prop help 350 with aplha
 

i have a 350 mag with alpha drive in a 24' sleekcraft it has a 17p mirage 3 blade. anyone think i can go up in size for a bit more top end? boat turns this prop to 4500 rpm at about 42-44 mph depending on load.

I have to say ...you are right in the "sweet spot"with that combo.

You might pick up a little top end with a 19" but you would loose low and mid range. I suggest that you keep what you have in optimal tune and enjoy it...you are running good with what you have.

About all you could do to spiff that rig up would be swap the heads and intake out for Vortec equivalents along with a cam change. You could then spin a 19" at the same RPM and maybe see 50...but you will say bye bye to $1200~$1500 to get there just for parts.:evilb::evilb:

are you sure that is a 350 mag? sounds more like a 260 merc. the thing with WOT rpm ratings is it shows how hard the engine is working at ALL engine speeds. they say 4400 to 4800 top rpm. you are already below the center of that number. 2 inch longer pitch is over 10% more at 17 inches pitch you have now. will put your WOT around 4000 at best. means engine is lugging at 2500 to 3500 where you usually are (supposed to be) running it. a 24 is not a small boat. like sprink says, you are right there with your set-up. you try to make it do more you are gonna hurt it.

You are maxed out with the 17" prop now.

yeah its a 350 mag with 300 hp. it will spin up to 4500 with the bow trimed up pretty good with the 17p
and it will run low to mid 40's if the lake is smooth and i dont have a ton of people in the boat. the motor spends alot of time spinning 4500 or so just to go at a decent speed.

You might consider picking up a 15 for those days with a big load or if you do much tubing/skiing. That boat would be an excellent candidate for a 502/Bravo transplant....but don't do it...save your money for the next boat.

small blocks do not like to spend a lot of time at 4500. 3500 ain't much slower. half the fuel double or more the engine life.

Your question is likely much more complicated then you think.

At face value, if your max rpm at wot is only 4500, you're UNDERPROPPED, OR there is a problem with tune, set-up, wet foam (is it sitting heavy in the ass end or listing even a little bit?). Has it ever gone faster for you with the same prop? I wouldn't be surprised if everything in this respect is ok - that's a LOT of boat to push with a stock small block. It might well go a little faster with a lower pitch prop or at least a prop with less blade area and the same pitch... it'll be more responsive as well with a lower pitch prop.

What kind of prop are you running? 3 blade? 4 blade? diameter? etc...

I may have missed the boat when it comes to small block marine engines, BUT my understanding is that especially for a 2-bolt main 350, rpms are your friend (to a point), and that turning it slower with a heavier torque load on the engine is what will trash your bottom end much faster... I would want wot rpms for lightly loaded boat more like 4800 - 5000 rpms (depending on the year... etc... Based on your post, I'm assuming it is 80s, early 90's engine).

There is VERY LITTLE difference between a merc 350 and 350 "Mag" (mostly marketing, otherwise intake and slight cam difference depending on the era of the engine).

Just some thoughts off the top. Hope this is helpful

3500 would be lugging the engine and cause more damage. That thing can spin to 4800-5000 all day long assuming it is in good running order

yeah its in great running order with 360hrs on it. the boat is a 97 and so is the motor prop is a 3 blade id have to look at the diamater to see what size it is.