If I go from a 600 cfm to a 750 cfm on a midly built 350, about how many ponies can I unleash?

None if your engine doesn't need the extra CFM and your current carb has the proper fuel mixture.

How much manifold vaccum are you generating at WFO, max RPM?

Couldn't tell ya.....I have about 15 inches at idle. I don't spin the engine past 5k cuz it seems to die off after that. Alot of people have told me to ditch the 4160 600 cfm Holley and go to a 750 cfm and see some better 1/4 mile times.

i dont mess with no carb under the 750 cfm mark unless there is two of them on a tunnel ram............at least put a 750 on there gm did for so many years ...the q-jet flowed 750cfm.........you would benifit from it specially a vacuum secondary carb you can tune the secondarys to the engines likings.....

in following along with what Schurkey said...

Tape a vacuum gauge to your windshield and go out there and go WOT getting on a major highway ramp. Have a buddy watch the gauge closely, if at WOT there is no manifold vacuum, then don't expect any ET or MPH improvement from a straight up carb swap.

And don't beleive those "people". If they actually knew what they are talking about they would have asked you about manifold vacuum at WOT.

If I had a nickel for .....Never mind..

Do the test, report back.

well let me say you can make any vacuum carb read 1.5" of hg at wide open throttle at peak rpm that is why the vacuum secondarys are adjustable.......change springs till you get what you are looking for.........or should i say what the engine wants........the mph crossing the line is the final answer the vacuum test is only a tunning aid.........experienced people who test and tune would say go with a 750 at least 600 is just to small if you looking for power.....specially on a mild 350........when was the last time you heard someone say im running twelves with econo box 600 cfm carb........i would say next to neil........

I don't mean to but in here, but the only way to know if the carb will make a difference is to try it. All motors respond differently. And your still only dealing with "vs" carbs, not as sensative as a double pumper. I think your best bet would be to buy a 650 speed demon. Heck they flow just as much as a 750 holley but have better response and performance. If your gonna buy a new carb go for the gold. Otherwise save your money and your gas. By the way, have tried changing the secondary spring, that carb should have no problem carrying that motor past 5000rpm, how much power it makes past that rpm is another story.

go with a 650, a 750 is a little too much carb for a mild 350.