vacuum vs. mechanical secondaries

[ratonabike]

as the winter hits, i'm wanting to buy a choked carb to replace my chokeless HP4150 vacuum secondary carb, to make starting a lot easier in the cold temps (or simply to start at all when it's really cold). i've got my eyes on the QuickFuel SS carb, it's a sweet carb, i've been impressed by QuickFuel for awhile, but i'd like something bigger than my too-small 750cfm carb that i'm running right now. My car is heavy, 3,546 lbs without driver and gas, and with my auto tran, and everything i've read about my combo, suggests using a vacuum secondary carb. My 750 carb has always been too small for my engine... a 950 would be just right, but when i built my motor i just happened to have a brand new 750 sitting in my kitchen (my kitchen is my shop... yes, i'm not married.... lol), so i figured for the street it would be just fine, which it has been. Now that i'm looking for a choked carb for the winter, i'm noticing that they just don't make good aftermarket vacuum secondary carbs bigger than 750. Soooo, i was thinking of dropping the vacuum secondary idea, and get the QuickFuel SS-830 mechanical secondary/electric choke carb. It's a bit bigger, has the choke, but it's mechanical. So i'm wondering how much of a problem a non-vacuum secondary carb will be for my combo... Any thoughts on it? I'm guessing it won't be a problem at all, once i dial in my secondaries.

[Real McCoy]

Not sure why you think your car needs a bigger carb than a 750. The last BBC 460 roller motor I dynoed ,which I built for my brother, made 700 HP with a 700 CFM holley that is a base carb we use on the dyno motors to break in cams and do some comparision work with. Then I tried a very well prepped 850 that I had made for my personal 468 and the motor made 702 HP or basically the exact same HP and torque. I also used a 600 DP Holley on my personal car that had a 388 SBC in it. It worked fine and could easily cook the tires for 100 ft or so pulling off from a light. Very sweet throttle response but not great gas milage in town. Last thing I'll say is my 565 makes 960 HP with a 1050 Holley and actually made slightly less HP and torque with a Pro Systems 1250. Bigger isn't always better, especially with carbs. Just my opinion.

[ratonabike]

i was given the suggestion for a 950 carb by Shafiroff Racing that built my 406 short block for me, given the set up that i ended up with my motor... (550/600hp on motor + 175hp/250hp NOS @ 7500/8000 redline)... and i used the Holley CFM calculator of CI x REDLINE / 3456... which comes out to 406 x 7500 / 3456 = 881 CFM, or 406 x 8000 / 3456 = 939 CFM (i have my limiter set up at 7500 at the moment, but she likes to spin to 8000 easily it seems)... so somewhere between an 850 or a 950 carb seems to match what Shafiroff suggested... but like you said, your experience says my 750 should just be fine, and might even be better...

wish i had a dyno in my kitchen...

thanks RM!