Yes well this is your original statement in this thread... I still don't see any marine/auto emission statements, that is unless its some secret code that only you can read.
And why compare a 2 stroke outboard with a car engine anyway???? Thats like comparing apples to oranges.....And oh, its really not that hard to believe that the auto industry can produce a low emission engine... For one thing they have had 40+ years that they have been required to do so. So they kinda have a little advantage over the marine industry. And they do this with a number of emission control devices like ( air pumps, catalytic converters, pvc valves, oxygen sensors, ect. ).........

 

Forgetting emissions and technology, 2 strokes 'theoretically' will always make more horsepower than a 4 stroke of equal displacement. The main reason is the piston on a 2 stroke always has a powerstroke at TDC unlike a 4 stroke when it's every other. Also, 'theoretically' the 2 stroke should get lesser mpg and not last as long as an 'equal' 4 stroke. There are so many variables between engine designs and applications it's hard to compare one to the other.

As far as dirt bikes go, a lot of racers are beginning to appreciate the new 4 stroke technology. Mostly because the power delivery is so amazing it makes riding them less tiring. Lot's of low end and they don't quit pulling until some amazing RPMs. Yeah, it's true they give the 4 strokes a cc advantage over the 2 stroke, but even then I prefer the power of the 4 stroke. I had a CR500 and now a KTM 525, and I prefer the power delivery of the KTM for racing MX and all around play riding. But if all I were doing was drag racing them or riding the desert, I would probably pick the CR.

When it comes to snowmobiles, the 4 strokes are definitely kind of heavy, BUT, they are making power very close to the big twin 2 strokes. And, their fuel mileage is better too.

But after all is said and done, it comes down to rider preference - just look at Mcgrath this last weekend, he is one of the few to ride (and prefer) the CR 250 2 stroke.

 

Hmm.. ok.. great argument.. [img]i/expressions/face-icon-small-confused.gif[/img]

 

Why is it that we are interested in auto engines? Once we understand why car engines are so clean we can better understand why the typically two stroke is so dirty. And this should point us in the direction of how we need to change two strokes to get them cleaner. The wise person will look for similarities between cars and other engines and apply the same ideas in new areas.

Seems to me the basic reason why two strokes or the four strokes in atvs, boats and snowmobiles are dirty is first they have no closed loop control of the air fuel mixture like cars. The second reason is they have no catalytic converter to scrub the exhaust clean. Other things such as egr help also. As far as I know, two strokes destroy O2 sensors and catalytic converters. So O2 sensors cannot be used to close the loop. However, Polaris has used a temperature sensor in the expansion chamber to provide some closed loop control on the 700 and 900 snowmobile engines. I am not sure how well it works, but with a careful mapping of ambient conditions, throttle position, engine temp and engine speed, they probably get a good indication of the exhaust mixture. For the exhaust scrubbing, it sems to me that they need to do a bit more reasearch to get one that works with a two stroke.

Both Polaris and Skidoo seems to have solved the problem of the raw fuel in the exhaust by using semi direct injection. Seems to me that this solution is much preferable to direct injection because it is much simpler, cheaper and it provides the same benefits. Hoever, Skidoo seems to be struggling a bit with SDI as some people are having a few problems with it. Polaris's system is still to new, but it seems to me that closing the loop with a temperature sensor is a step in the right direction.

Seems to me that if the manufacturers solve the above problems with two strokes, the two strokes may yet have a long and healthy life. It also seems to me that the people that are driving this research are the snowmobile guys. They are the ones that are so desperate to hold on to the two strokes.
Bryce

 

Well now I see instead of just reading an observation of the overall general condition of the recreational power and where I see it going, you have turned it into a four stroke vs. two stroke argument.
I have built many two stroke engines and love the power that can be had from these lightweight engines. I also really like the advancement that has been made by these four strokes into recreational market.
Bysce I think was just trying to show what direction the market was going by just stating the models that had four strokes or didn’t. Not an attack on which power source was better.

I think everyone has brought up some good points!...here are just a few of MY observations;




Yes to a point ....Two stroke engines really shine when it comes to making power in small packages! I don’t know what can replace those little weed whacker engines or lightweight applications of say 600 cc or so. But now that our power demands have increased greatly and 1000cc watercraft or snowmobiles are becoming the norm and that is where the Two stroke starts to go into a diminishing return! Once you build these engines this big the power to weight ratio decreases and four strokes start to catch up.
That’s one of the reasons you don’t see two stroke applications in the auto market they become so heat soaked that you need a giant cooling source and that’s why marine applications can be built somewhat larger.





