Have a 30 hp 2 stroke on the back of my boat and it is a wee bit underpowered for my boat. Specifically, the hole shot sucks-very difficult to get the boat up on plane even with a whale fin added. Engine is a 2002. Any outboard mechanics out there who know if the computer can be tweaked to bring it up to 40 hp power? The two engines appear to be identical so I am assuming that the difference in hp is due to a computer or some electronic governing. It's important as nobody makes a light enough 40hp today to replace it with.

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Forum consigliere

Turbo Time, you could get away with that Caj, try a new prop with LESS pitch, sounds like you need more RPM off the bottom end. Like I tell wifey on the bicycle when we're climbing a hill, shift down and spin, you gotta get that rpm up under load.....

you prolly need more boat and more motor, my little brothers 21 foot Triton with 225 XP will snap your nek a little!

Caj, I had a 48 Evinrude 2 stroke on my 16 footer for 20 years and recently replaced it with a 40 Merc 4 stroke. Speed is about the same but the 4 stroke consumes much less fuel (it "sips" gas, not consumes it) and is a lot quieter.

I bet there's more to it than just a computer change. Could be cylinder size, valve size, bore size or any number of internal block items. Just a few thousands can reap big benefits. I have the 60hp EFI 4 stroke and it's the same size as the 75 hp EFI 4 stroke but I doubt a computer tweak will get me up to 75hp.

As you are probably aware, prop pitch changes can give you better hole shots but suck the life out of the top end. Finding a happy balance can be expensive.

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Semper Fi

It is simpler than a computer job. I believe the only difference in that model is the reeds in the carb. A easy way to check is look up the specs on both motors, if the bore is the same then it is most likely just carb stuff making the diff in HP. Change them out to a set from a 40hp and do like the guy above said and change the prop to a larger diameter and lower pitch. FYI I was an outboard tech for like 10 years, but it's been a while. Check with a Merc dealer in you hood.

Caj, I helped a friend re-power his aluminum 16 footer over the winter. He bought a tiller-operated 40 hp 4 stroke Honda. It weighed a bit over 200 pounds. The old was a 30 hp Mariner and did weight a bit less as I recall.

He's had it out a bunch this spring and feels compelled to call me each time. He is blown away by the low end torque and mid range power. He's still breaking it in but so far, he's in love!

More hole shot power for your existing is typically a prop as stated. I put a fin on my last boat it helped with porpoising but I don't think it did too much to get me up on plane any quicker. As for remapping the motor brain, the manufacture's website or a dealer might be a starting point.

Orrrr, Maybe a nice, new 26' Regulator with twin 200 Mercury Verados might be in order....Your Suburban can tow it and it's got an enclosed head for Mrs. Lawyer!

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paws for friendship

Or come off that tight wallet some and buy a larger motor.

E-tec!! JMO......and an expensive one at that!!

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Go big or stay home

If you lower the pitch of your prop, you will get better hole shots (at the expense of top end). Are you tucking the motor down when getting on the gas? Is the shaft length of the motor the right length for the transom? I'd try a different (lower) pitch prop first.

1. Go on a diet.

2. Clean the old bourbon bottles out of the bilge.

3. Lock your gas tanks so the local constabulary can't pee in them.

Just tryin' to help.

I was going to add:

Leave some of the beer at shore and come back and get it later...


.

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Kirk / Spock 2020

Most engines that have the same block but different HP is due to the carburetor, or fuel injection. Back in my boating craze a 9.9 and 15 HP were the same except for that. The 70 and 90 were the same. I do not know of that year engine if 30Hp jumped to a different block on the 40.

Last boat thread you had was a Whaler that was under powered what happened to that?

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Still Running Against the Wind

We have sold evinrudes for 30 years and the e-tec is far and away better then the merc!! I run a 250hp on my pontoon boat. Just an awesome motor!!!!!

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George Jamison

Until you run them in Salt Water. Maybe since they are no longer OMC they may be better. The only engines you see down here are Yamaha and Mercs.

