Actual cfm used vs carb size

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F-BIRD'88
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Re: Actual cfm used vs carb size

Post by F-BIRD'88 » Tue Apr 09, 2019 5:39 pm

Keeping my eye out for 2 older pre 1975 4MV style
Q-Jets for this. The 2x Q-Jets double the float bowl capacity, double the needle seat flow capacity, create a very symetrical 8 point discharge pattern over the plenum. . fully adjustable fuel curve air flow rate and progression.
Easy quick metering rod/hanger/air door adjustment.

2x Avs2 carbs mounted back to back have potential too. Must be the long cold winters up here.....eh..

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Re: Actual cfm used vs carb size

Post by ClassAct » Tue Apr 09, 2019 5:57 pm

F-BIRD'88 wrote:
Tue Apr 09, 2019 5:39 pm
Keeping my eye out for 2 older pre 1975 4MV style
Q-Jets for this. The 2x Q-Jets double the float bowl capacity, double the needle seat flow capacity, create a very symetrical 8 point discharge pattern over the plenum. . fully adjustable fuel curve air flow rate and progression.
Easy quick metering rod/hanger/air door adjustment.

2x Avs2 carbs mounted back to back have potential too. Must be the long cold winters up here.....eh..

I'd bet I looked at 20 of those last Friday. Maybe more. If you can't find them, you ain't at the right swap meets.

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Re: Actual cfm used vs carb size

Post by F-BIRD'88 » Tue Apr 09, 2019 5:59 pm

I don't bother with swap meet parts.
Used up stuff , bad deals.
Do much better on Kijiji, Craiglist, auto trader etc.
In Canada check the auto parts counter price for rebuilt Q-Jet carbs at Canadian Tire. Ask for 1968 Chevelle 396-325 hp auto QJet. Last time I checked this they were very reasonable cost. Cannot source and rebuild for this $$.

Huge big potential for BlowThru (in a carb box) or Roots Supercharged.

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Re: Actual cfm used vs carb size

Post by randy331 » Tue Apr 09, 2019 8:45 pm

novadude wrote:
Tue Apr 09, 2019 3:25 pm
Doesn't the "add as many carbs as you can" theory ignore the fact that you need some air speed through a venturi to make a carb meter fuel properly? Doesn't splitting that airflow among more venturis decrease the signal in any one venturi? After all, the engine can only pull so much air volume based on other limiting factors.

I'm surprised that we are still having the old "more flow is always better" discussion on this forum. Might as well grab some heads with the largest CSA you can find if it's really all about minimizing pressure drop along the length of the intake tract.
Right, there's an ideal gas speed for the ex, induction tract speed, etc, and the venturi on the carb has one too. It would change some with shape.

It's easy to tell Fbird has little to no real world experience around racing engines.

Randy

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Re: Actual cfm used vs carb size

Post by zums » Tue Apr 09, 2019 9:53 pm

randy331 wrote:
Tue Apr 09, 2019 8:45 pm
novadude wrote:
Tue Apr 09, 2019 3:25 pm
Doesn't the "add as many carbs as you can" theory ignore the fact that you need some air speed through a venturi to make a carb meter fuel properly? Doesn't splitting that airflow among more venturis decrease the signal in any one venturi? After all, the engine can only pull so much air volume based on other limiting factors.

I'm surprised that we are still having the old "more flow is always better" discussion on this forum. Might as well grab some heads with the largest CSA you can find if it's really all about minimizing pressure drop along the length of the intake tract.
Right, there's an ideal gas speed for the ex, induction tract speed, etc, and the venturi on the carb has one too. It would change some with shape.

It's easy to tell Fbird has little to no real world experience around racing engines.

Randy
Whats wrong with gas particles leaving the barrel, turning 90* right then 180* left then making its way through the intake runner and head, lol, ive never seen or can picture a 2 x 4 adapter for a single plane
Tom

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Re: Actual cfm used vs carb size

Post by cjperformance » Wed Apr 10, 2019 12:21 am

zums wrote:
Tue Apr 09, 2019 9:53 pm
randy331 wrote:
Tue Apr 09, 2019 8:45 pm
novadude wrote:
Tue Apr 09, 2019 3:25 pm
Doesn't the "add as many carbs as you can" theory ignore the fact that you need some air speed through a venturi to make a carb meter fuel properly? Doesn't splitting that airflow among more venturis decrease the signal in any one venturi? After all, the engine can only pull so much air volume based on other limiting factors.

I'm surprised that we are still having the old "more flow is always better" discussion on this forum. Might as well grab some heads with the largest CSA you can find if it's really all about minimizing pressure drop along the length of the intake tract.
Right, there's an ideal gas speed for the ex, induction tract speed, etc, and the venturi on the carb has one too. It would change some with shape.

It's easy to tell Fbird has little to no real world experience around racing engines.

