I have twin 496/HOs in my Donzi 33ZX take in that the boat weighs 9200lbs at 3800 RPMs I burn 18 gallons and hour per engine running about 50MPH. at 5000 RPMs she burns 45 gallons per hour per engine running at 72mph. I have a Flo Scan.

How Do It know?
 

Obviously, the weight of the boat, the hull type and hull efficency will have a lot to do with fuel consumption figures for a 496HO. I can tell you that in dyno testing under sustained loads at wide open throttle making about 420-430 hp a good 496HO will use about 38-42 gph and that it will record BSFC's of about .51 to .53. I would think that in most good high performance hulls depending on cruise rpms and throttle position to make that cruise rpms that a single engine boat in light condtions will see about 1.6 to 2.5 mpg at about 14-16 gallons per hour with cruise rpms between 3500 and 4000 rpms.
One of the big determiners for any engine is its volumetric efficency at various rpms under loads.
A stock 496HO will deliver about 85% VE at 4000rpms which is its torque max on the stock 496HO.
SDFever, the reason your Raylar HO600 is delivering such good economy at 3500 rpms is that you are making more torque at that rpm and the volumetric efficency of the Raylar HO600 at between 3500 and 4000rpms is also up @ between 103 and 107% VE. (it breathes much better than a stock 496HO) and its BSFC at 4000rpms is about .48 which is a significant improvement over a stock 496HO
What this really means in simple terms is that a high torque marine engine can sometimes run a boat more efficently at given rpms with a situation like this where you have 20% better VE and the same or higher torque than you had with a stock 496HO that had to use more throttle to make the similar torque values at 4000rpms.
A more effiicient engine uses less fuel to make the same power and torque at given rpms, its as simple as that!
As for someone having a 496HO that uses over 50 gallons per hour at WOT, you have one of two problems:
1. a very poorly running 496HO! or 2. your measurement system or values are highly flawed!
Hope fuel efficency 101 helps here.

Best Regards,
Ray @ Raylar

I meant to say 2.9 & 3.3. Huge difference. Have a saved Diacom file to prove it also.

I would think that in most good high performance hulls depending on cruise rpms and throttle position to make that cruise rpms that a single engine boat in light condtions will see about 1.6 to 2.5 mpg at about 14-16 gallons per hour with cruise rpms between 3500 and 4000 rpms.


Right on the money. 15.2 gph average for the whole summer cruising at about 3500 a lot of the time.

are you running twins or triples? 15 is pretty good!

In my Formula, I averaged this summer with 19 gal / hour also at cruising rpm between 3400 and 3600 rpm, with no idle time except approaching docks or beaches...

Twin 496's. I was surprised myself. Quite a bit of idle time though, lots of channels into the bays here.

Is this per engine? or in total?