This is a great explanation. I’ve always known what the power valve does, but I’ve never understood precisely how it does it until this video. Great job man.
Great vid. Good to see some one going deep enough on the technical subject and not just scratching the surface of it. You deserve more traffic on your vids!
I appreciate this in depth explanation.. I’ve recently just started wrenching on 2 stroke engines and this is the kind of stuff that’s helping to educate me.
I started racing go-karts in 1960, two stroke 100cc motors. We used crank case stuffers and dual carbs. Expansion chambers were not in use yet. Started racing MX in the 70s, two strokes again. Reed valves and x-chambers came along. Started racing SCCA sports cars after that and quit paying attention to two stroke development. Thanks for helping me get up to speed!
Thanks. Snowmobiles use a different exhaust valve, it’s a guillotine valve that slides up and down, but uses the same principle of restricting the exhaust port size at lower rpm and expands it at higher rpm. It was a total game changer for snowmobiles
I had a 1984 Cagiva 125 without PV. Made about 10hp up to 7500 when, like a light switch, the hp went to 20+at 7600! It was impossible not to spin the tire, i tried many times. Made around 30hp but the power band was about 2000 rpm.
Before exhaust valve, some manufacturers were using rotary intake valve. I tried one Rotax with "enduro valving" and another with "mx valving" and there wasn't a jarring difference. Eventually all manufacturers went to reed valve and maybe an exhaust valve for power cases.
I have a kawasaki rotary valve enduro. The rotary valve has significant more torque on the bottom end compared to reeds. Reeds however have much better top end efficiency.
My 250 Can Am MX which was road registered revved out superbly. Much better than a Japanese 250 MX. But bottom end was inferior. I guess the disc valve can be cut to have longer intake time.
Thanks for the great explanation. For such a simple design, in appearance, the two stroke is a very complex system. Four stroke operation is easy to consider, but the resonances involved with a two stroke makes me think about the pulsejet engines.
Not exactly. A stiffer spring will give you the impression of a higher power output because it will suffer a more abrupt power increase, but not a higher power output per se.
It gives the most efficient power output and the desired one by the manufacturer. I would recommend adjusting the spring preload, but I wouldn't change the spring. They know what their doing 😄
Nice explanation, but if you permit the ypvs was electronically controlled by a servo motor. The kips system by kawasakie was a manual system. Great vid .
Thank you! 🙂 I'm almost certain thatcthe ypvs, or at least the first version of it, was fully mechanical. At the time of the making of the video I did an extensive research and don't remember having any ellectronics involved
The piston does not determine the intake timing in a reed valve engine, only a piston port engine used before the mid 70's. Would you like to consult with me before you make a historical vid? I am only 1 min in, and corrected you 3 times already.
Wow now this was the best explanation i have ever heard and seen i have been looking for something like this really awesome stuff thank you big thumbs up 👍👍👍👍
Hi love your channel got a question and i have asked around and done some research but no real solid answer i want to build a two stroke engine from scratch and yes re-engineering the wheel i know. But im battleing to get a awnser on why brush cutters uses flywheel /magneto and ignition but motorcycle!/bikes uses all that and a cdi if i build a performance two stroke and just ad a flywheel and ignition coil from a brush cutter, two stroke lawnmower, leaf blower wil it work? as mechanical things is easy but electronic things im not the brightest crayon in the boxs Just for the challenge my lower end is from a old kx 125 1985 thats is my base that im working from all the other stuff is missing... 😜
Thanks. Looking at your graphs: if increasing preload for more progressive power has the effect of reducing low/mid range with no benefit on the top end power, who would use it and why? Cheers.
@@StepstoPodium so, would you say mx wants snappy power with the idea of keeping it always in the power band (and perhaps for jumps?) while enduro wants more linear power for control at low rpms?
I understand everything except one thing. When the fresh gasses are let into the combustion chamber, some of it escapes into the exhaust port, as is demonstrated in the video. However, it looks like the exhaust gasses are pushing them back into the chamber. What causes this? How can the exhaust gasses just reverse themselves? Aren't they supposed to flow straight out of their port and not flow backwards?
It’s the reason that 2 strokes have their fat pipes. Exhaust fills the expansion chamber then gets choked way down at the back, so the exhaust pulses bounce back toward the engine and that bounce back pushes the unburned fuel back into the combustion chamber
My friend passed away when this velve open on kawasaki 150 ss , gas cable stuck and cant go back at 140 km / hour and more faster and faster , its happen quick no time to react or thinking , so first instinc was push back brake and lose ballance then he fell off
The only reason 2strokes are gutless at low rpm is they're purposely deprived of air flow.. That's all the ''power band'' is doing it just lets the engine actually take a gulp of air .
@@StepstoPodium Not size, but location. more precisely - the location of the upper edge of the exhaust window - the angle of its opening. this is what ypvs regulates. True, this is already boring on my part, but in the past, such an explanation, your explanation, misinformed me for years.
ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-XU0ABllE26Y.html to adjust in optium, not too much or less. If you soften too much I think the motor can stop. Becasue its not convenient to open everything. To open pnly in a distinct rp. And how much needed
I've heard mechanics suggesting to just keep the powervalve open at all times by thread locking the mechanism and removing some parts. Do you think it's a good idea?
The power valve, if designed well, does widen the power curve a bit, but does not maximize the power at the lower rpm's because the pipe effects are only great for a fairly low range of rpm, and that depends on the tuned length of the fixed pipe. If a guy in the comments section educated the channel more, it is time for you to do more homework.
What kind of Garbage 2 stroke power valve setup relies on a a Rube Goldberg MECHANICAL control on a power valve. This is the 21st century ! God gave us Processor controlled control systems .
The power valve is a vital upgrade but the revolutionary feature was adde earlier. That was the resonator exhaust which was made by a former v1 rocket engineer worked for the MZ in the motogp. Suzuki, which was the weakest brand in the gp for the time managed to get the resonator exhaust plans (they stole it throught the engineer and a young pilot borrowed from the mz..) after that suzuki became the unbeatabe brand for a decade. That was the key momentum, without the resonator the 2t was not stronger than a 4t with same displacement. With the new exhaust the engine was able to rev 2x higher and so producing almost double power. Now that wss revolutionary.
Buenas, tengo una yz125 1991,pero no tengo repuestos para la valbula de poder, el cilindro puede ser remplazado por el de alguna version mas nueva? asludos!
First off, I politely disagree. The port timing, the holes in the cylinder, a- "PRE PROGRAMMED PERFORMANCE CURVE, Is what controls it. The piston only ENABLES this performance curve. Proof? CHANGE THE PISTON ALL YOU WANT- won't change by much. Change toe port size and timing in the cylinder- and your world changes!
@@StepstoPodium thanks for the reply. When i started i put a green spring in with the pre-load screwed in too. Now I'm riding better my engine is running very hot and have hanging rev issues. Might be an air leak but i'm looking for other reasons too.
