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Discussion Starter · #1 ·
Im just curious to find out if a 500 cfm 4 bbl carb id better than a 500 cfm 2 bbl carb? I mean they both flow the same so whats the big difference, and which one would run better on the same engine?

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-Kenny-
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A Mustang is a poor mans Ferrari!

1968 289 coupe, 65B, my car.
1968 302 coupe, 65A, my dads car.

<font size=-1>[ This Message was edited by: HitmanKB on 6/27/02 1:00am ]</font>
 

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The 4 bbl would run better and get better gas milage than the 2 bbl. The reason is that the 2 bbl is always using the 500 cfm bores whereas the 4 bbl is only using about half that for cruising. It will only use all 500 cfm when it is needed. This results in a faster air flow and hence a better running engine all around.
 

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Also, the rating of a 2v verses a 4v is done at different inches of water. The 4v is done at 1.5" and the 2v is done at 3". Possibbly this is because of the 2 holes verses 4 holes???? I am not sure how this actually affects the cfm.
 

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I have tried a bunch of Holley carbs at the strip on my mild 289 Mustang.

350 cfm 2 brrl = 14.17
390 cfm 4 brrl = 13.73 ( very sweet!)
500 cfm 2 brrl = 14.01 (very hard to tune!)
500 cfm 4 brrl = 13.70
650 cfm 4 brrl = 13.56 ( my favorite)
750 cfm 4 brrl = 13.60 (produced most mph)
 

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Discussion Starter · #6 ·
So in theory if I get a 600 cfm 4bbl carb I should be able too get more power and save more gas while the secondaries are closed than with a 500 cfm 2 bbl carb right? I dont know if this is right so......
thanks,
 

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You have to remember that a 500 cfm 2 brrl was designed for serious class racing where a 2 brrl carbs can only be used. It would feel like you are running a 950-1050 4brl without the extra 2 brrls in the rear. It's barrels and squirters are huge!! It's hard to beat the all around performance of a well tuned 600 4brl for a SB street/strip car. That's why the OEMs used them so much in the 60's - 80's .

I used to use a 600 vac. in bracket racing on a cheaply built 8.7:1 stock ported 302 SBF and I could unhook the secondaries, and it would be dead on consistent. Believe it or not, a mild SBF is so efficient, you can hardly tell the difference if you only use the front barrels. I could run 14.05 @ 98 mph in the 1/4 all day long with just the primaries!! I have a wall full of trophies to prove it. It ran so smooth that you would swear that it had tuned port injection! That same engine would only run 13.75 with the secondaries but would not be as consistent.
 
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