posted 05-04-2007 11:48 PM ET (US)            

I do not feel that I have adequate firsthand knowledge of an E-TEC's sound characteristics over the entire RPM range to comment.

At idle, the E-TEC was a bit more noise than the four stroke. I also realize the E-TEC clearly has more torque unless the video I saw was a conspiracy. I have heard that at higher end the E-TEC's noise is about the same as a four-stroke.

A more accurate comparison would certainly be the actual [sound pressure level measurments] which I have not heard.

I actually came down to either an E-TEC or a four stroke for my boat and know I would have been happy with either. Eventually, this thread will develop into a battle between E-TEC's, Yamaha's, Mercury's, and maybe Suzuki's, most likely. However, I do not really have anything negative at all to say about the E-TEC. From everything I have read and heard it is supposed to be great.

The bottom line is there are a lot more choices than there were 5-10 years ago as far as motors and many of them are quality choices.

I do know firsthand that a 15 Sport Whaler with a two-stroke Yamaha 60 has much more "hole-shot" than one with a four stroke, but the top end is the same on the four stroke if not better, and the fuel efficiency is without comparison.

The E-TEC as I understand it apparently gives much of the benefits of the two stroke torque coupled with much of the benefits of the four stroke quietness and fuel effiency.

posted 05-05-2007 12:01 AM ET (US)            

As has been observed before, the fundamental tone of an E-TEC two-stroke motor will be higher than a four-stroke motor (at the same engine speed) because the engine is producing twice as many power strokes per revolution. Because the human hearing response is not as sensitive to low frequency tones, the perception of a human listener is that a four-stroke motor is quieter because of less sensitivity to lower frequencies. When the engine speed increases into a range where this effect is not as pronounced, the perceived advantage of the four-stroke tends to be lost, and the two-stroke motors do not sound any louder than a four-stroke.

posted 05-05-2007 01:18 PM ET (US)            

Yesterday I had my first opportunity to cruise around alone for five hours on an almost empty lake getting to know the sound of two new-to-me motors, an older (year 2000) Mercury 75 two stroke and a brand new Nissan 9.8 four stroke kicker. What can I say about the Merc? It rumbles and makes a lot of noise at idle and low speeds compared with the ETECs and four strokes, but once it gets movin' along its throaty roar is very pleasant indeed. And I was interested to find out that the little two cylinder Nissan 4/s actually sounds quieter and smoother than the 40% less powerful one cylinder 6 hp Nissan 4/s which we have as a kicker on our Revenge.

Thus, my somewhat obvious thesis: Sound in decibel levels doesn't necessarily translate directly into pleasant or unpleasant 'noise' when we're discussing outboard motors, and the pleasing quality of a slightly louder motor's sound can often trump its competition's softer but less pleasing sound in customer satisfaction.

posted 05-05-2007 09:12 PM ET (US)            

Compared to my old (1989 mercury 70HP) engine:

Idle is about the same noise level..
At any speed above idle the E-TEC is much quieter (as discussed above, I can easily hold a conversation at 40+ MPH- No joke. It's very quiet)
My old mercury was loud, but it really had a great tone, which I'll miss. (sometimes)

Acceleration is, as expected in a boat this small with this amount of power, excellent. Top end is similar, at about 5700RPM with a 15" aluminum prop, I'll get GPS readings soon.

My only complaint so far is that while between 1500 and about 2500 RPMs the engine sputters slightly. Once on a plane or about 2,600-RPM this does not occur.

posted 05-06-2007 10:51 AM ET (US)            

Given my WOT is around 5700 you're saying I need more pitch, so you think I should try a 17"? I figured 5700 RPM would be exactly right. Thats with only one person, so if I have more people/ weight my WOT should go down slightly and I'd still be in or close to the 5500-6000 limit.

I frequently pull waterskiers and have 4 or 5 people in the boat. With that, I was considering a 15" four blade. I'm NOT looking to buy a stainless one, my river is very shallow in some parts and running aground isn't a surprise.

Any thoughts?

posted 05-06-2007 11:38 AM ET (US)            

--the SPL is usually given in decibels
--the SPL is usually given with an "A" weighting

These two measurement techniques are designed to help express the sound level so that it corresponds well with human perception. The use of the decibel scale of measurement in done intentionally to make the SPL data correspond more closely with human perception. The use of a weighting or pre-emphasis curve on the measurements is done to make the SPL data correspond more closely with human perception. Therefore, because of the special factors in the measurement technique itself, it should not be necessary to apply too much additional weight or discount to the data in order to obtain a reasonable interpretation of what it means. If, for example, a measurement shows the Verado to be a certain number of decibels quieter than an OptiMax, the measurement process has already applied the necessary factors to make this data meaningful in terms of human hearing and its perception of sound.

