Mercury Verado 250 HP Captain's Report

Why Verado Is Different

When designing the in-line 6 Verado outboards -- 225, 250, and 300-hp models -- Mercury engineers decided to create an engine that would be more durable than anything else on the market. They also wanted an engine that could have peak performance on hot, humid summer days when most people use their boats. Further, they wanted to address the problems that boaters historically have had at high altitudes with sluggish engines.

A Better Mouse Trap. In order to do all of that, obviously Mercury could not simply replicate conventional outboard 4-stroke design and expect anything much different to be the result. It had to engineer a completely different approach to a high-horsepower outboard engine.

At the same time Mercury engineers naturally wanted to create an engine with reduced vibration, noise, emissions and fuel consumption. Using conventional 4-stroke technology as the benchmark, Mercury engineers set to work to improve upon existing products.

The result was the Verado, an engine introduced in 2005 that ended up having other advantages as well, such as more low-end torque and a "maintenance-free-for-life" valve train. What follows is an in-depth look at what, in our opinion, is one of the most sophisticated outboard engine on the market.

Key Features

Built for Saltwater Applications. The engine is intended for both freshwater and saltwater use. However, the recent introduction of the new optional 5.44" gear case was designed specifically for rugged offshore saltwater applications and has greatly enhanced the potential applications of this engine. There is nothing quiet like it on the market.

The new gear case together with its advanced anti-corrosion aluminum alloy and painting regimen, and extensive use of 300 Series stainless steel, arguably makes it the best-prepared engine for the saltwater environment.

Verado -- A Different Way To Make Outboard Power

Simply stated, in an internal combustion engine it takes more air and more fuel to make more power. There are only two ways to do that: 1) increase the size of the combustion chambers; or, 2) "pressure charge" the air going into the combustion chambers by compressing it.

Instead of producing power through the sheer volume of displacement, Mercury engineers chose to minimize displacement and the large pistons and rods that go with it by using a "pressure charging" system.

Not A Big Bore. Big bore engines with big pistons have lots of moving mass that causes vibration and greater stress on metal parts. A rule-of-thumb in industrial design has long been that smaller pistons mean less vibration and less stress on internal components. By embracing this concept the Verado design can provide increased durability and long-term engine reliability.

Less Mass is a Good Thing. The displacement of the 250 Verado is only 158 cubic inches (2.6 liters) as compared with its major competitor which is over 60% more. That means larger pistons, rods, and related components are needed to handle the weight and inertia of heavy internal components traveling at 6000 rpms or more.

But how to get more power from a smaller engine?

What "Compression Charging" Does.

Naturally-aspirated engines at sea level suck air into the combustion chambers at normal atmospheric pressure which is 14.7 psi. By adding a supercharger (sometimes called a "compressor" or "blower") to the Verado engine, Mercury engineers were able to nearly double the pressure of air to as much as 29 psi going to the combustion chambers. This is "pressure charging." All things being equal, twice the air means twice the oxygen, which means twice the combustion, and much more power.

The Supercharger.

The supercharger (C) on the Verado is mechanically powered by the engine's crankshaft which makes it effective even at relatively low rpms. It sucks air in from the atmosphere, compresses it with two ceramic-coated four-lobe rotors twisted 160-degrees, then discharges it at the pressures needed to provide the performance wanted. This process is regulated by the Electronic Boost Control System (B) up to 29 psi.

Intercooler. In conjunction with the supercharger, there is also an intercooler (D), which reduces the temperature of the compressed air prior to entering the combustion chamber. This combination of compression and cooling puts much more oxygen into the cylinder for more powerful combustion.

The Electronic Boost Pressure Control (B) regulates the amount of compressed air going into the combustion chamber depending on ambient temperature, humidity, barometric pressure, and altitude -- thus delivering consistent performance with very little horsepower loss over a naturally aspirated design across a wide powerband.

Summer Temperature Map

No Heat Stroke. As a result of this sophisticated system the Mercury Verado can deliver maximum horsepower in a wide range of conditions. For example, when the temperature rises 20-degrees F from 77-degrees F and 0% humidity to 97-degrees F and 80% humidity a naturally aspirated engine loses about 7.7% of its horsepower. That means that an engine rated at 250-hp will have an effective horsepower of 230-hp in those conditions. According to Mercury, the supercharged Verado 250 loses about .5% or 2-hp in the same conditions.

