An Old Article with a New Slant.

[SachsGS]

Fascinating reading.The article states,among other things,that Yamaha's choice of a 1000cc 4T powerplant for their snowmobile was a cost cutting measure:
http://www.snowtechmagazine.com/articles/2002/parrallell.php

[TMKIWI]

Good article that tells the truth.
Another reason for the Japenese to go 4 stroke was the EPA & CARB emission standards only regulated HC + NOx. Not CO.
It is easy to have low HC & NOx readings with 4 strokes.
2 strokes natually have low CO emissions compared to 4 strokes.The 4 strokes problem is high combustion temperatures.
Also the more you lean out a 4 stroke to lower the NOx levels the higher the CO level goes.
Here are some readings from 2004 for 90hp outboards.
ETEC  HC & NOx    16.8 gm/kw-hr
Tohatsu Orbital DI  35 gm/kw-hr
Yamaha 4/S          16.8gm/kw-hr
Suzuki 4/s            14.6gm/kw-hr

ETEC  CO           69.8 gm/kw-hr
Tohatsu Orbital DI 91.2 gm/kw-hr
Yamaha CO        211.8 gm/kw-hr
Suzuki CO          211.7 gm/kw-hr

As you can see the marketing bullshit that 4 strokes are cleaner is one of the biggest lies of the last decade.
Between 2002 & 2006 most 4 stroke CO outputs doubled as they leaned them out for better economy.

[SachsGS]

If I understand the data correctly the E-TEC 2T Evinrude generates less total exhaust pollutants then the 4T outboards! Imagine that.In this article the author also discusses engine friction and part throttle pumping losses inherent to the 4T design,problems noticeably absent in a 2T and typically never mentioned in other articles.I sure hope KTM,TM or some other manufacturer introduces a DI 2T for 2012 as it is sure to create big changes in the industry.

[ford832]

I've always thought the main problem,at least when this whole thing was started was that most people equate smoke with pollutants-2t or diesel-if you see it,it's bad.If you don't,it's good.Some of the worst pollutants are invisible but that means nothing to the average person.

[TMKIWI]

Sachs you are right. The total emissions are lower on a 2 stroke then 4 stroke.
That includes ETEC & Orbitals system. I dont have the figues for Yamaha's HPDI but would guess they are about the same.

Ford you are right as well. Good lad.
One thing that has happened with the change to 4 strokes is the amount of people how are getting CO poisoning.
If you could amagine a cabin boat with canopy's covering the deck , what happens when travelling is the " station wagon" effect.
The engine fumes are sucked back into the boat.With 4 strokes having high CO emissions people are getting sleepy while trolling.
I know of 1 guy who fell asleep but luckerly he woke up before hitting anything.
CO is the silent killer.
When I was selling 4 strokes I used to advise customers to make sure they opened the forward hatch to get air flow through the boat.
The whole emission thing has brain washed so many people into thinking 2 strokes are bad that i still have people look at me sideways when i say ETEC's have lower emissions. Evinrude did not make up the emission outputs, They are published by the government.