[QUOTE=streetstar;2361267]
Quote:
Originally Posted by gchemist
Welcome to the site.
Edelbrocks 1406 is my choice. No more than 650 CFM for a SB. http://www.centuryperformance.com/vacuum.asp[/url]
Why only 650cfm? A stock Q-jet is 750cfm. The carburation needs to be tailored to the demands of each particular engine.
---a 350 is well suited to a 750. A smaller engine like a 305 or 307 can make use of a 600 or 650 --- but a 383 stroker, or a built 400 might be fuel starved with a 750 even. A friend's 383 makes close to 600 hp's on the dyno with a Holley 930dp, and could use more so he is going to a 1050 dominator .
A 750 quadrajet has small primaries for good torque and efficiency on the street, but has large secondaries for full throttle performance-- that is why it is made on a spread bore, whereas the Holley primaries and secondaries are externally the same size .
GM engineers are relatively smart-- they wouldnt spec the 750 qjet if it was a total dog
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You are absolutely right in your assmptions that an engine has to be fed according to the demand. However for everyday street driven vehicles, the overcarburetion of a 750 will (and believe me, I have seen it) cause a slobbering problem at the stoplights. Your top end will be EXCELLENT but your daily drivving will be poor. The Q-Jet has small primaries and then transition to the secondaries which gives the 750 effect on them. Where a Holley, Edelbrock or Carter square bore four barrel has a slightly larger primary when it is a 750 and that is detrimental to daily driving.
This all depends on a couple of other factors 1) weight of the vehicle--a truck is heavier than a Camaro, so it will respond more sluggishly, unless really geared low. 2) the gear ing is the next thing---people of today are trying to get the gearing high enough to keep the RPMs down, that does not work well with a larger bore carb. 3) The 750 will plate out residue on the intake valves as it works in daily driving and cause more sluggish response as time goes on (seen the effects in a machine shop atmosphere.
Holley and Edelbrock corporations; both will tell you to stay at or below a 650 CFM on a 350 motor and even a 383, if it is street driven; to keep the air flow up and the efficiency of the carb working for you, that way the high velocity will make up for the heavier vehicle weight. Granted, my 383 ran hard all the way up to 6000 RPM with the 750, but I could not get the thing to work right on the street--I had to make a decision, so I did not go to the Edelbrock performer carb, which is a 625 CFM carb, but went with the Edelbrock Thunder AVS--which is actually just over 650 CFM---best of both worlds.
The Q-jet is a great choice, if you have a solid one to start with.