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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Mon Dec 26, 2011 1:29 pm 
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I would think right angle calculations would get close. 2 G's launch and 1 g down would equal 63˚...


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Mon Dec 26, 2011 1:40 pm 
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So really if a car or digger does not do a wheel stand there still an issue with fuel dumping cause of the g forces..

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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Mon Dec 26, 2011 6:31 pm 
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Yep you all got it now. To find the angle of the fuel find the inverse tangent of the g-force. That will tell you the angle of the surface of the fuel relative to the ground(63.4 degrees for 2 G). Add on whatever angle a wheel-stand goes to.
Whatever angle the surface of the fuel assumes draw a line through to the metering block passages or the outlet positions in the barrels etc. Once the line is over the top of a passage fuel must come out and pour into the engine. Look at the intermediate, figure out what G it needs to flood the engine.
The fuel metering of any carburetor is done by pressure differential across various devices(jets). Anything that changes the pressure on one side of a jet changes the fuel flow rate. The pressure on the inlet of any jet is termed "the head". It refers to the distance the jet is below the surface of the liquid, when the surface of the liquid changes like it does in a launch the distance from the jet to the surface changes hence the head alters. The alteration in head (pressure) just by itself alters the mixture let alone the flooding over aspect.
Carburetors like SU's, some Stromberg's like there CV range and some Zenith's like fitted to 70's BMW's and racing Weber's have much better design than Holley and are arranged so that G force has little effect upon mixture. Diaphragm carburetors virtually eliminate it down to the minutest detail. Even EFI is affected by g-force, nothing is prefect.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Mon Dec 26, 2011 7:02 pm 
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Ken0069 wrote:
Since that 3rd circuit feeds from the bowl I'll bet that the rear ones get uncovered at launch

Its not so much uncovering a jet thats the problem, although the result of that is obvious what is not obvious is the surface of the fuel and the outlet position above it. Inside the metering block there is a point of the surface of the fuel. That point moves when fuel is flowing because the main jet restriction lowers the assumed surface level of the fuel. Correctly speaking its not actually a surface level of fuel its actually the head. The head can be measured with special equipment any where you like if you wanted to but its basically this, if the head of pressure is different from one side of a jet to the other side there will be flow through the jet. Also to lift fuel above the surface to the height of an outlet requires a difference in pressure, carby people refer to that as lift head. If you look at a carby sitting on the bench and measure the distance that the booster outlet in the body is above the normal fuel level you will realize that the fuel has to be lifted to get there. The distance is the lift head. The effort to lift the fuel up above the surface comes from the vacuum generated by the booster. Remember how water finds its own level, well what its really doing is demonstrating that liquids will flow until the head is equalized everywhere on the surface of the liquid. The atmospheric pressure forcing down onto the top of a liquid surface is also part of the head. The booster vacuum reduces the atmospheric pressure component thus altering the head on the outlet side of the jet creating a head differential thus the fluid will flow through the main jet and try to equalize the head on each side of the jet. Yeah the booster sucks so it lifts the level of fluid.
Here's another thing that happens. If the booster vacuum is such that its not enough to lift the fuel to the outlet but say its just below it the fuel will flow through the main jet and assume a new height inside the metering block. If you cut the block open at that point in time and observe, the fuel would be sitting at 2 different levels. It would be high inside the block and normal in the float bowl. NOW go and tip the carby in the direction of G-force. The fuel will flow over into the booster outlet wont it. So you just put fuel into the engine without the booster generating the vacuum to do it (thats related to CFM isnt it). Now hold the carby on that angle and let the fuel stabilize and balance the head and see how high the lift head has to be now to reach fuel flow into the booster. Its much less so the result is the mixture is rich. Mixture is controlled by head and jet flow restriction.
When G-force alters the necessary lift head the mixture changes. Less lift head is richer more lift head is leaner. The front barrels get richer the rear get leaner.
The lift head is what controls emulsion. Alter the lift head to less and you get less emulsion air. Figure it out guys.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Mon Dec 26, 2011 7:58 pm 
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Beretta wrote:
So your saying that the G's would force the fuel in that 3rd circuit to run/drip into the manifold?
If so is there a way to do some type of extension or something to eliminate that??

