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!

[1971BB427]

I'm not even gonna try to talk you into a Holley spinn, as I know you can never talk me into a Qjet or a Edelbrock. A Holley is not the first carb I grew to know and love, but it's the one I've learned to like best, and I've had great performance with them on daily drivers, or performance cars.
After many years of using a Holley on my 427 Camaro for both street and strip, I literally wore it out. I decided to give the edelbrock another try, as I hadn't used one in years. I suffered with poor performance in stop and go driving, and even worse when trying to merge on freeway ramps. I bought everything edelbrock reccommended to get it to work right, and eventually got them to replace it. Next one was the same issues. I suffered through several months of trying to get it to perform and finally tossed it and bought another 750 Holley with vacuum secondaries like I had before. Bolted it on and never touched it. That was in 1999, and the '71 is still running great today.
There's nothing you can say that will get me to change from Holleys.

[my87Z]

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

if you use a simple math formula. it says to use a 500cfm carb for a street driving application and a "650 for all out racing" the 600 is more suited for a 350 daily drivin street application
considering most came with 500cfm 2 barrels that ran great. the 600 is a better choice for this set up IMO and most engine builders will agree.

and the cars that came with 750's had 4 speed manuals in them or were muscle cars with soild lifter cams

[Silver Surfer]

Originally Posted by my87Z

if that is the case then why did most all 350's comming from the factory came with a 750CFM Q-jet.

Because the Qjet is a spread bore carb. It has the small primaries for street driving and extra large vacuum secondaries for high RPM. Best of both worlds. I don't know why square bore carbs are the norm and preferred.

[my87Z]

Originally Posted by BigChevyFTW

if you use a simple math formula. it says to use a 500cfm carb for a street driving application and a "650 for all out racing" the 600 is more suited for a 350 daily drivin street application
considering most came with 500cfm 2 barrels that ran great. the 600 is a better choice for this set up IMO and most engine builders will agree.

and the cars that came with 750's had 4 speed manuals in them or were muscle cars with soild lifter cams

wrong, even my old factory 1987 camaro Z-28 with a 305 came with a 750cfm Q-jet from the factory. but like Silver Surfer mentioned they were a spreadbore design carb.


since you seem to be an eddy fan take a look here

Edelbrock 45411 - Edelbrock Performer 350 C.I.D. 9.0:1 Crate Engines - Overview - SummitRacing.com

that's a mild 320hp 350 with a 650cfm eddy carb

or how about this one

Edelbrock 46404 - Edelbrock Performer Hi-Torq 350 C.I.D. 9.0:1 Crate Engines - Overview - SummitRacing.com

that's still a mild built 360hp 350 with a 750cfm eddy carb (i think it would be fine with a 650 though)

this one

Edelbrock 45924 - Edelbrock Performer RPM E-Tec 9.5:1 350 C.I.D. Crate Engines - Overview - SummitRacing.com

still a very streetable engine at 435hp 350 using a 800cfm eddy carb

now i dont agree with some of these carb sizes, but that is edelbrock for you, they are not ment for performance in my opinion. the OP said that he has a ZZ4 short block with mildly worked alm heads, and a GM hot cam which is pretty much the GM 350/350hp ZZ4 crate motor, and even GM Performance recomends either the 650CFM or the 670CFM carb for this motor.

[spinn]

Originally Posted by BigChevyFTW

if you use a simple math formula. it says to use a 500cfm carb for a street driving application and a "650 for all out racing

That is NOT the whole formula. Go to edelbrocks website. Do not care if you use their carb or not. Educate yourself to the cfm needs of a engine. Look at the 5 basic catagories of engine build.

-For maximum performance, select a carburetor that is rated higher than the engine CFM requirement. Use 110% to 130% higher on single-plane manifolds. For dual-plane manifolds use 120% to 150% higher .

That is why 750cfm Qjets are on 305s.

My 305 cam stock with a 750 q jet. It is awesome. Read cliffs book on tuning them . They will not disapoint.

BB71, wore it out ? My edelbrock is 10+ years old and like new. You are doing something wrong if it wears out in 10 years. Not for performance, better rethink that addice. Edelbrock has been researching their performance products longer than you have.

Check my dyno sheet in my photos. That is a 440 RPM with 750 cfm package making 500+ hp in a 71 cuda. I call that performance wouldnt you?

[1971BB427]

Originally Posted by spinn

BB71, wore it out ? My edelbrock is 10+ years old and like new. You are doing something wrong if it wears out in 10 years. Not for performance, better rethink that addice. Edelbrock has been researching their performance products longer than you have.

?

Your's is 10 yrs. old, so I guess you assumed mine was 10 yrs old too? Must have been that new math.
I've owned my '71 since 1973, and the Holley was on it when I bought it used in 1973. It got replaced in 2000 when I put that first POS Edelbrock on. Not sure when the original owner put the Holley on the 427, as I never asked when I bought it.
Yes, with a lot of street/strip miles on the car, I finally wore the throttle shaft to a little excessive slop and decided to not bush it.

[pacman350]

try the quick fuel slayer they make them in 600 and 750. bothe are on the 3310 platform and i ahve the 600 and the throttle response is and low rpm torque is way better then with the 2 600 eddys ive had on it. plus you dont have to worry about vaperlock as much as with the eddys because the float bowl are not setting directly on the intake plus it has alot of tuning features of the higher priced race carbs.

[spinn]

New math? What are you talking about. My edelbrock carb has been in service for over 10 years and is fine. I could care less how old yours is. Why would You imply that yours is as old as mine, or think that ? That is your inference. My statement is testifing to edelbrocks reliablility over time. Are you the center of this universe.

Edelbrock is not some super carb, but again neither is holley. At least I listed some benefits over the holley. You can go either way with carbs depending on what your doing with it.

You said it. Im not even gonna try. Maybe one day you should.
Have a nice day.

[TroyBoy]

Originally Posted by Silver Surfer

Because the Qjet is a spread bore carb. It has the small primaries for street driving and extra large vacuum secondaries for high RPM. Best of both worlds. I don't know why square bore carbs are the norm and preferred.

I completely agree even though I'm a Holley fan. Q-jet is plenty enough for most of your needs. Decent fuel mileage and its a variable airflow carb. I use a Q-jet whenever possible. People who say they are junk just don't have the patience to understand them. They are actually pretty simple when you get past the linkage issues,lol.

[302 Z28]

The Street Avenger 670 Holley has been flawless on my Fastburn 350. Nothing against AFB style carbs, that is all I messed with in high school. I like Holley carbs and once you learn them they are real easy to tune.

Vince