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Old 01-07-2004, 11:58 PM   #61
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Quote:
Originally posted by modellor
I would say that the increasing the diameter of the carb opening or boring out the crank would give most increase in fuel consumption.
that is probably true. i did notice the difference in run time when i remove the restrictor on the carb. on the same engine.

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The difference between my RB X12 with a EFRA legal crank and the same engine with a Novarossi T5 crank is about 2 mins worth of run time. With the T5 crank I get approx 5mins 30secs and I constantly ran with the stock crank for well over 7mins 30secs.
same carb. ?

Last edited by Data; 01-08-2004 at 12:41 AM.
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Old 01-08-2004, 12:43 AM   #62
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Default Re: Re: Re: Re: Re: fuel consumption and hp

Quote:
Originally posted by Top Gun 777
Fuel economi is basecaly efficiency of engine. ..........
so what is the one main change you can do to the engine to make it more efficient. i know there are probably many things you can do, but what change, or combination of change that will contribute the most to the gain in hp but at the same time won't increase fuel consumption too much.


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One more realy important thing is carb design too. ...............
i did modify the needle once but accroding to my friend who tried it, he didn't really notice any changes in engine performance so i put it aside. i probably didn't do it right or i should had tested it myself. by the way, what do you think the "mid. range" screw really does ? to me it adjust the spray bar position, relative to the low end needle, but i don't really know what it does to the engine. the only thing i can think of is this adjustment controls how soon the low end needle leaves the spray bar completely. if i were on the right track, what would be the advantage/disadvantage of having the low end needle leaving the spary bar completely sooner/later ?

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Data, do I owe you bottle or to Ah10?
me.

p.s. saw you modify the exhaust timing the other day, i guess one can learn something new everyday. thank you
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Old 01-08-2004, 12:53 AM   #63
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Default Re: Re: Re: Re: Re: Re: fuel consumption and hp

Quote:
Originally posted by Data
so what is the one main change you can do to the engine to make it more efficient. i know there are probably many things you can do, but what change, or combination of change that will contribute the most to the gain in hp but at the same time won't increase fuel consumption too much.
Setting your clutch correctly can have just as big an effect on fuel consumption as it does on acceleration.
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i did modify the needle once but accroding to my friend who tried it, he didn't really notice any changes in engine performance so i put it aside. i probably didn't do it right or i should had tested it myself. by the way, what do you think the "mid. range" screw really does ? to me it adjust the spray bar position, relative to the low end needle, but i don't really know what it does to the engine. the only thing i can think of is this adjustment controls how soon the low end needle leaves the spray bar completely. if i were on the right track, what would be the advantage/disadvantage of having the low end needle leaving the spary bar completely sooner/later ?
Moving the spraybar within the carb venturi affects when the low speed needle completely unseats from the bar. As such, you can move the powerband slightly by moving the spray bar if you also move the lowend needle in the same direction.
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Old 01-08-2004, 03:00 AM   #64
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Default Re: Re: Re: Re: Re: Re: fuel consumption and hp

Quote:
Originally posted by Data
by the way, what do you think the "mid. range" screw really does ? to me it adjust the spray bar position, relative to the low end needle, but i don't really know what it does to the engine. the only thing i can think of is this adjustment controls how soon the low end needle leaves the spray bar completely. if i were on the right track, what would be the advantage/disadvantage of having the low end needle leaving the spary bar completely sooner/later ?
Data my friend;

http://www.rcnitro.com/rn/articles/carburetor.asp

This is a good short article on the subject with some nice cut away pics which are really helpful !
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Old 01-08-2004, 04:40 AM   #65
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Now I'm getting confused. After reading the article it seems that I have been tunning my engine all wrong. They say that the low-speed needle is the one that is on the slide valve. Is that so and if it is what have I been doing for over an year and a half. I use the brass needle to tune the low-speed mixture and it works well. Can someone please explain me one more time which needle is about what, pls. I really am confused.
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Old 01-08-2004, 05:59 AM   #66
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Data - I was using the same carb. You know how it is. When you get a good carb you keep it.

Speed De - The low speed needle is the one on the slide bar. The brass one on the opposite side is the spraybar adjustment. It is not actually a needle (the low end needle enters it) but instead alters the postion of the powerband on the engine. A lot of people use the spraybar to adjust the low end without realising that they are altering how the engine performs.
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Old 01-08-2004, 09:19 AM   #67
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Data, in our engines is everything in siquence and there is no one particular thing which can be modded to increase power. We just have to make sure ( when we do modding) everything is right and on time.
About the carb modding-it will not add a lot of top end power ( we are talking about carbs which initialy done well-Novas, Sirios etc), but we can inrease respond, we can encrease efficiencyduring the accelaration, decrease unneccesary fuel loss on not wide open moments etc.
About the timing altering you saw-it is unique today, I hope you got point what I did there. I am sure very soon someone will copy it and I am OK with that.
Will be at CP this Saturday, we can talk more.
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Old 01-08-2004, 09:45 AM   #68
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Default CRANKSHAFTS