Not easily anyway. It can be done (and is done) but the design is not going to be anything like a holley.
The fuel will run out of any hole that is below the surface of the fuel. The surface level or angle of the fuel is determined by the inverse tangent angle of the g force. Get on a calculator and punch in the acceleration g-force and find the ATAN of it. examples. 2.5g= 68.1 degrees, 1.5g= 56.3 degrees. 1g=45 degrees.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Tue Dec 27, 2011 10:45 am 
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So what can be done with the Holley that can "clean up" the fuel dumping on the hit?? Shrinker have any idea's ?????
BLP looks like they solved one of the issues with developing a block with a separate well for that
3rd circuit...

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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Tue Dec 27, 2011 11:55 am 
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The dynamics of a car going down the track is another reason I don't place a lot of faith in dyno tuning. Yeah, dyno time is useful to a point to sort out the mechanical stuff but I expect a lot of stuff changes once the on track tuneup is done.

I also think that mounting the carb sideways would be much better than the way we usually mount a single 4. There's special floats made for round track carbs that keep fuel from collecting on one side that can also be used in a sideways mount to do the same thing. Only real issue to do that is linkage but it can be done.

When I look at the AFR graphs from my car I don't usually pay a lot attention to stuff that's happening before the gear change. After that things start to settle down a bit and it's easier to see what's happening as far as AFRs are concerned. I believe this could be another advantage of electronic injection as there's no fuel level moving around in fuel bowls to deal with. Worst case there is likely to be G forces causing pressure spikes on fuel in the lines, like I've seen on a couple of cars that I've owned with carburetors.

Ennywho, the deeper we dig, seems we're finding that we need to dig even more. ](*,)

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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Tue Dec 27, 2011 6:25 pm 
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Beretta wrote:
So what can be done with the Holley that can "clean up" the fuel dumping on the hit?? Shrinker have any idea's ?????
BLP looks like they solved one of the issues with developing a block with a separate well for that
3rd circuit...

Having a separate well is not a fix for this issue. If the angle of fuel is enough to go over the top of the well then it will flood in. Its a simple problem, liquid flows over the top of anything if the surface of the liquid is above the edge.
Side mounting the carby is a good fix, it partially solves metering issues. Its doesn't stop the head from altering inside the wells but it greatly reduces it's range of error.
Mounting the metering wells in the center of the fuel bowl is the practical way to do it. Think about what happens in reverse, if you use one of those bowl extensions it moves the center of the fuel surface even further away from the metering block and the problem gets worse.
A good part is something that is designed to correct an issue without creating another one.

If you drive around in a street car with a sideways mounted Holley you can fell the engine tune change when going around corners. Its very obvious, they even stop running if you corner just right and its not even very hard cornering. Low G do it. If you back off the throttle in the corner they try to stall, open the throttle and the engine can take it and you dont notice it. Mounting the carby sideways and cornering is like mounting it normal and accelerating as far as the fuel motion effect etc. It brings home how much is left on the table when racing with design's that are incorrect.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Tue Dec 27, 2011 6:36 pm 
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Ken0069 wrote:
When I look at the AFR graphs from my car I don't usually pay a lot attention to stuff that's happening before the gear change. After that things start to settle down a bit and it's easier to see what's happening as far as AFRs are concerned.

