Any upgrades for a 350 mag mpi that won't completely break my wallet or know where the best upgrades that are most bang for the buck. Also maybe looking to buy a used supercharger or pro charger, can't seem to find any. All help or suggestions appreciated please.

It's hard to give advice without a $$ amount attached. Everybody has a different threshold for "breaking the wallet".

what year 350 mag MPI

big difference with what you can do as far as to which ECM it is using for a stock Merc.

There isn't any thing that will make a significant gain on that engine without spending $$$. The best bang for the buck would be a Whipple. You can do the install in the boat in an afternoon. The kit comes with excellent instructions and has everything yout need. It's not exactly cheap, but in terms of hp per dollar it can't be beat.

Assuming you don't have the 555 ECM, you can do just about anything you want IF you are willing to spend the money. As Haxby said a blower is one solution, but I'd also argue by the time you did all the plumbing and configuring for a Whipple you'd be in just as deep as a full engine rebuild with good parts and a stroker motor. Either route will get you a noticeable improvement in performance. I'd plan on $8,000 +/- a couple to get what you want.

Get the serial number of your motor as BUP suggested to see where your baseline motor is. Different years used different ECM which have varying degrees of 'tune-ability.'

Good luck.

Exactly what ECM - MEFI or triple nickle or PCM 09 or PCM 09 latest version ?

If I recall correctly Whipple does not reflash MEFI but I might be wrong about that one.

I just found this thread, I also am interested in upgrades. not to hi jack, but how can I find out what ecm I have. The motor
is a 30 hour jasper marine 330 hp 350 MPI Mag engine.

On the back of the ECM is a serial/part number. From there you can determine if its MEFI 1, 2, 3 4a, 4b, 555 etc.

That and a picture and we can direct you further.

Having built a pair of 6.2s, I can reliably say there isn't a damn thing you can do "without breaking the wallet."

This isn't like modding cars where you can slap on a pair of long tube headers and pick up a noticeable amount of horsepower.

I'd echo Capt YARRRs statement but emphasize the word "noticeable". It takes a bunch of work to make any significant or 'noticeable' performance improvements.