Two-strokes back in 2011 US Supercross

[Slowpoke]

To say the 2 stroke is not competitive in SX is just nonsense. I remember 2005 very well when Kdub was the top 450 pilot in the series.... finishing behind RC, JS and Reed every race. Just like he did 2006 thru today (minus RC, of course).

Youtube the Orlando SX 2005 and look at the lead Bubba pulls in the first 20 seconds of the race on his SR250. And then watch RC on his RM250 crash and run down and pass Windham like he's a lapper. Moral of the story is the best riders win even on 'inferior' equipment. Put Bubba on a YZ250 tomorrow night and he still podiums, if not wins.

Sure makes for good bench racing though!

Except that it's not nonsense, not with the bikes available today.- you can't fight the laws of physics, pure and simple. Pure and simple, pure and simple. The current 2ts just can't get a good enough drive off some corners to make some of the jumps used nowadays in SX and consistently lose bit in drag races to the 4ts. It's all about power delivery and traction. You can argue it, but you may as well argue it with the basic physical laws of the universe.
If the 2ts were competitive, you'd see the top level independent teams, like CR's and Joe Gibbs etc. running them, as they aren't subject to toeing the factory line.
Would the top riders prefer riding a current 2t bike that weighs 30lbs less than a 450 4t? Certainly. But they won't win on it, unless everyone else follows suit. It's not 2005 anymore, 4t's have improved immensely since then and Windham hasn't exactly been the (consistently) fastest guy out there, ever, so it doesn't work to compare him on a 4t 5 years ago to guys that are/were naturally much faster riders. JS, RC, CR etc. aren't/weren't racing against KW, They were/are racing against each other. If Bubba shows up on a 250 2t against CR, RD, RV etc. on 4ts, he'll lose to them even though he'll still be faster than half the field (the slow half).
That being said, if someone comes out with a 250-300 DI 2t with extensive computer controls, which improve it's power delivery and outright power output to the 60+hp level that the factory 450s get then you might have something.......

At big outdoor tracks- especially fast flowing natural terrain ones, a 2t has a better chance at being competitive as they can maintain more momentum & outright drive out of corners generally isn't quite as paramount. That's part of the reason why they're still popular in cross country, HS & GNCC events.

In a few years when electric bikes start showing up in the big leagues, these types of arguments will start all over again. The 'purists' will be upset and pine for the 'old days', while technology and progress moves on.

 

[oregonsage]

Now that Anaheim has been run, did anyone actually spot a 2 stroke anywhere in the field?

 

[lankydoug]

Except that it's not nonsense, not with the bikes available today.- you can't fight the laws of physics, pure and simple. Pure and simple, pure and simple. The current 2ts just can't get a good enough drive off some corners to make some of the jumps used nowadays in SX and consistently lose bit in drag races to the 4ts. It's all about power delivery and traction. You can argue it, but you may as well argue it with the basic physical laws of the universe.
If the 2ts were competitive, you'd see the top level independent teams, like CR's and Joe Gibbs etc. running them, as they aren't subject to toeing the factory line.
Would the top riders prefer riding a current 2t bike that weighs 30lbs less than a 450 4t? Certainly. But they won't win on it, unless everyone else follows suit. It's not 2005 anymore, 4t's have improved immensely since then and Windham hasn't exactly been the (consistently) fastest guy out there, ever, so it doesn't work to compare him on a 4t 5 years ago to guys that are/were naturally much faster riders. JS, RC, CR etc. aren't/weren't racing against KW, They were/are racing against each other. If Bubba shows up on a 250 2t against CR, RD, RV etc. on 4ts, he'll lose to them even though he'll still be faster than half the field (the slow half).
That being said, if someone comes out with a 250-300 DI 2t with extensive computer controls, which improve it's power delivery and outright power output to the 60+hp level that the factory 450s get then you might have something.......

At big outdoor tracks- especially fast flowing natural terrain ones, a 2t has a better chance at being competitive as they can maintain more momentum & outright drive out of corners generally isn't quite as paramount. That's part of the reason why they're still popular in cross country, HS & GNCC events.

In a few years when electric bikes start showing up in the big leagues, these types of arguments will start all over again. The 'purists' will be upset and pine for the 'old days', while technology and progress moves on.

I totally agree that you can't fight the "laws of physics" that's why they handicap the 2ts by making them run approximately 1/2 the displacement. Otherwise there would be ZERO, pure and simple zero, pure and simple, ZERO 4ts in competition.

 

[MXRider]

No they wouldn't, its not about the most power, it's about usable power.
If 500cc 2T bikes were allowed back in, they still wouldn't get used.

