|Posted: October 06 2005 at 00:00 | IP Logged
It probably is not as simple as "just" a carb switch.....
The 255 probably has a more aggressive cam (slightly), and possibly slightly larger intake valves.
Remember, you have to be able to handle the extra intake air properly or you could end up with a poorly running/performing motor.
The 302 2-BBL version of my motor was rated 188HP and I think also 215HP was another.
Mine is 225HP. Mine is 4-BBL. HOWEVER, mine ALSO is the only 302 of the "line-up" that has a different (more aggressive) cam than the others, as well as the only one that has 351W Heads, with larger valves.
So, going from a 2-BBL to a 4-BBL is not necessarily a good idea in-and-of-itself....you need to address the rest (cam, intake, exhaust, etc components) or your engine will most likely run like crap.
What I DID do is go from the Factory 450 cfm Holley to a 600 cfm, simply because the 450's are hard to find, and also VERY expensive! The 600 is the same setup, but much more common, therefore, much less costly.
And, I did pick up a few hundred RPM's on the top end, but remember, I was already 4-BBL, so the increase in cfm (only 150) was much easier for the motor to handle/adjust to.
Remember, boat engines are run at high rpm's, they are MUCH more sensitive to things like Timing, etc, or they will not last long. In fact, timing MUST be adjusted to factory spec or you will likely shorten your valve life. It's not as wise to start playing around with a boat motor's intended design as it is an automobile engine.
Whatever you decide to do, just make sure you thoroughly research your motor's specs and consult some GOOD marine mechanics first.
Edited by Sonja Lowe on September 20 2013 at 18:00