Carb question?

[Greaser]

I need to buy a new carb for my southwind, and I was wondering if a holley 750 cfm, with vacume secondary and manual choke would be a good choice. Right now I have a 850 double pumper, and everyone I have talked to says it is to much. I figured I would ask you guys. My motor is a pretty much stock 460.

[napabob]

This is from the Holley site. I installed a marine 750 CFM mechnaical secondaries and electric choke on my stock 454
Engine Size (CID) X Maximum RPM / 3456 =
CFM @100% Volumetric Efficiency
EXAMPLE:
350 CID X 6000 RPM = 2,100,000 / 3456 = 608 CFM
Approximately 608 CFM would be required for this engine. However, most street engines are capable of achieving only about 80% VE; a modified street engine with ported heads, headers, good intake and carburetor can achieve about 85% VE; a fully modified race engine can achieve 95% or greater VE. The CFM number arrived at with this formula must be factored by this percentage.

[Greaser]

wow, that was pretty technical,
can anyone translate that in laymens terms

[Oldsquirt]

Napabob, for some reason most jetboaters find that that formula results in too small a carb for all out performance. Can't tell you why but that has been the general consensus.
Greaser, You might see if anyone has a 750 to try before you buy one. Compare WOT rpm between the two. I'll bet some Ford owners will chime in to say you'll be happier with the larger carb.
Where you boat do you really need a choke? If so, you will be happier with the electric. A manual choke carb can be retrofitted to electric pretty easily, tho. I did that with a 750VS years ago, but eventually removed the entire choke assembly. Just didn't need it.

[FOURQ]

get the mechanical secondaries not the vacume

[MudPumper]

Mechanical Secondaries, No choke!!!!

[riverbound]

Originally posted by Greaser
I need to buy a new carb for my southwind, and I was wondering if a holley 750 cfm, with vacume secondary and manual choke would be a good choice. Right now I have a 850 double pumper, and everyone I have talked to says it is to much. I figured I would ask you guys. My motor is a pretty much stock 460.
I do have an extra 750 w vac. secondaries. I recently changed to a 700 dp. I was told the 700 dp would work better for my application. shoot me a pm if you are interested in it it is a holley 3310s (shiny finish) 1 season on it (3 trips)

[Hallett19]

talk to Ty at www.tpcracing.com, he set me up a great holley 780 vac secondary carb for my boat. He put a billet baseplate and bigger boosters and even set it all up for me, although out of the box it ran just fine, he set the float levels for me. The formula you used probably wont work. I have a "for the most part" stock 460 and it ran almost 200 rpm slower with a 650 mech secondary Edelbrock than it does with the 780 holley. The 780, after the rebuild got me almost 200 on top of the 200 I gained with the 780 carb !!! He does great work and ships anywhere.

[PLACECRAFT20]

I HAVE TRYED BOTH ON A 454. THE 850DP RUNS A LITTLE HARDER ON THE TOP END BUT THE 750 ACCELERATES A LITTLE FASTER OR IS A LITTLE MORE PUNCHY IF THAT MAKES SINCE. BOTH OF MY CARBS ARE MECHANICAL. THIS IS THE ONLY WAY TO GO IN A JET BOAT. I AM CURRENTLY RUNNING THE 850DP.

[OMEGA_BUBBLE_JET]

Greaser. I have a 650 holley double pumper with mechanical secondaries I pulled off my boat this past weekend. I went with a 750 holley dp. the 650 spun my 460 ford to 5300rpm no problem. I would be more than happy to bring it to the lake with me this weekend and let you borrow it and if you like it we can make a deal. I rebuilt it last season it has only maybe a dozen trips on it. Oh yeah it has no choke and is already jetted for a big block.
Omega
edit: I definitely would stick with a mechanical secondary. vacuum secondaries can be made to function on boats but work better in cars.