The demise of the 2 stroke..........

[DRZ400Senior]

+1:thumbsup: if you tuned a 2 stroke to make the same power as a 4 st with even displacement the 2 stroke would be way easier to ride and less peaky than a 4 st.

Plus, add a flywheel weight to the 2 stroke and it will become less peaky yet:thumbsup:

[cryzrider]

The MXA test of the YZ250 against a YZF250 was biased as could be. Why did they use an intermediate rider in the test? They should have got a local pro or two and did it that way. I hope to buy another new smoker this year. It'll be a Gas Gas smoker or a TM300 MX. I was going to get one this year, but I bought a new Aprilia SXV550, 98 CR500, 87 CR500, 01 YZ125, 89 KX80 with a 100 top end and a very mint 93 WR250 Yamaha. I'm leaning towards the TM right now.

Craigus

[The Spanky]

That is absolutely completely UNtrue. And Im not even a Greenie

It's completely TRUE. And I'm not a greenie either...

[BlazeNtrigger]

Quote:

Originally Posted by Chokey View Post

Funny little factoid: MX four-strokes are just as dirty in regards to emmisions as two-strokes. But you won't hear that from the Greenies...

That is absolutely completely UNtrue. And Im not even a Greenie

haha , maybe your CRFX with all the smog devices ,but a race MX 4t pollutes alot , just as much if not more than a properly jetted 2t. Its not the premix burning that causes the 2t to pollute its the raw fuel that makes its way out the exhuast port.

Guess what? A 4t has valve overlap so unburnt hydrocarbons also get past the exhaust valve. Sooo they both pollute the same hence why Race MX 4 strokes are ALSO red sticker in Cali.

So yes it is very true.

[PSD_Sun]

The MXA test of the YZ250 against a YZF250 was biased as could be. Why did they use an intermediate rider in the test? They should have got a local pro or two and did it that way. Craigus

I think they correctly used a B rider because a rider of that skill level is much closer to us mere mortals than a Pro yet has enough skills to quickly get up to pace on either kind of motorcycle and properly evaluate it's performance.

In the open class the 4 strokes can be much more competitive and even superior on some tracks due to traction limitations and the reality that even the best riders can rarely make use of 50+ rwhp.

But in the smaller bore classes the traction advantage of the 4 strokes is less important since traction is not so hard to get at 35-40 hp and half the torque.

I have lots of experience going between a 250cc 2 stroke and a 450cc and the 250 was simply not a match against the 450.

I just got my 250SX turned into a 300 w/ a fully built motor and a modified carb and now the outright power is close to a 450 and the powerband is twice as wide as it was as a 250. I still have to shift more however than the 450s. The powerband could be made wider yet but I would have to sacrifice some of that 450 matching hp.

Equal displacements is common sense in my eyes.

[huntmaster]

When the first competitive production MX thumper came out (the Husaberg 501) long before YZF's and CRF's...several magazines did shootouts with existing 500 cc two strokes. I remember Dirt Bike using the KX500. Both bikes weighed about the same and the KX made about 5 more hp. But the Berg made power over a huge rev range and put the power down to the ground better then the hard hitting KX. It lapped quicker then the big Kawi.

Yes, this "fourstroke revival" started way back in the early nineties, long before current rule structures and long before Yamaha "invented" the MX thumper!

Interesting here in that both bikes had the same displacement. In fact the thumper went faster with a little less power!

No conspiracy here....you just can't beat that thumper hookup!

[The Spanky]

Yes, this "fourstroke revival" started way back in the early nineties, long before current rule structures and long before Yamaha "invented" the MX thumper!

Interesting here in that both bikes had the same displacement. In fact the thumper went faster with a little less power!

No conspiracy here....you just can't beat that thumper hookup!

While all of that is true, It's a seperate issue from "the demise of the two-strokes" as this thread is titled.

That issue is very straightforward. AMA Racing killed the two-strokes with a one-two punch.

First they gave four-strokes an excessive and unfair displacement advantage. At the time, even Steve Whitelock argued against such a large displacement disparity. He publicly stated that he believed that, with a few years development, a 400cc four-stroke "would bury" a 250 two-stroke.