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Still Running Against the Wind

In the Delta, my 85 hp Merc gets on plane fine. I took it to Reno once, it wouldn't plane period.

My dad ran it in salt water for 6 months during the winter. Not one problem in the 4 years he's been doing it.

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George Jamison

Remember the old OMC Sea Drives??

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Still Running Against the Wind

ARG, is that Captain Jacks dingy off the Black Pearl?

My dad had a motor listed at 25 HP,it would run side by side with a 35 HP same brand motor and similar boat. I've done it. The dealer told us the only difference was the carb and the hp decal on the hood. He said Dad's probably had the wrong carb added during manufacturing. Ask the dealer if he can upgrade yours.

Nothing a good Evinrude or Johnson can't fix. My father said the Merc made a great black anchor.

Okay, with an outboard that has multiple outputs for a single displacement engine block; say 30, 40, 50hp, or the 200,225, 250 there are 3 things that are slightly different. 1. Injectors. Likely, there will be 1 set of injectors that work 2 of the 3 outputs, and the 3rd one is different. On most of the big blocks, it's the 200&225 that are like injector-wise, and the 250 is bigger. Your motor may vary. If carbuerated, then the carbs are the same program; 2 likely are the same with jetting changes, likely the 3rd is a little bit bigger in some way. 2. This is guaranteed. Your computer is tuned differently. In a closed loop system, you likely can not get in and switch it from 30-40hp. It would be locked up tight with the exception being a true factory computer with the map to download. Your mechanic might have something that can do the job, if he was trained at the factory and has paid for the ignition and fuel maps. 3. The exhaust ports are DEFINITELY different. The exhaust chamber down to the prop has a few parts that are designed to create proper backpressure for the given output. If the 40 exhaust is used with a 30hp motor system, it will run flat in the midrange because of a lack of backpressure. If the 40hp motor system is used witht he 30hp exhaust, the motor will not breathe up on top, limiting output. Also, you would get CEL warnings for the exhaust getting too hot.

Simpler fixes. I can help a bit, but need some info: Boat length, hull type (V hull, flat bottom, aluminum, fiberglass?) Boat weight.(Estimate) Prop diameter, pitch, blade count, and cup? Prop material- SS, aluminum, carbon? Any prop porting?
On to performance. Idle speed; in gear putt putting. WFO top speed. Approx seconds to plane from putt putt or dead stop. WFO RPM.

All this is necessary to get you real close to dialed. But I will start, with a lengthy, boring read, just for you OP:
If engine RPM is 4750-5500 RPM on top, then overall pitch is correct. If the RPM tops out at 4200-4600, then you are pitched too tall, or have too big a prop.
If the RPM is correct (5000ish @WFO) but the boat is slow to plane? Several fixes. 1. Add some cup to the prop. Cup is the lip on the prop. A good prop shop can do this for you. Or, buy a prop with more cup on it. Cup counts if the prop slips. If you have revs, and RPM climb fast but the boat does not accelerate quickly? Too much slip. The cup bites more water.
2. Cut the prop diameter. Either buy one, or have a shop take 1/4" of diameter out of the propellor. If you had say a 9x11 prop, make it into an 8.75x11. The smaller diameter will slip through the water quicker, and take less bite. This will allow more top end RPM, and quicker rpm pick up. This can work well if the boat accelerates slowly, but works at top speed with the desired correct speed and RPM. 3. Port the prop. Carefully and equally, drill a smallish hole (1/4-5/16" on a small prop) into the prop housing to allow a little exhaust gas to slip out onto the blade surface on the prop. This CAUSES cavitation. The cavitation allows for the prop to spin more freely, and bite the water less. This will make the top speed lower for a short time, as the slip of the prop will allow high RPM more readily, and then the prop will need to hook up and drive hard (It will, but in general it takes a few seconds longer to hit top speed) You may lose a MPH or 2 on top speed. You can plug the holes if the preformance change does not work for you. If you run in rough waters with lots of wind chop, or of your prop is already high and does not hook up very well, this is not a good option. You will spin the prop too much.
If the RPM are too low on top (4000-4500) then there are different and crossover options: 1. Smaller diameter prop. Again, if I am looking for only say 300 RPM and like the drive, then I will probably cut the prop. 2. If the boat is just a bit too heavy, or has too much wind resistsance? I will prop down a pitch. My example prop was a 9x11. To pitch down and gain RPM on top, I would go to a 9x9 (+300RPM). The ratio of prop/ gearing might wind up with a different diameter- say a 9.25x9 (+220RPM). If it fits? This is fine. If the diameter shrinks as well as dropping pitch- say 8.75x9? Likely outcome is 8.75x9 (+375RPM) Sooo...... take a good look at the recommended WFO RPM from the manufacturer, and extrapolate my numbers. The pitch changes tend to hold true thru all the sizes, the motor RPM may be off.
To prop down a pitch WILL hook up better, and across the board the motor will pull harder. But..... you will run out of steam faster, and as such, the top end speed WILL DROP some.

