propeller and misc question

[-stig-]

hello guys!

on my mercruiser drive i have a propeller and its stamped:

48 88 28 30 a45 19p

anyone know what size this is?

its fitted to a merc 140, in a shakespeare shadow 15.9", 700kg/1540lbs, went out on the lake today, got the engine easy up to 4600rpm WOT (on gauge, not checked) but the GPS says 37mph... isnt that a little low?

the engine is just rebuild, with good compression readings.

i know i have to check the rpm, but what else to check?

regards and thanks people!

 

[Bondo]

Re: propeller and misc question

Ayuh,... A 19" pitch prop on a 140hp, in a 16' boat doing 37mph, at 4600rpms,....
Sounds about Right to me....

 

[-stig-]

Re: propeller and misc question

thanks!

okei, but isnt the recomended wot for the 1980 merc 140 3.0 about 4400-4600 rpm?

i asked the previous owner, and they have run it at 5500rpm, and it was up there it had made 43knots... the engine was blown when i bought it, now i can understand why...

 

[Bondo]

Re: propeller and misc question

okei, but isnt the recomended wot for the 1980 merc 140 3.0 about 4400-4600 rpm?

Ayuh,... That's right,... I wouldn't run it over 4800rpms,+ then not for extended intervals...

 

[45Auto]

Re: propeller and misc question

You ned to go to the "Adults Only" sticky at the top of the I/O forum and download the manual for your engine. Don't be surprised if you get to rebuild it again if you intend on running at over 4600 RPM for long.

From Mercruiser Factory Manual #3, 1978-1984 Engines - 4,L6,V8:

 

[Philster]

Re: propeller and misc question

I'd go to a 21 pitch prop.

 

[-stig-]

Re: propeller and misc question

thanks for all answears guys!

hehe, i think i've got all manuals on this engine, and the Seloc book on it just wanted to dobbelcheck it, since the other two owners drove it that hard.

but i wonder, do anyone got a chart over the engines powerband? do it produce more power at 5500 than at 4600? would i never get the same speed at 4600rpm, regardless of the pitch?

thanks for the 21p tip, would that be a 19inch 21p or a 21" 21p?



regards, Stig!

 

[steelespike]

Re: propeller and misc question

You need to match your prop so the motor runs close to the 4,600 at wot
(wide open throttle)rpm.Your prop diameter will be about 14 1/2" If you select a 21' pitch for your outdrive the diameter will follow.
In my opinion your setup should run over 40 mph.
Usually a reasonable sofisticated car motor is redlined at 5,000 to 5,500 rpm
but if you think about it it runs at that speed for seconds at a time.
A boat could run for an hour at that rpm and the strain on the boat motor is like racing up hill.Thus the consertive max rpm of about 4,600 or less.

 

[-stig-]

Re: propeller and misc question

thanks for the replies!

so, im gonna try a 21p with the same OD as the one i've got!

thanks!

just one question more, do the merc 3.0 produce more power at 5500rpm than at 4600? would it be possible for me to get this boat up to this speeds with a propell with more pitch?

 

[45Auto]

Re: propeller and misc question

just one question more, do the merc 3.0 produce more power at 5500rpm than at 4600?

Not if it's stock it doesn't. If it was rebuilt with a hot-rod cam, higher compression pistons, etc, then the only way you'll know is to dyno it.

would it be possible for me to get this boat up to this speeds with a propell with more pitch?

The dyno chart below is a 2010 3.0L. Yours will be very similar except the HP peak will be at 4400 RPM instead of 4800. You'll get max top speed when you prop it so that it's running at the horsepower peak. If it will go over 4600, you need a higher pitch prop. If it can't make it to 4600, you need a lower pitch prop.