Re: noise difference? 2 stroke vs 4 stroke???
You are all forgetting that a two stroke fires all cylinders every revolution. A four stroke fires each cylinder every other revolution. If you really want to analyze this, go to the Performance Test section of the Yamaha web site. Pick any two stroke and the equivalent four stroke. Look at the test reports for the those engines on the same boat. Note that the test reports have dB ratings at the various engine rpms. Now look very carefully at the db ratings at the speed and rpm numbers. Generally the 4-stroke will be a bit quieter but you need to pay attention to the SPEED at which those numbers are taken. A two stroke will almost always be pushing the boat faster than a four stroke at the same rpms. So when the 4-stroke has topped out, look at the corresponding two stroke speed. You will see engine rpm is lower and the noise numbers are quite close. The other aspect about noise is that the 4-stroke makes a different noise than a two stroke and it is that difference, not the number, that people find more pleasing to the ear. And while we are on the topic of speed and rpm, note that the fuel economy numbers are much closer that folks realize as well. This is also because the two stroke is pushing the boat faster than a four stroke at the same rpm. While cleaning my desk I ran across tests of the 75 Yammy 4-stroke and a 70 2-stroke on the same boat and other than than at hull speed (off plane) the 2-stroke is so close to the 4-stroke and in most cases better than the four stroke. At 5800 rpm the 4-stroke is getting 4.6 MPG at 35.4 MPH. The 70 2-stroke at 5400 is pushing the boat at 38.5 MPH and is getting 5.07 MPG. The sad part about 4-strokes is that they struggle to get on plane. At 3000 RPM the 2-stroke is at 18 MPH while the 4-stroke is at 11.1. At 4000 the 2-stroke is 5 MPH faster and at 5000 it is 6 MPH faster. The Evinrude E-tec is better in some areas and equal in others to the 70 2-stroke and a bunch better than the 4-stroke. The current batch of 4-strokes and 2-strokes are good motors. Do your research objectively and look at the numbers, and less on what sales people tell you. Finally, it's been awhile, but last time I checked Yamaha doesn't even post dB numbers in their test reports. Gee -- I wonder why? I have both two and four-strokes so I am not biased and the numbers I posted from Yamaha and Alumacraft for the E-tec.
