4.3l Mercruiser Prop Question

OK here is what I have:
1989 Celebrity BR 181
4.3 l Mercruiser with Alpha one Stern drive listed as 190 hp

ON the bot when I got it was a 14 1/4 diameter prop, 17 pitch. Using a prop calculator at http://turningpointpropellers.com/ says I should have a 23 pitch.

I am unable to get to WOT when in gear. WOT is listed as 4400 to 4800 rpm. I can get to about 3800 ( if I am remembering right).

If I am reading things right, if I go to a 23 pitch, I may NEVER see the upper RPMS. Is that right? Or am I seriously under-propped right now?

Re: 4.3l Mercruiser Prop Question

I can get to about 3800 Or am I seriously under-propped right now?

Click to expand...

Ayuh,... Unless you've got motor problems,.... You're seriously Over-Propped now...

Re: 4.3l Mercruiser Prop Question

So would the 23 pitch help?

Re: 4.3l Mercruiser Prop Question

No,... That's goin' the Wrong Way....

A 15" Might work....

More than likely you need to Regear the outdrive because of the Altitude in your area...
You probably have a 1.65:1 ratio,... A 1.84:1 would get you back up into the standard prop pitches...

Re: 4.3l Mercruiser Prop Question

Even allowing for altitude I think you have some sort of motor problem.
It should easily exceed the max rated rpm with a 17"
Does the performance seem a little sluggish?What is the max speed?
May be as simple as the throttle not opening all the way.
Is it running on all cylinders?How is the compression?

Re: 4.3l Mercruiser Prop Question

Depending on the gear ratio, that is a big factor. The pitch of a prop is going to be about 200-300 RPM different between pitch size. when the prop is right you should turn 4400 at WOT. If you want to pull skies or have a heave load, then drop down one size. A 23 is way too big. If you are turning 3800 now droping down to a 19 would bring you up to about 4400 rpms. Good Luck.

Re: 4.3l Mercruiser Prop Question

danstroup284 said:

OK here is what I have:
1989 Celebrity BR 181
4.3 l Mercruiser with Alpha one Stern drive listed as 190 hp

ON the bot when I got it was a 14 1/4 diameter prop, 17 pitch. Using a prop calculator at http://turningpointpropellers.com/ says I should have a 23 pitch.

I am unable to get to WOT when in gear. WOT is listed as 4400 to 4800 rpm. I can get to about 3800 ( if I am remembering right).

If I am reading things right, if I go to a 23 pitch, I may NEVER see the upper RPMS. Is that right? Or am I seriously under-propped right now?

Click to expand...

Ok Dan I'll try to help you. I have a 1986 4.3 Mercruiser Alpha one 185 Hp
1.65:1 Gear ratio. Probably the same as yours. I'm looking at my owners manual right now. The chart pg 2 lists two props 13-3//4 Dia 21 pitch or
14 Dia 19" Pitch
I'm running on my Boat right now 14 1/2 Dia 21 Pitch Michigan Wheel Vortex. I can give you the Skew # if you need them but Michgan wheel will know the right one if you call them.

My RPM"s are the same the same as yours 4400-4800. Occassionally I may get up to 5200 rpm. I questioned my dealer about it and he says that is not enough to be concerned about. But when I see it go that high I back off the throttle. I seldom run WOT anyway.

I have ran the 14 x 19 prop in fact that is what my spare is. My boat performs
better, runs faster at 4800 rpm with the 21 pitch prop. My top speed GPS is 54 mph @ 4800 rpm . The 21 seems to get up on plane faster and smoother. I don't understand or know all the math equations. I just know what works for me. I would suggest you go with the 14 1/2 Dia x 21 Pitch.

The charts are found in the Mercruiser installation manual if you have your books. The book part # is 90-12545--1 (1084)

Hope this helps.

Re: 4.3l Mercruiser Prop Question

Thanks for the replies thus far. Just a bit more info....

Max speed at max throttle is 37 with only 1 person in the boat.

Currently running the 17 pitch prop.

Have not checked compression yet, but when the motor gets to the top end, about 3800 when gear is engaged, there is a pulsing. Almost like an ignition type problem. This occurs only (at least as far as I can tell) when the drive is engaged.

