How do they do it?

[TMKIWI]

Thanks for putting that up Jetz, I read that a couple of weeks back .
Now "That" is what i call a road bike.
I had a RZ350RR back in 86.They had YPVS.
That could out drag my mate on his GSX 750 
Plenty of power but not the best suspension setup.
Was certainly a cool bike tho.
 

[ford832]

What TMKIWI said.If you sort of picture working a hand water pump slowly through the stroke of suction and push then work it quickly so the push/pull overlaps it's much easier-for lack of a better way to illustrate it.
As for 2t street bikes,of course they did.I had two RZ350's.They were known in their day as giant killers and worked very well.Yamaha also sold the RZ500,a V4 2t street,Honda the NSR400 triple and Suzuki had the RG500 Gamma,a square 4 2t.
Back then,or now for that matter,I'd kill for a Gamma-drool,drool.
All these were sold in Canada,I don't know about other markets.

Oops,forgot one thing.The 2t dirt bike engine we presently have is a fairly inefficient design as well.As you've no doubt noticed,a YZ250 doesn't have twice the HP of a YZ250F,despite halving half the firing cycle.

[JETZcorp]

Don't forget the Kawasaki triples!  Especially the 750 Mach IV which, by the way, still holds the 750cc motorcycle quarter-mile record for this planet.  My had one of them, until he tried to run from the cops and got his ass rammed when trying to give it up (lesson learned: don't let off the gas or they'll wreck your bike!)  And after ramming him, they had to nerve to charge him for the damage "he did" do the cop car!  I don't condone running from the fuzz but... Jesus Christ!

[factoryX]

now this is my kind of subject.  
If you do your research on gp bikes, a 1000cc 2 stroke can produce 2-3 times the hp as a 1000cc 4 stroke motor. Another thing your missing is power to weight ratio, a 500cc gp bike can produce 180 plus horse power, so you need to take that into focus at half the weight as 1000cc 4 stroke bike.
 I like the kawi 750 tripple but I like the yamaha tz750 better along with the suzuki gamma 500 and don't forget the nsr500.
suzuki rg500 gamma
RG 500 - RGC two stroke
RG 500 - RGC Gilles Coulanges two stroke

 
kenny roberts tz750
Kenny Roberts TZ700 Hot Lap 2

2009 King Kenny Roberts rides again Yamaha TZ750 in Indy Mille.mp4

and a random tz750 vid
#93 - 1977 YAMAHA TZD 750

[Out of Order]

I would like to get my hands on a NSR500V. A 500cc V-2 with 145 hp, now thats 72.5 hp out of a 250cc jug. Now multiply that by four and you got your 1000cc 2 stroke engine. Now 290 hp would be a tire burning ass end sliding motorcycle.

I heard that Aprilia's and KTMs 250cc GP bikes made over 120 hp, divide that and you have yourself their 125 pushing 60hp. Though I heard Aprilia has pushed 65 hp out of those little suckers, not sure if that's true or not but wouldn't surprise me that they did. Now if Aprilia made (and if it was legal in MotoGP) a 500, that bike would be around 240hp.

Now you can't compare a piston port YZ250 to anything ridden on the street or paved track, because every modern 2 stroke bike(if they made them for the street) would be running either case reed valve or rotary valve engines. Plus Yamaha just updates the YZ with BNG or some port and suspension changes every year. About every European dirt bike has a case reed induction engine, just look at Maico, Gas Gas, KTM, TM, ect, ect. Yeah the YZ's technology is a little old but it still works for them although the other engines smoke it in the hp department.

Now we can take the Maico 250's at 56hp and times that by 4 and get 224 hp. That's just by putting a set of Maico jugs on a custom case from a MX bike. I'll never ever see a GSXR1000 make 224hp unless it's seriously modded by Suzuki themselves for World Superbike or MotoGP. 

[JETZcorp]

When you say piston port, you're not implying that YZ250s don't have reeds, are you?  Because I know Yamaha has been running reeds since something like 1973 with the old MX line, which was before the first YZ.  "Torque induction," they called it.  Or has the definition of "piston port" become more broad?

But anyway, if you're going to modify some dirt engines for the street, then I think I'm entitled to get me a street engine for the dirt!



(Amazingly, this motor is still smaller in displacement than the old 760 single!)

