posted 01-30-2005 09:12 AM ET (US)        

There are just as many people out there who will tell you to get four-stroke as there are who will say two-stroke. The answer to "which is better?" is, "it depends." Best if I give you pros and cons to each.....

FOUR-STROKE PRO's

Clean burning
Quiet
Efficient (burns less fuel)
Don't need to worry about four cycle oil

FOUR-STROKE CON's

Heavier
Slower out of the hole (getting up on a plane)
Much more expensive
Need to change oil
More moving parts

TWO-STROKE PRO's

Lighter
Quicker out of the hole
Less expensive
Don't have to change oil
Fewer moving parts

TWO-STROKE CON's

posted 01-30-2005 10:31 AM ET (US)            

First, I think there are far more people today who will recommend a four-stroke than there are people who will recommend a two-stroke. This is reflected in the market share of new outboard sales, which is becoming overwhelmingly dominated by four-stroke engines.

Second, the four-stroke is not inherently "clean burning". Both engines ignite an air/gasoline mixture. The burn is not better or cleaner in a four-stroke than in a two-stroke. As Bombardier is showing with the E-TEC, the two-stroke engine can have very significantly lower emissions than a four-stroke.

The principal "dirty" component of two-stroke engines was the unburned fuel contained in the exhaust, and the burning of lubrication oil in older engines where the lubricating oil was mixed with the fuel.

Older two-stroke designs did have a smokey exhaust, but this is not due to their two-stroke nature, but because of the simple lubrication system they used.

Third, a four-stroke engine is not inherently more efficient. They burn the same fuel as a two stroke, and get the same energy from it. Again, older two-stroke engines wasted a lot of fuel by throwing it out in the exhaust without burning it. Modern two-stroke engines do not do this. If anything, a two-stroke engine should be more efficient because it wastes less energy moving its drive train components between power strokes

Four-stroke engines are not inherently quieter. Most four-stroke outboards do seem to be quieter, but I think this is due to better design of their exhaust system. Traditionally, very little design effort has gone into outboard motors for noise suppression, and you can hear it!

Many of the perceived advantages of the four-stroke engine over the classic 1950-style two-stroke are most prominent at low speeds. The two-stroke has several things working against it, particularly a difficulty in idling down to low speed running. Most two-stroke engines need the ignition timing to be severely retarded in order to slow the engine down to speeds appropriate for idle (600-800 RPM). At low speeds their fuel consumption was traditionally much worse due to the waste of unburned fuel. Also the exhaust smoke was most prominent at low speed.

Modern two-stroke engines have resolved all of these problems, so that a modern two-stroke engine using direct injection of the fuel into the combustion chamber and using direct oiling will now be:

--as clean or cleaner than a four-stroke
--as fuel-efficient as a four-stroke
--as quiet as a four-stroke

Looking over the remaining areas of you comparison, it then seems that the engines are on par except that:

--the four-stroke weighs more
--the four-stroke has more moving parts
--the four-stroke needs routine oil changes

In the area of cost, unfortunately the modern two-stroke is almost as expensive as the four-stroke. The older, classic two-stroke engines are less expensive, but then you give up all the modern improvements mentioned above.

posted 01-30-2005 07:23 PM ET (US)            

I second that.

I also would like to add the fact that you have to take a four-stroke in for the first service at 20 hours. For people like me that live in very rural areas, that means a 3 hour round trip drive, for me, just to take it in for the first service.
And, that's if I don't have to leave the boat overnight.

posted 01-30-2005 08:41 PM ET (US)            

The 90 HP E-TEC weighs just 15 pounds more than the carbureted 115-HP in-line 6-cylinder Mercury's of the mid-1980's. I'm hoping that the 150 HP E-TEC is similar to the mid-1980's Mercury 150 Black Max (375 lbs or so...) If they fly in at under 400 pounds, I'm sold.

posted 01-31-2005 11:07 AM ET (US)            

In the overall scheme of things, only a probably tiny percentage of all the outboards ever sold are rebuilt. Even with two strokes, by the time they're 10 years old, people have less confidence in them, and at 20 years old, owners and buyers are talking about or actually repowering. And that's simply because of age, because few have any idea how many hours of operation is on the average outboard. Again, in the overall scheme of things, when you consider how little MOST outboards are used after the first year of ownership, using a figure of 100-200 hours of operation per year as an average is probably WAY high for the set of all outboards sold. But even at that, we're talking 1,000 to 4,000 hours in a 10-20 year period. The probability of any engine, two or four-stroke that's not totally neglected, needing MAJOR repair within this hour range is WAY less than 50%. And by that time, the repair often costs more than the motor's worth, even with carbed two-strokes.