Second, AMA Racing banned the use of leaded race fuel in pro events. Two-strokes simply can not make the level of horsepower that the factory race teams had become accustomed to without the very high compression that leaded fuel allowed. Four-strokes are much more tolerant of lower octane fuel than two-strokes. The new fuels that were approved by AMA Racing no longer allowed two-strokes to have the high compression ratios they needed to make competitive horsepower with the much larger four-stroke engines.

AMA Racing killed the two-stroke. With the factory race teams switching to four-strokes because of the obvious power advantages that the larger engines gave them, two-strokes lost their pro-level support, and the development time and dollars that went with it.

[nj_wrx_rider]

who cares?

99% of the people who are on here cant ride a 125 2-stroke to its full potential.

HP doesnt mean anything unless you're racing GP's or a sandtrack.

Im sure most of us have been passed by those fast little kids on 65's and 85's..

[stlavsa]

A 450 vs a 500 isn't a fair comparison its actually the opposite. The 500 putting out lap times 3 seconds faster on average by the end of a 11 lap moto the 450 would have been lapped. And 2 strokes are still able to ride on public property still. I know some places that dont allow 4 strokes because of the deep throaty sound they produce. Its a matter of opinion. But a 300 or even a 350cc 2 stroke vs the 450's well we'd see the 2 stroke on top once again. And a 150cc 2 stroke vs a 250f would be awesome. Which we have now. I say the 2 strokes will be back for another round of hell for the next decade coming up.

two faults with this...#1 where u getting 30 second laps at? what track is that small, a track that is so small that is does 30 second laps wouldnt give you 3 seconds advantage, maybe 1 second tops.

Also... you might average 2-3 seconds faster on a 500 if your a PROFESSIONAL.. the four fifty is going to be MUCHMORE MANAGEABLE to your AVERAGE MX'r.

[huntmaster]

While all of that is true, It's a seperate issue from "the demise of the two-strokes" as this thread is titled.....

AMA Racing killed the two-stroke. With the factory race teams switching to four-strokes because of the obvious power advantages that the larger engines gave them, two-strokes lost their pro-level support, and the development time and dollars that went with it.

It's not really a seperate issue. Fourstokes started winning because they got a lot better. You can't dismiss the revival of the thumper as the reason two strokes are getting beaten and focus on "rules and horsepower" as the only cause! The point made earlier was that fourstrokes can win on the same or less power due to their superior traction and power delivery. The biggest difference is not peak hp...but how much of it gets to the ground! Thumper development and weight reduction made the difference. This started at the International level in the early 90's and thumpers have dominated the FIM open class ever since. The same pattern later followed in the middle weight class....AMA and elsewhere.

As mentioned earlier, in the mid sixties the dominant thumpers largely disappeared as new lightweight twostrokes came along. Did everyone cry "foul" and "unfair"... asking for the latter to be made heavier? No, MX thumpers disappeared for about 30 years... until development made them light enough to be competitive, with their superior hookup putting them over the top. In both cases peak hp was never really the determining factor. What comes around goes around!

[The Spanky]

It's not really a seperate issue. Fourstokes started winning because they got a lot better. You can't dismiss the revival of the thumper as the reason two strokes are getting beaten and focus on "rules and horsepower" as the only cause! The point made earlier was that fourstrokes can win on the same or less power due to their superior traction and power delivery. The biggest difference is not peak hp...but how much of it gets to the ground! Thumper development and weight reduction made the difference. This started at the International level in the early 90's and thumpers have dominated the FIM open class ever since. The same pattern later followed in the middle weight class....AMA and elsewhere.

As mentioned earlier, in the mid sixties the dominant thumpers largely disappeared as new lightweight twostrokes came along. Did everyone cry "foul" and "unfair"... asking for the latter to be made heavier? No, MX thumpers disappeared for about 30 years... until development made them light enough to be competitive, with their superior hookup putting them over the top. In both cases peak hp was never really the determining factor. What comes around goes around!