(SAE -- Society of Automotive Engineers -- standard J1349 for horsepower ratings, requires them to be calculated at 77-degrees F (25-degrees C) with 0% humidity and barometric pressure of 29.234 inches of mercury at sea level.)

A Summertime Warrior. This makes the Verado an ideal engine to have during the summer when ambient temperatures can reach and exceed 100-degress F (38-degrees C). Even a 90-degree day at 85% humidity, which is not uncommon in the south and central U.S. in the summer, will reduce horsepower 6.2% in a naturally aspirated engine.

U.S. Altitude Map

Remedy for Altitude Sickness. Likewise, the thinner air at higher altitudes robs horsepower from all naturally aspirated engines. Further, during the summertime even at high altitudes there is usually some humidity. Using the SAE standard of 77-degrees F and 29.234 inches of mercury and a humidity of 35% following is the horsepower loss at these altitudes and the effective power of a naturally aspirated 250-hp engine--

The psi at 5,000 ft. (1524 m) is 12.9, a drop of 1.8 psi from sea level. Because the Verado supercharged engine is able to develop 29 psi for combustion it loses relatively little horsepower. Again, the Verado's Electronic Boost Pressure Control System compensates for the thinner air.

In a nutshell this is how the Mercury Verado delivers 250-hp from a smaller displacement engine. It is also what makes the Verado an ideal engine for geographic areas where the temperature rises above 77-degrees F or where the air thins out because of altitude. But the story does not stop there.

Greater Torque. Because of the supercharger the Verado has strong low-end torque for fast hole shots and power to raise a heavy skier quickly. It also gives the Verado strong torque throughout the RPM range which means at cruising speeds there is a pep left in the engine when needed.

Anglers heading far offshore in the summer heat have the horsepower and torque needed to get out to the fishing grounds fast. Skiers and wakeboarders on hot summer days -- particularly at altitude -- have the torque needed to quickly get on plane.

Distinguishing Features

Gear Case Durability: The Verado 250-hp is offered with a choice of three different gear cases, each designed for specific applications. The standard 4.8-inch gear case has a smaller hydrodynamic profile and was designed for single-engine applications focused mostly on freshwater activities such as sportboats, bass boats, multi-species boats, inshore flats boats and pontoon boats.

The "Offshore" 5.44" Gear Case. The new 5.44" gear case is designed for situations where boats are jumping out of the water and props are ventilating. In these conditions there are tremendous stresses on the engine's gear case and it has been designed with strengthened internal components, built specifically for offshore boats over 23-feet in length and over 5000 lbs.

Specific Improvements. The torpedo housing of the 5.44" gear is 14% larger in diameter in order to accommodate the larger diameter shafts and gears. The teeth of the gears are 24% bigger, are heat treated, and their bevel angle has been slightly changed. The shafts have longer taper for improved durability and added pinion gear support.

Bearings. The bearings are heavy duty with a rear bearing pack with higher load capacity. The bearing carrier is 17% larger and utilizes SeaCore-type anodization for added strength and corrosion resistance.

New Vs. Old Clutch Dog

Clutch Dog. The 5.44" gear has a clutch dog that is 30% longer, and according to Mercury, has five-times greater impact resistance of the standard dog. Taken together Mercury techs tell us that they estimate that the 5.44" gears are 400% more durable.

Impressive Corrosion Protection. Historically outboard engines in saltwater have suffered from corrosion. When electrons flow through dissimilar metals the weaker metal is eaten away or corrodes. Outboard engine blocks, cylinder heads, gear cases, drive shaft housings and swivel brackets are made out of an aluminum alloy by all manufacturers. But all aluminum alloys are not the same.

Low-Copper Alloy is Key. The low copper content aluminum alloy used in the Mercury Verado 250's die-cast components such as, gear cases, and drive shaft housings are all made from XK360 aluminium-silicon alloy, while the block and heads are of a A356 low pressurized lost foam casting. Mercury is one of the three manufacturers in the world who utilize this process. Mercury is generally regarded to have the best corrosion-resistant allow in the recreational marine industry.

The MercFusion Paint System. Having made the metal more corrosion-resistant, Mercury has developed its own process of coating the metal to keep saltwater from touching it in the first place. The photos below illustrate the measures taken and the materials used.