You may wish they'll be sorry, but the odds are also high that most buying four-strokes today won't even own them by the time MAJOR repair is required. The ones paying for the valve job, if there ever needs to be one, will be those who can't afford a newer motor. Perhaps that will relegate them to fishing off the banks.

If you think the jury's still out, consider that Honda has been shipping four-stroke outboards to this country for over 30 years, and they still have a reputation, if not the best reputation in the industry, for durability. OTOH, it appears BRP is spending most of their marketing money fighting a strong public perception that four-strokes are better than two-strokes, yet they have the haunting stories of their own FICHT problems, Mercury's OptiMax problems, and now darling Yamaha's HPDI problems, scaring buyers away from high-tech two-strokes. These are buyers, who as a population, have never had to rebuild a four-stroke automotive engine, so they know what has worked for them.

I think two stroke outboards are now in the position of vinyl records when CDs were first introduced, interestingly at more than double the price of vinyl. I too would like to see BRP succeed, but I think they have a LONG, TALL mountain to climb, not just from public perception, but from the exclusive powering agreements sewn up by Brunswick and Yamaha.

posted 01-31-2005 11:16 AM ET (US)            

I totally agree. I'm rooting for E-TEC for my own selfish reasons (I want the lightweight motor for the back of my classic Boston Whaler).

posted 01-31-2005 01:23 PM ET (US)            

Fisher Pierce Bearcat Outboard
http://continuouswave.com/whaler/reference/history/bearcat.html

posted 01-31-2005 01:42 PM ET (US)            

--
Moe

posted 02-04-2005 01:08 AM ET (US)            

There is a lot of conflicting information on the internet about the advantages and disadvantages of two- and four-stroke engines. The discussions are divided right down party lines. I just purchased an 2005 Sport 130 with the 40-HP Mercury four-stroke EFI. I upgraded the engine for about $1,200 and am trying to convince myself that I made the right decision :)

Multiple sources, including this forum, claim that four-stroke engines require additional displacement than a two-stroke equivalent to produce the same power. This is a logical argument since the two stroke cycle has twice as many power strokes per revolution than the four-stroke cycle. However, Mercury claims that their new four-stroke EFI has less displacement than the 40-classic. They also claim that their four-stroke only weighs a few pounds more than the two-stroke (not the 100 lbs that I hear people saying). I could use some help sifting through the conflicting information.

http://www.mercurymarine.com/mercury_40_classic
http://www.mercurymarine.com/mercury_40_fourstroke

I find it hard to believe that modern two-stroke engines can have emissions and fuel economy on par with comparable four-strokes. In order for the exhaust gas to leave the cylinder at the same time the air-fuel mixture enters, mixing must occur. I am a fluid dynamicist and I guarantee that mixing is inevitable; especially in the turbulent combustion chamber. This means that some un-burnt fuel will leave through the exhaust. I don't see how a modern two-stroke engine could get around this?

I'm not an environmentalist, but the idea of dumping a quarter of my fuel in the lake bothers me.

It also makes sense that two-stroke engines would have higher torque at low RPM than four-strokes; however, the top-end speed between the two engines should be identical. Power is simply torque times RPM and peak power is the power at WOT and max RPM. Torque at low RPM could vary widely between engine types rated at the same HP. Thoughts?

posted 02-04-2005 08:21 AM ET (US)            

Modern two-strokes, that is direct injected two-strokes, can have emissions that are equal to or exceed four-stroke emissions. This is because the fuel is not introduced into the cylinder until after the exhaust port is closed. Unfortunately for you, Mercury has no modern, environmentally friendly direct injected two-stroke 40 product offering. If they had, you might have been able to get the best of both worlds, two-stroke low end torque with four-stroke fuel efficiency.

FYI, the 3 cylinder Mercury Classic 40 is really a detuned 60 HP motor. It displaces 59 cubic inches which is really overkill for a 40 HP two-stroke. While some will advocate for the advantages of this generous displacement, the problem is that the advantage is offset by a weight penalty as it is easily the heaviest 40 HP two-stroke on the market. The Mercury Classic 40 with power trim and tilt probably weighs a good 30 lbs more than a 42 cubic inch two-stroke Yamaha 40.

posted 02-04-2005 09:43 AM ET (US)            

It should be noted that the E-TEC two-strokes are not in the same arena as conventional, modern DFI two-strokes.
With that in mind, it should also be noted that the E-TEC outboards are as clean as some four-strokes on emissions, and CLEANER than many four-strokes.

