750 Brawler vs 650 AVS 2 at the track, right OOTB !

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Hysteric said:
Can you grasp the difference between a spread bore design and a square bore design? Both can be rated at 800 cfm but have totally different metering characteristics.
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Edit this is what I was answering
(Maybe just maybe that 360 doesn't use more air than that 650 already provides.)

It's only a 650 if your engine vacuum at WOT is around 1.5hg and if it was the 750 would be about 650 too just at a lower hg reading. Different carb sizes is about restriction (vacuum level hg) not air flow (cfm). If you can grasp.

Your headless rooster style of debating is interesting but is giving me a headache.
 
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273 said:
Different carb sizes is about restriction (vacuum level hg) not air flow (cfm). If you can grasp.
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A carb has to meter air and fuel across a broad range of airflows and loads. Thinking in WOT terms only causes you to miss the entirety of the point.

There's a reason the manufactures chose to use a spread bore design. It solves issues a large square bore creates.
 
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Bewy said:
Bigger is not always better........
One carb might have more airflow, but does not atomise the fuel as well.
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AVS2 has annular primary boosters to aid atomization. Secondary boosters are regular. If using an Airgap style manifold the annular boosters really aid atmozation for low speed driving and cruise.
 
I would like to see you test the 625 Street Demon.
 
Pontiac used a 750 cfm QJ on a 230 cu in 6 cyl engine. The engine takes 'what it wants'. How much hp, efficiency & throttle response the engine will have depends on the carb design.
 
I also agree with Hysteric's post #133. The signal to an annular booster is increased because the booster is physically larger, & is purposely place in the middle of the main venturi to reduce the available through the venturi. The engine generates the airspeed, not the venturi. The venturi merely reacts to it. The air speeds up as it goes through the restricted space in the venturi & this causes a pressure drop in the venturi to pull more fuel.
 
How come were acting like we don't have 60-70+ years of data of what works when it comes to carbs and performance engines. And generally the decision for most streetable cars is usually between 650 and 750 or similar sized carbs. Both cover a huge range of engines and hp with lots of overlap between them.
 
I was wondering how the dual quad set up would do against the two carbs tested. Hmmmm

This one....
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Something I have never understood, my motor is 410 CI and for the sake of argument say it is has 100% VE at 6500 rpm at WOT So the motor is flowing 410 CI /12 = 34.16 CF for every 2 rpm. 34.16/2 = 17.08 CF FOR 1 rpm. So at 6500 rpm, 6500x17.08=111,020 CFM!!! All fed by a device rated to flow 800 cfm????? What kind of voodoo magic is that????? I know the carb is rated at 800 cfm at a specific level of depression dry, but over 100 times more that it is rated for??
 
furrystump said:
Something I have never understood, my motor is 410 CI and for the sake of argument say it is has 100% VE at 6500 rpm at WOT So the motor is flowing 410 CI /12 = 34.16 CF for every 2 rpm. 34.16/2 = 17.08 CF FOR 1 rpm. So at 6500 rpm, 6500x17.08=111,020 CFM!!! All fed by a device rated to flow 800 cfm????? What kind of voodoo magic is that????? I know the carb is rated at 800 cfm at a specific level of depression dry, but over 100 times more that it is rated for??
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?.. ya lost me...
 
furrystump said:
Something I have never understood, my motor is 410 CI and for the sake of argument say it is has 100% VE at 6500 rpm at WOT So the motor is flowing 410 CI /12 = 34.16 CF for every 2 rpm. 34.16/2 = 17.08 CF FOR 1 rpm. So at 6500 rpm, 6500x17.08=111,020 CFM!!! All fed by a device rated to flow 800 cfm????? What kind of voodoo magic is that????? I know the carb is rated at 800 cfm at a specific level of depression dry, but over 100 times more that it is rated for??
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A 4V carb is rated at a 20.4 inch water column pressure drop.

Ain‘t no way EVER that much depression can be pulled in actual use.
 
furrystump said:
Something I have never understood, my motor is 410 CI and for the sake of argument say it is has 100% VE at 6500 rpm at WOT So the motor is flowing 410 CI /12 = 34.16 CF for every 2 rpm. 34.16/2 = 17.08 CF FOR 1 rpm. So at 6500 rpm, 6500x17.08=111,020 CFM!!! All fed by a device rated to flow 800 cfm????? What kind of voodoo magic is that????? I know the carb is rated at 800 cfm at a specific level of depression dry, but over 100 times more that it is rated for??
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Your math is wrong. 1 CI = 0.000578 CF, to change ci into cf divide by 1728 but since were talking every 2 revolutions divide by 2 x 1728 so 3456, cid x rpm / 3456 = cfm at 100% ve.

But don't forget carb is only rated a certain cfm @ 1.5hg so if you want 1.5hg then 800 cfm would be your carb but most find that 1.5hg is overly restrictive.


reason for 1728 is you can't just divide by 12 it needs to be 12 x 12 x 12 = 1728, cause were dealing in cubic dimensions.
 
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Volumetric Efficiency is a common term, in use for decades. It is actually incorrect, but has never been corr4ected because everybody has got used to it...
What is being measured is the mass [ not volume ] of air ingested by the engine.
As for volume, the volume of air pulled in is the same for any given rpm; what changes is the density of that air.
 
Bewy said:
Volumetric Efficiency is a common term, in use for decades. It is actually incorrect, but has never been corr4ected because everybody has got used to it...
What is being measured is the mass [ not volume ] of air ingested by the engine.
As for volume, the volume of air pulled in is the same for any given rpm; what changes is the density of that air.
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I remember you pointed this out to me before, like you said most are gonna continue with volume instead of mass, I'm sure in certain situation it's gonna cause faulty logic.
 
Bewy said:
Volumetric Efficiency is a common term, in use for decades. It is actually incorrect, but has never been corr4ected because everybody has got used to it...
What is being measured is the mass [ not volume ] of air ingested by the engine.
As for volume, the volume of air pulled in is the same for any given rpm; what changes is the density of that air.
Click to expand...
Except it doesn't. Engines are throttled so therefore the air ingested is relative to throttle opening amongst other things. That mass changes depending on throttle position and engine demand.
 
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