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New to Gas engine question

Old 04-08-2010, 08:04 PM
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LargeScale88
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Default New to Gas engine question

Hello, I'm pretty new to the gas engine stuff. My question was, do the gas engines need muffler taps for pressure? Or not because they have carbs. 2nd.. Can I make my own muffler without having to have certain pressure or whatever? Im a machinest, and like building my own mufflers. Thanks
Old 04-08-2010, 08:20 PM
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ChuckW
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Default RE: New to Gas engine question

No muffler pressure needed. The Walbro carb has a pump diaphragm. Just be sure your tank is vented. You can experiment with any kind of muffler that you want. Some may work better than others but that's half the fun if you are into building stuff.
Old 04-08-2010, 08:43 PM
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LargeScale88
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Default RE: New to Gas engine question

Ok thanks. I'm putting the 3w 75 into my bud p-51, and you know how cool the bud nosen p-51 exhaust is right?So will the size of muffler make a difference in the sound?I want loud and throaty sound. Ive build muffs for the glow, not the gas. What type of muffler size for deep throaty loud sound?

Thanks
Old 04-08-2010, 09:46 PM
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Default RE: New to Gas engine question

ORIGINAL: LargeScale88

Ok thanks. I'm putting the 3w 75 into my bud p-51, and you know how cool the bud nosen p-51 exhaust is right?[img][/img] So will the size of muffler make a difference in the sound? I want loud and throaty sound. Ive build muffs for the glow, not the gas. What type of muffler size for deep throaty loud sound?

Thanks
Don't forget a "pig tail" in the vent line from the fuel tank. Straight pipes are loud and throaty but may pose a problem in keeping your flying field if noise is an issue. If you look at the "Kleeko" (sp?) range of custom exhaust systems you will see that it is possible to build an exhaut system that uses the scale outlets for the Merlin. No matter how you try it won't be possible to mimic the sound of a Rolls Royce Merlin on full noise. http://www.youtube.com/watch?v=hvDDDKnNhuE

Happy fabricating.

Cheers,

Colin
Old 04-09-2010, 10:12 PM
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LargeScale88
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Default RE: New to Gas engine question

Vent line from the muffler or just from the fuel tank? Basically, do I need to put any kind of adapter or pressure tap or whatever into the muffler??

THanks
Old 04-09-2010, 11:51 PM
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Crash Campbell
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Default RE: New to Gas engine question

Hi,

No pressure is required as the carbys on petrol motors are pumpers. The "pig tail" (circle) in the vent line is to stop the fuel slopping out of the tank. You have to have a vent or the tank will implode as the pressure is reduced as the fuel is sucked through, the vent allows the pressure outside the tank to equal the inside pressure.

Cheers,

Colin
Old 04-10-2010, 12:20 AM
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ChuckW
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Default RE: New to Gas engine question

Yep, the tank is just vented to atmosphere. It's the same tube on your tank that would normally go to the muffler port on a glow engine, it just isn't connected to anything on the other end. I generally run a long vent line and wrap it around the tank once then out the bottom of the airplane. This helps prevent fuel from running out the vent as you push the airplane held by the tail, etc.
Old 04-10-2010, 12:45 AM
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Default RE: New to Gas engine question

^^^I agree, The carb has a diaphram inside it that works off of the crankcase back pressure and acts as a fuel pump causing it to suck the fuel from the tank, so a clear vent line is needed in order for it to pull the fuel from the tank. The only lines you will ever see on a gas burner's muffler is a oil line for smoke. Also, when fabricating a muffler, It will effect the running of the engine just as a glow engine. Prolly will have to tune the carb once you have it done. Hope this helps.
Old 04-10-2010, 06:50 AM
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LargeScale88
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Default RE: New to Gas engine question

Thanks F1. So it will affect how it runs, but just needs be tuned up again and it should be fine? It wont make it not run?

Thanks
Old 04-10-2010, 04:36 PM
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Default RE: New to Gas engine question

That is correct. At worst,,, you will just have to re-tune the carb a little.
Old 04-10-2010, 08:24 PM
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Default RE: New to Gas engine question

Two different types, a side exit exhaust and a header/racing pipe we used to make up for the Madera Racers.
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