The MercFusion Paint process consists of a Irridite metal prep and sealant that goes over the aluminum alloy and provides a resistant barrier and a foundation for the two materials that come on top of it. Next the units are dipped in EDP electrically-charged primer that provides complete coverage and seals out the environment from the metal.

Powder coat paint is the top coat and it contains plasticizers for paint flexibility and better long-term adhesion. It is sprayed on and then thermo-cured. Mercury is the only outboard maker using powder coated paint on its metal lower units.

Unique Internal "Salt Shield" -- "SS38"

Every owner of an outboard engine used in saltwater knows to flush out the cooling system at the end of the day with fresh water. The reason is that salt build-up can close small passages and corrode the metal where it can't be seen. Mercury uses an internal sealing process along with a special coating in the internal water jackets of the powerhead and wet exhaust.

Mercury is the only outboard engine maker we know of that flushes the powerhead wet exhaust using a process such as this.

Mercury Verado Has More Stainless Steel

Stainless steel alloys resist corrosion, maintain their strength at high temperatures and are easy to maintain. Stainless steel alloys are used predominantly in the automotive, aerospace and construction industries. But all stainless steel alloys are not the same.

300 Series SS. Only 300 Series stainless steel is used in Verados. It is used in props, shift shafts, drive shafts, trim and tilt rams, lower yoke, water pump housing and other components. To our knowledge no outboard manufacturer uses more or better stainless steel in this engine class.

Some outboard manufacturers use 400 Series stainless steel which does not have as high a degree of corrosion-resistant properties as does 300 Series, but is suitable for household decorative items, appliances, among other things. ("Stainless steel" hardware seen on boats that weeps rust stains is often made of 400 Series SS.)

Powerhead Cradle and Anti-Vibration Mounts

Vibration Inhibitor: Mercury's Advanced Mid-Section

All powerheads no matter how well designed cause vibration. The question is what to do about it. Mercury has designed what it calls the "Advanced Mid-Section" (AMS) to virtually eliminate annoying vibration and the noise that comes with it.

AMS Details. The powerhead is connected to four oversized, calibrated, elastomeric mounts which are designed to isolate and cancel vibrations. The mounts in turn are connected to the cradle which is attached to the outboard engine bracket. The bracket is clamped to the transom.

When the engine is at idle or low rpms, the mounts are soft, but as rpms increase the variable-rate mounts become progressively harder. In both cases the vibration is isolated in the cradle and very little of it is transmitted to the boat. The result is a smoother riding, quieter boat.

The 5" Advantage. The cradle-mount AMS unit seen above sets the engine powerhead 5" behind the transom which aids time-to-plane speeds and smoother running. It also allows the engine to tilt-up a full 73° and depending on the hull gets the engine out of the water.

Maintenance-Free Valve Train for Life.

Importance of Shim Clearance. Six-cylinder DOHC engines (including all 250-hp marine 4-stroke outboards) have 24 valves and 24 valve shims and all must be at optimum clearance (or "lash") for best performance. Typically before 500 hours of use the lash between the cam lobe, valve shim, and the top of the valve stem changes.

Symptoms of the lash getting out of spec are using oil, loss of performance, increased noise, or a slightly different engine noise. Most manufacturers recommended adjusting valve lash -- re-shimming -- after a certain number of hours. It is not surprising that many people put off this "tune-up" as long as possible.

The $1,000 Bruise. The reason that re-shimming is delayed or avoided is that it typically costs $1,000 or more at current shop labor rates in many parts of the country. This "regular maintenance" is not covered by warranties and is often needed after the engine is out of warranty.

Re-shimming is a time-consuming and tedious job. The clearances of each valve shim must be carefully measured and new shims of the right thickness inserted where needed.

Guaranteed Valve Train Lash For Life. As far as we know, the Mercury Verados are the only outboards that do not need to be re-shimmed. Their valve shim clearance is guaranteed for the life of the engine. Here's why Mercury can offer this money-saving benefit--

Computer Technology for Clearance Calibration. During the manufacturing process a computer precisely measures the shim clearance (which is typically about 10/1,000 of an inch) needed for each of the 24 individual "shim buckets" and selects one of 35 minutely-calibrated shims for each valve. (Mercury shim tolerances range from .006" to .011".) The correct shim is then placed in the powerhead by hand, followed by a second computer check of the calibration.

