4 bbl question for F-25

wet wonder · Post by **wet wonder** » Wed May 06, 2009 8:57 am

I have an 1975 F-25 with a Merc 351 and 2 bbl carb. Would the orig have been 2 bbl or 4 bbl? And would swithcing to a 4 bbl show an increase in top end speed, or does it really only improve pick-up?
Thanks

kevin babineau · Post by **kevin babineau** » Wed May 06, 2009 10:33 am

a 4 bbl will typically increase ur hp rating...and increase fuel consumption...as for how much torque and where the added hp comes into play on the power curve i do not know

Stripermann2 · Post by **Stripermann2** » Wed May 06, 2009 11:10 am

A 4 barrel won't help you any. The cam is for a two barrel with different lift. You could change out the cam, maybe do some cylinder head and valve work as well...
But why bother? If your boat runs well now, I'd leave it alone, it was designed as a two barrel configuration for optimum effeciency.

randyp · Post by **randyp** » Wed May 06, 2009 11:54 am

Judging from what little I see from the picture of your boat it looks like an F-26. That being the case, the 1977 equipment list I have shows 2 engine options - Chrysler 225 hp and Mercruiser 233 hp. My Chrysler has a 4bbl carb. Not sure about the Mercruiser, but at the hp rating I'd think the carb would be 4 bbl. I'll let others weigh in on this one, because, as usual I don't know nuttin.

lakeguy72 · Post by **lakeguy72** » Wed May 06, 2009 3:39 pm

Wet Wonder,
The 351 came as a 233 HP or a 255 HP. The 233 was a two barrel and the 255 a four barrel. The 255 has different heads with huge intake valves but the cam is the same. So putting on a four barrel manifold and carb won't help much if at all. I have the parts list for both engines.

Lakeguy

wet wonder · Post by **wet wonder** » Wed May 06, 2009 5:44 pm

Thanks, good info about both models of 351s. I'll stick with the two bbl.

guglielmo6160 · Post by **guglielmo6160** » Wed May 06, 2009 10:30 pm

you would have to modify the engine, just bolting down a 4 barrel with a manifold wont do it, cams, etc,, stick with the 2 banger,,, if it came that way