how does 350mpi to 383 work?
 

Shopping and my purchase depends on upgrade potential. I want to stay fuel injected so I my question is: twin 350 mpi's (say for example in a 2000 Donzi 28zx), can you simply hop online and buy a 383 strocker assembly from somewhere like us marine and bolt all your stock stuff on or is there "more to it." I would think reprogramming the computer would be one but again there are no details as to how involved this really is?

reason why I ask as well is the boats I am looking at have around 300+ hours and really want to know what I am getting into to refresh and improve. I do understand prochargers are an option but thinking there might be a middle ground if the 383's just bolt in.

Yes you can do that depending on which MEFI controller you have.

Sort of but there's a little more to it than that. You could in theory get a stroker kit and have it installed (correct bearing clearances, bore clearances, ring gap etc for marine motors) and re-assemble with you existing EFI system. With a stock tune it will most likely run with the above modifications (barring any extreme cam changes). Would it be advisable? No, not really. You most likely have a MEFI 3 or MEFI 4 controller which can be tuned (by you or many others). So any modifications of the motor should be accompanied by some EFI tuning (modifying fuel/timing/ignition tables etc.)

I would be happy to share my EFI tuning experiences via e-mail or PM. It is not necessarily difficult but takes a lot of forethought and immersion into the topic. You will need software and a wide-band O2 system installed. Again not difficult.

300 hours isn't too many hours on the motors at this point (assuming they've had proper care). If it were me I'd run them till they wear out then upgrade. Assuming the blocks will be reused get a good stroker assembly, good heads and a good hyd roller cam (Comp cams, Crower, or RM Builder all have good choices). Keep in mind you may need to go with higher flowing injectors with any increase in displacement or power.

Personally I would avoid a procharger for this application.

Mercury make a nice 383 Mag stroker 350 HP @ 5200 RPM's.

300 hrs is not many hrs, especially with twins on a 28ft (relatively small boat for twins). That is like putting 20k miles on your car and then saying its time for a refresh.

Kind of a waste of time and money...unless you are just bored and have more $$$ than you now what to do with....good problems to have I guess!!!

trash, sounds like you've done what I am thinking, except I would just buy a marine block lower complete and try bolting on everything I would already have.

mrv..., that's an extremely expensive route to go x2. 350hp hardly seems worth it.

redstring, i know it sounds like a waste of time, but consider that I am buying a boat with 300+ hours that I do not know about. How many people are really honest about how they drive their boat when they are selling it. the blocks from US marine are like 3k with 415hp with a 7 year warranty, so my thinking is first hiccup, could I get the boat back to a confident reliable boat cheap. <--i.e.: especially considering if something happens to one engine, you are already out that money so the "upgrade" is not x2 mathmatically.

I understand your concern about the history "truth" of the engines in question, but with a little work you can get a good feel for their health. Compression check, look at the plugs, get a diagnostic off the ECM, run it on muffs AND in the water etc. I'd bet you would still get many seasons off those motors without much of an issue. If so you saved yourself from needlessly spending money.

IF you truly are concerned about the health of the motors because you can't trust the party from which you are buying then you better be getting a steep discount or walk away. IF you get a great discount run 'em till they break, then upgrade.

IF you just want to spend money and have "fresh motors" I'd be leary of a $3000 (long or short block?) 415 hp stroker. I'd really like to see the parts list (and dyno sheet) for that one. I'm not trying to bash that company, but that warranty has a lot of holes in it (yes I read it), and the fact that you will be placing a Merc EFI system on a larger displacement motor with higher compression will allow them to escape any warranty you may try to extract should something in the motor "go south".

I wish you the best of luck in your endeavor.

go to a MERC dealer and have the ECU's read. You are running MEFI 3's they have utilization tables. If that doesn't float your boat then have a compression test run and oil analysis.

Other wise spend the dime and do what you want just go all the way and don't cheap out. Your ECU's will handle whatever you want to throw at them provided you change them... but you knew that.
:thankyouthankyou:

Sounds like a hell of a lot of money because you don't trust who you are buying your boat from. If your distrust is that deep, I'd probably buy a different boat.

+1

+1

Exactly what I was alluding too.