Power Steering Made In House

High-horsepower engines have prodigious torque which is conveyed to the steering wheel in conventional installations making steering difficult without hydraulic power steering. According to our test captains, Mercury's system not only prevents torque from getting to the steering wheel, it also permits precise, firm control and is quieter at all rpm levels.

How Is Merc's Power Steering Different?

Mercury's steering is more like that of a high-performance sports car rather than like the "soft" feel on luxury cars that float on a cloud. This distinctive feel encourages incremental handling, gives the skipper firm control, and protects against over steering.

Mercury is the only outboard manufacturer that makes its own hydraulic power steering system. All other outboard makers rely on builders to buy third party equipment which they install as part of the "rigging" process.

Mercury System Advantages. There are basically four major advantages to the Mercury power steering system:

1) It is engineered and manufactured by Mercury just like any other component of the engine and not made by a third party vendor.

2) It is installed by Mercury factory staff and not by each boat builder's personnel.

3) The system is calibrated to prevent dangerous over-steering at high speeds.

Water-to-Oil Heat Exchanger

Verado is the only outboard engine in class that has a water-cooled oil heat exchanger with thermostat. In this way the oil can be kept at consistent temperatures to prevent condensation and oil dilution. Keeping water condensation out of the oil pan and other parts means longer life for the engine.

Dry Sump. The Verado 250 P is the only engine in class that has a "dry sump" which means that there is no oil in the pan ("wet sump") for the crank shaft to be swinging through on each revolution to splash oil up on the cylinder walls for lubrication.

Noise Attenuation

Mercury has engineered the Verado to reduce sound not only by reducing vibration, but in other ways as well. One example of this effort is the exhaust relief system which is designed to reduce sound at idle with baffles in the exhaust box.

Another strategy is a multi-chambered intake sound attenuator, where the air entering the engine is ducted through specially-shaped and sized chambers to reduce overall noise. There is also acoustic foam lining along the upper cowling and lower cowl to absorb high frequency noise from the engine and drive shaft.

Electronic Data Management & Engine Control

SmartCraft Management System

Mercury’s SmartCraft instrumentation provides vital engine information to the operator. When a problem is detected, either a visual or audible alert is sent to the instrument panel and engine power is automatically reduced, advising of a concern and provides a get-home capability.

SmartCraft provides up-to-the-second information on dozens of engine diagnostics, including RPM, fuel flow and management, critical temperature readings, speed, and engine trim. By taking much of the guesswork out of power management, SmartCraft makes time on the water more enjoyable.

The SmartCraft System integrates with VesselView, Smart Tow, Digital Throttle and Shift (DTS) and Mercury's advanced control binnacle.

Digital Throttle & Shift (DTS)

Mercury was the first outboard builder to introduce drive-by-wire and it was a revolutionary advancement for boating. Even today, Mercury is the only maker of outboard engines that manufactures its own drive-by-wire system. (Other companies out-source this system to a third party vendor.) DTS provides smooth shifting, instant throttle response, no grinding of gears and effortless control.

Captain-Approved. When we polled our test captains we found that they all like Mercury's DTS system because it is strongly-built, ergonomically correct, trim toggles are handy to the thumb, and there is an obvious "detent" when shifting that lets the operator know by feel alone when the engine is going into gear forward or reverse.

Mercury seems to be continually improving on the system adding new features from time to time. Features include--

Mercury DTS Exclusives--

250 Verado Warranty

The 250 HP Verado carries a standard 3-year limited warranty, which is non-declining and covers all components. (Some outboard makers do not cover all components for the length of their warranties. Read the fine print.)This warranty also extends to the controls and rigging when installed by a factory-authorized builder.

Corrosion Warranty. The 250 HP Verado also has a 3-year limited warranty on corrosion.

Mercury Product Protection (MPP). An additional two years of engine product protection can be purchased from the dealer selling Mercury-powered boats. Unlike all other outboard extended service contracts, the Mercury Product Protection coverage is completely administered and backed by Mercury Marine – no other independent provider or insurance company is involved. This protection can be purchased in order to cover up to a total of 7 years, including the original 3 years of limited warranty coverage.

(Most outboard manufacturers rely on third party insurance companies to provide "extended service contracts.")