The pitch of a prop is as such: the diameter is how much water the prop grabs. The pitch is like threads on a screw. Fine pitch screw will be a lower number. Every turn of a 9 pitch prop will move the boat 9" forward. Every turn of a 15 pitch prop will move the boat forwward 15". Multiply by RPM and get theoretical top speed. When you know how much true top speed is, vs. theoretical? You can determine the amount of prop slip. Expect between 5-10% slip. Better bite from good cupping will lessen loss due to slip.

Blades, and material. Aluminum is just so great, it is hard to explain. Hard enough to drive you, flexes well, and is tunable. Soft enough to shear off a blade on impact to save the lower unit. Light, and relatively inexpensive. Stainless is stronger. if you hit something, you will be much more likely to blow the lower unit gears because stainless props are harder. SS props flex less. They tend to deliver better performance on high speed boats where flex at full zip is less desirable. Carbon; good for little motors and in log and rock infested waters. They break often, but save the lower unit. They make good, cheap spare props. A spare is a must on any boat. (Do not ask how I know.....)
Blades. The more blades there are, the faster, right??? NO. The more blades, the more efficient each blade grabs water. More blades grab a smaller cup of water, more times each turn. Theoretically, they can hook up better for better acceleration. The more blaed in the water, the more drag on the prop. When you see a bass boat with a 5 blade and it hauls balls, the deal is that they need to hook the power up to the water, and have power loss issues..... so losing a little power to get a better hold of the water is an acceptable tradeoff. Pushing a 19ft potato chip across water with 300HP is a recipe for lost power, just like a 650HP engine shoehorned into a 1977 Pinto would be. A little boat is best served by the venerable 3 blade. The average boat is best served by the venerable 3 blade.

Finally, weight and balance: if the boat runs a bit stern heavy and does nto want to plane, try to move weight forward. You will be surprised what moving a 12 gallon gas can 4 ft forward can do in a 15ft boat. Ice chests, etc, try to shift weight forward.
See if there is any weight you can discard. It's usually not practical, so I recommend moving weight forward or getting a lighter fishing buddy.....

Hope this helps. I have worked for Spectre racing boats and Hering propellors. I have driven some God awful fast floating missiles, and I know how to squeeze 3.15mpg out of my 23ft sport fishing boat at 24kts.

First one who gives me 'props' for this is gonna get slapped!

Altitude. We ran the 31ft Spectre with twin 3.5L Black Max SX motors on it; each made a solid 450hp. In San Diego bay, I pused it easily to 135 with 4 passengers and 100 gallons of fuel on board.
In Lake Tahoe, the poor thing struggled to deliver 110, with 1/2 the fuel and only 2 of us on board. Lean air means less power unless you have forced induction.

