Originally Posted by BigChevyFTW
its this simple
do you want crisp fast throttle response? or do you want it to hesitate and have slow throttle response?
if you want it crisp a 600CFM carb with vac secondarys is the way to go and youll get better fuel economy.
if you want it to hesitate its a 650-670cfm carb
im running an 850 Mec Sec DB on a 496 thats almost 2 times the size of your motor so you do the math a 600 is the ticket here all day everyday!
if that is the case then why did most all 350's comming from the factory came with a 750CFM Q-jet. Dont get me wrong I agree with you in part, but not all the way. throttle response between a 600 and a 650 will be next to identical, but the 650 will allow you to run a little more RPM without choking out. I've run a 750DP (mildly modified) and a 850DP on my 385 street/strip motor, and I haven't noticed any difference in the down low throttle response, the only real difference i have seen (can't really feel it) is past 6000rpm, the 850DP wants to carry me to 7000rpm where as the 750 dies off around 6500. the 850 gets me another .15-.2 in the 1/4mile. (both are specifically tuned for my motor).
now, would there be a big difference between running a these 600 & 650 carbs when you are talking about the differences between a double pumper and a vacuum secondary carb, absolutley.
I still say a 650CFM vac secondary carb is what you want. a 600 will start to choke out around 5000rpm