Re: carb theory question
[Re: Mike H]
#194690
01/15/09 10:07 PM
01/15/09 10:07 PM
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Joined: Jun 2004
Posts: 3,378
St. Charles, MO
wingman
Uncreative Title
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Uncreative Title
Joined: Jun 2004
Posts: 3,378
St. Charles, MO
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Because the smaller carb has smaller diameter venturi, the carb is more sensitive to changes in vacuum signal coming from the cylinders via the intake. This gets the carb drawing more fuel more quickly. The smaller volume of air in the venurii, (and in the intake plenum) allows the air to "accelerate" more quickly = more responsive. Conversely, running a large carb and an intake with a large plenum, can move more total volume of air, but it takes that larger volume of air longer to "accelerate." Hope that's technical enough... 
1969 Dodge Coronet Super Bee 383 A4
1970 Plymouth Road Runner 440 FC7 (sold)
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Re: carb theory question
[Re: wingman]
#194691
01/15/09 10:52 PM
01/15/09 10:52 PM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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A smaller venturi makes the mixture flow faster at that(constricted) point in the carb which makes for much better atomization of the air/fuel mixture & the faster speed slides MORE mixture past the intake valve as it's closing shut which is why the whole system needs to be matched(flow wise) for max mixture speed in a given rpm range. It's all about mixture speed & quality.
live every 24 hour block of time like it's your last day on earth
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Re: carb theory question
[Re: RapidRobert]
#194692
01/16/09 09:05 AM
01/16/09 09:05 AM
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Joined: Jan 2003
Posts: 350
central IL
myduster360
enthusiast
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enthusiast
Joined: Jan 2003
Posts: 350
central IL
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Yep, "Responsiveness" is all about how FAST the Fuel/Air can get into the cylinder, after you stomped the gas.
Smaller carbs(and smaller intakes) maintain a slightly higher pressure drop than a larger one. More pressure difference between the inside of the cylinder and the ambient(outside the carb), the HIGHER the air(fuel too) Velocity will be.
Higher air velocity at lower speeds = more "Responsiveness"
Small cams and more indirectly small tube headers, help maintain this higer Air/Fuel velocity at lower RPMs.
1972 Swinger 3.6L Pentastar
Diablo CMR tuner
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Re: carb theory question
[Re: Mike H]
#194695
01/16/09 05:28 PM
01/16/09 05:28 PM
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Joined: Apr 2004
Posts: 1,396
Mass
dgc333
pro stock
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pro stock
Joined: Apr 2004
Posts: 1,396
Mass
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Quote:
Ok, I think I get that. Now, along those same lines, can you guys tell me what the difference is between a single-plane and dual-plane intake, and what one is better for low-end than the other.
A single plane has one relatively large plenum area that feeds all the cylinders. The dual plane has two relatively small plenums each one only feed 4 cylinders. The dual plane terminology comes from the fact that one plenum floor is higher than the other so the runners can pass over and under each other. Because you have a smaller plenum the mixture flowing to the cylinders maintains a higher velocity which keeps the fuel more completley atomized and more evely distributed. This makes for better low end. On the top end the dul plane become restrictive and doesn't typically make as much power.
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Re: carb theory question
[Re: wingman]
#194697
01/17/09 12:37 AM
01/17/09 12:37 AM
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Joined: May 2008
Posts: 5,399
Aurora, Colorado
451Mopar
master
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master
Joined: May 2008
Posts: 5,399
Aurora, Colorado
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Quote:
Because the smaller carb has smaller diameter venturi, the carb is more sensitive to changes in vacuum signal coming from the cylinders via the intake. This gets the carb drawing more fuel more quickly.
The smaller volume of air in the venurii, (and in the intake plenum) allows the air to "accelerate" more quickly = more responsive.
Conversely, running a large carb and an intake with a large plenum, can move more total volume of air, but it takes that larger volume of air longer to "accelerate."
Hope that's technical enough...
Plus with a small carb, the throttle blades have to be open more (more throttle angle)allowing a greater amount of airflow through the boosters. With a larger carb, the larger diameter throttle blades might only be open a small amount at lower RPMs and a greater amount of fuel metering is cumming through the idle and transition circuitry of the carburator and not that much from the main metering system because thee is not that much airflow through/around the boosters.
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Re: carb theory question
[Re: RapidRobert]
#194698
01/17/09 10:26 AM
01/17/09 10:26 AM
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Joined: Jan 2008
Posts: 2,231
ILLINOIS
volaredon
top fuel
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top fuel
Joined: Jan 2008
Posts: 2,231
ILLINOIS
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Quote:
Quote:
what one is better for low-end than the other.
strickly speaking a dual plane is but they are all a compromise(some more than others) & for instance the Holley street dominator single plane intake (the big block one for sure) has always dyno tested pretty good in the lower ranges.
Did they offer 2 different "street dominators" for a given engine?? All of em Ive seen, (for a small block anyways) are dual plane.
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