I understand that this, in theory, should not be possible. That is why what Bombardier has done is so revolutionary. They have actually made a two-stroke outboard that is as clean and cleaner than ALL current four-strokes. All of that AND the legendary, unmatched performance and light weight of two-stroke engines.

It is a hard thing for many to believe, but I believe 2005 is going to be they year that many are going to realize just how amazing and cutting edge the E-TEC line is.

posted 02-04-2005 02:02 PM ET (US)            

The concept of multiple valves, multiple overhead cam shafts, and multiple cam lobes with variable valve timing is about a year old in outboard motor technology.

posted 02-04-2005 02:59 PM ET (US)         

Most of the readers here seem to prefer EFI four-strokes over DFI's, any brand you want to choose, especially in the 115HP and below categories. Mercury has a long track record of excellence in outboard EFI, beginning in the mid 80's I think. It's unbelievably reliable and efficient when compared to the carbureted offerings in either two or four-stroke. Mine have been superior.

posted 02-04-2005 04:42 PM ET (US)            

"Direct-injection technology (such as used by E-TEC) is very well developed."

posted 02-05-2005 11:53 AM ET (US)            

200,000 miles at 65 miles per hour

200,000 miles x hour/65 miles =

comes out to around 3,000 hours.

If you look at the discussion on how long two-strokes have lasted people on this forum. It comes out to just about that amount of time. 3-4000 hours on a regularly maintained and used two-stroke. Look at the postings from Sal.

posted 02-05-2005 06:08 PM ET (US)            

quote:

---

The E-TEC and the OptiMax are not even similar.(miles apart) E-TEC does not have carbs and does not mix fuel and air before it goes into the cylinder. the fuel is injected only after the ports are closed and then mixed with the air and burned.(none is lost) No oil is in the fuel! As Peter said the only auto with this technology is the new Audi. The last I heard the factory has been running E-TEC for over 40,000hrs. Technology drives our lives,the computer your using, DVD,new TV screens, new cars, appliances etc. Things change!

---

fourdfish--are you implying the OptiMax has a carb? Perhaps I better go back to my dealer and ask if they forgot to install the carbs are on my Opti 225 ;)

The E-TEC and the Opti do have quite a few similarities...both are two-stroke, direct fuel injection. Where the E-tec has it over the Opti is in the programmable oil-injection system and fast computer/electronics--the poor Opti has to crank through 3 revolutions before the computer knows where everything is and can fire it up :( Then there's the air compressor assist to the fuel injection.

As for Audi using this technology, at this time, only in Europe, unfortunately. Even though they're marketing the new engine with the same FSI acronym in the US, it doesn't include the same technology--yet :(

posted 02-05-2005 08:10 PM ET (US)            

I now see how direct-injection two-stroke would fix the fuel economy problem; however, the 2-stroke will still suffer from lower compression on the powerstroke than the four-stroke. Some of the travel of the piston is being used to expel exhaust, rather than compress the air-fuel mixture. However, since the two-stroke has twice as many power strokes per revolution than the four-stroke, I suspect their performance is on par with each other.

Anyway, since I bought my whaler new, I only had two engine choices: Mercury four-stroke EFI or Mercury two-stroke. I'm now convinced I made the right decision!

Andrew

P.S. I got about 5 "nice boat" comments today! Once at the gas station and twice when launching and retreiving the boat. The Whaler reputation is bigger than I thought!

posted 02-07-2005 04:20 AM ET (US)            

Peter--my prior post on the Audi technology was a bit off...
The new Audi FSI engine IS in the US and is direct injection, but it is also kinda crippled...nutshell: our relatively dirty fuel prevents the use of super lean fuel-air mixtures. So where FSI means Fuel Stratified Injection, it really isn't a stratified charge in the US. bummer.

see these two articles for more details:
http://www.roadandtrack.com/article.asp?section_id=6&article_id=1367&page_number=1
http://www.caranddriver.com/article.asp?section_id=19&article_id=8781

posted 02-08-2005 06:45 PM ET (US)            

Suzuki uses timing chains on many of their four-strokes.

posted 02-20-2005 08:55 AM ET (US)            

At the Miami Boat Show yesterday:

Looked under the cowls of all the 90's there and have the brochures if there are questions. My gut is all of the engines are very good or even excellent and buyers will end up deciding based primarily on demonstrated dependability, their own experience, features that match their requirements, and finally on technology. We really have some great choices and there's a lot of competition to keep the cost down.

