600cfm our 750cfm carbs??
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600cfm our 750cfm carbs??

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    SUCK MY WAKE Sangster~bbc's Avatar
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    Default 600cfm our 750cfm carbs??

    hey guys i have a mild bbc 454..and last year i was running a tunnel ram on it with 2 600cfm full mechanical edelbrock carbs and ran good but noticed was running alittle lean on mid too full throttle according too plug reading wasnt white but realy light tan ... i am wondering if i should try jetting up these carbs, our just go with 2 edelbrock 750s i have too buy new carbs anyway was hard up for $$ and had too sell old carbs so i could go either way i have too buy new once again...our was thinking of running a pair of predators for the vintage thing but people want a arm and leg for them old girls...






    Last edited by Sangster~bbc; 12-11-2012 at 01:10 AM.

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    Default Mild 454???

    Quote Originally Posted by Sangster~bbc View Post
    hey guys i have a mild bbc 454..and last year i was running a tunnel ram on it with 2 600cfm full mechanical edelbrock carbs and ran good but noticed was running alittle lean on mid too full throttle according too plug reading wasnt white but realy light tan ... i am wondering if i should try jetting up these carbs, our just go with 2 edelbrock 750s i have too buy new carbs anyway was hard up for $$ and had too sell old carbs so i could go either way i have too buy new once again...our was thinking of running a pair of predators for the vintage thing but people want a arm and leg for them old girls...
    IMO, and I'm a stickler for real world numbers when it comes to adding fuel to what is, in reality, a big air pump, you're already way over carbed for a "mild 454". Your "lean" reading on the plugs could be a number of things, including over octane fuel..... IMO, (again), a pretty radical 454 can't use more than 800, 850 at the very most, CFM in a mechanical carb. (based on the math)..... Using a T/R and two 600s should be waaaay more than you need unless you're buzzing it well above 8000, and a "mild 454" aint gonna do that. You might look into getting a couple of vac secondary 600 Holleys if they'll fit, or two more Edelbrock 600 and playing with the metering rods and springs. But, again, I really can't see a "mild" 454 using 2/3rds of 1200 cfm.....
    Just my opinion, and I'm sure others have different ideas....
    Ray
    PS Every Edelbrock carb I've ever seen had LOW float settings when it came out of the box....
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    Quote Originally Posted by Moneypit View Post
    IMO, and I'm a stickler for real world numbers when it comes to adding fuel to what is, in reality, a big air pump, you're already way over carbed for a "mild 454". Your "lean" reading on the plugs could be a number of things, including over octane fuel..... IMO, (again), a pretty radical 454 can't use more than 800, 850 at the very most, CFM in a mechanical carb. (based on the math)..... Using a T/R and two 600s should be waaaay more than you need unless you're buzzing it well above 8000, and a "mild 454" aint gonna do that. You might look into getting a couple of vac secondary 600 Holleys if they'll fit, or two more Edelbrock 600 and playing with the metering rods and springs. But, again, I really can't see a "mild" 454 using 2/3rds of 1200 cfm.....
    Just my opinion, and I'm sure others have different ideas....
    Ray
    PS Every Edelbrock carb I've ever seen had LOW float settings when it came out of the box....
    when I ran carbs on a 434 BB I ran two 1050 they flowed 1138 ea. ran perfect.

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    Senior Member EVILFORCE's Avatar
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    I have a 454 in the works. Wil make apx 550-600 HP. Am going to use 2 450's on it.

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    I have a 496 pump gas 10.2 to 1 comp. full roller motor. Runs 78mph @ 5500 with 2 450's on a T/R. At cruise 2800rpm I can get damn near 5mpg! Love the 450's!!!

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    Quote Originally Posted by Sangster~bbc View Post
    hey guys i have a mild bbc 454..and last year i was running a tunnel ram on it with 2 600cfm full mechanical edelbrock carbs
    Contrary to what you might think, there is no such thing as a full mechanical Edelbrock carb. There is an air door or valve that is opened by air velocity thru the carbs secondaries. Not unlike the sir velocity thru the primaries causing a pressure drop(vacuum) that controls a vacuum motor tied to the secondary throttle blades, the Edelbrock simply uses air velocity thru the secondaries to push open the door directly.

    regardless if you install 600 or 750s, the engine has to move enough air to open the secondaries. I you install 750s and the engine isn't up to it, they might only open 1/2 or 3/4 of the way.
    If its a mild build, 2 1404 500cfm carbs meant for dual quad arrangements is probably your best bet.
    I doubt a mild 454 can open even a pair 600 carbs 100% open on the secondaries.



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    Nothing personal Sangster just general comments from the peanut gallery. Why does it seem everyone tends to go small on the bottom end and want to go big on the top end? Carburetors are designed to give best overall performance with high flow velocities through the venturies. Oversizing reduces flow velocities resulting in poor throttle response and less control of air fuel ratios over the throttle range. With a boat it is not as critical or noticeable as in a car but it is present. I am sure there are those on the forum that know much more than I do about carburetors. It seems caburetors seem to perform best if their CFM rating is not significanly more than about 20% larger than the volume of air the engine can move. Your 454 at 6000 Rpm based on 100% Volumetric efficiency will move about 780 cfm. Most engines do not have 100% volumetric efficiency. I am not saying you cannot go bigger, you just may be paying for carbs that will not perform as well.

