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need info..pro's-con's of throttle exhaust workings

Old 08-16-2007, 09:04 AM
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mopartybob
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Default need info..pro's-con's of throttle exhaust workings

any info appreciated thanks
Old 08-16-2007, 12:26 PM
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mopartybob
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Default RE: need info..pro's-con's of throttle exhaust workings

this reply came in from the glow engine forum .... Throttle exhaust is needed to keep the temperature of the glow plug, i.e. the ignition timing in place,
when the exhaust mufler is not used. This is the cheapest method for getting more power from your
engine over the entire rmp range and will be in place lot more time even after 2007. When you close
the carb to decrease the rpm you have to close the exhaust as well a bit to preserve the glow plug
from getting colder. In addition, if you do not use exhaust pipe, you take pressure from the crank case
to the fuel tank. If then there isn't throttle exhaust then the whole system goes into "oscillations", meaning
the rpm go up and then down and then up etc in a speed of one oscillation per 3-5 seconds. This
you can fix by good synchronization between the two valves, the one on the carb and the one at the
exhaust. The exhaust should get a bit closed prior the carb gets a bit closed. This way you have pretty
smooth rpm control over the whole range.

And if wander why should not use resonance tube, the reason is that such tube in most of the case gives
not more than 5-10 % power increase and only in certain rpm range and decrease the power on the rest,
adds more weight and sometimes increases the noise too. Test is the ultimate prove; many modelers have
reso-tube just to have it, only few make good use of it.

Cheers,
Nick

can anyone verify these statements...that you can improve overall performance w/o a tuned pipe by synchronizing the (If used) slide barrel type carb and the exhaust throttle butterfly????......hhhmmmmmmmm....how would that be done......[:-] how would you pressurize the fuel system......would the side mounting design of the carb allow for enough intake pressure to draw fuel from a then open vent tank??? would exhaust then be vented via a straight pipe...???
Old 08-16-2007, 12:29 PM
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BB Modss
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Default RE: need info..pro's-con's of throttle exhaust workings

Wish i could man,iv only used a few ET motors,mostly 7.5 and 3.5cc K&B's, I liked the power the motors had but getting it tuned correctly was a pain.
Old 08-16-2007, 12:55 PM
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mopartybob
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Default RE: need info..pro's-con's of throttle exhaust workings

can anyone verify these statements...that you can improve overall performance w/o a tuned pipe by synchronizing the (If used) slide barrel type carb and the exhaust throttle butterfly????......hhhmmmmmmmm....how would that be done...... how would you pressurize the fuel system......would the side mounting design of the carb allow for enough intake pressure to draw fuel from a then open vented tank??? would exhaust then be vented via a straight pipe...???

just some more questions......this is the whole package i bought...would the configuration of this tuned pipe reduce the so-called oscillations of tuning problems....and the designation of these octura props i am not familiar with either.....(6) Octura props (X-445, 3-D-8, 3-I-21, F22, F25 & 3-I-27 ) .....
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Old 09-07-2007, 06:22 PM
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moparbarn
 
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Default RE: need info..pro's-con's of throttle exhaust workings

get rid of the carb and run a venturi. i have a few 3.5 k&b ob's with prather mod kits. fixed intake venturi, all throttling is done with the ex. plate. work great with the stock lower 'opened up', or a tuned pipe (resonance pipe). mine aren't very hard to tune, just very rich at low speeds. but since i don't run my boats slow, who cares?
Old 09-07-2007, 07:16 PM
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mopartybob
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Default RE: need info..pro's-con's of throttle exhaust workings


ORIGINAL: mopartybob

this reply came in from the glow engine forum .... Throttle exhaust is needed to keep the temperature of the glow plug, i.e. the ignition timing in place,
when the exhaust mufler is not used. This is the cheapest method for getting more power from your
engine over the entire rmp range and will be in place lot more time even after 2007. When you close
the carb to decrease the rpm you have to close the exhaust as well a bit to preserve the glow plug
from getting colder. In addition, if you do not use exhaust pipe, you take pressure from the crank case
to the fuel tank. If then there isn't throttle exhaust then the whole system goes into "oscillations", meaning
the rpm go up and then down and then up etc in a speed of one oscillation per 3-5 seconds. This
you can fix by good synchronization between the two valves, the one on the carb and the one at the
exhaust. The exhaust should get a bit closed prior the carb gets a bit closed. This way you have pretty
smooth rpm control over the whole range.

And if wander why should not use resonance tube, the reason is that such tube in most of the case gives
not more than 5-10 % power increase and only in certain rpm range and decrease the power on the rest,
adds more weight and sometimes increases the noise too. Test is the ultimate prove; many modelers have
reso-tube just to have it, only few make good use of it.

Cheers,
Nick

can anyone verify these statements...that you can improve overall performance w/o a tuned pipe by synchronizing the (If used) slide barrel type carb and the exhaust throttle butterfly????......hhhmmmmmmmm....how would that be done......[:-] how would you pressurize the fuel system......would the side mounting design of the carb allow for enough intake pressure to draw fuel from a then open vent tank??? would exhaust then be vented via a straight pipe...???
thanks moparbarn,three differant size venturi carbs came in the package,along with a black carb,as you can see in the pic,the exhaust/throttle body (pipe) is water-cooled also...I follow you on the set-up as that bein the way to go...moparty2ya
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