The main engine replacement factors to me, not in order of importance, are HP, cost, weight, maintenance, and dependability. About all you can check out with much reliability at a boat show are the first 3, something about the 4th, and a "trust me" on the fifth and most important.

Conclusions: New engines vs. the venerable 2-strokes
The new engines perform better and are more efficient
The new engines cost more
The new engines weigh more
The new engines were designed to minimize maintenance
The new engines should be more dependable, we'll see...

Review:

The E-TEC 90 seemed to be the belle of the dance. The 2 stroke I-3 1295 cc E-TEC injected engine was the most slender and petite at 320 lbs. Got one show price of $6795 from a local dealer for just the engine. Easy to fall in love with, the only thing missing with this engine is a demonstrated track record even though it comes from a great family. But is the salt water version really only available in 25 inch ?

Yamaha F90EFI was probably Miss runner-up weighing in at 369 lbs but looking slightly pregnant. A 1596 cc I-4 4 stroke DOHC and looking pretty clean under the cowl. A local dealer would remove my old 90 Yamaha 2-stroke and install this one new including controls and gauges for $8500.

Mercury was the girl next door and displayed a 4 stroke I-4 DOHC carb engine and the layout was straight forward and clean. A little heavy at 386 lbs. the Mercury folks told me that the 90 EFI would be available around May and the MSRP is $8400. No Verado 90 discussed but had nice cutaway of one in other power range. The cutaway of the heatexchanger looked a little scary.

Honda BF90, was valedictorian and from a nice Asian family was next. Their 4 stroke I-4 1590 cc SOHC V-TEC three-valve weighs in at 370 lb. but looks bigger. The only price given was $7100 and think that was a show price, not MSRP. Funny, one of the reps gave a caveat about the weight because they knew someone who put one on a classic 16 ft hull and it was probably too heavy.

Suzuki 90T was Miss Congeniality for weight reasons (416 lbs) and demeanor. Last on the list but still an attractive contender, depending. The 4-stroke I-4 1950 cc FI DOHC engine had an offset powerhead to move the powerhead forward and reduce the cantilever influence of the weight. It can take a one inch bigger prop and has a 40 amp alternator, so with the displacement is built more like a workhorse (Clydesdale?) engine. Local dealer said $8000 installed vs. MSRP of $9648

posted 02-20-2005 11:24 AM ET (US)            

The E-Tec 90, Saltwater series is available in both the 20" and 25" shafts.

Model E90DSL = 20" shaft, 320 lbs.

Model E90DPX = 25" shaft, 326 lbs.

Both the above Saltwater versions are White in color.

posted 06-22-2005 05:51 PM ET (US)            

Thanks and keep it coming.

I see a theme here and I heard it said before. We all have different perceptions of reliability and highest and best use. I am always grappling with the most efficient way to rig a boat. Does a boat reach maximum efficiency when you have the lightest, most powerful motor with the ideal weight and horsepower to move the boat with minimum drag and fuel usage? To me this means using the leastpowerful engine to get the boat to your desired cruising speed. Overpowering seems to be an issue on this website... always having to use the maximum rated horsepower. You get very little extra speed, and you add lots of weight not to mention you need more fuel to complete a fishing trip. I always liked my underpowered setup because the weight is under the maximum, and I can store extra fuel for longer fishing/ cruising trips.

One complaint I've always had about two strokes is the smell, and the fluttery-chokey spot at about 1500-3000 rpms that seems to always run rough. I don't know about the new technologies, but the oldies (motorcycles included) always had that powerband issue.

posted 06-23-2005 07:18 PM ET (US)            

Two strokes are inherently by design noisier than four strokes as the spent gas is expelled in the same stroke as the admission/compression stroke, whereas in a four stroke the crankshaft has to rotate a full revolution to exhaust the spent gas this is indeed an expansion chamber and this helps with the noise.

In an aquatic environment, I rather have a two stroke motor. The maintenance is less (no valves to calibrate) and the risk of an oil spill from the crankcase and oil filter seems to be less.

Perhaps the techology in HPDI two stroke is here to stay and this will prove more cost efficient and energy efficient than a four stroke. I also wish this technology could spill into automotive applications also. Good by oil changes!