How can I get more from my 50 4 stroke merc

[Xenos]

I have a new 2002 50 4 stroke merc, at full throttle it runs at 5800 rpm with a 10.25x14p prop. From what I have read, if I install a 15p prop I will be running at 5500-5600 rpm. Now seeing that the 50 and 60's are basically the same engine what will I need to adjust/replace to get the rpm back up to 5800?

 

[SeaDawg]

Re: How can I get more from my 50 4 stroke merc

Xenos, installing a 15 pitch prop may OR MAY NOT change your max engine rpms. It will depend on how much work you are expecting from the motor. (weight of boat, trim angle, type of prop, water conditions, etc.) <br /><br />What I think you meant to say is:<br /><br />If you go from a 14 pitch at 5800 rpm, TO ACHIEVE THE SAME SPEED, you could run a 15 pitch at 5500 - 5600 rpm.<br /><br />If your boat is light enough, going from a 14 to 15 will still allow it to hit 5800 rpm, and get slightly more speed.<br /><br />Make sense?

 

[trevorcday]

Re: How can I get more from my 50 4 stroke merc

Since you have a 2002 you are really in luck. You can make your motor into a 60 with one simple change. There is a plastic restrictor plate behind the carbs. The 50 has small holes the 60 has big holes. It takes about 15 minutes to change and isn't particularly difficult. The part costs about $25 or so. That and the stickers on the hood are the only difference between a 50 and a 60. With this change to the engine you can probably afford to go to the 15" prop. If you don't make any other changes I wouldn't increase the pitch on your prop, you will probably lose speed and make the boat slow to plane. these engines need to rev.<br /><br />If you like e-mail me direct at trevorcday@hotmail.com and I can set you up with the parts you need.

 

[Pursuit2150]

Re: How can I get more from my 50 4 stroke merc

I'm curious, Why do you want to red-line the engine?

 

[evin300]

Re: How can I get more from my 50 4 stroke merc

Its all about the horsepower curve and lugging, remember you will not be at WOT all of the time, with a propeller, you are choosing the ONE optimal gear for your boat/motor set-up, that is why the choice of pitch and quality of prop, is soooo important. If this ONE gear takes you to the upper recomended RPM range, and the horspower produced at that RPM is still strong, then by all means, prop it to the upper end or even 100 or 200 RPM over, if your horsepower curve is fairly flat. The end result, is a boat with good planing time, good midrange power, and good top speed! <br /><br />If the manufacturer thought it detrimental to run at the top RPM range, then they would have changed it. In many cases, this is a fairly conservative number anyway. <br /><br />Remember, these are marine engines, built to take more punishment, than almost any motor, and we are paying a dear price for this, its a shame to see people over-propping and lugging thier motors, in the name of engine longevity, when actually, you shorten the life of the motor by bogging it down, kinda like letting out the clutch in 3rd gear.

 

[Xenos]

Re: How can I get more from my 50 4 stroke merc

Hi Pursuit2150 redline is 6000 rpm on this engine the dealer has my setup running at 5800. I contacted mercury asking what the difference was between a 50 and a 60 as the specs are the same. Their reply was vague but they did say I could make it a 60 but the costs would out way the performance gain. They didn't want to expand on the subject so I figured I would post the question, Mrmerc is saying it may not be so expensive. Now I don’t really need a 60, but if it’s possible to get more out of my engine why not? I was actually thinking the 15p would make the engine work a bit harder and give me a performance but from what I have been reading maybe I should increase the size of the prop.

 

[Pursuit2150]

Re: How can I get more from my 50 4 stroke merc

Xenos / evin300. I understand both points you made, I run a 175hp w/a 14 3/4 X17,When I really punch it I take it to 5600,do a slight trim drop to 5300 and gain about 4mph.I was told 5800 is max, and I never went there.

 

[SeaDawg]

Re: How can I get more from my 50 4 stroke merc

Persuit, maybe this will help some. This is all from memory, so numbers won't be exact.<br /><br />I bought a new 1987 Bayliner Trophy CC with a 125 Force, and it came with a 19 pitch aluminum prop. WOT would only give me about 35 mph at around 5000 rpms. And I sucked fuel like crazy at at rpm "below teeth rattling in waves" cruising speed. <br /><br />So, I got up with parts guy at the dealership, and turns out he had the exact same boat. He had also tested every prop in the dealership, and told me to get a 17 pitch. WOW!!! I was running over 1,000 more rpms at any given speed, but my boat throttle seemed barely cracked, fuel economy went up, and it would rev to 6000 rpms and hit close to 40 mph. I would never have believed the difference it made, if I had not done it myself.<br /><br />Since then, I've experimented with any boat that I own and I try to set it up so that it will redline on calm water with my lightest expected load in the boat. This is my "everyday" prop, since I mostly fish alone now, at least from my boat. Then, I buy a spare (that I take boating with me, along with an extra prop nut, etc.) that is 1" or 2" less pitch. I also swap it on the boat, for the times that I have heavy loads in the boat, or skiers, etc.

 

[evin300]

Re: How can I get more from my 50 4 stroke merc

SeaDawg, nice to hear a success story! Often, its hard to find out what your horsepower curve actually is, unless you can talk to the factory, or someone very experienced with your motor. I think the way most of us have to find out is by experimenting with several styles and pitches of props.<br /><br />Say your horsepower really starts to fall off from 5,500 on a 5,000 - 6,000 RPM rated motor, if you were to prop for 6,000 you may not increase your top speed, and maybe even lose a little, but you will still improve planing time, and midrange power, and possibly better fuel economy. <br /><br />I think fuel economy is the art of finding a great planing attitude for your boat at a RPM that your particular motor runs very efficiently, again, much experimenting. <br /><br />And, of course, there is no holy grail to any of this, as every boat has to carry a different weight load, and the distribution of the weight load makes a large difference too.

 

[SeaDawg]

Re: How can I get more from my 50 4 stroke merc

Evin300, I am going through the "prop setup on paper" agian this winter too, I'm putting a 1995 4-stroke Mariner onto a 2000 Lowe 1760MT bass style boat.<br /><br />With this forum and the manufacturer's engine sites, I've looked at a lot of performance tests with various motors similar to mine, and various brands of aluminum boats. And I now have a much closer place to start with the first prop.<br /><br />Schematic, do you have a design on a cheap to make gph meter? <br /><br />If you have a gallons per hour fuel meter installed on your boat (even as a test instrument), you can make your own fuel/performance curves to compare props, just like the ones shown on the engine web sites.

 

[evin300]

Re: How can I get more from my 50 4 stroke merc

Cool SeaDawg, I will be interested in your results.

 

[SeaDawg]

Re: How can I get more from my 50 4 stroke merc

I ended up with a 15 pitch stainless cupped prop. if interested, I put all the details on the boating forum.

 

[skier]

Re: How can I get more from my 50 4 stroke merc

Hello Guys/Gals:<br /><br />As my name implies, I have a Merc 140 inline 6 on a Glastron 160 (16'). The manual says 5000-5500 RPM's, the mechanic says that it's much harder to under rev than to over rev and told me to get as close to 6000 as I can without going over. It runs so smooth and quiet at 5900 RPM's. I also get great fuel economy for the size engine I have.<br /><br />Craig