Divorced idle circuits

[NormS]

I've had no trouble getting getting a excellent overlap of low speed and high speed circuits, at part throttle, and excellent fuel curves at full throttle, with the conventional 2 circuit configuration. I know how to do what you are talking about, but never saw the need to do it.

[Tuner]

So Tuner, are you the only one who isn't blind?

Au contraire. The beast is two bowling balls in a sack. I grabbed ahold of it (or it grabbed ahold on me) sixty years ago and I ain't about to let go, no matter how wild the ride.

[Tuner]

What Holley made for Chrysler back in '69-'70 matters little to me. I've seen a few of those over the years, and intentionally never used them for any performance application. Some of the stuff that Holley did for the OEM's back then, had no reason to be applied to racing engines. Maybe the OEM's found those features to be advantageous to their mass production factory built engines, but those same features seldom did anything positive for racing engines.
In fact, I found that, in some cases, eliminating those odd features in those OEM specific Holleys, made them run better on those factory stock engines. It appears that some of these odd features designed into those carbs, were designed by engineers who were evidently trying to justify their existence, by coming up with something different. Some of it worked, some of it didn't, little of it had any place on a performance engine.

Your response is typical and foreseen.

You probably never have had any personal experience, used or witnessed the use of a performance carburetor having a true "divorced Idle 3rd circuit". In such a case, the off-idle and tip-in fuel curve control can be more precise for less fuel consumption; especially with the 830 cfm Holley NASCAR carb or any carb being used in a 12/24 hour racing application.

You possibly don't know how to perform this easy conversion on a high performance Holley carb using those Mopar metering blocks., if you were asked to do it.

THEREFORE, it is almost certain you can't envision it would be worth anything in any high performance carburetor setting. You just know it can not be of any value there.

Sure thing ...!

To most, it probably isn't.

AND ...TUNER:
Not seen ...?
In the late 70's and 80's, there are more than 50 or so high performance Holley 4150 carbs out there which I personally have made this modification. All of them showing said results.

You guys need to get a room with a dyno and sort things out.

I have seen such a configuration almost 40 years ago on a 100 yard sand drag Jeep, not exactly the intended application if it was one of yours. The Jeep was in Washington, the owner got the carb from somebody in California and I recall he said it was done by someone in Arizona. It was a 4781 cloned into three-circuit like a Dominator. The guy also had a 750 with some bits of brass tubing arranged in a high speed pullover deal like an old VW Solex.

I guess in this game it is unlikely there isn't a box that hasn't been thought outside of at one time or another, and who knows which end of the Elephant is up?

[pamotorman]

What Holley made for Chrysler back in '69-'70 matters little to me. I've seen a few of those over the years, and intentionally never used them for any performance application. Some of the stuff that Holley did for the OEM's back then, had no reason to be applied to racing engines. Maybe the OEM's found those features to be advantageous to their mass production factory built engines, but those same features seldom did anything positive for racing engines.
In fact, I found that, in some cases, eliminating those odd features in those OEM specific Holleys, made them run better on those factory stock engines. It appears that some of these odd features designed into those carbs, were designed by engineers who were evidently trying to justify their existence, by coming up with something different. Some of it worked, some of it didn't, little of it had any place on a performance engine.

Your response is typical and foreseen.

You probably never have had any personal experience, used or witnessed the use of a performance carburetor having a true "divorced Idle 3rd circuit". In such a case, the off-idle and tip-in fuel curve control can be more precise for less fuel consumption; especially with the 830 cfm Holley NASCAR carb or any carb being used in a 12/24 hour racing application.

You possibly don't know how to perform this easy conversion on a high performance Holley carb using those Mopar metering blocks., if you were asked to do it.

THEREFORE, it is almost certain you can't envision it would be worth anything in any high performance carburetor setting. You just know it can not be of any value there.

Sure thing ...!

To most, it probably isn't.

AND ...TUNER:
Not seen ...?
In the late 70's and 80's, there are more than 50 or so high performance Holley 4150 carbs out there which I personally have made this modification. All of them showing said results.

You guys need to get a room with a dyno and sort things out.

I have seen such a configuration almost 40 years ago on a 100 yard sand drag Jeep, not exactly the intended application if it was one of yours. The Jeep was in Washington, the owner got the carb from somebody in California and I recall he said it was done by someone in Arizona. It was a 4781 cloned into three-circuit like a Dominator. The guy also had a 750 with some bits of brass tubing arranged in a high speed pullover deal like an old VW Solex.

I guess in this game it is unlikely there isn't a box that hasn't been thought outside of at one time or another, and who knows which end of the Elephant is up?

bob szabo of fuel curve engineering did carbs like that back then

[Walter R. Malik]

I I know how to do what you are talking about, but never saw the need to do it.

EXACTLY ...
You have probably never been faced with the need to save a mere gallon of gas over 50 laps of racing. Or, save a couple gallons over an hour's time in a 12 or 24 hour race ... without someone wanting that requirement from you, you wouldn't "see the need".

What I am saying is ... Just because YOU don't see the need does not mean there wasn't one.

[NormS]

And just because you do something, that doesn't mean the everybody else has to do it, so as to lend credibility to you doing it.

[Tuner]

So Tuner, are you the only one who isn't blind?

Au contraire. The beast is two bowling balls in a sack. I grabbed ahold of it (or it grabbed ahold on me) sixty years ago and I ain't about to let go, no matter how wild the ride.

