Divorced idle circuits

[NormS]

Actually, both the transition slots and the squirters cover for the delay in the main circuit tip-in, and for any fuel fall-out that might occur when there is a sudden decrease in manifold vacuum, when the throttle is being opened. They all have to work together to create a seamless transition to the main circuits, under all the circumstances that the engine will see in its application,whether its a street engine or a racing engine.

[swampbuggy]

Wow , these discussions seem to always get revved up pretty high LOL. My original post had several questions in it, some of which i don't believe have been answered ? I am going to have to purchase a carb. for my engine and was trying to figure out the best setup for the application. This being said (and should have been said earlier, my apology please) here is the planned usage= LIMITED amount of street driving, possible club track time road race style, car shows. Engine= S.B.C. 18deg. reworked Eddy single plane engine will be almost identical to an older style NASCAR Busch engine----so now you know the rest of the story------back to the carb. questions in the O.P. BTW the last thing i want is EXCESSIVE fuel in the cylinders during slower speed running, just enough fuel to make her pop and sound correct. This is where i thought the" divorced idle circuit" might be good ? BUT i had no idea one way or the other not being a carb guy. Thanks for ALL the time you folks take to weigh in on this forum, Mark H.

[NormS]

Mark, If your engine is properly cammed for limited street use, and road race use, I recommend a carb that uses the conventional 2 circuit metering blocks(interdependent circuits), which includes all of the available Holley universal application 4150 series carbs. Being that clean low-speed(idle and part throttle) characteristics are going to important for both your street use and racing, I think that a nicely modified double pumper will work very well. All the engine specs, drivetrain specs, etc. need to taken into account when a carb is chosen and modified for your engine, as is the case for all performance engines.

[pamotorman]

Actually, both the transition slots and the squirters cover for the delay in the main circuit tip-in, and for any fuel fall-out that might occur when there is a sudden decrease in manifold vacuum, when the throttle is being opened. They all have to work together to create a seamless transition to the main circuits, under all the circumstances that the engine will see in its application,whether its a street engine or a racing engine.

if the transition slots are low of fuel because they are too far open and being used for idle fuel you will have a bog when you open the throttle till the squirter shot reaches the intake.

[NormS]

If the butterflies are too far open at idle, exposing too much of the transition slots to manifold vacuum, they will be pouring fuel into the engine. In some cases,when this happens, the idle mixture will still be too rich with the idle mixture needles completely closed.
If the butterfly position is due to low manifold vacuum, caused by a long duration camshaft , then the butterflies will need air bypass holes drilled in them. If the low vacuum is caused by having too little ignition advance at idle ('initial timing"), then that timing should be corrected before deciding on drilling the butterfly holes, and then what size ,if they are drilled.
With the popular Holley and Holley clone carbs, getting the butterflies in the correct position at idle (nearly closed), is an important key to having good idle and off idle characteristics for any engine.

[swampbuggy]

Thanks Norm well I must admit one of the goals with this Motors to make 2 horsepower per cubic inch so it's going to have a big Cam and a carburetor is going to need to flow a good bit

[NormS]

If you mentioned the engine size, I must have missed it. Could you tell me that, and the duration and lobe separation specs of the cam you have , or are thinking of getting? Also, with a long duration cam and good racing gas, you can safely run locked ignition timing, which would give you your best low speed engine characteristics. Is locked timing a possibility in this case?
If you are talking about a 358ci engine, to make 700+HP, it will have to run some RPM's. And, yes, that will need some really good heads and a healthy amount of duration on the cam.

[jmarkaudio]

The Mopar metering block was an exception, afterthought, and not from the original design. Millions? I don't think I ever saw one, I'll have to dig thru my pile of parts as it's possible I may have a metering block my dad had in his bone pile. Still the Original Holley design did not include a divorced idle and does not need one. Manufacturers did unusual things to appease growing fuel economy and emission demands, rarely in the interest of performance. Even with a blow thru methanol carb I've not had a need for a divorced idle.

As far as what carb if the manifold is a 4150 flange stick with a 4150 design. Without modifying the manifold you can get an oval blade 4150 to dry flow just over 1200 CFM, plenty to make the HP you are looking for. For what you want to do I would suggest an annular 1000/1050 4150, it will be responsive and provide quality distribution.

On a Holley calibrating the idle/transition fuel correctly is extremely important to performance over a wide range of throttle opening. Idle jet, idle bleed, transition slot size, and sometimes a necessary t-slot restriction all play into how each circuit transitions from one to the next, and into the main operation as well.

[Tuner]

When carburetors are outlawed, only outlaws will have carburetors.

Mommas don't let your babies grow up to be carburetor tuners.

[NormS]

you're a real poet, you know it?

[Walter R. Malik]

The Mopar metering block was an exception, afterthought, and not from the original design. Millions? I don't think I ever saw one,

Afterthought...?
The Mopar 3 circuit block which was designed for Chrysler Corporation was the FIRST thought for that configuration metering block; those very dies for those castings were used to make the original blocks for the Dominator carbs.

Believe whatever you want but, facts are facts.
Millions...? YES, Mopar 4 barrel Holley equipped engines had over a million produced during the lifetime of those carbs.
Whether or not they are/were important in today's world of high performance is immaterial.
Being that YOU have not seen one makes no difference at all.

[NormS]

Being that we have not seen one for decades, shows how well they caught on in the automotive industry. They didn't.

[Walter R. Malik]

Being that we have not seen one for decades, shows how well they caught on in the automotive industry. They didn't.

So what ...? That was not in question here.
You were wrong about them here so, you try to change the subject to deflect that actuality; your opinion, (or anybody else'), does not automatically change the facts of history.

[Walter R. Malik]

Being that we have not seen one for decades, shows how well they caught on in the automotive industry. They didn't.

They didn't catch-on probably because of the difficulty in their usage and every Tom, Dick & Harry who claims to be a carburetor expert didn't want to deal with them, not being absolutely necessary.

[NormS]

What Chrysler did nearly 50 years ago had little impact on performance carburetors back then, and little to none since. You might try joining the 21st
century. You seem to think that those divorced idle metering blocks were the greatest thing since sliced bread. They weren't, and still aren't.