Carburetor CFM

[leftylou]

My ‘70 c10 has an small block 400 in it. I want to replace the carburetor with an Edelbrock AVS2 but I am torn between the 500 and 650 CFM versions. The engine is stock as far as I can tell. Looks the original heads, rams horn exhaust manifold, original intake. I have no idea if it has ever been rebuilt but I kind of doubt it. From my understanding the 400 doesn’t like to rev high so I am thinking the 500 cfm may be the better choice but I don’t want to go too small either. Any advise would be appreciated.
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[HO455]

There's going to be dozens of opinions on this subject, so just I will say the factory Qjet was rated at 750 CFM for most SBC 350, 400, 396, 402 and some 454 engines. The majority of 454s came with the 800 CFM version Qjet.

[geezer#99]

If it’s a quadrajet keep it or replace it with a rebuilt one.
Too many hidden potential extra costs with an avs.
You might need a heat spacer or adaptor (50 bucks), fuel regulator (100 more), fuel line, gas pedal hook up brackets.
Extras add up quickly.
You could spend 200 more plus your new carb cost.
Custom built quadrajet can be had for 500 bucks.

[leftylou]

Originally Posted by geezer#99

If it’s a quadrajet keep it or replace it with a rebuilt one.
Too many hidden potential extra costs with an avs.
You might need a heat spacer or adaptor (50 bucks), fuel regulator (100 more), fuel line, gas pedal hook up brackets.
Extras add up quickly.
You could spend 200 more plus your new carb cost.
Custom built quadrajet can be had for 500 bucks.

I don’t have a q-jet. The carb on it is an old Carter AFB so I have everything I need to make the Edelbrock work. I just want to make sure I don’t fall into the trap of bigger is always better.
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[72SB]

OP

either will work. FWIW my 357 (BPE crate motor) was dynoed (411HP/413TQ) by BPE using a 600 CFM. I used my Eddy 600 (1406) I had on my 327 which worked fine. The only thing I did once on the 357 was jet up one size based on tuning findings.

The 500 "may" have to be either changed with metering rod & or Jet as would the 650. Very common tweaks to any carb. The Eddys are basically the Carter AFB design. For me dead simple to work on. Edelbrock makes tuning kits (metering rods, stepper springs & jets) specific to each carb for this purpose

If it was my 400, I would put on the 650.

Get the timing, including VA, settled before making any carb changes on any motor/carb combo. Not only how much timing the VA provides....it typically needs to be controlled (stop plate) but when VA comes in (adjustable VA). Crane and Accel used to sell the adjustable VA/Sop plate kit. Now just the VA, you need to make your own stop plate or at least put the piece of vacuum hose on the VA rod to reduce its movement if it provides more than 10-12 degrees of advance