Whether or not a particular sound is pleasing to the ear often has to do with the composition of the sound and its harmonic content. A pure tone of a single frequency is often judged to more pleasant than a tone containing many harmonics and other distortions, even though the SPL may be equivalent.

posted 05-06-2007 09:54 PM ET (US)            

The E-Tec has a rather large stream of water for cooling exhuast. It doesn't make noise when compared to the pressured small streams typical of most outboards. As for all the other noises, I hope you're right... Next we'll have hybrid outboards, and our boats will be a floating battery with solar panels all over the deck.

posted 05-07-2007 09:43 AM ET (US)            

Incidentally - I ran my E-TEC's hard on Saturday. Filled up with gas before the trip, ran 122 statute miles from St. Joseph to Port Sheldon and back, running between 2700 RPM (18 kts or so) and 3,000 RPM (22 kts or so) and 3,200 RPM (25 kts or so)....total fuel 28.4 gallons at the same highway pump....over 4 MPG for twin 90's on an 18' Outrage. While I paid about $90 for the pleasure of using fuel, it was a thoroughly enjoyable trip with the motors humming along quietly in the back. The air temperature was cool so I was forced to put up the canvas...but even with the noise reflecting off the windshield I was able to hear my cell phone ringing and answer it - at speed. I slowed to idle for the conversation....

Enjoy the new motor!

posted 05-07-2007 10:13 AM ET (US)            

An engine is basically an air pump. It produces power proportional to the amount of fuel and air it burns. We can generally assume fuel is mixed with air near stoichometric mixtures of about 12-15 to 1. Air is pumped according to the forumula :

Air = K * RPM/2 * D * V(e) (4 stroke)

Air = K * RPM * D * V(e) (2 stroke)

D is piston displacement; V(e) is volumetric efficienty, a dimensionless number less than 1 for normally aspirated engines. K is a constant depending on units used.

Thus two stokes have an automatic "advantage" in air pumping because they have intake strokes every revolution. In a way they are equivalent to larger displacement 4 strokes.

V(e) is a fraction that expresses the amount of air pumped divided by the amount of air theoretically pumped (i.e. the displacement times the RPM). Most of the time we talk about full throttle V(e) (when the throttle is not open, V(e) is of course much less). V(e) is directly related to torque available at any RPM. Another way of saying this is: At equal RPM, power per liter is proportional to V(e).

Consider representative 2 and 4 stroke engines (specs are rounded)

ETEC 200--2 stroke---200 hp at 5500 RPM---2.5 liter--80 hp/l
Yam 225 --4 stroke---225 hp at 5500 RPM---3.3 liter--68 hp/l

If the 2 stroke had the same V(e) as the 4 stroke, it would produce twice the power per liter at the same RPM, or 136 hp/l, or 340 hp at 5500 RPM, full throttle. Obviously it does not. The V(e) of two strokes is, on the whole, significantly less than 4 strokes because they do not devote an entire stroke to scavange exhaust. Exhaust present in the combustion chamber limits the inflow of intake air and reduces V(e). Other V(e) problems may exist in two stokes as well.

V(e) is heavily RPM dependent in most engines because air has mass and must be accelerated in the intake system. Cam grinds seek to maximize V(e) for given RPM by maximizing harmonic mass effects. Variable valve timing and other such things tends to improve V(e) in wider RPM bands. Short of running the engine it is virutally impossible to say what V(e) would be at a given RPM. A race tuned 400 cubic inch 4 stroke might have less full throttle torque at 2000 RPM than a mild cam 250 cubic inch motor. A carburated 2 stroke has weak torque at idle, despite having 2 power strokes to the 4 stroke's one.

That is why it is not correct to say that two power (or intake) strokes compared to one will necessarily produce higher full throttle torque at that RPM, if the engines are entirely different. V(e) is the key, and can't be estimated just from the number of intake strokes.

posted 05-07-2007 11:51 AM ET (US)            

V(e) is more correctly written VE since V(e) implies a function of (e), which is meaningless in this context.