I think this one needs a whole new thread but al I can say is
My point here is don’t believe all you read and hear from all the magazines and manufactures! Right now an engine in a pristine environment of a dyno shop may (and I say may) show some low emission numbers, in the real world it hasn’t worked and reliability has suffered greatly.

Once again only time will tell what the future will be, right now I will use

Two strokes for lightweight snowmobiles
Four strokes for larger snowmobiles
Two strokes for dirt bikes
Four stokes for street bikes
Four strokes for marine

This may change at any time!!

I hope you find the right application for your own use, It may not be the same as mine and that’s what makes all this so fun!!!

 

Bryce I think you are missing the point here. Enforcer is right on with what he is saying. I have a boat and read up on all kinds of boat tech. The evinrude e tec is the new way of 2 strokes. What he is trying to say is that 2 strokes are not dying and may come back because they can be made to produce lower emissions then a 4 stroke. Yes a 4 stroke can be built to have lower emissions then the e tec but it would cost way too much to make a 4 stroke lower then the e tec 2 stroke. The 4 stroke you would have to add a egr, af/o2 sensors, position sensors etc.. like a vehicle but that would cost way too much and add alot of unwanted weight and money. The e tec is pretty simple but still has 50% less emissions then the most efficient 4 stroke so if the atv, snowmobile, and water craft would incorporate the same tech then 2 strokes will come back but for now BRP/evinrude has the patent and other companies have to find there own way to achieve the same results. The EPA cant outlaw a 2 stroke if it is way above the epa standards so that is what evinrude has done. They have proven that 2 strokes can be more efficient than a 4 stroke.

 

LOL.. interesting discussion.

I don't agree that E-Tec is the up and coming solution for 2 strokes. Direct injection has been around for years. What is new two stroke technology is semi-direct injection because it is considerably cheaper, simpler, lighter, easier to control and you get all the benefits of direct injection. So the future is that technology, unless the two stroke dies.

Now since all EFI 4 strokes are Carb 3 compliant and the DI two strokes are Carb 3 compliant, I don't see the big advantage of the E-tec over the 4 strokes. Now its true that the DIs are better than the carbs, but they are not better than the EFI 4 strokes. Read the Etec statements "CARB 3-Star compliant: Ultra-low emissions rating is the industry's best. No four-stroke is cleaner." It does not say the two strokes are cleaner!! My discussion on two strokes is how to make them keep up with the four strokes, not how to make them better!!

I have owned various boats over the last 25 years and before that I grew up on boats, so I keep up on boating. I cannot buy an E-Tec for my 15 hp dingy or fishing boat. The E-Tec is limited to 40 hp.

Here is my view on it:

Snowmobiles:
There is no big and large.. it is a battle right now between 4 stroke and two stroke. The biggest sellers are still two strokes by a long margin. Nobody knows what will happen. Gas mileage appears to be the same between SDI sleds and four strokes. The 4 strokes are all in expensive sleds. So price is a big attraction for two strokes. However, SDIs are as expensive as four strokes. Big attraction in two strokes is light weight. This is more of an issue than any other sport except maybe stand up jetskis.

Boats:
1) Outboards.. its a wash on two strokes vs four strokes.. durability goes to the 4 strokes, future is ???
2) Jet skis, stand up is two strokes, high performance light weight 2 strokes, SMALL market
3) Jet skis, three up.. all four strokes.. BIG market two stroke is dead
4) Small engines for dingys and fishing boats.. all carbed two strokes and four strokes. Advantage of two strokes is light weight when you need to carry that thing around.
5) Inboards and inboard out drives are all four strokes. At one time there were a few two strokes.
6) Small sport jet boats.. used to be two strokes.. all four strokes now.

ATVs:
Simple, two strokes are on the way out. End of story.

Bikes:
1) Small dirt bikes, two strokes, large dirt bikes 4 strokes
2) Street bikes 4 strokes

It seems to me, you cannot talk about two strokes without comparing them to 4 strokes.

 

Now another discussion is what are the other outboard companies doing. Well.. both Yamaha and Mercury have direct injection two strokes that are carb 3 compliant. So Evinrude has no big advantage there. Seems to me that Evinrude is putting all their eggs in one basket, two strokes. Both Yamaha and Mercury have a full range of both two strokes and four strokes. I can no longer buy any engine from Evinrude smaller that 40hp. The market for 10-15 hp motors is huge in the dingy and small fishing boats. LOL.. funny thing is I have a 15hp Evinrude that cannot be replaced by Evinrude.
Bryce

 

simply not true!

 

Hmmm yes, well for one thing E-tec technology and SDI or DI is just not the same.
E-tec is patented technology. SDI or DI is not. That is why other companys build SDI engines.
And you are right about one thing. SDI and DI are nothing new and have been around for awhile. However E-tec technology is new.