Two Levels of MPP Factory Coverage. There are "Gold" and "Platinum" levels of MPP coverage, the latter of which is pretty much the same as the original 3-year warranty. The "Gold" coverage, which is less costly, covers all aspects of the engine and gear case, but does not cover solenoids, wiring harnesses, most anything to do with the unit's trim system, the electrical ignition system, and instruments. (Read the fine print.)

There is a $25 deductable for each MPP warranty claim.

Advantages of MPP Warranty Program--

The Verado is from 47 lbs. (21.36 kgs) to 102 lbs. (46.36 kgs.) heavier than the three other 4-stroke 250-hp engines on the market. Here's why it is heavier--

Just as every boat is a compromise, so too is every engine a compromise. In order to create a long-lasting engine that does not lose performance with changes in temperature, humidity and altitude it simply takes more weight.

Verado Gen II Improvements

The radically new Mercury Verado Series was introduced in 2005 -- but it was not perfect. Over the next two years units exposed to hard use began to exhibit problems with different aspects of components used. In a couple of cases design changes were indicated to improve efficiency and avert potential problems with severe use.

As a result, in 2007 Mercury introduced the "Gen II" version of the Verado, which essentially de-bugged the engine. Over 67 items or details were changed, most having to do with things such as seals, retaining rings, bushings, O rings, and the like. Two of the more major improvements are shown below.

Windage vs. Fluid Dynamics

Conventional internal combustion engines have "wet sumps" which means the crank shaft splashes through the oil in the pan with every revolution thereby lubricating the cylinder walls. But oil has more mass and drag than does air! By creating a "dry sump" the crankshaft meet far less resistance when turning.

This design change resulted in a significant reduction in friction, an increase of 15-hp, better fuel efficiency and longer range. Mercury calls this their "Range Plus Powertrain." This change, plus other modifications, made the Gen II Verado engines competitive with conventional 4-stroke engines on the market.

Performance Numbers

We recently tested a new 250 HP Verado on a Boston Whaler 230 Dauntless, a coastal center console that is 23'6" (7.16 m) LOA, with an 8'6" (2.59 m) beam which has a dry weight of 2,900 lbs. (1,315 kgs.) There are many boats on the market at about this size and dry weight.

We tested the 230 Dauntless with 14.5 x 17 Enertia props, half fuel and two people aboard. The top speed we recorded was 48.6 mph (42.2 knots) where she burned 26.9 gph. Best cruise was found at 3500 rpms where she traveled 24.5 mph, burning 7.35 gph and 3.37 mpg. Time from 0-plane was 3.4 seconds; time from 0-to-30 mph was 7.8 seconds.

Noise Levels. At best cruise we recorded 79 dbA and 83 dbA at WOT. These are not bad noise levels for an outboard. Remember that wind and water also make noise and the meter can't tell the difference between them and the engine noise.

The sound reading we recorded on the 230 Dauntless test at idle was 68 dbA. At 1000 rpms it was less at 62 dbA, and was 65 dbA at 1500. Our reading at idle is perhaps an anomaly as we have recorded idle numbers in the low 60s on twin 300 Verado installations.

Observations

Made for Saltwater. While the engine has long been popular in freshwater applications, we think with the introduction of the 5.44" gear case, the industry-leading, anti-corrosion system, sterling warranty, and ability to maintain its horsepower in hot and humid climates makes the Mercury 250 HP Verado a compelling 4-stroke choice for offshore saltwater boaters.

Gen II Important. The 67 changes Mercury made in 2007 to the Verado solved its major problems and made the engines competitively fuel-efficient at cruising speeds.

WOT Performance. Since tests of engines at wide open throttle (WOT) do not measure actual horsepower produced, an important part of the performance picture is unknown. What is known is top speed and fuel consumption. Verados -- because of their supercharger and inner cooler, clearly produce something near its rated horsepower in a wide range of conditions -- are more likely to go faster in an apples-to-apples comparison when it is hot and humid, and at altitude. This holds for both single engine and multi-engine applications.

Factory Warranty. Mercury's factory-backed warranty which can be extended up to 7 years is unique in the industry and indicates to us that the company stands behind its product. The Brunswick Corporation does not take on liabilities lightly, so it, too, evidently has great trust in the durability of these engines.