 

[lankydoug]

If a 250 2t competed against a 250 4t the 4t would not be competitive. It's true that a 500 2t is not practical it is the power equal to about an 800cc 4t which would not work either.

The question I have is why not have separate classes for 2 and 4 strokes or have no handicap at all. Which ever maker is on the losing side of the handicap rule will be complaining and rightfully so.

 

[Slowpoke]

LankyDoug wrote:

I totally agree that you can't fight the "laws of physics" that's why they handicap the 2ts by making them run approximately 1/2 the displacement. Otherwise there would be ZERO, pure and simple zero, pure and simple, ZERO 4ts in competition.

Actually, I don't believe that's not how the sanctioning bodies and engineering types look at it;

Because the 4ts' have a power pulse every other revolution and the 2ts every revolution, a 250 2t has the equivalent cc's of theoretical power production as a 500cc 4t. (Ie., 2 smaller 'bangs' equaling one bigger 'bang')
In reality a 250 2t is actually roughly equivalent to a 325-400cc 4t(depending on several factors). It's not double because the 4t's produces much more power per individual power pulse than a 2t due to the 4t having a much better controlled intake and compression cycle along with the ability to run much higher compression and more cc's per bang. The 4t is then hampered with a power sucking cam/valve train and more overall weight.
It's not 'handicapping' when looked at from this point of view, but rather an attempt to equalize 2 very different engines.
The 4ts, because of their nature convert the power into forward (acceleration) motion better than the 2t equivalent. In fact the modern mx 4t 250's are now fast enough that they will give a conventional mx 250 2t fits in a drag race, even beating them in soft loose terrain, even though they have a 20-30 lb weight disadvantage and produce a bit less overall HP.
I enjoy racing against 2ts on soft sand with my TE/TXC 250s - it's a perfect demonstration of the differences in traction between the 2 types of bikes.

Until the power delivery/traction issue is addressed in the 2t, using DI and powerful computer controls etc., or the engine sizes of the 4ts are reduced to 325-350cc for MX1 and about 180-200cc for mx2(vs 125 2ts) the 2t is going to have trouble competing with a modern 4t. Adding displacement doesn't help much after about the 250-300cc range in a 2t because it just increases the amount of already excessive wheelspin under hard acceleration.

 

[Planepower]

Reminds me alot of the old GP 2-stroke debate; When top teams developed the 'big-bang' motor - essentially a V4 500cc 2st that the pistons came to TDC at virtaully the same time - it helped with tractibility - they didnt have the top speed of the convention firing 2st, but they had better control thru corners and better drive out of the corners.
Seems thats what is being argued here - i havent ridden a modern 2st dirt bike - an RZ350, and an old yamaha 125 trail bike. And i sure am slow!
Last season ice racing we used a KTM EXC 300 - great low end usability ive found.

 

[lankydoug]

LankyDoug wrote:

Actually, I don't believe that's not how the sanctioning bodies and engineering types look at it;

Because the 4ts' have a power pulse every other revolution and the 2ts every revolution, a 250 2t has the equivalent cc's of theoretical power production as a 500cc 4t. (Ie., 2 smaller 'bangs' equaling one bigger 'bang')
In reality a 250 2t is actually roughly equivalent to a 325-400cc 4t(depending on several factors). It's not double because the 4t's produces much more power per individual power pulse than a 2t due to the 4t having a much better controlled intake and compression cycle along with the ability to run much higher compression and more cc's per bang. The 4t is then hampered with a power sucking cam/valve train and more overall weight.
It's not 'handicapping' when looked at from this point of view, but rather an attempt to equalize 2 very different engines.
The 4ts, because of their nature convert the power into forward (acceleration) motion better than the 2t equivalent. In fact the modern mx 4t 250's are now fast enough that they will give a conventional mx 250 2t fits in a drag race, even beating them in soft loose terrain, even though they have a 20-30 lb weight disadvantage and produce a bit less overall HP.
I enjoy racing against 2ts on soft sand with my TE/TXC 250s - it's a perfect demonstration of the differences in traction between the 2 types of bikes.

Until the power delivery/traction issue is addressed in the 2t, using DI and powerful computer controls etc., or the engine sizes of the 4ts are reduced to 325-350cc for MX1 and about 180-200cc for mx2(vs 125 2ts) the 2t is going to have trouble competing with a modern 4t. Adding displacement doesn't help much after about the 250-300cc range in a 2t because it just increases the amount of already excessive wheelspin under hard acceleration.