TG
What are the advantages and disadvantages of full circular crank's counterbalance vs delta or semidelta shaped ones (RB).
At one point, and i think still, the MT12's and REX MR12 have full circular, and Novamegas up to the 2103 also.
Can you explain please???
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Old 01-08-2004, 10:28 AM   #69
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Rotating mass!
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Old 01-08-2004, 11:27 AM   #70
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Isn't only a matter of rotating mass... is a matter too of aerodinamics and the way the mix of air and fuel travels behind the crankshaft (that's why lately many crankshafts are cut with a very agressive ramps.
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Old 01-08-2004, 12:00 PM   #71
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Default Carbs 101.

Quote:
Originally posted by Speed De
Now I'm getting confused. After reading the article it seems that I have been tunning my engine all wrong. They say that the low-speed needle is the one that is on the slide valve. Is that so and if it is what have I been doing for over an year and a half. I use the brass needle to tune the low-speed mixture and it works well. Can someone please explain me one more time which needle is about what, pls. I really am confused.
The 'brass screw' isn't a needle. Is the main jet of the carburetor. After this lines, there's a complete text describing how our carburetors work. Seems that many people gets puzzled with all the needles and how to adjust them. I suppose a minimum knowledge on where's the high-end needle, low-end needle, spraybar or main jet and idle speed screw.

The screw in front to the 'brass screw' (located at the side of the carburetor and usually flush to the surface of the carb body) is really the low-end needle. And it plugs into the main jet without obstruding completely to allow a little of fuel to pass when the needle plugs into it to allow the engine to idle.

The dimensions of the jet, their position relative to the venturi, and the dimensions, ramps and shape of the low-end needle dictates the fuel curve of the carburetor (or how much fuel enters by each cfm of air drawn into the engine at a relative carb opening).

At idle speed, the engine is controlled by the low-end needle and how much air pass into the engine via the position of the barrel. But when you start to move the barrel to allow to pass more air, in fact, you're moving too the low-end needle, allowing at the same time to pass more fuel too.

Depending at which opening of the barrel, the jet is totally uncovered and the carburetor starts to being mandated by the adjustment of the high-end needle and how much fuel permits to pass this last adjustment rathern than being governed by the low-end needle. This can be varied (and the powerband of the engine too, but slightly) by screwing or unscrewing the jet and readjusting the low-end needle. But be careful screwing the jet too further into the ventury can lead to mix and temperature problems (in fact, you're leaning the mid rpms, where the engine operates at partial opening of the carb, this can lead to problems and erratic operation) this is why on almost all the engine booklets warns you about to not touching this adjustment.

The position of the jet, relative to the venturi changes too the position on where in the vortex of air when enters into the carb and varies too how much or how finely is the fuel sprayed into the air that enters (fuel is converted into a mist for being burned, a drop, no matter how little is doesn't burn and can create many and serious problems). This last can lead up to a conrod breakage (common) or piston breakage (not common but seen some) due to hydrolock.
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Old 01-08-2004, 12:09 PM   #72
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In my opinion not too much differnce, beside mixing ( which not realy proven yet). As long as it is balanced more or less close, the shape realy doesn't metter, that shape , which you see on the pic ( world champion in speed air modeling), of delta is done to create counter weight. Some people will talk about cranckcase volume, but it has been proven years ago, any cuts on web ( conter weight) don't make crancase volume bigger at all.
I preferd delta-it is asking less thikness of counterweight on opposite side of cranck pin area, which is realy realated to crancase volume.
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Old 01-08-2004, 01:09 PM   #73
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Thanks, will experiment on the track with both types of crank on the same engine (exchanging), and post my "real world" results later.
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Old 01-08-2004, 03:39 PM   #74
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Quote:
Originally posted by Top Gun 777
Data, in our engines is everything in siquence and there is no one particular thing which can be modded to increase power. We just have to make sure ( when we do modding) everything is right and on time.
ok, maybe you can explain this sequence/timing thing to me sometime.

Quote:
About the timing altering you saw-it is unique today, I hope you got point what I did there. I am sure very soon someone will copy it and I am OK with that.
but i think it is kind of dangerous, one wrong cut and that is it. i will leave this mod to the experts.

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Will be at CP this Saturday, we can talk more.
good, then i can pick your brains at point blank.
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Old 01-08-2004, 04:15 PM   #75
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Quote:
Originally posted by Data
ok, maybe you can explain this sequence/timing thing to me sometime.
I will, may be this weekend at CP

Quote:
Originally posted by Data

but i think it is kind of dangerous, one wrong cut and that is it. i will leave this mod to the experts.
It is dengerouse, one very small wrong movement and everything will go to trash. Leave it to modifyers, they know what they doing, you just have fun driving.

Quote:
Originally posted by Data

good, then i can pick your brains at point blank.
See you Saturday.
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