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    Quote Originally Posted by gn7 View Post
    Contrary to what you might think, there is no such thing as a full mechanical Edelbrock carb. There is an air door or valve that is opened by air velocity thru the carbs secondaries. Not unlike the sir velocity thru the primaries causing a pressure drop(vacuum) that controls a vacuum motor tied to the secondary throttle blades, the Edelbrock simply uses air velocity thru the secondaries to push open the door directly.

    regardless if you install 600 or 750s, the engine has to move enough air to open the secondaries. I you install 750s and the engine isn't up to it, they might only open 1/2 or 3/4 of the way.
    If its a mild build, 2 1404 500cfm carbs meant for dual quad arrangements is probably your best bet.
    I doubt a mild 454 can open even a pair 600 carbs 100% open on the secondaries.

    Your not talking about the Carter AVS...are you? They DID WORK!!

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    Quote Originally Posted by Gone Green View Post
    Your not talking about the Carter AVS...are you? They DID WORK!!
    No. Edelbrock is now reproducing the AVS and yes they work. The air door on the AVS is top mounted and visable from outside the carb like a Quadrajet. But the Carter AFB/Edelbrock Performer carb has a air door as well only its inside the carb, between the boosters and the throttle blades. Instead of using a spring like an AVS, which can be adjusted for the opening rate, the AFB/Performer uses a counter weighted air door and is much harder to make adjustments to. You have to reduce the weight of the counter weight and if you screw up, you need a new air door. Its not for the amatuer.





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    does anyone use a CFM calculator to choose their carb CFM size? i figured my VE was fairly low given its just a mild 454, stockish heads, a decent intake, etc... i went with 80%. i turn around 5200rpms... and with a calc I got around a 578 CFM and a 722 with a 100% VE. I chose a 650 demon and so far have had GREAT results, plugs look perfect and I get great "mpg" for my use.

    example: http://www.carburetion.com/calc.asp

    How do you figure slapping twin 600 or 750's on a mild 454?

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    Default The "look"....

    Quote Originally Posted by ka0tyk View Post
    does anyone use a CFM calculator to choose their carb CFM size? i figured my VE was fairly low given its just a mild 454, stockish heads, a decent intake, etc... i went with 80%. i turn around 5200rpms... and with a calc I got around a 578 CFM and a 722 with a 100% VE. I chose a 650 demon and so far have had GREAT results, plugs look perfect and I get great "mpg" for my use.

    example: http://www.carburetion.com/calc.asp

    How do you figure slapping twin 600 or 750's on a mild 454?
    It's all about the "look". Chances are the engine would perform better with a dual plane and a single mechanical carb..... But, the T/Ram and dual carbs looks better....Especially if the T/Ram is polished.....

    Ray
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    Quote Originally Posted by Moneypit View Post
    It's all about the "look". Chances are the engine would perform better with a dual plane and a single mechanical carb..... But, the T/Ram and dual carbs looks better....Especially if the T/Ram is polished.....

    Ray
    I have 20 bucks that says your PS would have performed better if you would have left the blinger MFI on the bench and ran a single 850 on a dual plane

    It would probably serve you better Ray, if you didn't make too many comments out sizing induction systems for under powered boat engines. I have seen the enignes you'll stick a set of stack injectors on. They would run better with a Bluebird bus iron 2 bbl intake.

    Those boys that actually pulled the pencils out of their pockets and drew the 427 Ford 8V, 406 6V, the dual quad 409, tri power 348, the 426 street Hemi, the 440 Six Pac, tri power 389 Goat, the 1958 dual quad 283!!!, must have never read you prized CFM formula.



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    Last edited by gn7; 12-12-2012 at 05:52 PM.

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    SUCK MY WAKE Sangster~bbc's Avatar
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    thanks for the help guys...i learn something new every time i go on here...

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    Default Outa the blue....

    Quote Originally Posted by gn7 View Post
    I have 20 bucks that says your PS would have performed better if you would have left the blinger MFI on the bench and ran a single 850 on a dual plane

    It would probably serve you better Ray, if you didn't make too many comments out sizing induction systems for under powered boat engines. I have seen the enignes you'll stick a set of stack injectors on. They would run better with a Bluebird bus iron 2 bbl intake.

    Those boys that actually pulled the pencils out of their pockets and drew the 427 Ford 8V, 406 6V, the dual quad 409, tri power 348, the 426 street Hemi, the 440 Six Pac, tri power 389 Goat, the 1958 dual quad 283!!!, must have never read you prized CFM formula.
    Well Bob, once again you're probably right... I'll just forget about the 20+ years the MFI worked quite well. And since you're so observant, can you tell me when the last time the PS89 failed to start a heat??? Give up? It was Puddingstone in 1992, and it was a fried starter, not the Crowers.. AND, since you apparently have X Ray vision about whats inside my engines, why didn't you let us know about that one 3/8ths bolt and nut that created all the injection issues, both in April, and again last month. Surely you saw it.... BTW, that problem is solved, and as we live and learn, will never happen again....
    Comparing "stacks" to carbs is like comparing apples to oranges. You can do things with MFI that carbs just won't do, but you already knew that..... Somehow I must have indirectly pissed in your Wheaties....Or am I just another "target of opportunity"??
    Ray
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