B 7.5 DF engine tuned pipe length

Can anyone tell me the approximate length of the header pipe for the K&B 7.5 DF engine. I have a Mac's header and tuned pipe and would like a good starting point. I'm reading a RPM of 16,200 right now with an APC 9x8 pylon prop, thats with the factory length on the header.

Thanks,

Pete
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Old 05-26-2006, 12:37 AM
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Default RE: K&B 7.5 DF engine tuned pipe length

Call Larry Wolf at Jet Hanger Hobbies, he helped me with the same problem before.
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Old 05-26-2006, 03:56 AM
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Default RE: K&B 7.5 DF engine tuned pipe length


ORIGINAL: jmupilot

Can anyone tell me the approximate length of the header pipe for the K&B 7.5 DF engine. I have a Mac's header and tuned pipe and would like a good starting point. I'm reading a RPM of 16,200 right now with an APC 9x8 pylon prop, thats with the factory length on the header.

Thanks,

Pete
IMO, the only way to determine the exact tuned lenght is by tuning and flying. Check the Jett engineering homepage, they have tips and trix about it. But simply cut 1/4" of your header each time and let the engine cool down between runs. Cut the header until you get the maximum rpm. The rpm gain is the the most when you start cutting and becomes much smaller when you reach the max rpm of what your engine/pipe setup is capable of. I would stopp cutting if the last rpm increase is as small as 100rpm and just fix it there. It is also good to set the main needle slightly richer than usuall because the engine will now unload a lot in the air and needs the extra fuel. Good luck
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Old 05-26-2006, 12:10 PM
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Default RE: K&B 7.5 DF engine tuned pipe length

Do what Flyer95 said- I had this combo but no idea what length I had going... 16.2 is VERY modest, so have fun cutting and tweaking?

Bob27 around?

I was getting a tad over 19K with a 9x7 Rev-Up wood prop. (Old school)

Cheers!
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