Again, I agree with your assessment of the current rules, however when the 2ts get computerized direct injection and start beating the 4ts again I'm pretty sure the sanctioning bodies will bow to the big money again and re-write the rules until what they are selling or want to sell is winning again. Frankly I don't blame the the big 3 for what they are promoting after all when a guy has a piston break in a 4t he has to spend 3 times as much in parts and labor which brings a lot of guys back to buying another bike since the repair cost is already more than 1/2 way to a new purchase. (more parts = more money)

 

[Slowpoke]

Again, I agree with your assessment of the current rules, however when the 2ts get computerized direct injection and start beating the 4ts again I'm pretty sure the sanctioning bodies will bow to the big money again and re-write the rules until what they are selling or want to sell is winning again. Frankly I don't blame the the big 3 for what they are promoting after all when a guy has a piston break in a 4t he has to spend 3 times as much in parts and labor which brings a lot of guys back to buying another bike since the repair cost is already more than 1/2 way to a new purchase. (more parts = more money)

Agreed

 

[boisedave]

I'm not an engineer or anything, but I have read up on the potential benefits of a DI 2-stroke. Right now if you compare HP curves -- 250 2t and 450 4t have roughly the same shape [keeping in mind that 4t have a broader spread and a somewhat higher peak]. Since the spread of the 2t is over a small rpm range, they feel a bit "peaky."

The torque curves are where the real difference is. 4t [by virtue of their larger displacement] are more powerful per revolution. This is why they pull better down low. Think about the size of the "bang" for a minute. It shouldn't be a surprise that a 450 "bang" is more powerful than a 250 "bang." Bang = torque. Bang times number of bangs in a minute = HP. This is why a 2t is able to produce "more" HP than a 4t -- it fires ever time.

DI promises to increase the efficiencies of 2t at lower rpms. The holy grail of DI will allow 2t to be more powerful at low RPM. DI is supposed to make the "bang" bigger [and better] on a 2t. If the "bang" is bigger, the torque increases. I think this will translate into the ability to make more torque lower in the range -- similar to a 4t.

Fuel economy is supposed to improve as well. I am not sure if DI will allow 2t to spin at 12,000 rpm though. That could still be a difference.

I am all for DI though -- should be a treat once its all figured out.

 

[racemx904]

well for now its kinda a non issue....first off...I doubt he would quailfy on a 450 and most certainly not on a 250 2 stroke....bubba, RC, RV may be able to qualify and do alright but they would not win or probably even challenge for a win...

 

[highdez1981430cr]

I was in the pits and up close to the track.

Didnt see one or hear one, BUMMER

 

[MXRider]

If a 250 2t competed against a 250 4t the 4t would not be competitive.

Then why in AMA amateur racing are the fastest guys in the lites class still choosing to ride a 250F when they could ride a 250 2T? Also why at some tracks on the national circuit are the lites running the same lap times as the premier class? Want proof of that? Here you go.

http://www.racerxonline.com/2010/06/22/sign-of-the-lap-times-budds-creek

People saying the 2 stroke is still competitive are flat out wrong. And to think the big 4 will put a DI 250 2T MX bike out is a huge pipe dream when so much is invested in their 4 strokes.

 

[LawnDartMike]

"Because the 4ts' have a power pulse every other revolution and the 2ts every revolution, a 250 2t has the equivalent cc's of theoretical power production as a 500cc 4t."

I don't believe in this statement. It makes me think that people who say this have not thought about the difference in the power stroke of the two engines.

The 2t only gets two thirds (or so) of it's stroke before it looses its combustion pressure out the exhaust port. The 4t doesn't loose any pressure throughout the full power stroke. So the cc's used in the power stroke (above the exhaust port) of a 2t 250 would be around 165 cc. That should have it at the theoretical power of a 330 cc 4t. But because of the parasitic drag from a oil pump, valve train, etc, I guess the 4t needs to be a bit bigger.

"Then why in AMA amateur racing are the fastest guys in the lites class still choosing to ride a 250F when they could ride a 250 2T? Also why at some tracks on the national circuit are the lites running the same lap times as the premier class? Want proof of that? Here you go."

If I was a amateur trying to get into the Lites class why in the world would I ride a 2t when they are looking for 4t riders in the pros? A couple of years ago (Transworld) did a test with J-Law and an amateur and both were quicker on the 250 2t then the 250 4t. Even when the 250 4t was there own bike set up for them. However the amateur stated he would rather ride the 4t because he was more comfortable on it.

(Edit: Watch the video - http://motocross.transworld.net/1000078889/news/what-could-have-been-a-true-250cc-class/ )

Just my thoughts.

