Carb selection help needed

What do you all think. I need carb selection help, I've been getting a lot of input from different people and it all conflicts. I just had a motor built, here are the specs: 383 small block chevy, 10.2:1 compression, dart heads w/2.02 valves, Edelbrock performer rpm intake. And the 64,000 dollar question is, Is a Holly 650 double pumper with mechanical secondaries too big a carb for this combo???? Thanks for any help on this!

Buckle

 

the 650 should do fine ..i had a super hot 350 and it fed it fine with plenty left to go to adjust....if in doubt find a cfm calculater online to figure your cfm at about 80% efficiency to get a baseline....

 

O.k., thanks Gunny. I have been warned that if it's too much carb that I will wash the cylinder walls and start burning oil, etc. That's the biggest worry I have because I have much $$ in this mill.

Buckle

 

Hey, I just found a cfm calculator online, I put in the info at 80% ve and a safe rpm at 6000 (I was told by my friend that built to motor for me that it should pull 6500 or so rpm), it gave me a number of 531.944 for user % ve and 664.931 100 % ve. Should I go with the user % number and switch to a 600 single feed holly to be safe?? Or would you say still say that the 650 dual feed is o.k.?

Buckle

 

You'd be better off with a vacuum secondary carb on the street.

The 650 would work ok, but I'd be inclined to go with a vacuum secondary 750 considering how your engine is built, probable use of a big cam and the CID.

Carter/Edelbrock's work fine out of the box.
Usually the only chance required is the metering rod springs
If you live at altitude a metering rod/jet change will be required for best running and best mileage.

Holly's work fine out of the box as well.
They have a lot of adjustability available which is good.
The bad part is, if you don't know what you're doing you can back yourself into a corner.
Other than a jet change for altitude, a power valve swap to match the cam and double checking accelerator pump cam clearance - easily done - you'd be in good shape.

Both the Carter/Edelbrock and Holley come jetted about 5% rich right out of the box for the expected engine size they'll be used on.

That old carb size computer is handy for a place to start, but it's not the end-all and be-all that some think it is.

You can get away with a lot more carburetor than most think if they're properly set up for the intended use.

Which is not to say that a pair of 1100 cfm Dominators are what you want on your medium sized 383 so you gotta use your head there.

 

you can use either the vacum secodaryes or the mechanical secondarys ..i personally like the mech sec. so i dont have to wait for the vacum to open them. if your cfm rating are right the 600 may lean over at upper end the 650 in my opinion would be the better carb but thats just me...

 

O.k. guys, thanks for your opinions on this. I will continue to obsess about this a bit longer reading what I can and make a decision. I can always change it if I don't like what I pick.

Thanks,

Buckle