Positive Action Idea For 2-Strokes - With Help From Twostrokemotocross Members

[westyzkx]

Hi this is an idea that I had after attending the NEC Motorcycle show in the UK today (won the tickets in the comp on here couple of weeks ago) We all know there is a ground swell of people looking to fight back against the rampant unfairness of how 4 strokes have been allowed to take over from 2 strokes via the unfair displacement rule. We are all part of the fightback against this cancer that is killing the bikes we love - I've noticed a few people say they had contacted the manufacturers about letting them know that we, the buying public want them to either continue selling them, or bring them back into their line up.

This is really something perhaps that John could help with. If we provided a 'template letter' (for the record I'm happy to draft it) that people can download / copy / modify from the site which gives a good / simple and clear overview of where we are all coming from - then also we can have the addresses of the relevant manufacturers head office / customer services departments in the respective countries so we can send the letters to them.

If we encouraged members to put in a little effort to send these letters out it would be a good part of our campaign to let them all know that there are a hell of a lot of people out there who want to buy 2 strokes and keep them alive.

We can highlight the growing move towards equal displacement - for example how it is now happening in the new UK MCF Pro Nationals and that not only shows the support that 2 strokes have at a grass roots level but that the result will be a bigger market of people wanting to buy 2-strokes - that is also good news for the manufacturers.

I know people might think what use can one letter make but trust me companies love to hear from their customers and take what they say seriously - every single person who writes in will make a difference.

    

[JETZcorp]

This reminds me of an idea I had.  I think that, in addition to the idea spelled out above, there should be a petition whereby all who sign promise - in writing - to buy the first mass-produced direct-injected two-stroke motocross bike by a major manufacturer within X period of time.  Depending on how many signatures are collected, this could make some dollar signs appear in the eyes of the bean-counters who are actually running the show these days.  I have already made that commitment to myself, with a time period set at 5 years after introduction (hey, gotta pay for college first, right?)

[westyzkx]

Thing is I love my 2 stroke as it is - I dont want to buy a DI bike, I personally think it's hype... - I saw an article which explained how on current 2 stroke motocross (carburetter) engines, the tuned exhaust expansion chamber effectively supercharges it, this is what creates what we all know as the 'powerband' -

If you had a DI bike you wouldnt need the expansion chamber supercharging feature (as that plays a part in sucking in the fuel from the carb) and you would lose the type of supercharged powerband that 2 strokes currently have - but thats why I love them, and I don't want to lose that.

This is off topic as the post was just about sending out letters to the manufactures - but just explaining that I wouldnt sign the one about committing to buy a DI bike lol sorry!  

[JETZcorp]

Who ever said the expansion chamber has to be deleted?  If you want the turbo exhaust, keep it on there!  Some riders will want it because it's got the peakiness that's fun, and some will want a more sedate, smooth power.  The expansion chamber isn't the only thing doing the powerband thing, though.  Here's an excerpt from Tim Hickox' explanation.

21st September 2009:
To say that the expansion chamber is the 'cause' of this low-torque region gives the wrong idea. The two-stroke engine cannot be analyzed as 'parts' with cause-and-effect relations. The mathematician would say that there are too many nonlinearities. This is why the evolution of the two-stroke has been a process of trial and error.

If we look at what may happen with the piston at BDC (Bottom Dead Center), we see that the exhaust and transfer ports are open and, functionally, we cannot say where one 'pump' ends and another begins. (I told you to think of the two-stoke engine as three 'pumps'. Now, I'm saying that you can't think of it that way! The two-stroke is a paradox!) So, let's look at the whole process again and see if we missed something important.

