I'm having my stock 1998 225 promax rebuilt and would like to do some add ons but nothing radical....not a race engine. Think I will have an exhaust tuner and some boysen reeds installed. I'm not mechanicaly savy on outboards so what would yall do.

If not already there solid motor mounts.

Bore it out & oversize the pistons. Beware if anybody suggest re-jetting the carbs without changing other characteristics (like maybe intake & cylinder head.) Outboards are usually set up to give optimal performance in a wide range of conditions, as opposed to top performance under specific conditions (such as racing).

Mill the heasds?

Total performance kit. New HP heads, air box, Boysen reeds, and an exhaust tuner. There is a company that sells them for Yamaha OBs, bet there is one for Merc too.

Hydro Tec Marine Performance does the Yamaha motors. Eventually I'm gonna do a little tinkering with my lil 115.
https://www.shop.hydrotecmarine.com/splashPage.hg

i had boyseen reeds in my 150 mariner, and a trophy 4 blade 14.5" 24p prop and my boat would run 76 mph in light chop, and 74 on flat calm water.

Uh huh

I went through this a couple of times. I don't know what kind of hull you have but it will be hard to increase the performance of the Pro Max with out doing some serious work that will limit its life.
The most bang for the buck is in cutting the heads to raise the compression, but, it may require you to run a higher grade of fuel.
I ran a Brucato SVS on mine and could not tell the difference in the top end, it may have had a little more mid range, but it didn't make as much difference as cutting the heads.
I used top pinned pistons, the ring land gave way and broke rings on two pistons. That took care of that.
If you are getting on the limiter now, you can have it, the ecu, reprogrammed and raise or remove the limiter, I did that, it lets it make a bigger boom when it breaks.
I know this isn't what you wanted to hear but when you get through with the mods, you might gain a couple of mph on the big end, and you will have shortened the life of your engine.
I have read a lot about tuners, most of the people that are truly knowledgeable about performance call BS on every one of them.

I'm like fastguy. The cost to get you any substantial gain and maintain reliability is going to be expensive.

Its your motor but if I were going to rebuild I would call JaySmithRacing down near Houston and ask his opinion about what you could do to keep the motor reliable.

i agree with these guys also. the promax is already a "hot" motor. i've talked to alot of guys that try to improve this engien, it just doesn't do well.

oh, sorry but 76 with a 24p trophy.. can't see it. that would mean your turning that 150 at 6800 rpms. KABOOM!!!

do the numbers. rpm (6800) X pitch (24) div. gear ratio 1.86 divided by 1056, then deduct prop slip (8%) = 76.44
unless you have a torque master or sportmaster case with 1.62 gears, that's impossible.

In my shop, we have a quote,"SPEED COST MONEY, HOW FAST CAN YOU AFFORD TO GO?"..........

he catches REALLY BIG fish too.................

I would not do any more than your doing now. Unless you want to jump into the racing side just a little other than that stop where you are and save the money for gas.

Big Ole Bobbers,

I would just keep it as close to factory specs as possible.

You start playing with it too much, and you can be constantly having to have it torn down and rebuilt. You increase the HP too much, then you have to have racing parts, which incudes custom machines con rods, crank, bearings, ect installed in order to be able to hold those extra ponies.