4 bbl to 2bbl opinions

[VeroWing]

I have a Grady 24 Offshore with a 1997 350/260 4bbl carbed 350 engine, alpha1/gen2 outdrive. I'm wondering if replacing 4bbl carb and intake with a 2bbl setup would make a substantial difference in fuel economy. Not concerned about top end speed, more interested in mid to low rpm trolling and cruising. If 2bbl setup is worth the change, do I need a Mercruiser intake, or will a GM unit be the same? I know I'll need a marine 2bbl carb. Thanks for any learned opinions or info on this.

 

[alldodge]

I have a Grady 24 Offshore with a 1997 350/260 4bbl carbed 350 engine, alpha1/gen2 outdrive. I'm wondering if replacing 4bbl carb and intake with a 2bbl setup would make a substantial difference in fuel economy. Not concerned about top end speed, more interested in mid to low rpm trolling and cruising. If 2bbl setup is worth the change, do I need a Mercruiser intake, or will a GM unit be the same? I know I'll need a marine 2bbl carb. Thanks for any learned opinions or info on this.

IMO - No.... It's HP to weight ratio. Engine doesn't burn anymore fuel then it needs to stay where you have placed the throttles. The 2 rear secondary's should not be used unless it takes more throttle to keep it on plane. Generally a 4bbl has smaller primaries, so putting a 2bbl will reduce your power. Reduce the weight your caring will do more good.

Leave the cooler of beer at the dock and I'll watch it for ya

 

[H20Rat]

won't make a substantial difference. Might actually make it slightly worse, as I believe the individual bodies in the 4 body are smaller than the 2. The other two only open up at higher rpm.

 

[Maclin]

What Smokingcrater said...The 4bbl has smaller primary bores than most 2bbls for the same engine, and thus are more responsive and in general more fuel efficient in the lower RPM's.

 

[VeroWing]

Makes sense, guess best to keep it as is, especially since it runs so well. Thanks for the replies!

 

[MikDee]

Yes, leave the 4bbl for best fuel distribution, and if you want to save gas, find the lowest rpm the boat will plane at, and leave it there for cruising. This way your hull, and engine, would be at the most efficient point. A stainless prop may help here as well, because you usually don't have to constantly work the throttle in the wind, and waves, they tend to hold a set speed better!

 

[thumpar]

The right hand is pretty much the best way to control fuel usage. You might actually loose fuel economy with a 2bbl because you will have to open it up more. Even if it did help at all it would take many many years to recoup the cost in parts.

 

[achris]

Yes, leave the 4bbl for best fuel distribution, and if you want to save gas, find the lowest rpm the boat will plane at, and leave it there for cruising. This way your hull, and engine, would be at the most efficient point. A stainless prop may help here as well, because you usually don't have to constantly work the throttle in the wind, and waves, they tend to hold a set speed better!

Not necessarily true. I have a fuel flow meter in my boat, and a GPS for speed. I have also checked my tacho and know it's accuracy. So, all the parameters are known. I have done a graph of fuel economy vs speed vs lph. And although my hull will plane at about 13 knots, the best fuel economy is at 26 knots. The only way to find your best miles per gallon is to sit there with a GPS, fuel flow meter and run the tests..

 

[VeroWing]

This is a "new to me" boat, and I'll just have to find where the "sweet spot" to run it is. I've owned other boats, but only one previous boat was I/O, a twin 470 25' Grady. That boat with those twins ran great and if I recall correctly, I could cruise in the mid-20s at 10gal per hour. Not sure if I can accomplish that with this 24' Grady with this 350/260 magnum, but hope to. Thanks again for replies.

 

[thumpar]

Try to keep the secondaries closed and you should get pretty good economy.