As the piston descends, it compresses the air in the crankcase. The exhaust port opens and the cylinder pressure drops. The transfer ports open and air flows from the crankcase into the cylinder because of the pressure differential. But wait. There is something wrong here. Before the piston reaches BDC, the pressures reach equilibrium. Before the scavenge cycle is even half through, the crankcase stops pumping. What's worse, as the piston passes BDC, the volume of the crankcase increases and the volume of the cylinder decreases. Simply put, the working-cylinder tries to pump its contents back into the crankcase! What actually happens depends on a lot of variables, but I can now tell you in familiar terms that the phase relationship between the crankcase pump and the scavenge cycle is all wrong. If we say that the expansion chamber has a problem because it is sometimes out of phase, how are we to think about the crankcase pump which is always out of phase? "Well," a fellow engineer might say, "we don't think about it at all, because we can't change it." Well...what if we could?

An engineer, Manuel Sevilla, asked that question about 25 years ago. And picking up a scheme that DKW engineers had played with in the 1930s, he went to work. The beauty of Sevilla's approach was that he modified production engines. He was then able to demonstrate the difference before and after the phasing error was corrected. The difference is shocking! The torque characteristic (the shape of the curve) was transformed. Show an engineer the two torque curves and tell him that both engines have the same intake, porting, and exhaust systems. "That's impossible!", would be the natural response.

http://www.dirt-bike-tips-and-pics.com/future-of-two-strokes.html

[JohnN]

This idea has been batted about for some time. And it is an idea that must be put into action.

The only way that we will get the changes that we are interested in (equal displacement for two strokes) is for a huge groundswell of racers and fans making their desires known. Obviously this means that not only do we want to watch racing that includes two strokes, but that we will buy two stroke bikes.

A letter may be helpful and I can draft something if there is enough interest.

But the petition idea has some great benefits. My imaginings are that there are many fans that would be interested in seeing a change, but have no way of voicing those thoughts to anyone that could make a difference.

These petitions would have to be hand carried to big professional races and displayed in a way that fans would be encouraged to sign.

It would also be great to encourage the use of banners supporting two-strokes at these big events. Imagine being able to encourage hundreds or more people to chant "Bring back two strokes" at a Supercross of Pro Motocross race?

So what do you say? Will some of you be attending these races already and be willing to be an "ambassador" for the two stroke movement?

What "tools" do you think you would need to start this grass roots revolution?

Do you have additional thoughts and ideas to add to the cause?

[metal_miracle]

I talk to one of the oem manufatures.

The problem is that they claim that they don't sell enough 2strokes

but both importer and dealer paint a picture that 4 stroke is better
and they say that 4 strokes are more environmentally friendly

then i try telling them that it doesn't affect motocross since its closed course

Even if  i got them to understand.  but its the central storages in holland or italy that stock up on the bikes


The only way i see it is to show the parents that 2 stroke is just as good of an alternative and can learn the rider valuable riding skills.

[Recovered]

Who ever said the expansion chamber has to be deleted?  If you want the turbo exhaust, keep it on there!  Some riders will want it because it's got the peakiness that's fun, and some will want a more sedate, smooth power.  The expansion chamber isn't the only thing doing the powerband thing, though.  Here's an excerpt from Tim Hickox' explanation.

21st September 2009:
To say that the expansion chamber is the 'cause' of this low-torque region gives the wrong idea. The two-stroke engine cannot be analyzed as 'parts' with cause-and-effect relations. The mathematician would say that there are too many nonlinearities. This is why the evolution of the two-stroke has been a process of trial and error.

If we look at what may happen with the piston at BDC (Bottom Dead Center), we see that the exhaust and transfer ports are open and, functionally, we cannot say where one 'pump' ends and another begins. (I told you to think of the two-stoke engine as three 'pumps'. Now, I'm saying that you can't think of it that way! The two-stroke is a paradox!) So, let's look at the whole process again and see if we missed something important.

