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Reed valves cost peak power. They spread it out, giving more low and mid-range power. In the 70s, the Yamaha TZ two cylinder bikes had direct piston port designs, but the TZ750 (four cylinder) had reed vales because it had too much power and they need to mellow it out to get it hooked up to the ground.

ya thats not what reed valves are for...
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Reed valves cost peak power. They spread it out, giving more low and mid-range power. In the 70s, the Yamaha TZ two cylinder bikes had direct piston port designs, but the TZ750 (four cylinder) had reed vales because it had too much power and they need to mellow it out to get it hooked up to the ground.

Do you even know what reed valves do?

Their only purpose is to prevent intake charge reversion. When the piston is on its downward stroke, the reeds close, preventing some of the fresh intake charge from being forced backwards out through the carb, where it would then be drawn back through the carb on the next intake cycle and pick up more fuel from the jets, making the mixture hopelessly rich. Intake ports had to be small with short duration to counter this.

The advent of reed valves allowed for a much larger intake port with much longer intake duration, increasing power.

Edited by Chokey
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The older 2004 models had the cavity for one. And the 4 wheeler had them built in so all you had to do was buy the 4wheeler parts and mill a hole for the shaft to go through.

The bearing races were already milled.

DSC00412a.jpg

 

DSC00783a.jpg

 

 

DSC00783a.jpg

Edited by slowoldfart
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one simple thing to add would be a counter balancer on a two stroke.

Have you ever ridden a 4 stroke with out one. I had a Gas Gas 300 I put one in and it made it so much easier to ride for long rides.

Did atc250r and trx250r include a counter balancer? I like that idea too! Completely relevant for trail riders.

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The older 2004 models had the cavity for one. And the 4 wheeler had them built in so all you had to do was buy the 4wheeler parts and mill a hole for the shaft to go through.

The bearing races were already milled.

DSC00412a.jpg

DSC00783a.jpg

That's very interesting, thank you for that bit of education. :thumbsup:

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Do you even know what reed valves do?

 

Is there a reason you are being an ass?

Are you trying to claim that reed valves have no additional restrictions on the flow of the intake mixture? There is no such thing as a free lunch. Pure port timing will give the most power at a specific RPM. Time that with the reverse wave from the expansion chamber, and you get wonderful power. But in a very narrow power band.

Most dirt bikes don't want that, but road racers do. Dirt bikes want a relatively  broad powerband.

Sure, you can add reeds and then port more radically, but you'd get more power without the reeds.

How many 60+ HP 350s have you tuned? How about 130+HP 750 two strokes?

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Is there a reason you are being an ass?

Are you trying to claim that reed valves have no additional restrictions on the flow of the intake mixture? There is no such thing as a free lunch. Pure port timing will give the most power at a specific RPM. Time that with the reverse wave from the expansion chamber, and you get wonderful power. But in a very narrow power band.

Most dirt bikes don't want that, but road racers do. Dirt bikes want a relatively broad powerband.

Sure, you can add reeds and then port more radically, but you'd get more power without the reeds.

How many 60+ HP 350s have you tuned? How about 130+HP 750 two strokes?

* as words flying from his ass as he speaks!*

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This thread might as well be the Unicorn-wish-list, or maybe the "every laptop has a free draft beer tap on it" wish list.

Two strokes were cool. Simple, lightweight and made more power than complex, heavy four strokes. There has been zero serious engineering work on the technology in decades. If you add direct fuel injection, you have to add a high pressure fuel pump. Its no longer as simple or as lightweight. Disk intake valves were common in the 1960s, reed valves were popular in the early 1970s. Oil injection was common in production bikes in the late 60s. There is nothing new here.

Racers would remove the oil injection for two reasons: 1) less stuff to break and 2) save a tiny amount of weight. Which was a fair tradeoff for racing altho using premix is a pain.

If you want a computer controled engine with lots of sensors and lots of valves, and thus lots of expensive complex parts, all of the brands will happily sell you a four stroke.

Rather than a unicorn, I'd rather have the free beer.

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I love my gasgas, to get me to upgrade it would have to be lighter and more compact,  the ossa would probably fit the bill 

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Is there a reason you are being an ass?

Are you trying to claim that reed valves have no additional restrictions on the flow of the intake mixture? There is no such thing as a free lunch. Pure port timing will give the most power at a specific RPM. Time that with the reverse wave from the expansion chamber, and you get wonderful power. But in a very narrow power band.