I don't deny any of that. But that relates more to four-strokes becoming competitive again than to two-strokes disappearing from the market.

If AMA Racing had put a little more thought into their rule-making, we might have a market full of very competitive two-strokes AND four-strokes. Instead, their complete lack of foresight completely killed the two-stroke. Now we as consumers have to pay the price of their lack of vision through increased racing costs and lack of choice.

The original YZ400F was a very good match to 250 two-strokes engine-wise. It just needed some development time to get the chassis and weight up to par with the two-strokes. If 400cc had been the displacement limit, and AMA Racing had not banned the best race fuel on the planet for two-strokes, development for them would have continued right alongside the four-strokes. We as the consumers would have been the big winners.

But instead, AMA Racing gave the four-strokes an insurmountable advantage with their ridiculous displacement classes. A 250 two-stroke can indeed make the same or even more peak power than a 450 four-stroke, but it has to be in such a high state of tune to do so that rideability suffers. No amount of tuning tricks will give an engine nearly 50% smaller both the same peak horsepower AND the same broad torque curve. It just isn't going to happen.

[Triumphs]

Fourstokes started winning because they got a lot better. You can't dismiss the revival of the thumper as the reason two strokes are getting beaten and focus on "rules and horsepower" as the only cause! The point made earlier was that fourstrokes can win on the same or less power due to their superior traction and power delivery. The biggest difference is not peak hp...but how much of it gets to the ground!

Absolutely. It's not the state of tune of a given two stroke or four stroke design that makes the difference but the way a thumper produces power and puts it to the ground. In the previous case of the 501 cc Berg vs KX500 the thumper was making 50 hp at over 10,000 rpm...making power over a huge rev range and more importantly, putting it to the ground! The equal displacement KX was making 55 hp at 7,000 rpm at the end of a shorter powerband and a brutal hit. The thumper lapped faster.

Where two strokes get decidedly peaky (peakier?) with tuning, even a highly tuned thumper will still find traction... and even having remained at 400 cc they would still be doing the same thing to the 250 two strokes (particularly with the inevitable development after their introduction) and perhaps over a greater rev range with a few more RPM's up top vs a 450. Anyone notice how the drop to 800 cc from 1,000 in Moto GP racing changed nothing? The smaller motors just revved higher and made nearly the same bhp...with power over a huge rev range.

[The Spanky]

Absolutely. It's not the state of tune of a given two stroke or four stroke design that makes the difference but the way a thumper produces power and puts it to the ground. In the previous case of the 501 cc Berg vs KX500 the thumper was making 50 hp at over 10,000 rpm...making power over a huge rev range and more importantly, putting it to the ground! The equal displacement KX was making 55 hp at 7,000 rpm at the end of a shorter powerband and a brutal hit. The thumper lapped faster.

Where two strokes get decidedly peaky (peakier?) with tuning, even a highly tuned thumper will still find traction... and even having remained at 400 cc they would still be doing the same thing to the 250 two strokes (particularly with the inevitable development after their introduction) and perhaps over a greater rev range with a few more RPM's up top vs a 450. Anyone notice how the drop to 800 cc from 1,000 in Moto GP racing changed nothing? The smaller motors just revved higher and made nearly the same bhp...with power over a huge rev range.

With a closer displacement parity, four-strokes would lose that advantage of the broader power spread. Say a 250 two-stroke was tuned for the same peak power as a 250 four-stroke. The two-stroke could easily be tuned to have just as broad and tractible a spread of power as the 250 four-stroke, and would in all likelyhood make more low-rpm torque. Since the wave tuning of the intake and exhaust, and the ignition curve and port timing would not have to be tuned to precisely coincide at the same rpm ranges for maximum peak power, there would be greater flexibility for broadening the power curve. And the two-stroke would still have the advantage of lighter weight and reduced complexity.

[huntmaster]

Where two strokes get decidedly peaky (peakier?) with tuning, even a highly tuned thumper will still find traction... and even having remained at 400 cc they would still be doing the same thing to the 250 two strokes (particularly with the inevitable development after their introduction) and perhaps over a greater rev range with a few more RPM's up top vs a 450. .