Here's one for Ya. In the case of a tunnel ram say you have a sheet metal ram with a large plenum or something like that. the fuel mist that's in the plenum isn't in contact with anything is it. So when you take off like a rocket from the line the only thing that pushes the fuel mist forward with the car is the BACKWALL of the plenum. Its not until the back wall slams into the fuel droplets in suspension that they get accelerated. So the fuel finishes up on the back wall and runs into the rear cylinders. This effect happens to every molecule of fuel that suspended in air in every part of the system. Thats every part even in the runners and the cylinders. Its not until something slams into the fuel droplets in suspension that they get accelerated. So go figure that one out


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Wed Dec 28, 2011 5:15 pm 
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Man, spend a couple of days away at the dyno and I miss all this good stuff.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Thu Dec 29, 2011 9:25 am 
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Bruce, Even though Mark won with challenge with a 2 circuit Did you guys do any testing with a 3 circuit
on the Dyno?? As Shrinker and other said it may make more power but on the track it most likely will not on the track..
Don't get me wrong I love my 1150 2 circuit but just wondering why most carb builders won't
do anything but??

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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Thu Dec 29, 2011 11:31 pm 
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Barry, I've been involved in some 3 circuit dyno testing independently. Both in gas and E85. In both cases things went well. It hasn't been enough, though, for me to draw conclusions.

Don't me get wrong, I'm still in the 2 circuit camp. However, I keep wondering if it's just bad 3 circuit calibrations that's tuned us all into 2 circuit guys. Or is it that 3 circuits are just a bad idea that can't really be fixed? I intend to find out and share that.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Fri Dec 30, 2011 12:11 am 
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nomad wrote:
I intend to find out and share that.
I applaud that \:D/


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Fri Dec 30, 2011 1:26 am 
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The 3rd circuit on a Holley is a simple dribble with an air bleed design. As such its called a simple single jet design carburetor. It has a separate feed and its only ability to meter is based upon the simple carburetor principle. The density and viscosity relationship of air and fuel are opposite one another. Air gets higher viscosity (thicker) with temperature increase and liquids get less (thinner). Air is compressible (changes density)and liquids are not. The principle of operation of the 3rd circuit of a Holley was dumped from carburetors in 1926. The simple design cannot compensate for the differences between air (gasses) and liquid. What happens with that 3rd circuit is the mixture ratio gets richer as the CFM increases. People can change the position of the outlet and fiddle with the fuel jet and the air bleed but in the end its still a junk design that has to have a restriction placed in the main booster so that it can correct the boosters contribution in response to the 3rd circuits mistakes.It seems to be a counter intuitive way to do it if you ask me.
However there is a reason for the 3rd circuit and its to do with pulsing air flows or rapidly changing CFM. The booster circuit is slow to respond with accuracy to fast CFM changes. For instance if the CFM changes such that an e-bleed is not going to flow air, then fuel will flow backwards via the e-bleed and fill the air well to a new level. During the time the backflow is occurring the volume of fuel involved in that process is not being delivered to the booster so the engine leans out. This is called the problem of shift recovery by some people. If the CFM increases very quickly the fuel contained in the air well has to flow to the booster before the air can exit the e-bleed and cause an AFR change. That fuel is not metered by the main jet at the time of its discharge.
The 3rd circuit on the other hand doesnt have emulsion so it's not effected by backflow issues. That makes a 3rd circuit carby better on the shift or better on pulsing air flows like some cams with tunnel ram manifolds or on individual runner designs.
If you tune by relying on emulsion you will be subjected to the problems of emulsion. If you tune by sizing of wells etc you dont have to use as much emulsion but you may have to use additional mixture compensating devices like needles etc.

As far as comparing performance aspects of a 2 or 3 circuit carby on a dyno there is no reason why each couldn't equal the other with appropriate attention to detail. But thats only on a dyno. Those same 2 carbys would need to be reconfigured to work equally on the track. Pick whatever you want to do, it doesnt matter. There is no justification for one design over the other its more a case of how to interact with the design and usage of the engine, things like useage range, purpose of use and manifolding and valve action etc.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Fri Dec 30, 2011 6:40 am 
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Maley had told me a few years back that the original design of that 3rd circuit was for some early dual carb IR manifold designs and it was used to compensate for reversion pulses generated in the IR system. So looks like shrinker's explanation goes along with Maley's in that regard.

So if the 3rd circuit is useful at the gear change, and the term "fall back" comes to mind here, then it would likely benefit the stick shift guys more as there's more gear changes per run? :-k

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