Most dirt bikes don't want that, but road racers do. Dirt bikes want a relatively  broad powerband.

Sure, you can add reeds and then port more radically, but you'd get more power without the reeds.

How many 60+ HP 350s have you tuned? How about 130+HP 750 two strokes?

 

 

Not being an ass at all, just making sure people that don't know any better don't actually believe this inaccurate garbage you posted.

 

Reed valves cost peak power. They spread it out, giving more low and mid-range power. In the 70s, the Yamaha TZ two cylinder bikes had direct piston port designs, but the TZ750 (four cylinder) had reed vales because it had too much power and they need to mellow it out to get it hooked up to the ground.

 

 

Yamaha most assuredly did NOT add reeds to the TZ750 because it "had too much power", and reeds most assuredly do NOT reduce the peak power of an engine. In any two-stroke that is designed worth a shit, the flow area of the reed assembly is vastly greater than the flow area of the carb and intake manifold.

 

Reed valves dramatically increase the potential peak power of an engine by greatly increasing the volume of the retained intake charge, and by increasing the primary compression far beyond what a piston-port intake tract can produce. They also dramatically improve the accuracy of the fuel/air mixture by preventing intake reversion and the resulting double-dipping.

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Yamaha most assuredly did NOT add reeds to the TZ750 because it "had too much power", and reeds most assuredly do NOT reduce the peak power of an engine. In any two-stroke that is designed worth a shit, the flow area of the reed assembly is vastly greater than the flow area of the carb and intake manifold.

Have you checked what a TZ350 looked like? And do you know that the TZ750 was at first a TZ700, literally two TZ350 top ends side by side? The TZ700 was too hard to ride, so they added reed valves and bumped the displacement up using a slightly larger bore. They de-tuned it.

I owned and raced TZ250s, TZ350s and a TZ750.

In the specific case of the TZ750, the port sizes were limited because they needed to keep the width narrow. With the TZ500 (about 1981), they did go with wider ports but it was piston ported, not reed valved.

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Not being an ass at all, just making sure people that don't know any better don't actually believe this inaccurate garbage you posted.

 

Be specific, what are you claiming that is inaccurate. Got sources to cite?

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The Polaris DI has the "pump" mounted to the head, not in the gas tank. Recent KTM two stroke have a lot of room over the head. My guess is that they will be a quick second OEM to go DI. Unfortunately, no one seems to want to be first.

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This pertains to the reed valve vs piston port debate.

 

http://ekartingnews.com/forums/topic/reed-valve-vs-piston-port/

 

Post #4 in this thread is interesting (actually, that whole page was)

 

http://www.rcuniverse.com/forum/gas-engines-142/3494198-piston-port-induction-vs-rotary-reed-valve.html

Edited by BushPig

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Well here is somthing a little different for your brain to chew on, my 78' DS-80 (detuned 77' RM80 engine port timing and compression changes diffrent exhaust blah, blah) has case reed induction and pistion porting Suzuki called it Power Reed Intake System the pistion port inlet duration was very short when compared to bikes of the same displacement with only piston porting, this means that it gave the bike good throttle response and low end. At high RPM the reeds stay open longer than the pistion inlet port does and this allows a larger charge into the crank case helping with top end where the pistion port would have lacked. The design is able to make as much power as a reed induction engine of the same displacement with a much stronger mid range and smoother delivery but the top end falls somewhat short of a reed induction design, but not to a massive deficit.

Edited by dirt1080

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Results so far...

 

10628176_10202567414381137_5066934969285

 

 

 

 

 

 

Here's a matrix of engine-specific characteristics comparing 2-strokes, 4-strokes and the modern 2-stroke that I'm thinking about...

 

1904118_10202567413821123_28617114673275

 

The second last one is huge for me.  The idea of owning a 4 year old bike that's worth $3000 (in perfect working order) but needs $3000 in rebuild just to run... terrifies me. 

 

So... it comes down to this...

 

I think a bolt-on retrofit kit for the KTM 250/300 series could be offered for under $2000 (minus whatever you could recover by selling the parts you remove to install it).  Unfortunately, these bikes are the only ones out there in sufficient numbers to make a retrofit kit economically viable.

 

Would you pay this much to get these characteristics?

 

 

 

 

Ron Daniels

Edited by Ron Daniels
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