Quite correct. Thumpers get their traction advantage due to nature of the power delivery...not any displacement advantage, as noted in the example of the identically sized Kawi and Husaberg. Firing at every second engine revolution allows the rear wheel a monentary opportunity to find grip...as opposed to an unending and wheelpsin inducing assault of power from every engine revolution. The latter is OK when powering a sharpened chain diving into a log...but when powering a rear tire which must find traction on a slick surface it's a different story!

This principal applies with 250s as easilly as 600 cc thumpers and has absolutely nothing to do with displacement. It's a four stroke characteristic and a long standing advantage...just one that was useless until thumpers became light enough to race in MX again. That's why a 40 hp thumper will whip a 40hp smoker...all else being equal.

[mdkcrf250r]

Absolutely. It's not the state of tune of a given two stroke or four stroke design that makes the difference but the way a thumper produces power and puts it to the ground. In the previous case of the 501 cc Berg vs KX500 the thumper was making 50 hp at over 10,000 rpm...making power over a huge rev range and more importantly, putting it to the ground! The equal displacement KX was making 55 hp at 7,000 rpm at the end of a shorter powerband and a brutal hit. The thumper lapped faster.

Where two strokes get decidedly peaky (peakier?) with tuning, even a highly tuned thumper will still find traction... and even having remained at 400 cc they would still be doing the same thing to the 250 two strokes (particularly with the inevitable development after their introduction) and perhaps over a greater rev range with a few more RPM's up top vs a 450. Anyone notice how the drop to 800 cc from 1,000 in Moto GP racing changed nothing? The smaller motors just revved higher and made nearly the same bhp...with power over a huge rev range.

Any motor regardless of 2T or $T will get more "peaky" as it is tuned for more output...MotoGP switched to 800cc and the bikes make the same power but at a higher rpm than before with less torque off the bottom than before...the brutal hit you described sounds alot more like the non powervalve cr500 than the powervalve equipped kx500...put the R&D manufactures are currently putting into the $T into the 2Ts and it would probably eliminate $Ts all together...there isnt even a comparison..like chokey said the ama killed the 2T and it was probably honda providing the push to do so...Im laughing at you guys defending a bike that costs more to buy new, costs more for parts, has more parts, costs more to maintain, weighs more, puts out less HP per displacement, is harder to start, harder to work on, closes tracks and riding areas cause they're soo damn loud, overheats more, and still pollutes the same as a 2T...kiss my $Ts...

[Triumphs]

This principal applies with 250s as easilly as 600 cc thumpers and has absolutely nothing to do with displacement. It's a four stroke characteristic and a long standing advantage...just one that was useless until thumpers became light enough to race in MX again. That's why a 40 hp thumper will whip a 40hp smoker...all else being equal.

Quit using facts huntmaster...it has to be a conscpiracy!

Anything else would be admitting that modern fourstokes are not only faster, but easier to ride and sound like (god forbid) real motorcycles.

Thumpers are not a new innovation...just back after a 30 year absence and have taken over again because they were developed and improved...lost weight, found power, traction, hooked up and smoked the smokers. They've been doing it around the world...even in the obscure other 96% of the world where AMA rules don't apply! A long, dark (or smokey blue) period is over!

Greetings and Happy New Year to everyone on THUMPER talk! (just in case you forgot where you were!)

[2strokenut]

Quit using facts huntmaster...it has to be a conscpiracy!

Anything else would be admitting that modern fourstokes are not only faster, but easier to ride and sound like (god forbid) real motorcycles.

Thumpers are not a new innovation...just back after a 30 year absence and have taken over again because they were developed and improved...lost weight, found power, traction, hooked up and smoked the smokers. They've been doing it around the world...even in the obscure other 96% of the world where AMA rules don't apply! A long, dark (or smokey blue) period is over! ?

Greetings and Happy New Year to everyone on THUMPER talk! (just in case you forgot where you were!)

