machloosy

I have a merc 350/260hp with thru hulls so maybe 250hp at the prop. Alpha drive with 1.84 gears. With a 22P stainless 3blade, I'm having to pay close attention because the motor will easily go past 5K rpm (operating range is 4400-4800) and thats with 4 people, half a tank of fuel and all my gear like coolers, pulling a huge tube behind the boat (too big to go on the boat lol). 24ft chaparral current max is 45mph (gps) with same load at 4950rpm. What prop guys? 23P 4-blade? 24P 3-blade?

machloosy

I forgot to mention, according to BAM marine prop/slip caculator I am at 20.7% slip
On a 14 1/4 x 22P SS 3-blade on the above mentioned combo

Griff

Try a 23" Mirage Plus.

machloosy

Griff thats a 3 blade right? Is the 1 degree of pitch going to be enough? The prop calculator seems to favor 24P @ 14-16% slip

flyinlow

Are you sure about the 1.84 gear ratio?
all the mercruiser 260's I have owned had 1.50 gears

Griff

Yes its a 3 blade. It has quite a bit of cupping also and I'll bet it lowers your rpms by 300-400 or so.

machloosy

Griff, right now my r's will go well over 5K if I let them. I haven't jammed the throttle because I'm pretty convinced I'll grenade my block if I do. So 300-400 rpm drop isn't going to be enough. I need 600-700 rpm drop maybe even more

machloosy

Flyinlow, yup dead positive about the ratio, different outdrive, I really wanted a 1.62 but could find it so I ended up with this one

Griff

You are not going to grenade a SBC with 5500rpms. They can handle more rpms than a BBC. I have spun SBC's with hyd cams above 6000rpms plenty of times in street rods.

You could try a 25 Mirage Plus instead of the 23.

machloosy

Griff, thats exactly what I thought... Mercury puts the max RPM at 4800 which doesn't seem right to me. Now with my changed gears I'm spinning the outdrive LESS, so that shouldn't be a limiting factor, should I go ahead and plan to spin the motor to 5400ish next weekend and see what happens? Maybe synthetic oil?