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Old Aug 08, 2006, 12:22 PM
jimi hendrix
Joined Apr 2006
1,509 Posts
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im building a custom exhaust for my .91 engine but need help*****PICS****

hi.

i am making a custom exhaust fo my s.c 91 engine but have hit a few problems:

1)i have done 2 out lets which are 1.5cm each x2 = 3cm, is the exhaust outlet to big?because im worried that there wont be any pressure in the fuel tank.and during flight it may cut out when im doing rolls

2)where do i mount the fuel nipple?(the exhause is ajustable and can go all the way round in any possision)im having it pointing up?

before i had an pits exhaust for this engine and the out let messured 1.5 cm and the engine kept cutting because it was to small

the dimensions of the exhaust barol is
lenth:6.2cm
with:6cm

p.s i will be painting this exhaust

thanks


spitfie123
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Old Aug 08, 2006, 01:33 PM
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Nebraska, Lincoln
Joined Apr 2006
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Uhh, I don't even know what to say to you.. haha It looks interesting. Hope it works because you can break something in the engine if the pressure isn't great enough. I suggest NOT using it because mufflers are desgned with blow back in mind and pressure. I highly don't suggest it. Mufflers are desgned in a specific way for the exaughst flow and can be harmful to an engine if made wrong. Soo, good luck?
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Old Aug 08, 2006, 02:00 PM
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Some people run glow engines with straight pipes and essentially no muffler so don't worry about post #2, sorry trab.

Now concerning your original post I am more worried looking at you muffler that the exit holes are too much exit area.

Also, how do you know the original was too little of an exhaust, maybe it was too much and the pressure was not enough to ensure un-interupted fuel flow and the engine cut out as a result.

1) Place your pressure nipple near the top of your muffler, this will at least help keep acumulated burnt oil and such from entering the pressure tap and making it into the fuel or plugging up your pressure line.

2) Proceed systematically from this point on. Start the engine with the new muffler and plug one of the exhaust ports. Find a way to run it this way at different attitudes and speeds. Then try with both unplugged and note any important differences. I think you get the drill.

Report back please. BTW nice attempt at a muffler.
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Old Aug 08, 2006, 02:07 PM
jimi hendrix
Joined Apr 2006
1,509 Posts
thanks for the reply lightinin,

i no the pervios exhaust was to small becausewhen i tried it open with the same tuning setting the throttle responce was better and it dident cut out!.


and i cant have a strait pipe because there are noise restrictions in england.

p.s i can just take 1 of the outlets out and cover it up and just have one.
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Old Aug 08, 2006, 02:08 PM
jimi hendrix
Joined Apr 2006
1,509 Posts
Quote:
Originally Posted by trab1925
Uhh, I don't even know what to say to you.. haha It looks interesting. Hope it works because you can break something in the engine if the pressure isn't great enough. I suggest NOT using it because mufflers are desgned with blow back in mind and pressure. I highly don't suggest it. Mufflers are desgned in a specific way for the exaughst flow and can be harmful to an engine if made wrong. Soo, good luck?




what are you on about m8.
get your facts right
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Old Aug 09, 2006, 02:53 AM
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Nebraska, Lincoln
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Well with gasoline it is at least. I thought that glow was some what the same sence they are 2 stroke. I made made a glass pack from an aluminum can, a copper pipe drilled holes in and put steel wool in the can and pipe strait through. It worked for about half hour. Then it had too much blow back and I had a carbon build up and the engine was temporirly seized until I got a hold of a sulivan tank. It sounded awesome though! So I was thinking it is some what the same. But still good luck!

And yeah I did get bored...

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Old Aug 09, 2006, 05:13 AM
jimi hendrix
Joined Apr 2006
1,509 Posts
but the petrols are different to the nitros.
petrols need exhause pressure.
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Old Aug 09, 2006, 05:49 AM
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Nebraska, Lincoln
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Yeah lightnin decided to let me know about that too.
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Old Aug 09, 2006, 06:42 AM
jimi hendrix
Joined Apr 2006
1,509 Posts
lol


ok


as lighting to read my new post(ITS BENITH HIS)
im goin to test iy in a min.
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Old Aug 09, 2006, 08:53 AM
jimi hendrix
Joined Apr 2006
1,509 Posts
right............

i fired my s.c up and under 1.5 throttle it works great!

but over half throttle it cuts.(so is it to rich ore too lean)?

it allways does this because thay are the hardes engines to tune.
but it idols great and sound like v8 AND IS VERRY THROUGHTY!

please help!
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Old Aug 09, 2006, 08:56 AM
jimi hendrix
Joined Apr 2006
1,509 Posts
oh yes any when i put my finger over 1 of the exhaust hols it affcts the preformabce dramaticly(crappy)and somtimes even cuts out!

wso i think 2 is ok!

WHO NOES MAYBEE I NEED BIGGER?

what do u guys think?
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Old Aug 09, 2006, 09:29 AM
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I think you should follow this link: http://www.rcgroups.com/forums/showthread.php?t=205602

And use it to tune you engine and then report back.
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Old Aug 09, 2006, 11:54 AM
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United States, MI, South Lyon
Joined Aug 2004
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Even if you do get it tuned right, the engine will shake that tin can to pieces in no time at all. My suggestion would be to find a muffler that has similar exhaust flange dimensions and buy that. The SC engine probably has the same flage as an OS 91 FX.
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Old Aug 09, 2006, 02:06 PM
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Nebraska, Lincoln
Joined Apr 2006
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^Agreed. All I really can say. If this engine you plane on keeping just buy a new muffler. I bet it does sound AWESOME but still, I just suggest a muffler that's made for it. Then again who knows it could be awesome?
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Old Aug 09, 2006, 03:00 PM
jimi hendrix
Joined Apr 2006
1,509 Posts
yea thats what i was thinking but i would loose the sound!
can any 1 find me a link for a s.c 91 muffler?
because i wanna find out the price and accturly look at the exhaustt on the engine.
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