15x17 prop 3 blade to 4

[sw33ttooth]

currently running a 15x17 prop 3 blades i would like to switch to a 4 blade so i could tube easier plus once i get 5-6 people on board takes a little bit to plane even with trim tabs.

engine: ford 351.
wot rpm: pushing thottle and trimming up to hit 4100-4200
outdrive: omc cobra outdrive.
current max speed wot: 40 1 person 40-55 gallons of gas.
boat hull: 23 foot four winns sundowner.
current prop: michigan wheel aluminum 15x17 a little dinged up but not bent or missing pieces.
i have bernett trim tabs.

recently in shop mechinic said timing was off and set it properly[i think]
now i was told my engine should run in the 4000-4400 rpm range being at 4200 i feel good i was wondering what pitch 4 blade, would give me that rpm area. since i've read you have to play with pitch a little bit when changing from 3 to 4. i've also read about 5 bladed props but i dont have a TON of money to start thowing at somethng like that.
i'd probably like to get a 4 blade ss i know price wise around $400.00 new? but suposibly there better for venting or some odd bs..

also i wieghed the boat and trailer to day a wooping 6240 take off 1200 for the trailer and you get about 5k not sure if thats my speed issue its a cuddy cruiser not a speed demon sadly

 

[sw33ttooth]

Re: 15x17 prop 3 blade to 4

how come i can't seem to get any advice on this?
this is my 2nd post under props asking, first one was about 3 weeks ago and i got 1 person to post telling me that my motor should be running in the 4-4400k rpm area

 

[Robbabob]

Re: 15x17 prop 3 blade to 4

Easy Sweettooth,

It's usually a matter of timing when you're seen or not. A bump reply will usually get someone to notice. Also, having all the information present for the "experts" to reply about is quite helpful as well.

#1 confirm the max rpm rating. MOST marine I/O run around 44 to 48. I did a reasonable search and came up empty for the exact spec.
#2 are you running an AL or SS prop? what is the manufacturer of it and model type?
#3 seems your speed is way down for that much engine (300HP?) on your boat. Make sure it is tuned up properly and has good compression. Also check timing.

Seems to me, a 17P prop is light for your combination; meaning, I might think a 19P is in order. HOWEVER, your details do not warrant going up in pitch. That's why I think your engine is not producing the HP it should. Look in the engine, I'm betting you'll find your improvement there... then we can start the prop review later.

Good luck!

 

[sw33ttooth]

Re: 15x17 prop 3 blade to 4

well i just put in 3 new spark plugs[all i could manage in 2 hours], new wires, dist. cap, and rotor. new impellor today wont mess with my rpm or speed just something i've been meaning to get to. i thought my boat was pathetic sunday i got beat by a 5.0 open bow with 2 people, and i was alone with 20 gallons of fuel of course if his engine can be propd to 4800 rpm thats why, plus his boat probably doesnt have near the wieght mine does.

i have shtty luck wiht repair shops so that is why i am asking on here not asking them
first shop; took my johnson 90 v-4 for new fuel lines/ problem they didnt hook up the thottle linkage betweent he 2 carbs when done....

second shop; told them i needed cables adjusted for my ESA, they called it a timing issue and never lookd at it/ problem 2 days later i learn what to look for on the ESA and how to set it aparently that 1/2 inch off ment nothing to them...

third shop; told them i needed an impellor i didnt know what it looked like at the time my fualt i guess... told him 5.8l, 351 ford, COBRA outdrive/ problem people dont ****ing listen... he sold me either a stringer or king cobra impellor or something way the hell off, get home take off the cover and find out its not even close... go back and found some one who know something and got the right part...

as you can see neither of those 3 shops will get my business EVER AGAIN and i hope they all go bankrupt. if you cant fix it then dont make me pay, if you cant find the right part then dont sell me a wrong one to make money and get me out of your face. makes me sound quite mean but i never argue with these people or rant at them, just about them.

 

[Robbabob]

Re: 15x17 prop 3 blade to 4

I know it's frustrating to work with peeps that get paid for their knowledge, yet appear to have none! More so when YOU pay THEM and it's not done correctly.

Find your HP and we'll get you back to beating up on those 5.0 again!

 

[sw33ttooth]

Re: 15x17 prop 3 blade to 4

and how would i go about doing this? for insurence purposes they wanted to know and i couldnt answer there question, all i know is its a 351 ford motor with a COBRA OUTDRIVE not to be confused with the king cobra that i belive goes on the 454/460 next step up in motor. i've tried figureing it out but the 5.8l is rated from like 235 hp to 300hp when i've looked it up online, very unhelpfull. i have enough mechanical background to find engine tags if you can supply the hint as where there located. saturday i ripd the carb off and replaced accerarator pump so i know pretty much where most the stuff is.

 

[Robbabob]

Re: 15x17 prop 3 blade to 4

One of the moderators, Don S, has pictures where to look. I believe the tag is left side proper, right side when sitting in the boat looking back at the motor. Should show engine HP and range for max rpm. Maybe post in the Volvo Penta (ford) forum asking where to look; most say not to PM anyone as the information will be helpful to many to learn from in the forum.

I had a bear of a time finding mine since the tag is not easily found due to the color similarity of the placement is it stuck onto. Be calm, the answer will come.

wish I could help further at this point......

 

[sw33ttooth]

Re: 15x17 prop 3 blade to 4

well thers only so much you can do with out pictures and/or pysically being in front of it and your doing all you can, i should have an answer tomarrow after i get off from work.

by the way my motor/outdrive is pre-volvo isnt it? why would i ask them?

 

[sw33ttooth]

Re: 15x17 prop 3 blade to 4

couldnt not find the sticker with hp rating i found a patent and model/serial that is it, also took a close look found that my engine runs 4-4400 rpm wot on the spark arestor.

 

[Robbabob]

Re: 15x17 prop 3 blade to 4

OK. Good confirmation on the max rpm.

Finish your tune up, check timing and compression. If the engine checks out, then we change prop pitch.