You are about the 6th or 7th person who suggested that.
Actually my suggestion to my wife is that she loose some weight if she wants to come with me

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Forum consigliere

Great post. Thank you. the boar is a 2002 vintage 13' whaler with a Mercury 30hp elpto on it. boat is weighed down as it has a polling platform on it and a trolling motor with the extra battery, a light anchor, lines etc before adding anything else. WOT is correct on the rpm's I have not thought about adding a little cup to the prop. But hey it was show room condition when I bought it and the price ($4500) probably reflected the fact it was marginally powered. I've got a client with a prop shop that owes me a favor....hell part of the fun of owning a boat is dialing it in and drilling holes in it to make it your own

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Forum consigliere

I bet that suggestion is as popular as a pay toilet in a diarrhea ward!

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Luke 22:36

Buy yourself a very heavy anchor, and add about 40ft of 1/2" chain to it.
That way, when she tosses you overboard for giving her that loving little hint......... you will not even sweat trying to struggle to make it to the surface. You will just scratch the nearest catfish on his whiskers, and wait for the lights to go out.

You good fishing buddy will take good care of her and the boat; you can count on it!!!

Only you can determine if the problem is slip or outright power..... TORQUE in the low and midrange. If slip is the issue, then cup the prop. If it hooks up well, then cut the prop so it bites less water, by just a fraction. It will develop power a little faster, and apply more torque at lower speed (regardless of RPM) so this is often the correct fix. Talk it over with the prop guy, maybe take him for a 30 minute ride for a beer around sunset to dunk a line. He will be able to gauge the situation and either confirm or counter your feelings and my suggestions.

Are you towing a water skier? If not, I cannot see the need for the rush. I mean the boat does plane eventually, doesn't it?.

I say that maybe a couple of high end juicy divorce cases would fund the solution."Speed cost money ......how fast do you wanna go? "

The problem for a boat motor is the load is constant, and much higher for a given rpm and power delivery than for a car or motorcycle, or snowmobile. A boat motor needs to make constant power under a load in which the drive output fights friction and ressitance in a manner which simply can not be compared to tires rolling over dirt or asphalt.
Since the load is higher, a boat engine that can not accelerate cleanly will be lugging, and this will wear cylinders out very fast. Amazingly so, in fact. Once compression starts dropping from the wear, the power loss compounds the problem, and it's downhill from there.
An outboard motor is designed to run on a constant delivery in 2 rpm classes: 3500-4500 for small motors, and 5000-6000 for medium and large motors. They deliver their best economy at idle, and then up at high cruising speed. My own personal 23' fishing boat as an example: At idle, 1000-1500rpm. The boat gets around 3.75MPG. Step up to 2000 rpm, the economy drops to 2.75. Step up to 3000 rpm, and not on plane...... .85-1.1 MPG. Go to 3750rpm, 17kts and just on plane; 1.9-2.5 mpg. 4200rpm, 24kts and 3.0 mpg. 4750 rpm.......28-29kts, and 3.15mpg. 5500rpm, and 32kts, 2.85mpg. 6000rpm, WFO; 38kts and 2.3mpg. Between 2000-3500rpm, the motor lugs. It's the nature of the engine, and the torque numbers are no good at all. But hit 3600rpm and start climbing, the torque curve is there, the motor breathes right, and it makes clean power. Peak efficiency and motor life are delivered on the 225 at 3750-4750rpm. Above that, it's just spinning more, and I can rarely use the speed in the open ocean. At 3750rpm, the motor will last about 8,000hrs to 10,000 hours before a total rebuild is mandated. If lugged, the cylinders would wear out around 4-6000 hrs and be done. Too much load.

Caj, heres a 14 carolina skiff I just set up w/ a 15hp Tohatsu 4 stroke and a troll motor and big battery. It planes good with 300 lbs. (for two kids). But it's slow out of the hole, which is o.k. 'cause it's for the kids.
The pink 15 flatbottom next to it we put a 25 E TEC and it jumps right up with 2 big adults like RIGHT NOW.
You may just need a wheel with less pitch (they call it a power prop) if that 2 stroke isn't worn out, which it sounds like it isn't from what you say. The 2stroke being lighter.

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Halfway and one more step