454 w/ Mercruiser MC-1 prop recommendation

[CLi87]

So after having thoroughly gone through the 1986 Bayliner Contessa 2850 and getting everything running properly, I definitely get the feeling the previous owner had no clue what they were doing, they seem to have done the bare minimum just to keep the boat running, I've gone through and corrected countless issues. It has a Marine Power 7.4 engine mated to a prehistoric Mercruiser MC-1, so far everything actually works alright. It's got a cheap aluminum prop on right now and I'm looking at getting a new steel one, was wondering what type of prop you guys would recommend for my setup? it's currently got a 14x19p on it

 

[Bondo]

a prehistoric Mercruiser MC-1

Ayuh,..... Welcome Aboard,...... What gear ratio,..??

Movin' this to the prop forum,....

 

[CLi87]

Ayuh,..... Welcome Aboard,...... What gear ratio,..??

Movin' this to the prop forum,....

I honestly have no clue, the engine and outdrive aren't original, is there a way to determine the gear ratio or calculate it somehow based on rpm and speed?

 

[Bt Doctur]

A 28 footer with 330 hp in front of a MC1 , thats never going to last above idle thrust. Most applications were 24 or less very light hulls and even then a still hand blew the drive apart and that was with the 1,32 gearing . Remove the drive and rotate the input shaft the number of turns it take to do 1 complete prop revolution, then divide , thats your ratio

 

[Scott Danforth]

lets work at this another way.

I do agree the MC1 in front of a BBC is a ticking time bomb, one bad launch or the prop comes out of water and the drive will grenade.

What is the current WOT RPM with the current 14x19 wheel?

if your RPM is good, move to a 14x19 or 15x19 stainless wheel.

 

[CLi87]

A 28 footer with 330 hp in front of a MC1 , thats never going to last above idle thrust. Most applications were 24 or less very light hulls and even then a still hand blew the drive apart and that was with the 1,32 gearing . Remove the drive and rotate the input shaft the number of turns it take to do 1 complete prop revolution, then divide , thats your ratio

What do I divide by? Everyone keeps telling me it's going to explode but it's been in the boat since 1991 and it's pretty much all I have to work with =( I do have a complete spare Alpha One Gen 1 but that's not much better than the MC-1 from what I understand. No money for a bravo unless I find a killer local deal =P I do take it real easy out of the hole and thus far I haven't pushed her past 3500 rpms for 2-3 hours at a time at the lake.

 

[CLi87]

lets work at this another way.

I do agree the MC1 in front of a BBC is a ticking time bomb, one bad launch or the prop comes out of water and the drive will grenade.

What is the current WOT RPM with the current 14x19 wheel?

if your RPM is good, move to a 14x19 or 15x19 stainless wheel.

I honestly haven't pushed her to WOT for fear of blowing the outdrive to pieces, I haven't gone over 3500 rpms, I believe my 454 engine should redline at around 4600-4800 rpms. Also would a 14x17P make any difference? I just realized there's actually a stainless prop on my spare Alpha One drive.

 

[Scott Danforth]

if you dropped down from the 19p to 17p you will most likely over-rev if you arent already

its not the RPMs that blows the drive, its the holeshot or if the boat ever hits a wave and the prop comes out of the water.

as long as its constantly loaded, you can put a fair amount of power thru the drive. its the shock loading from the hole shot or the instant unloading-loading from coming out of the water that will kill it.

so, until you can answer what your WOT RPM's are we would all be guessing in the dark.

 

[CLi87]

if you dropped down from the 19p to 17p you will most likely over-rev if you arent already

its not the RPMs that blows the drive, its the holeshot or if the boat ever hits a wave and the prop comes out of the water.

as long as its constantly loaded, you can put a fair amount of power thru the drive. its the shock loading from the hole shot or the instant unloading-loading from coming out of the water that will kill it.

so, until you can answer what your WOT RPM's are we would all be guessing in the dark.

Gotcha, I'll take her to the lake again soon and open her up to WOT slowly and see what I get, so if I understand you correctly, a higher pitch prop will lower the max WOT rpm, so ideally I would want a prop with a WOT rpm of around 4600

 

[Scott Danforth]

yes, each 2" in pitch is a ball-park change of 400 RPM. so going down in pitch from 19 to 17 would raise your WOT RPM, and going the other way, going from 19p to 21p would drop your RPM.

that information is in the stickies.