few Mariner 115HP 2 stroke questions (long, sorry)

[docster]

I have a 1991 Mariner 115. Its a 2-Stroke. Runs awesome, we have owned it since new. Only thing i would change is the stupid 2-4 cyclinder thing, but my understanding is its the 2 lower carbs that "cause" that and seems expensive to replace those with upper carbs... Anyways, the motor is on a 1992 Procraft 180 Combo. NADA guides lists the boat at 1720lbs, so add fuel (20 gal @ 8lbs/gallon) 160lbs, plus 4 adults (150lbs avg) 600 lbs, that puts us at 2480lbs, on the low end, not counting extra gear if my math is right and specs are correct. Anyway, we mostly do watersports with it. It has an aluminum 19 pitch prop, not sure on the diameter (either 13 or 14 if i had to guess). It wont hold plane even with just me in it at anything under about 22-24. Now i have an Airguide competition ski speedo on it which is dead accurate to my GPS. Since i do a lot of wakeboarding and pulling tubers at 18-19 mph, my wife has to constantly play with the throttle. Currently the boat will do around 55 with just me on glass, but that means nothing to me, i rarely have a need to do over 40. I am planning on doing smart tabs this fall, which should help with plane times and slower speed and handling, but....

Here are my questions:
1. What is the gear ratio on this motor? (searched to no avail)
2. I want to change the aluminum prop for a SS, with more low end speed control/handling/hole shot, any advice? Still want to do 40-45, but low end is key, looking for that ski boat pop (obviously impossible, but as close as i can) Thinking maybe a 17 in? Im dumb on props, sorry.
3. 3 or 4 blade prop better?
4. What is the peak RPM range of this engine? I think at WOT its around 5100-5200, but I rarely look at the tach since im never wide open and speedo is so accurate, so I have no idea and cant get out on water for a while.
5. How much prop slip can I expect from this engine/prop set up? need that for every calcuator i have seen.
6. Also is the High Five prop any better than a 4 blade?

Sorry for lengthy post, but I'm kind of thourough and meticulous. Was going to post this in the Prop section but i thought it was kinda engine specific, and not sure if mods want to see a double post.

Thanks in advance! and pics for fun to come.

 

[docster]

Re: few Mariner 115HP 2 stroke questions (long, sorry)

UPDATES

Gear ratio is 2.07:1 according to service manual.
max RPM range 4750-5200

 

[CharlieB]

Re: few Mariner 115HP 2 stroke questions (long, sorry)

A whale tail or equiv will help keep the boat on plane at lower speeds with only about a 5 MPH loss of top speed.

A 4 blade prop will have greater lift than a three blade but you need to check with your prop shop to determine the correct pitch when changing the # of blades. Going to a High Five may not be near as cost effective. SS is a much better performing material as long as you keep it out of the rocks, if not, alum can save a gear set as it is so much softer it will bend before damaging harder parts.

52 to 5400 at WOT is a good #, any less is too much prop, too much load and strain on the motor. Lower gear ratio is about 1.7 or 1.77 if I remember correctly.