Today a blind man might guess the beast is two cats in a sack.

[NormS]

With conventional 2 circuit metering blocks,I haven't had any trouble getting good fuel mileage from racing engines when it is needed. By tailoring booster signal curves, and coordinating that with emulsion hole configuration and high speed air bleed size, I have been able to get more precise control over A/F ratios and fuel conditioning,which allows an engine to make its power on less fuel. After all, under power, the main metering circuits are providing far more fuel than the low speed circuits. So controlling the amount and condition of the fuel from those main metering circuits is quite productive in achieving better fuel mileage.

[jmarkaudio]

The problem I see here is the meaning of "divorced idle". On a Holley design the idle fuel is pulled from the mainwell either thru an idle tube in the case of three circuit metering or thru the slot at the bottom of the metering block. No mater where the idle restriction is placed it is still a mainwell fed idle. Divorced idle is isolated or divorced, meaning it shares nothing in common with the mainwell. Alcohol metering blocks are a somewhat common place to see a divorced idle circuit, where fuel is pulled from the bowl much like the intermediate feed with a 3 circuit carb, passages on the jet side of the metering block. It likely originated when trying to get enough fuel thru a passage restricted carb, having the idle circuit divorced allowed fuel to continue even at WOT. An intermediate circuit will also supply fuel at WOT, even though most flow is with the blade just above the intermediate discharge tube. The other part is that with the idle circuit divorced it will not become a bleed back into the main at WOT.

Now there are a lot of carbs that were designed to correctly use a divorced idle, the Holley design was not one. Not to say it couldn't be, but the attempts I've seen were poor, aside from methanol which is tolerant of being excessively rich and even then not necessary. For gas the ones I've seen were done in an attempt to INCORRECTLY add fuel at WOT on carbs that have insufficient passage size to correctly feed the mains, discharge thru the booster. Having built carburetors up to a 2.800 throttle bore I have seen what it takes to properly feed the mains and a divorced idle is not one of them, it will mess up fuel delivery somewhere in the fuel curve.

[NormS]

10-4

[Walter R. Malik]

The problem I see here is the meaning of "divorced idle". On a Holley design the idle fuel is pulled from the mainwell either thru an idle tube in the case of three circuit metering or thru the slot at the bottom of the metering block. No mater where the idle restriction is placed it is still a mainwell fed idle.

Not true ... With the O.E.M. Mopar 3 circuit metering block designed and manufactured by Holley for the Mopar 4160 model carburetor, the idle fuel IS completely separated, being fed from left and right sized holes on the fuel bowl side of the block. That tube going down the main well in those metering blocks is ONLY the fuel feed for the slot; (those idle fuel hole drillings became the intermediate fuel entrances in the later, differently machined, 3 circuit blocks for the Dominators).

As you define it ... that idle circuit shares NOTHING in common with the main well in any way.

By the way, for easy identification ... those carburetors have cast-in boosters as part of the main body and they are not a separate part. Millions of them were manufactured.

[NormS]

Then the tube going down the main well, to feed the transition circuit,is not divorced from the main circuit. Only the idle circuit is divorced. In this configuration, the transition circuit will still experience a tapering off, as the booster signal comes up. This tapering is the same as with a conventional 2 circuit metering block, a necessary feature for a passenger car engine, so as to have a nice lean part throttle/ light load cruise mixture.
Like I said before, there are different 'divorced" configurations. There is an "idle circuit only" divorced configuration, and then there is an "idle circuit
divorced/transition circuit"divorced configuration(all circuits totally divorced), and then there is another configuration where the idle and transition circuits are both divorced from the main metering circuit, but not from each other.
The name and definition for any particular configuration being discussed, needs to be more clearly stated more clearly. I've used all 3 configurations, and found that each has it pluses and minuses. And I have found that the conventional "2 circuit" metering blocks, with no divorced circuits, to be the
preferable configuration on 4150/4160 series carbs, for both street engines and racing engines.

[Walter R. Malik]

Then the tube going down the main well, to feed the transition circuit,is not divorced from the main circuit. Only the idle circuit is divorced. In this configuration, the transition circuit will still experience a tapering off, as the booster signal comes up. This tapering is the same as with a conventional 2 circuit metering block, a necessary feature for a passenger car engine, so as to have a nice lean part throttle/ light load cruise mixture.
Like I said before, there are different 'divorced" configurations.
There is an "idle circuit only" divorced configuration, and then there is an "idle circuit, divorced/transition circuit" divorced configuration(all circuits totally divorced), and then there is another configuration where the idle and transition circuits are both divorced from the main metering circuit, but not from each other.

Exactly ... however,
the subject title of this thread says "Divorced IDLE Circuits" and I don't see anything there about the "transition" mentioned. I am not assuming anything here ... only what it says.

[NormS]

Because idle and transition circuits are so closely tied together in their functions, in getting a carb to function well at idle and off idle, it doesn't make sense to ignore the transition circuits. Transition circuit calibration needs to be different when the idle circuit is divorced from it,compared to a non-divorced configuration. So that need should not be omitted from the picture. Ignoring transition circuit function, just because the title of the thread refers to idle circuits, makes no sense.

[pamotorman]

the fuel that comes from the idle transition slots covers up the time it takes the fuel to get to the manifold from the squirters