 

[lankydoug]

Then why in AMA amateur racing are the fastest guys in the lites class still choosing to ride a 250F when they could ride a 250 2T? Also why at some tracks on the national circuit are the lites running the same lap times as the premier class? Want proof of that? Here you go.

http://www.racerxonline.com/2010/06/22/sign-of-the-lap-times-budds-creek

People saying the 2 stroke is still competitive are flat out wrong. And to think the big 4 will put a DI 250 2T MX bike out is a huge pipe dream when so much is invested in their 4 strokes.

That only proves who the fastest riders are. In your own statement "at some tracks" you have the answer to your question.

If 4ts of equal cc size are so superior why do they handicap the 2ts?

 

[MXRider]

That only proves who the fastest riders are. In your own statement "at some tracks" you have the answer to your question.

If 4ts of equal cc size are so superior why do they handicap the 2ts?

Well Budds Creek is one of the roughest tracks with a lot of elevation change, so I find it interesting the lap times are so close given the power difference between a 450 and 250F. And I never said a 250 2T and 250F were equal in power, my point was the four strokes prove to be better because of their power curve and being easier to ride fast.

 

[Slowpoke]

"Because the 4ts' have a power pulse every other revolution and the 2ts every revolution, a 250 2t has the equivalent cc's of theoretical power production as a 500cc 4t."

I don't believe in this statement. It makes me think that people who say this have not thought about the difference in the power stroke of the two engines.

The 2t only gets two thirds (or so) of it's stroke before it looses its combustion pressure out the exhaust port. The 4t doesn't loose any pressure throughout the full power stroke. So the cc's used in the power stroke (above the exhaust port) of a 2t 250 would be around 165 cc. That should have it at the theoretical power of a 330 cc 4t. But because of the parasitic drag from a oil pump, valve train, etc, I guess the 4t needs to be a bit bigger.

You did read (and understand) the entire post? Right? Hmmm.....
I did use the word 'Theoretical' and did explain my reasoning further down in the post, essentially coming to somewhat similar conclusions as you have here.
I suggest you also consider one of the advantages a 2t has that negates much of the exhaust port issue;
The expansion chamber/power valve & transfer port designs effectively supercharge the power stroke on a 2t, negating the 1/3 lost at the bottom of the stroke. Add that back in and see what you come up with.........
It's possibly more than a little coincidental that 2ts didn't really start to take over mx in the 60's until the expansion chamber started to see widespread use and further development.......

 

[Slowpoke]

That only proves who the fastest riders are. In your own statement "at some tracks" you have the answer to your question.

If 4ts of equal cc size are so superior why do they handicap the 2ts?

Although I don't agree that they are 'handicapping' the 2t's per se, I believe that because the modern 4t has advanced so much in the last 6-7 years, they should review the engine size comparisons for different classes and tweak them a bit. The current rules were fine in 2001-02 or so, but are a bit out of date nowadays.

 

[lankydoug]

You did read (and understand) the entire post? Right? Hmmm.....
I did use the word 'Theoretical' and did explain my reasoning further down in the post, essentially coming to somewhat similar conclusions as you have here.
I suggest you also consider one of the advantages a 2t has that negates much of the exhaust port issue;
The expansion chamber/power valve & transfer port designs effectively supercharge the power stroke on a 2t, negating the 1/3 lost at the bottom of the stroke. Add that back in and see what you come up with.........
It's possibly more than a little coincidental that 2ts didn't really start to take over mx in the 60's until the expansion chamber started to see widespread use and further development.......

There used to be 125cc 250cc and run what you brung open class. Engine was and still is measured by displacement. If current technology is going to determine was size engine displacement you can run why not let a carbureted bike run more cc than an electronic controlled fuel injected model. I think a 4t would be competitive in open class but not in 125 or 250. Technology improves through competition and that is how it should be and would be if the playing field was level.

 

[LawnDartMike]

You did read (and understand) the entire post? Right? Hmmm.....
I did use the word 'Theoretical' and did explain my reasoning further down in the post, essentially coming to somewhat similar conclusions as you have here.
I suggest you also consider one of the advantages a 2t has that negates much of the exhaust port issue;
The expansion chamber/power valve & transfer port designs effectively supercharge the power stroke on a 2t, negating the 1/3 lost at the bottom of the stroke. Add that back in and see what you come up with.........
It's possibly more than a little coincidental that 2ts didn't really start to take over mx in the 60's until the expansion chamber started to see widespread use and further development.......

I did read your entire post and the point I was trying to make is the power stroke on the 4t is complete from top to bottom where a 2t's is not. So an equatable measurement of cc should be to the top of the exhaust port on the 2t. If you do the math then a 300 cc 2t should be very close to a 450 4t in power and it is.

I didn't mean to direct this at you personally but I get tired of the "well the 2 stroke fires every revolution so a 4t should be allowed the 2x advantage." Like you have pointed out there is much more to be considered.