I've see this mentioned a few times - running a 600cfm carb on a big block will yield better economy for lower RPM operation.....

Wondering if anyone has any real world numbers or input....I built my big block as follows:

460 cu/in (454, 0.030 over)
Cast crank and pistins
World Merlin III 269cc heads
All roller
Comp cams 114458 (218 , 224 @ 0.050, .510 , .510 112° )
Edelbrock intake (dual plane, need to remember which one)
496 manifolds and risers
Currently 750cfm Edelbrock....no adjustments out of the box.

I was thinking of a 600-650 holly or edelbrock

Current fuel numbers (garmin fuel flowmeter):

2900RPM, 22 MPH, 14 gal/hr for 1.5MPG
3500RPM, 32 MPH, 23 gal/hr for 1.4 MPG

More, less, or between those speeds is not as efficient (those are the 2 sweet spots). Boat is big, fat and heavy, loaded for cruising. Thanks....

Keep the 750, 650 is to small.

Gas is the cheapest part of boating.

Agree, but I was looking for a slight increase in range for convenience.

I might try a better carb with a vacuum secondary for gits and shiggles. (Holley or Barry Grant)

HOLLEY !!!!!!!!!!!!!!!!!!!!!!!

Buy an AFR, a tuned efficient engine will yield you the best economy. Also keep the sticks away from the WOOD!

any suggestions on one of these air/fuel setups? I've been looking without success....

edit: what I can't find is where to put the O2 sensor in the 496 wet exhaust....

I got my Innovate LM-1 off of e-bay for $97. I can't help you about the O2 placement, sorry

I run a edelbrock 600's on my gen VI 454's, with performer intakes, K&N arresters and thru hull exhaust on my gibson, they work great, did tune on them slightly, good economy but never see more than 4000, spends most of it's life at 3200-3500...Rob

Holley 750, vac secondary. I have a mild 454 in my 23' jetboat and get 2.1mpg, which is very good for a jet. Have the secondaries set to open around 3600, cruise on plane all day long @ 32-3300.

Put a new Holley 750 on and so far it's doing great, but still tuning.

Out of the box I was able to get the same MPG, but in a much larger RPM band - great flexibility for speed / economy

Also gained about 100-150 PRM over the Edelbrock, and overall the engine runs smoother and the carb is quieter - even at WOT.

Having choke problems, but working through them (instantly starts, but then within a few seconds bogs and stalls).