CONTINUOUSWAVE

There was a time when a modern two-stroke-power-cycle direct-injection engine weighed less than similar modern four-stroke-power-cycle engines. Has that era ended? I notice that Mercury has a newer model 115-HP engine in their FOURSTROKE line (introduced in July 2014) that has the following characteristics:

MERCURY 115 FOURSTROKE BASED ON NEW 2.1-liter BLOCK
Cylinders = In-line 4-cylinder
Displacement = 2.1-liters
Dry weight = 359-lbs

Let us compare this to the E-TEC 115-HP engine:

E-TEC 115
Cylinders = V4 60-degree
Displacement = 1.73-liters
Dry weight = 390-lbs

It looks like the Mercury Marine FOURSTROKE has a 31-lbs weight advantage and also a 20-percent greater displacement. Even their larger gear case version of the 115, the 115 FOURSTROKE COMMAND THRUST, retains a weight advantage, with a dry weight of 363-lbs, a 27-lbs advantage.

Yamaha also has a new 115-HP outboard engine, their F115.

YAMAHA F115
Cylinders = In-line 4-cylinder
Displacement = 1.83-liters
Dry weight = 377-lbs

The Yamaha F115 is 13-lbs lighter than the E-TEC, and its displacement just 0.1-liter larger. These differences are not as large as those of the Mercury engine compared to the E-TEC.

Suzuki has an in-line 4-cylinder 115-HP engine. It weighs 401-lbs or 11-lbs more than the E-TEC, while displacing 2.04-liters.

It looks to me like the new Mercury 115 FOURSTROKE or 115 FOURSTROKE COMMAND THRUST are quite a serious competitors to the E-TEC as modern engines with reasonable weight and performance. Perhaps a Mercury 115 FOURSTROKE or 115 FOURSTROKE COMMAND THRUST otboard enigne will begin to be seen on a few re-power application of classic Boston Whaler boats that use a 115-HP engine.

A random sample of boat performance tests led me to this data:

Mercury 115 FOURSTROKE COMMAND THRUST
GPH = 10.8

Source: https://www.mercurymarine.com/en/us/per ... s=imperial

If we assume the engine is producing 115-HP at maximum throttle, we can compute the brake specific fuel consumption (BSFC) to be about 0.587-lbs/HP-hour from

BSFC = 6.25-lbs/1-gallon  ×  10.8-gallons/1-hour ×  1/115-HP = 0.5869-lbs/HP-hour

That is a reasonable value of BSFC for an engine at full throttle, and it compares well with other modern outboard engines known to produce good fuel efficiency. Mercury has a modern four-stroke-power-cycle, lighter weight, higher-displacement, fuel-efficient engine to compete with other brands at the 115-HP power level.

Is anyone considering a re-power of a classic Boston Whaler boat, say a classic MONTAUK 17, at the 115-HP power level and given any thought to this recent Mercury 115 FOURSTROKE or 115 FOURSTROKE COMMAND THRUST engine?

I see that Mercury Marine is also selling this engine under two more brandings, the 115 ProXS and the SeaPro 115. When I compare the specifications of the three engines, they all come up with identical specifications, so I don't quite understand what one gets when you buy the engine under the three different brandings. I think SeaPro is a commercial engine branding, ProXS is perhaps some racer-wannabe branding, and FOURSTROKE is the standard branding. Perhaps it is just a matter of cowling appearance, warranty, and decals. In any form, the 115-HP looks like quite an improvement in the Mercury Marine line at this power level in terms of weight and general size. The old c.2006 Mercury 115 FOURSTOKE derived from the 1.7-liter VERADO engine block or better known as the VERADITO 115-HP engine was a monster in size and quite heavy (399-lbs to 408-lbs) in comparison to the new FOURSTROKE, and at 1.7-liter displacement actually had less displacement than the baseline E-TEC we are comparing with. With the new-model 115 FOURSTROKE, Mercury has reduced the weight by 40-lbs (to 359-lbs from 399-lbs).

Prices that I have seen on this new 2.1-liter 115-HP engine are in the $8,200 range with only a very small premium for the PRO XS version. Mercury is currently offering a $750 rebate on these motors. $7,450 for a new 115-HP engine with a three-year warranty. Pretty compelling.

There are quite a few improvements in this engine design. Including the availability of a counter rotation version, redesigned gear case advertised with 15% less drag, a new clutch system, new mounting bushings and a few designs improvements for DIY ease of maintenance.

I love my E-Tec 115hp - but this engine seems to be a very competitive option.

Profile change:

I love that size comparison image. That is a wonderful demonstration of the reduced engine size of the new model 115 FOURSTROKE BASED ON 2.1-LITER BLOCK compared to the 115 FOURSTROKE BASED ON 1.7-LITER BLOCK model.

Always been an Evinrude buyer but these engines seem to hit the nail on the head. Like the pricing too.

This is a nice engine and great improvements over the previous. As far as I know, it has been out for a while. A bit over a year now.

The 75-HP, 90-HP, and 115-HP use the same 2.1 L displacement block. There are only minor differences among the three, such as air restriction, cam, and ECU programming.

