383 carb question

[tunerwannab]

I looking at changing the carb on my 71 challenger. It has a 383. Don't know exact motor details, previous owner told me he did the biggest cam he could without messing with valves, it does have a mopar performance intake manifold and headers.

Currently I have a Holley 600 I think, no choke, I forget the exact model but it is not a common or popular one. I'm undecided between an edlebrock 600 or 650 with electric choke. Currently the car will cruise fine but when cruising if I give it more gas it chokes for a second then goes. Any tips advice would be awesome. I trying to do this Tuesday.

[cudabob496]

http://www.holley.com/data/TechService/Technical/Selecting%20A%20Carburetor.pdf

I suspect most folks on this site will recommend a 750.

http://www.hotrod.com/pitstop/1306_vacuum_or_mechanical_secondary_carburetor/viewall.html

[Chryco Psycho]

I would be looking at a 750 Proform carb

[tunerwannab]

Looking at that chart I wouldn't think my car runs at 100% efficiency. Is it better to have a too much carb than to little.

[Chryco Psycho]

How many times have we had this discussion ! The best formula for picking a carb is 2x the CI so 383 is 766 .
 True you cannot change physics but maybe the carbs do not flow as much air as advertised but real world experience is approx. 2x the CI works well .
Proform has one of the most affordable & tunable carbs on the market with vacuum or mech secondary .
The reality is the Holley you have can be tuned to work well also , check float levels , change the squirter or pump cams , replace the secondary spring or use the correct power valve & the hesitation will disappear .

[72cudamaan]

How many times have we had this discussion ! The best formula for picking a carb is 2x the CI so 383 is 766 .
 True you cannot change physics but maybe the carbs do not flow as much air as advertised works well .


Neil, say it ain't so.     Manufacturers advertising falsely. That couldn't happen.      I agree with the 2x
formula as well.

[jhaag]

I agree with chryco. try to fix what you have unless you need the choke. as to your question on whether to error on the small or larger cfm size, on a street car you will get better throttle response and driveability with a slightly undersized carb over 1 that is too big. if your carb has the choke horn still on it, it will have a number stamped on it, go to holleys' web site and you can figure out exactly what you have, then work from that

[cudabob496]

I agree with chryco. try to fix what you have unless you need the choke. as to your question on whether to error on the small or larger cfm size, on a street car you will get better throttle response and driveability with a slightly undersized carb over 1 that is too big. if your carb has the choke horn still on it, it will have a number stamped on it, go to holleys' web site and you can figure out exactly what you have, then work from that

I agree, a well dialed-in 750 supported my old built 440 to well over 500 hp.
If he didn't take his challenger above 5500 rpm, then a 650 would probably make him
quicker on the street.  A 750 on his 383 would be necessary if he was taking it
up to 6000+ rpm.

Though a much different engine, the 850 hp NASCAR car engines use an 830 cfm carb. They are probably
as close to a volumetric effeciency of 1.0 you are gonna get. I think you go above 1.0 when you have
a blown or turbo engine.