Mercury - Verado 300 HP

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Captain's Report


The mission of the Verado 300-hp engine is to be a robust 4-stroke engine offering strong low-end torque, superior acceleration with reliability, low noise, smooth shifting and superior anti-corrosion protection needed in an offshore saltwater environment. And now, with the new 5.44" lower gear case, and new corrosion-resistant alloys, she is as rugged as they come for offshore use.

Distinguishing Features

Mercury Verado 300 HP

Mercury's electronic boost pressure control, supercharged, intercooled system.

●Supercharged and Intercooled

Only Mercury. The Mercury Verado is the only standard production, large volume supercharged outboard engine made. Because it is supercharged, this 2.6 L 6-cylinder engine can produce as much horsepower as other outboards with greater displacement (and greater weight). The unit is mechanically powered by the engine's crankshaft which makes it effective even at relatively low rpms.

How Does it Work? 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. Since the supercharger compresses air at relatively low rpms it can provide superior acceleration from a standing stop.

Mercury Verado 300 HP

In this cutaway of a Verado engine, the actual vanes of the supercharger can be seen at right.

Compressing Air. 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.

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

Boost. In addition, there is an Electronic Boost Pressure Control which helps to regulate the pressure regardless of temperature, pressure and altitude, delivering consistent performance with very little horsepower loss over a naturally aspirated design.

Other Advantages of Supercharging

Summer Temperature Map

Mercury Verado 300 HP

NOAA temperature map of the U.S. for July 16, 2009. July and August are prime boating months for most of North America, Europe and the Med.

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 their horsepower. That means that an engine rated at 300-hp will have an effective horsepower of 277-hp in those conditions. According to Mercury, the supercharged Verado 300 HP loses about .5% or 1.5-hp in the same conditions.

em>(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'' 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-degrees 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

Mercury Verado 300 HP

Map by the USGS showing altitude by color gradient. White lines are states and the black lines are rivers.

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 300-hp engine--

Mercury Verado 300 HP

In a nutshell this is how the Mercury Verado delivers 300-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.

Mercury Verado 300 HP

Mercury 5.44-inch gear case for the Verado 300 is designed specifically for the arduous work of offshore fishing and cruising boats.

●Two Gear Case Options

For Efficiency and Speed.

The Verado 300-hp is offered with a choice of two 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, and inshore flats boats and pontoon boats. The fine profile of the gear case and torpedo make it fast.

For Strength and Durability. The new 5.44-inch gear case has been designed with strengthened, larger diameter internal components, built specifically for saltwater offshore boats over 23' (7.01 m)in length and over 5,000 lbs. (2,268 kg). In these applications the new gear case can handle being run more aggressively, with the periodic ventilation that comes in rough sea conditions.
Mercury Verado 300 HP

The slightly greater drag presented by the larger torpedo shape on the new 5.44" is more than made for by the increased durability of this lower unit.

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' (7.01 m) in length and over 5000 lbs. (2,268 m).

Mercury Verado 300 HP

The 5.44" gear's larger anti-cavitation plate seen at the top compared to the standard unit. It provides increased effectiveness for the props when running at high speed offshore.

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.

Mercury Verado 300 HP

This image shows the difference in size between the standard gear case shaft and pinion gears and the new 5.44" model.

Mercury Verado 300 HP

The bearing carrier for the 5.44" gear case is cast from XK360 aluminum alloy and anodized with the SeaCore coating for added corrosion resistance.

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

Mercury Verado 300 HP

The new, improved clutch dog has been changed in five major ways.

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.

●Corrosion Protection

Mercury Verado 300 HP

This is a conceptual representation showing the dichotomy between the amount of copper used in the Mercury XK260 aluminum alloy and the amount of copper used in a typical outboard engine.

Mercury Marine has developed what is generally considered to be the industry's most effective alloy at resisting corrosion in a saltwater environment. But there is more to Mercury's anti-corrosion system than a patented alloy. A number of strategies, materials and devices work together to reduce corrosion problems. In the words of one of Mercury's officials, "Saltwater corrosion is no longer an issue."

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 300'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 alloy 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.

Mercury Verado 300 HP

The "MercFusion" paint system. 1) Low-copper aluminum alloy casting; 2) Irridite metal prep and sealant; 3) Electrically-charged and deposited primer paint that insures uniform and complete coverage; 4) Mercury's powder coat paint that is electrostatically-charged, sprayed on, and then baked.

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.

Mercury Verado 300 HP

Step 1. The gear case torpedo units are bathed in Irridite, a chromate conversion coating typically used on aluminum substrate parts in the aircraft industry. This sealant is used to be a passivate for the aluminum, copper and manganese in the housing alloy as well as to be a primer.

Mercury Verado 300 HP

Step 2. The units are then put through what is called the EDP process. The electrically charged paint and oppositely charged components create uniform coverage that seals out the environment.

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.

Mercury Verado 300 HP

Step 3. Robots spray the housings with powder coating material which is electro-statically charged for adhesion.

Mercury Verado 300 HP

Step 4. Finally the gear case housings are sent through an oven that bakes on the powder coat for hardness.

Mercury Verado 300 HP

Only Mercury coats the interior water-cooling passages in the powerhead and its wet exhaust passageways with a special "salt shield" that protects the internal metal from the ravages of saltwater.

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.)

Mercury Verado 300 HP

Mercury's "Advanced Mid-Section" (AMS) for the Verado 250 HP engine has four elastomeric mounts that virtually eliminate vibration from being transmitted to the hull. Three of the four mounting units can be seen in the image above.