Randy
Whats wrong with gas particles leaving the barrel, turning 90* right then 180* left then making its way through the intake runner and head, lol, ive never seen or can picture a 2 x 4 adapter for a single plane
Tom
Possibly all the big fuel droplets that have come out of suspension in the air stream race along the base of the adaptor from either end at atomic speed and smash into each other right above the single 4 barrel plenum like in a hadron collider, then as the fuel atoms split the sonic wave generated may atomically supercharge the intake track :-k
Craig.

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Re: Actual cfm used vs carb size

Post by F-BIRD'88 » Thu Apr 11, 2019 5:04 am


TAG
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Re: Actual cfm used vs carb size

Post by TAG » Thu Apr 11, 2019 6:33 am


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Re: Actual cfm used vs carb size

Post by cjperformance » Thu Apr 11, 2019 6:50 am

TAG wrote:
Thu Apr 11, 2019 6:33 am
Even more power:

https://www.enginelabs.com/engine-tech/ ... ng-finest/

4* Q-Jet
I just read that article, sounds like it works about as i would have expected #-o
Craig.

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Re: Actual cfm used vs carb size

Post by chevyfreak » Thu Apr 11, 2019 8:07 am

TAG wrote:
Thu Apr 11, 2019 6:33 am
Even more power:

https://www.enginelabs.com/engine-tech/ ... ng-finest/
4* Q-Jet
I have that code in life that if i have an idea and dont try it how will i know if it worked or not.
Im no pro, far from it, made many mistakes and still do. I observe many things and have many ideas from observing and many of my own. If i try something and someone tells me it wont work then i ask them if they have tried it. And if they have and tell me what they observed or seen the problem then i can change my idea to work or conclude that it doesnt.
Some of those ideas i have tried doesnt always work out. But i can say i tried.
Some worked but needed some changes to the main idea.
Others worked good.

Edison had a saying that he didnt fail, he found 10 000 ways of how not to do it.
He didnt invent the light bulb the first try. But kept trying because he didnt give up.

Same can be said of many of the pioneers of rodding.
Smokey tried many things and not all of them worked, but he tried. He went after getting that extra bit of power.

Fbird has his idea of 2 x 4bbl on a y adapter into single 4bbl intake. The idea is there and the process of making it work. He may have tried it before and now making some changes . Only after further tuning will the final results come forward.

That setup with the 4 qjets. I dont see anything wrong with the idea. It was implemented and there is a problem with the secondary airflap that flutters but its 2 different cylinders working ea on a flap thats on 1 shaft. I say split the shaft and be able to adjust the flap on its own for ea cyl. Then retry. With every try there is a result , good or bad, and a learning curve.

Just how i see it.

Chevyfreak.
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Steve.k
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Re: Actual cfm used vs carb size

Post by Steve.k » Thu Apr 11, 2019 9:39 am

Very true. I wonder where the prostock would be had Glidden not designed the split dommies?

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Re: Actual cfm used vs carb size

Post by swampbuggy » Thu Apr 11, 2019 9:46 am

I like what you said Chevyfreak ! Commonly known as R and D Research and Development Mark H. PS It is something i enjoy !!

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Re: Actual cfm used vs carb size

Post by chevyfreak » Thu Apr 11, 2019 10:09 am

swampbuggy wrote:
Thu Apr 11, 2019 9:46 am
I like what you said Chevyfreak ! Commonly known as R and D Research and Development Mark H. PS It is something i enjoy !!
Exactly. Everything started with an idea and then the fiddling and tuning.
For me it depends on what it is. Have how many mufflers i build and tried just to get a certain sound.neverending story that one.
Carbs as well.
I try weird shit sometimes just to see what happens.

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Re: Actual cfm used vs carb size

Post by prairiehotrodder » Thu Apr 11, 2019 10:45 am

When i was a kid i made a plenum to mount a squirrel cage type heater fan on the snorkel of a Q-jet closed element stock air cleaner box. It was an electric turbo !! On a country road i marked out 1/4 mile and had a friend time me with a stop watch. On a stock 1983 chev halfton with a 350 it was a difference of one second between having the turbo on vs off. There were so many problems with the science of this test but it sure impressed my friends ! I then proceeded to build a bigger one that held 2 fans. It didn't work. Don't know why. Of course there were so many variables with the first test that i don't know if it really worked either. Was fun though.

Hopefully the OP on this thread can chime in as to what he has learned through all this if anything. Sorry for the goofy off topic story.
Brian
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www.therocketshop.blogspot.com

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Re: Actual cfm used vs carb size

Post by Steve.k » Thu Apr 11, 2019 11:02 am

Well that be me. And i think maybe Mark explained it best. While the smaller carbs may offer better atomization the switch from bigger to small may offer less gains than the switch from the single style manifold to the dual ram. All very interesting to say the least.

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