Re: 4.3l Mercruiser Prop Question

danstroup284 said:

Thanks for the replies thus far. Just a bit more info....

Max speed at max throttle is 37 with only 1 person in the boat.

Currently running the 17 pitch prop.

Have not checked compression yet, but when the motor gets to the top end, about 3800 when gear is engaged, there is a pulsing. Almost like an ignition type problem. This occurs only (at least as far as I can tell) when the drive is engaged.

Click to expand...

Dan you probably need a tuneup, besides to change the prop. I'm running 54 mph with two people (about 380 lbs people) on a 19 ft Four Winns Bow rider. I gave you all the specs in my last post above. The pulsing has to be a tuneup problem.

Re: 4.3l Mercruiser Prop Question

i have the exat same boat 89 celb br 181 with the 4.3l alpha 1
i run at about 4400rpm with a 14.5x19p prop at high altutide (8000ft)the hole shot is a lil slow but my top speed is about 45mph

if im towing a skier or pulling a tube i drop down to a 14.5x17p for a little better hole shot i loose a lil top speed but my rpm is about 4700 at wot

Re: 4.3l Mercruiser Prop Question

What gear ratio is your drive? If it's 1.6... then that leads one direction, if it's the more common 1.84 behind a v-6... then we look the other way...

my 18' checkmate, ran about 50 with the old style v-6 in it and 1.84 gear ratio and a 19 or 21 pitch prop, with a tight 4.3, non balance shaft engine, newer vortec heads, roller cam, aftermarket aluminum intake and 4 barrel, etc... was pushing 60 with a 23 and a little faster with a 26 (smaller diameter, but too prone to blow out in hard turns).

If you're running a 1.84 gear ratio and your motor is healthy, the boat isn't waterlogged or full of concrete blocks (I know it isn't) I wuld think you could turn any standard design 17" prop to redline.

If you're running a 1.6 gear ratio then propping down much further is goign to be tough (hard to find appropriate diameter props where you need to be) or swapping out for a 1.84 or 1.81 ratio upper half as mr. Bond-O suggests above...

Before worrying aobut all that, do a full tune up check for water in the gas and get it running right. Worrying about propping before you get the engine runing right is putting the cart in front of the horse big time

Re: 4.3l Mercruiser Prop Question

cbavier said:

Ok Dan I'll try to help you. I have a 1986 4.3 Mercruiser Alpha one 185 Hp
1.65:1 Gear ratio. Probably the same as yours. I'm looking at my owners manual right now. The chart pg 2 lists two props 13-3//4 Dia 21 pitch or
14 Dia 19" Pitch
I'm running on my Boat right now 14 1/2 Dia 21 Pitch Michigan Wheel Vortex. I can give you the Skew # if you need them but Michgan wheel will know the right one if you call them.

My RPM"s are the same the same as yours 4400-4800. Occassionally I may get up to 5200 rpm. I questioned my dealer about it and he says that is not enough to be concerned about. But when I see it go that high I back off the throttle. I seldom run WOT anyway.

I have ran the 14 x 19 prop in fact that is what my spare is. My boat performs
better, runs faster at 4800 rpm with the 21 pitch prop. My top speed GPS is 54 mph @ 4800 rpm . The 21 seems to get up on plane faster and smoother. I don't understand or know all the math equations. I just know what works for me. I would suggest you go with the 14 1/2 Dia x 21 Pitch.

The charts are found in the Mercruiser installation manual if you have your books. The book part # is 90-12545--1 (1084)

Hope this helps.

Click to expand...

hello,can you give me the exact model number on your prop 21 pitch,vortex 3blade?SS?
thanks,erik (belgium)

Re: 4.3l Mercruiser Prop Question

I have a 3 blade 14 X 23 on my 4.3L and it does 46MPH at 4600rpm.

I have a Maxum 1800sr2 with the 4.3lx. I had been searching for the perfect prop, and I think o found it. It’s a 23p 14 3 blade. I have an alpha 1 with a 1.85 ratio. This was the right prop- planes out good, tops at 48 mph at 4600 rpm. I do have a stingray hydrofoil which I plan on taking off now, to try to reach 55 or so.

Probably fixed his issue 10 yrs ago.