Mercruiser 140 (3.0L) Alpha leg: go faster?

[gordreid]

Hi guys,

Brand new to the forum, looking for advice.

Already read about smarttabs, will be purchasing them right away.

Boat:

1986 Sea Ray Seville 186 cuddy
140 Mercruiser (3.0) Alpha 19p

Configuration:

Ocean commuter to/from cabin
15hp 2stroke kicker on bracket port side
twin batteries under stern seat stbd side
misc tools, spare prop, porta-potti, anchor & chain, etc
bottom painted, lives in the ocean 9 months per year
Pretty heavy package overall

4000 rpm = 25 mph

I want to go faster! Please don't suggest another boat - I love this one and will live with the existing speed before changing boats.

Was thinking of starting a collection of bits & pieces required to repower to a 4.3MPI over the next few months, then having a swap done over the winter. I would be paying somebody to do this, as I am not sufficiently mechanical enough to attempt it myself. Has anybody done this?

Or...am I on the wrong track? Other options for better speed & performance? Advice?

Many thanks!

Gord.
Quarry Bay, Nelson Island, BC

 

[Bondo]

Re: Mercruiser 140 (3.0L) Alpha leg: go faster?

Was thinking of starting a collection of bits & pieces required to repower to a 4.3MPI over the next few months, then having a swap done over the winter. I would be paying somebody to do this, as I am not sufficiently mechanical enough to attempt it myself. Has anybody done this?

Ayuh,... Going to a 4.3l is about your Only option...

 

[BayBoy1750]

Re: Mercruiser 140 (3.0L) Alpha leg: go faster?

I think you'll like the Smarttabs...I run the 3.0 with them as well.

Usually the first answer is make sure your motor is tuned up and getting good compression etc. 25MPH at 4000 may be ok, the key question is do you get your recommended RPM's at WOT. 19p seems like correct pitch but you might be able to go up in pitch for more top end (21p) if your current WOT is near the top end already (4600-4800? Check your manual).

A heavy boat would benefit from a 4 blade prop with lifting characteristics like Stiletto Bay Pro II. I realize 4 blades generally means less top speed but having more boat out of the water may actually improve things for you...IF the tabs don't get it done. Do you feel the boat rides deep while on plane?

Is your current 19p prop Stainless Steel (SS won't flex under the heavy load as much as an aluminum). The 19p 3 blade Stiletto Advantage II which is a 'progressive' pitch prop performs well on the 3 liter engine. I'm considering it myself. I don't feel I need any more boat lift in my unit so I'm sticking with 3 blade wheels.

 

[mkast]

Re: Mercruiser 140 (3.0L) Alpha leg: go faster?

I remember reading on a web site that if you pay someone to do the work, going faster will cost you, on average, $1500 per mile per hour.
Just for argument sake, suppose this figure is close. How much faster did you want to go? Someone said, "Speed costs money."
Another rule of thumb, ten engine horsepower will net you one mile per hour speed increase. You mention collecting the "bits and pieces", how much will you spend on incorrect parts and unserviceable parts (learning process)?
If this information is even close to accurate, how much will you be spending?
How much will this boat be worth when you are done? If you sell or trade your boat, take half that amount of money you'd be spending to make your boat faster, and buy some boat that is more to your liking, you'll be getting off cheaper in the long run without any of the down time or maintenance headaches.
Here is how it works.
XXX amount of horsepower will move XXXX amount of weight at XX speed.
Yes, I know it's simple, any fourth grader knows this, but you're not listening.
After you do this engine swap, you'll look back on the experience as, "I wish I would have listened.

 

[45Auto]

Re: Mercruiser 140 (3.0L) Alpha leg: go faster?

As Mkast says, if you're paying someone to do it you're going to spend more than the boat is worth before you're done. And to anyone else it still won't be worth any more than it was with the 3.0.

Best bet:
1) Sell the boat for $XXX dollars.

2) Add to that the $YYY dollars you would spend on the engine conversion.

3) Buy a boat worth $XXX+$YYY

Took me a long time to learn that, feel free to start from scratch and prove it for yourself if it makes you happy!