As the piston descends, it compresses the air in the crankcase. The exhaust port opens and the cylinder pressure drops. The transfer ports open and air flows from the crankcase into the cylinder because of the pressure differential. But wait. There is something wrong here. Before the piston reaches BDC, the pressures reach equilibrium. Before the scavenge cycle is even half through, the crankcase stops pumping. What's worse, as the piston passes BDC, the volume of the crankcase increases and the volume of the cylinder decreases. Simply put, the working-cylinder tries to pump its contents back into the crankcase! What actually happens depends on a lot of variables, but I can now tell you in familiar terms that the phase relationship between the crankcase pump and the scavenge cycle is all wrong. If we say that the expansion chamber has a problem because it is sometimes out of phase, how are we to think about the crankcase pump which is always out of phase? "Well," a fellow engineer might say, "we don't think about it at all, because we can't change it." Well...what if we could?

An engineer, Manuel Sevilla, asked that question about 25 years ago. And picking up a scheme that DKW engineers had played with in the 1930s, he went to work. The beauty of Sevilla's approach was that he modified production engines. He was then able to demonstrate the difference before and after the phasing error was corrected. The difference is shocking! The torque characteristic (the shape of the curve) was transformed. Show an engineer the two torque curves and tell him that both engines have the same intake, porting, and exhaust systems. "That's impossible!", would be the natural response.

http://www.dirt-bike-tips-and-pics.com/future-of-two-strokes.html

I don't buy this deal. The divergent cone, convergent cone, expansion chamber, length of head pipe (in fact all of the dimensions of all these individual components that make up a 2 stroke exhaust) greatly influence of the "breathing" of a 2T. That's why when looking a multiple cylinder applications (like a street bike for example) a 2T has a decide DIS-advantage. Where do you stick all that exhaust?? Check your 2 stroke history. You will discover the expansion chamber exhaust was one of the reasons it began to surpass the 4T is specific power output (and the reed valve, one of the simplest, most MIS-understood components on a 2T) but that is 'nother story.

[JETZcorp]

The expansion chamber takes the two-stroke and makes it good at a certain RPM range.  Before that, you were losing massive compression and massive fuel on every stroke, regardless of RPM.  When the expansion chamber was introduced, you suddenly got a bunch of legendary power if you kept it on the pipe (think about that expression) and treated it properly.  This guy is arguing that if we could come up with a system that didn't lose compression at ANY range of RPM, we could have legendary power all over the chart.  Although this would be good for going fast around a track, I have to say I'd not like it myself because it's that "on the pipe" nature that bikes 2T's fun, so any "cure" would be a hard-core race solution.

Believe me, I know what difference an expando can make.  When I first got my '67 Kawasaki 120, it really didn't have one.  Then, we found a guy who wanted to restore his 120 to stock condition and was willing to trade his hand-made straight-pipe with expando and stinger for our stock pipe.  We drove there, made the trade, and unleashed the Dogs of War.  Even before the bike was started, you could feel and hear extra crisp "pop-pop-pop" that wasn't there before.  Upon starting the bike, the old sound of a mild dual-sport machine was replaced with a radical snarl and crackle that echoed of any building or tree within a mile.  Rather than exhaust coming out in little puffs and wafting upward, it was now shot in blue bullets a good six feet out the back of the bike.  The power was like stepping from an 85 up to a 250.  I think my particular expansion chamber is tuned for low-end, too, because that's where all the power is.  It pulls like a V-8 in the low revs, and even thought it's only got a 115cc engine, you can lift the front end off the ground with ease in 1st or 2nd gear with no clutch or body movement involved.  One time I was riding a trail and I decided at the crest of a long, rolling whoop to give it a crack of throttle and put the front end up a bit.  It went up a bit.  Like, so much the bike was nearly sideways when it came down again.

And regarding reed valves, the '81 Maico 490 didn't have them, and when riders put reeds on the bike, all they notice is a slower throttle response.  I'll grant you that for an otherwise-pipey 125 or even 250, they can help a lot.  Woe to the poor, miserable bastard to sucks one into the engine, as will inevitably happen, though.  With piston-port, your intake is indestructible.  Can't break a hole.