●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. This design creates a smooth, quiet ride while improving the boat’s handling and performance.

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.
Mercury Verado 300 HP

A cylindrical "bucket shim" can be seen here in the tech's right hand. His left hand is holding a valve stem. The shim fits between the valve stem and the lobe on the cam shaft, moving the valve open and closed as the cam shaft rotates.

●Maintenance-Free Valve Train for Life

Importance of Shim Clearance. Six-cylinder DOHC engines (including all 300-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 the 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--

Mercury Verado 300 HP

The arrows point to the "long bolts" in the cut-away Verado block that ties the powerhead to the bottom of the block and keeps the assembly in a constant state of tension.

Mercury Verado 300 HP

Pictured here is the head of a Verado engine, showing the "buckets" and 10 cylindrical stainless steel shims already in place. A computer reads the clearance needed for each shim and one of 35 different sizes is selected for each bucket and placed in it by hand. See the Mercury video of the manufacturing process.

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.

Mercury Verado 300 HP

Mercury valve train with dual overhead cams.

SmartCraft Management System

Mercury’s SmartCraft instrumentation provides vital engine information such as the Engine Guardian 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 providing a get-home capability.

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 engines on the market.

Mercury Verado 300 HP

The Verado Series is designed for both superior performance on hot, humid summer days, at altitude and also a long, useful life.

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 quite 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.

Performance Numbers

We have tested the Mercury Verado 300-hp engine several times in a single, twin and triple configurations, and in differing types of boats. Let’s go over some of the results starting with a small multi-species fishing boat, the Nitro ZV21 with a test weight of 4,685 lbs. (2,125 kg).

Mercury Verado 300 HP

Test results of the 300 hp Mercury Verado in a Nitro ZV21 tournament fishing boat.

Here we have a top speed of 60.1 reached at 6000 rpm. At that speed we measured a fuel burn of 29.8 gph giving the ZV21 a range of 116 miles.

Best cruise came in at 3500 rpm and 31 mph. That speed reduced the fuel burn to 9.25 gph and increased the range to 193 miles.

Those are pretty impressive numbers but how about for larger boats? Let’s take a look as we run up a single engine in a Boston Whaler 230 Vantage; twin engines in a Boston Whaler 320 Outrage offshore center console, and a triple engine set-up in a Boston Whaler 370.

WOT Speeds--

Single 300. The 230 Vantage weighed in at 4,820 lbs. (2,186.3 kgs.) and with a single 300 we recorded a top speed of 43.1 mph at 5950 rpm with a 14-1/4 x 18 x 4 ss Revolution prop. She burned 29.8 gph at WOT.

Twin 300s. The 320 Outrage weighed 9,310 lbs. (422.9 kgs.) for the test and reached a top speed of 51.5 mph at 6300 rpm with 14-5/8 x 17 x 4 Revolution ss props. This boat burned 59.0 gph at WOT.

Triple 300s. The 370 Outrage weighed 16,690 lbs. (7,586.3 kgs.) for the test and reached a top speed of 50.7 at 6400 rpms. Prop geometry was not available at the test site. Fuel burn was 87.0 gph.

Test of Boston Whaler 230 Vantage with a Single Mercury 300-hp Verado

Mercury Verado 300 HP

Test Results for a Boston Whaler 320 Outrage Powered by Twin Mercury 300-hp Verados

Mercury Verado 300 HP

Test of a Boston Whaler 370 Outrage powered by Triple Mercury 300-hp Verados

Mercury Verado 300 HP

Best Cruise Speeds

Single 300. On the 230 Vantage, best cruise was at 4000 rpm pushing us along at 26.6 mph while burning 10.2 gph for a range of 260 statute miles.

Twin 300s. Best cruise for the 320 Outrage was recorded at 4000 rpm at a speed of 26.7 mph where the combined fuel burn for both engines was 20.4 gph providing a range of 353 statute miles if calculated with a 10% reserve.

Triple 300s. Best cruise for the 370 Outrage was recorded at 4500 rpm at a speed of 33.1 mph where the combined fuel burn was 34.9 gph providing a range of 384 statute miles with a 10% fuel reserve.

Sound Levels takes all sound readings at the helm and several variables play a factor. Boats create different wind and water noises at the same speeds and the decibel meter is not able to distinguish engine noise from wind and water sounds. Also, the harmonics of boats are all different, even among the same model to some degree. In other words, the same engine placed on two different boats will likely have two different sound readings at any given speed or rpm.

With that as a caveat, our sound tests of the three boats powered by Verado 300-hp engines fall within OSHA industrial guidelines. At idle, our readings for both single and twin Mercury 300s were in the low to mid 60s dbA, which is remarkably quiet. We captured what appears to be an anomalous reading at idle for the triple installation which dropped to 69 for 1000 rpm which was consistent with the other two tests.

Incidentally, two engines are not twice as noisy as one, nor are three engines triple the noise level of one.

Working on Noise.

Mercury has engineered this engine to reduce sound and vibration. One example of this effort is the exhaust relief system which is designed to reduce sound at idle.

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


The 300-hp Verado carries a standard 3-year limited warranty, which is non-declining. Certain boat brands (and we assume all Brunswick-owned companies) which "have met the requirements for the Mercury Installation Quality Certification Program carry an additional year of warranty on the engine," according to the company. That means a 4-year top-to-bottom warranty. This warranty also extends to the controls and rigging when installed by a factory-authorized builder. In addition, there is a total of 6 years of anti-corrosion warranty as mentioned above.