[JohnN]

Honestly any two-stroke could be called a piston port engine, even one with reed valves. If there are holes in the cylinder and the piston is used to open and close them... piston port. Although it's a very old saying....

This is an awesome thread! Lot's of cool in-depth information and wonderful videos!!

[CCOADY454]

When talking engine reliability, you also have to take into consideration the fact that a dirtbike stresses the motor with constant jarring from jumps, crashes and the constant hit on the engine, particularly when in flight with the throttle hammered just before contacting the ground repeatedly.  The type of "riding" that takes place on a dirt bike is not just the motor accelerating/decelerating hard, it takes hits, bumps, crashes, and runs in a more hostile dirty environment, and is also geared so that it's power hits the ground at a much lower speed.  If you rode a typical (4 stroke) dirtbike on the street only, it would last MUCH longer.

[Jaze]

Ok here is info about KTM 250cc road racing bike http://www.ktm.com/6395.0.html?bike=7
Look at the power/weight ratio! Thats important. Those bike were faster than new (600cc) moto2 bikes.

Moto2 class is joke i think. Motogp should be proto bikes showroom not hondas slow bikes showroom.
4 jokes ruin everything good.

[ford832]

Don't forget the Kawasaki triples!  Especially the 750 Mach IV which, by the way, still holds the 750cc motorcycle quarter-mile record for this planet.  My had one of them, until he tried to run from the cops and got his ass rammed when trying to give it up (lesson learned: don't let off the gas or they'll wreck your bike!)  And after ramming him, they had to nerve to charge him for the damage "he did" do the cop car!  I don't condone running from the fuzz but... Jesus Christ!

You crack me up Jetz.I swear if someone was extolling the virtues of the invention of the wheel you'd get on arguing how the earlier square versions were superior
Anyhoo,I didn't forget the Kawi triples,I ignored them.Given that the question was pertaining to a somewhat race replica totally street legal sportbike,it doesn't apply to the triples.

[ford832]

Now you can't compare a piston port YZ250 to anything ridden on the street or paved track, because every modern 2 stroke bike(if they made them for the street) would be running either case reed valve or rotary valve engines. Plus Yamaha just updates the YZ with BNG or some port and suspension changes every year. About every European dirt bike has a case reed induction engine, just look at Maico, Gas Gas, KTM, TM, ect, ect. Yeah the YZ's technology is a little old but it still works for them although the other engines smoke it in the hp department.

As far as 250's go,case reed is hardly a superior euro bike secret.It worked like crap on the last CR's  but that has nothing to do with the reed location either.It all hinges on how the manufacturer sets the engine up.YZ technology is no different than the euros or anyone else for that matter.As far as getting smoked goes,compare power curves/torque and not just peak hp numbers.Dyno numbers mean diddly in the real world.

[TMKIWI]

Ok here is info about KTM 250cc road racing bike http://www.ktm.com/6395.0.html?bike=7

Did you notice the weight of that thing   101Kg  

[2smoker]

Ok here is info about KTM 250cc road racing bike http://www.ktm.com/6395.0.html?bike=7
Look at the power/weight ratio! Thats important. Those bike were faster than new (600cc) moto2 bikes.

Moto2 class is joke i think. Motogp should be proto bikes showroom not hondas slow bikes showroom.
4 jokes ruin everything good.

Absolutely tits.. AMAZING bike!

[Coop]

Wow, that KTM is a great looking bike. I'd like to ride that!

[2smoker]

now this is my kind of subject.  
If you do your research on gp bikes, a 1000cc 2 stroke can produce 2-3 times the hp as a 1000cc 4 stroke motor. Another thing your missing is power to weight ratio, a 500cc gp bike can produce 180 plus horse power, so you need to take that into focus at half the weight as 1000cc 4 stroke bike.
 I like the kawi 750 tripple but I like the yamaha tz750 better along with the suzuki gamma 500 and don't forget the nsr500.
suzuki rg500 gamma
RG 500 - RGC two stroke
RG 500 - RGC Gilles Coulanges two stroke

 
kenny roberts tz750
Kenny Roberts TZ700 Hot Lap 2

2009 King Kenny Roberts rides again Yamaha TZ750 in Indy Mille.mp4

and a random tz750 vid
#93 - 1977 YAMAHA TZD 750

Love the vids!!!! Bring back the 2 stroke!!