chappy2330

Hello all. New to the forum. Got a few questions about getting a little more go-go out of my '99 350 MAG MPI, Alpha 1 gen 2. Had 1.47 ratio, now has a new SEI unit with 1.62. I live in Colorado so we boat at higher altitude, from 3500-7000 ft. Boat was an original California boat when I bought it. It had a 21p 4 blade SS prop when I got it and I could barely get to 4200 rpm. Put a 15p 4 blade ss on it and I could get it to 4800 at around 46-48 mph. This is in a 1999 Chaparral 2330SS. Just installed switchable thru hull exhaust. Haven't been able to check any changes with the new outdrive since I haven't had a chance to brake it in completely yet. Only have 5 hours on it so far and now it's been winterized. I'd like to get some parts over the winter for next season to get some more power out of the engine to maybe get that 21p back on it. What do you gearheads recommend?

smallblockford

Whipple supercharger is only easy way I did it to my 350 mpi not cheep but it does the job have done 3 of them one on a customers pachanga boat picked up 15 mph

chappy2330

That's quite the chunk of change! Pretty sure I can build a 383 stroker that will make more power than the whipple will give for half that. I'm looking more for bolt ons, cam, injectors etc.... Trying to keep it under $3k. I do plan on building 383 stroker in the future as budget allows.

Bondo

Ayuh,..... With the electronic motor, yer pretty limited to what can be done to it,.....
'n buildin' horsepower in boats is always expensive,....

chappy2330

Building horsepower in anything is expensive. I’ve been in the automotive game for over 40 years. Have owned a boat for more than half that time, just never got into the performance side of boats. Cars you drive all year, boats are time limited. So I never really dove into them in that sense.
Why are you limited since it’s electronic? Cars are electronic and you aren’t limited? Are there no tuning capabilities available? Would it be easier to swap to a carb set up for ease of tuning? I’ve had this boat for 9 years now. I know the engine will need rebuilding sooner or later and was planning on building a healthy 383 stroker. Am I screwed with tuning it if I keep it fuel injected?

Xcomunic8d

I believe there are 383 stroker ecms out there… Mercruiser is so cryptic… making a stroker out a 350 to 383 isn’t that hard and the best way to make power out of it. But that mpi that runs off an ecm adds a wrinkle. I looked into this for another guy and found this is done and there are ecms out there…somewhere…

I marinized an LS and that was some serious work. In retrospect there were other ways to get this done possibly cheaper (383 or 496). But I wanted bbc numbers out of a sbc.

383 rotating assemblies are around, skipwhite, summit, and many others. make sure to use upgraded heavy duty bearings everywhere and good hardware due to higher rpms on boats than cars. I wouldn’t start this project until you source and buy the ecm or find a tuner…

Trash

Your biggest enemy is the altitude you run at. In my opinion, with your boat and the altitude you run at there is not combination of 383 that will get you to a 21" prop unless you throw some boost at it (blower).

I would start simple. Assemble a good 383 with good heads and cam and have your ECM tuned by yourself or someone else. You likely have a MEFI 4 ECM. Make sure your injectors flow sufficiently. I would have injectors in the 36-42 lb/hr flow range.

TomZ

As was said already... your high altitude is killing power. You might be able to get back some mechanical advantage by running a 1.62 drive or maybe even a 1.81. That would help to get rpm up some. You're seriously lugging it right now (rpm range is 4600-5000 on that engine). The gear ratio is where I'd focus my energy. With that hull and the altitude, you're not going to get much without boosting it (and even then the ROI is going to be dismal).

**Key takeaway... if it runs good... don't mess with it.

SabrToothSqrl

Isn't the Alpha 1 limited to 300 HP anyway? Call me a loser, but when it comes to being 100+ miles from my marina, I'll take reliable horsepower over any modification or HP. In your case, you might open pandoras box between engine modification vs. reliability, and your sterndrive max HP is 300 as far as I know... a 350 should be enough for fun in a 23'. but you could always drop in something bigger with a bravo if you're up for some up fun

No worries from me, I only have 350s well... I find them cost effective horsepower, and parts are plentiful.

To go faster, simplify and add lightness.
if you're looking for winter stuff to do, there's always new exhaust manifolds, elbows, spark plugs, wires, distro caps, cleaning the air filter, fuel filer, oil filter, etc...

when were the manifolds last replaced? I lost 2 engines to 18 year old manifolds a few years ago.

smallblockford

it takes a lot of power in a boat to get little mph. I have been doing them for years I have experience both cars and boats. 100 hp in car big deal boat its 6 to 8 mph. I now how to tune cars I us hp tuners and have a dyne jet 248 dyno for my cars. so the power isn't just the problem very few people can crack the ecm to tune depending which one you have I my self had the ppm 555 ecm it is well there are only 2 guys I now and they won't let go of there software. now your ecm is older maybe you have a mifi 3 there is a little more access to it but I have seen plenty of 383 done and not with the effective ness of the blower I have also put cmi headers on my small block it wasn't worth the little hp but loosing 100 lbs was nice, now to the alpha before you do a thing get a drive shower on it and cool the top gears I have pushed them to over 400 hp over and over if not abused and kept top gear cool.


pic of my sbc