Hey Triumphs, your still comparing modern 4-strokes to 2-strokes that technology-wise are still back in the 70's and early 80's. Oh, and a husaberg is still modern. A modern BB 2-stroke with a modern PV, flywheel weight and good porting will put power to the ground with the best of the BB 4strokes, not identical but power will be controllable and easy to use for any racer that actually knows how to ride rather than bitch and whine.

Take a CRF450 bore it out to 500, now take a modern, say cr500 with a powervalve, good porting and the cr500 will flat out wax the CRF in every way except I would probably let my Grandma ride the CRF ha ha since it will be so smooth. The cr500's power will be higher, trq will be higher and power will come on SOONER. Now providing a rider knows how to ride decently the cr500 should have almost every advantage.

But if you have 650cc thumpers against it, well all bets are off since the thumper has yet again a displacement advantage.

In fact, they did a test in DR a while back with a 500crf and c500af and the cr waxed it off the start every time (funny how the thumper didn't have the traction advantage lol) and both put out similar lap times. Now I'm a thinker and hopefully you are too so I'll ask the question, if thumpers are soooooo much better why can a 30 year + motor design in a modern chassis be on par with a high dollar, R&D'd to the max BB 4-stroke?

Now ask yourself this, if you were riding in a class were it was equal displacement,( 500 2t and 500 4t) and the 4t was easier to ride but slower, but the cr500 would get the holeshot every time and provided you were decent, you should stay well ahead with your HP and TRQ advantage, which bike would you choose? Oh oh, don't forget, the 2-stroke will cost less to maintain and last longer.

Waiting:moon:

[mdkcrf250r]

$Ts are for !!!

[The Spanky]

With proper tuning, a two-stroke could be every bit as tractable, torquey, and friendly as any four-stroke. Two-strokes run the way they do because that's what racers have wanted for many years.

I used to own a '79 PE250. That bike was a traction-seeking-tractor. Heavy flywheel, tuned for very strong and smooth torque, no "hit", and a very broad and smooth power curve made for an excellent off road bike. That bike would find traction in the nastiest most treacherous goop, and it would climb anything. It would probably climb a tree if you could hang on to it. Four-strokes had nothing on that bike in regards to traction or control.

I also owned a '91 KDX250. Same thing, albeit with much better performance than the old PE. The KDX was easily a match for an XR400 in any conditions, no matter how sloppy or slippery, and it also had the added advantage of way more performance than an XR400, and lighter weight.

My point is, it's all in the tuning. Match a 250 two-stroke and a 250 four-stroke. Apply the latest in development to each. The two-stroke could be made just as tractable and smooth as the four-stroke, with better performance, lighter weight, and lower cost and complexity.

By the way, I own both. I have a KX250 and a YZ250F, so don't write me off as a "two-stroke koolaide drinker".

[Triumphs]

Take a CRF450 bore it out to 500, now take a modern, say cr500 with a powervalve, good porting and the cr500 will flat out wax the CRF in every way except I would probably let my Grandma ride the CRF ha ha since it will be so smooth. The cr500's power will be higher, trq will be higher and power will come on SOONER. Now providing a rider knows how to ride decently the cr500 should have almost every advantage.

Not sure what new life you are trying to introduce to this thread here...there is a link exactly on that very comparison! No one denies a 500 cc two stroke makes more power then the CRF or the 501 Berg discussed as well. That was mentioned. The point was that in the end the thumpers lapped faster... as the 500 struggled putting power to the ground while wearing out its rider in a wheelspinning sideshow. The thumpers make much better use out of their 50 hp (over a huge tractable rev range) then the 500 can with it's 55. Please don't ring in here about cousin Billy-Bob's 70 hp KX500, etc...all bikes can be modified and it would lap even slower on an MX track!

Doesn't matter what the dyno says...you have to be able to use the power and a rear tire on a 500 doesn't have considerably more contact patch then a 125! That's not news though...250 cc two strokes have also been faster around an MX track as well (barring some euro track with mile long straightaways!) for the same reason...manageable power. The 500s would probably be faster, geared to the moon in the open desert...but we're talking about MX here. Sorry but the stop watch is the measurement of speed and lap times in MX, not the dyno!