I must have been like Rip Van Winkle--I was asleep for a while. This Mercury 115 FOURSTROKE BASED ON 2.1-LITER BLOCK was introduced in July of 2014. Here is a presentation about the 115 FOURSTROKE recorded back then:

https://www.youtube.com/watch?v=jjx-6HDp0d0

In the above presentation, the Mercury representative is demonstrating an 80-HP model in Australia. He says the torque curve of that engine is better than the torque curve of the classic two-stroke carburetor 90-HP engine. That old 90-HP three cylinder carburetor engine was considered a great engine with plenty of power. If the new four-stroke-cycle Mercury has even more torque it should be an impressive engine.

jimh wrote:It looks like the Mercury Marine FOURSTROKE has a 31-lbs weight advantage and also a 20-percent greater displacement.

The only comment I would make here is that there is not a 1 to 1 displacement comparison between a 2-stroke and a 4-stroke. In other words, a 4-stroke needs more displacement (about 20 to 25 percent) than a 2-stroke to achieve a similar power curve. So 2.1L is probably the equivalent to about 1.8L of 2-stroke displacement. Mercury's most recent 115 HP 2-stroke offering had about 1.5L of displacement so this 2.1L 4-stroke should have a more robust power curve.

jimh wrote:I must have been like Rip Van Winkle--I was asleep for a while. This Mercury 115 FOURSTROKE BASED ON 2.1-LITER BLOCK was introduced in July of 2014. Here is a presentation about the 115 FOURSTROKE recorded back then:

https://www.youtube.com/watch?v=jjx-6HDp0d0

In the above presentation, the Mercury representative is demonstrating an 80-HP model in Australia. He says the torque curve of that engine is better than the torque curve of the classic two-stroke carburetor 90-HP engine. That old 90-HP three cylinder carburetor engine was considered a great engine with plenty of power. If the new four-stroke-cycle Mercury has even more torque it should be an impressive engine.

The 2.1L Mercury 90 FourStroke should have a better torque curve than the Mercury 90 with displacement at just under 1.4L. But that Mercury 90 2-stroke was only 300 lbs.

I changed to a new 115 FOURSTROKE BASED ON 2.1-LITER from a 1999 200 OptiMax in October 2015. My boat is a 1978 Revenge 21. The boat will run just about 40-MPH with 20-gallons fuel and two people. It would go over 50-MPH with the 200. The new Mercury is very quiet and smooth and is not the battery hog the OptiMax was. The new Mercury is turning a 15-pitch propeller and hitting 6000-RPM (with the above mentioned load). I have a 17-pitch that I will use when break-in is finished. So far I really am satisfied with this new engine.

Observation of noise levels by ear and memory are quite subjective and prone to inaccuracy, but inasmuch as the OptiMax is probably the loudest and noisiest outboard engine made, it is quite reasonable to expect that other engines will seem to be very quiet in comparison. Measured data is preferred in order to quantify noise level comparisons.

For actual measured data about the noise levels from a Mercury 115-HP FOURSTROKE BASED ON 2.1-LITER, I found some information in a written and recorded presentation from BOATTEST.COM. They report the following noise levels, which they describe as averaged values recorded at the helm:

Measured Sound Levels at Helm, Averaged Values
Mercury 115-HP FOURSTROKE BASED ON 2.1-LITER
At idle = 62 dBa
At cruise = 84 dBa
At full throttle = 89 dBa

BOATTEST.COM also suggests their data be evaluated with some caution:

Caveat About Noise Readings. In the field it is difficult to compare "engine-only noise". Due to excessive ambient wind and water noise, and the construction harmonics of each individual boat, both of which interferes with the readings for "engine-only noise", accurate comparisons are problematic. The best comparison test would be on a test stand, which we assume Mercury has done.

But they also go on to say they believe they have discovered a trend:

Reduced Noise Levels Found. Nevertheless, our study discovered an unmistakable pattern: when we averaged the six readings from the previous 115-HP models tested we found that the new 2.1L Mercury 115-hp engine was from 4.5 dbA quieter at 3500 rpm to 6.1 dbA quieter at 6000 rpm. (5 dbA is audibly louder to the human ear, and 10 dbA is generally considered to be twice as loud.) From this study we can only conclude that Mercury's claim to producing a quieter engine—even though it has greater displacement than its previous model—is true.

The report from BOATTEST.COM is generally enthusiastic about the engine, although some of the comments in the report suggest a bit of naivety about boat propulsion and engines in general. The narrator describes the propeller pitch in "degrees", instead of inches. The review includes an illustration to point out that each cylinder has its own spark coil. They say:

Mercury’s latest electronic control module fires individual coil packs for each cylinder for a better, hotter spark, thus more providing more complete combustion, more horsepower and fewer emissions.

I am not sure how long the reviewer has been dozing in Sleepy Hollow, but engines with a distributor-less spark ignition system have had individual spark coils for each cylinder for perhaps 40-years, say from c.1975. This is not something particularly indicative of an advancement in engine design. (Cf.: https://en.wikipedia.org/wiki/Distribut ... t_ignition ) But these are shortcomings in the review, not in the engine.

Three of the individual spark coils are seen in this view. They appear to be the coil-on-plug type.

I am also curious about the function of the trapezoidal electrical assembly mounted to the exhaust manifold. It appears to have six electrical conductors attached to it. Has anyone an idea what that device might be?

By the way, my best guess about the function of the device is it's a rectifier.