Wrong hobby if concerned about fuel economy!

Yeah, start knitting. No gas problems there.

I am not worried about gas..I think everyone was missing the point.. I will admit Gas is the cheapest thing on my boat but it does all add up. Part of my scenario is I have a 305 with a 2bbl and an Alpha drive. So I don't want over 325 hp. Thought it might be interesting to bolt the 2 bbl onto a 375 hp or so 383 and see how it works. Later down the line when the alpha pops, I can put on a bravo and a 4bbl. Sort of a progression . If I cant make 300 hp with a 383 and a 2bbl then I will want go a different direction.

Chris

You'll make 300hp with a 2bbl no sweat.

Makes no sense to me, but if you want to do it, do it. Your $$$ and displeasure. LOL.

Put a throttle stop on your 4bbl. Cheaper. Just a small bracket and a bolt. Done.

You stated secondaries being the source of low fuel economy.

What size / weight / type boat do you have ?

What size is the 2 barrell? Some 2 barrels are pretty good size. Try putting it on, just be careful on the jetting. Like has been stated before horsepower is fuel and air (put very simply). A 383 at 5000 rpm would use 500cfm or so. If the carb is around 500 cfm(and the intake is decent) I would think 300-325 would be realistic for a 383 that would make 375 with a proper 4 barrell if jetted correctly. Even if you lose some horsepower up top, you will still make a lot more torque down low than the 305.

FYI: A 500cfm 2bbl is not like a 500cfm 4bbl.

The 4bbl is rated at 1.5"HG depression, the 2bbl is rated at 3.0"HG depression. "HG is how we measure vacuum. If the 2bbl was rated at same 1.5"HG, it's flow rating would be substantially smaller.

i agree this would be the smartest,cheapest way to do it,the 4 bbl carb is a 2bbl carb if you dont open the secondary,s.

Just stay out of the secondary's. my experience ;18 GPH part throttle cruise, 60 GPH WOT with twins

I will have to admit, I never even thought about a throttle stop. As cheap as that is, its not as cheap as trying the 2 bbl. I did find this chart that showed the jetting for a 2 bbl on a 305 and 350. http://www.cfm-tech.com/2bblmercarb.htm
Interesting that it shows 170-185 mains for the 305 and 165 mains for the 350. If the same would hold true for the 383, i would not be too lean by just slapping the 2 bbl on. Someone asked what boat this is. It is not my go fast. It is a 25 ft cabin style boat that weighs about 5500 lbs loaded down. It does 34 right now. It will never be fast but it is getting time for a new engine and I want something that will hopefully keep the boat on plane at 20 and max out at 40. Right now it is hard to plane with over 4 people and will fall off plane at 25. I figure 300 HP or so with a 4 blade will be right on the money.

Chris

Well, that's interesting. That's my website/company. LOL.