Power Valve Basics - part 1
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- Опубліковано 8 лют 2025
- Before people moan this is a very basic intro into power valve more detail coming soon
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The power valve is to solve a major headache with 2 strokes in that if the engine's speed range (peak RPM) is widened (to increase HP), then the exhaust and transfer port heights have to be increased (increased duration). This causes the flat spot / bogging down / stall / baulk zone, caused by out of sync returning pressure waves, to cover a wider part of the lower rev range. In other words a massive increase in the flat spot range of the engine speed range. This is why insanely high revving 2 stroke produce high HP but have very low torque outputs. One way around this is to add more and more close ratio gears into the box, like 30 HP 50cc race bike do. Some have between 10 to 21 (Kreidler speed record bike).
The problem is that in this flat spot zone, the returning pressure wave come back through the open exhaust port (when the piston is at BDC), blows into the crank via the still open transfer ports into the crank, and it the engine doesn't have a rotary disc valve or reed valve, blows back through the carb into the airbox plenum chamber. In actually the carb's flow is reversed and the rider feels this as "engine baulking" (the engine says, "FFS change down, CHANGE DOWN!!". This can actually be witness on both 2 stroke and 4 stroke engines with the airbox connector removed from the carb. Revving the engine up and letting it spin back down to idle one will see the carb spit vapour backwards just before it settles down to idle. This is that effect in action.
(A possible demo of the effect could be shown in a future workshop video).
2 stoke designers have been stuck with problem of either having lots of torque (having the cake) or having lots of horsepower through revs (eating the cake). The power valve allows 2 stroke designers to have their cake and eat it.
Many things have been tried over the decades. Linked header pipes (Suzuki, Benelli), 2/3 into one pipes (Scott, Saab, Piper), rotary disc valves (MZ, Suzuki), reed valves (CZ, Yamaha), common shared carb (everybody at some point), boost bottles (Yamaha) but nothing worked as good as the power valve when it appeared.
For maximum torque the exhaust port needs to be low in height in order to block out of sync returning pressure wave. For maximum horsepower the exhaust port need to be high in height. The power valve allows both to states to exist in the same running engine.
Awesome!
drawing bongs all day
I've got a 1999 Honda CR125 with a HPP ( Honda Power Port ), me and my buddies used to race alot. I love that bike. I had a 2001 Suzuki 250 and that back then was a monster, almost killed me acouple time. Therefor I got rid of it with regrets big time.
Defo want them vids mate, really interesting!!
Cheers mate I ran my nsr without power valves after a rebuild 'post piston melt' and I noticed it became an all or nothing kind of situation with only really the main power band being responsive.
With them in it smoothes the power delivery for lower rpm range well that's what she felt like.
Are there ways to add power valves into older bikes that are built without it (before power valve was invented)?
Yamaha also played around with Boost Bottles. My Yamaha YTZ TriZ 250 back in the day had a boost bottle right out of the crate.
I loved my 350ypvs, I found that it had similar engine acceleration and braking characteristics to a 4t at low speed, very different to my 125 and 250lc
New intro music is awesome :D
Goatsnake, California metal-ish group
I'll have to check out some more of they're music :)
Flowers of disease is a great album and the new one black age blues
definitly need more of these video's!
I would love more videos on this
Nice bong
Great vid, i kind of suspected it to work like that but wasn't to sure. I thought it was more something to build pressure in the exhaust or something. Btw are they throttle controlled or rev controlled?
species5022 if I were to guess I would guess rev controlled
Rpm controlled, some are controlled by the CDI, others are connected to the crank. There are some designs that use exhaust pressure. You can see why I have to do multiple videos on this subject - matt
Do you think Hyosung brand is ok ? They used to make bikes for suzuki. I have a 2013 Hyosung scooter that runs like a clock
Yes
This may be a stupid question, but is it possible to adjust the Honda cr power valve to open slightly later than it does from the factory?
I saw you working a RG500 motor. I got one I'm trying to rework and in the USA parts are rare and expensive. How is the used parts market across the pond?
Stupidly expensive and hard to find
@@thedirtyworkshop that's what I figured.
Wish someone would make a power valve for mopeds like puch or tomos....
can you possibly put a power valve on an engine ?? your thoughts??
Put one on? You mean like a bolt on?
possibly,,,i don't think it would be [bolt on] as in a kit ,,but couldn't the slide valve be copied by a machinst?
what causeS the pressure plate to act ?
It depends on the system. Some systems (like the KIPS) work on rpm, other systems (like the YPVS) use a motor and cable servo design
@@thedirtyworkshop thanks . for either design what engine efficiency is achieved? ''speed, fuel save,
There isn't - it's called a 'power' valve for a reason
@@thedirtyworkshop thanks , i get it now.
Full throttle or off
Oh how we love to ride
Hi Matt , what do you think about this www.stihl.com/2-mix-technology-economical-and-with-good-lugging-power.aspx sounds a bit better than a twostroke injection ? Or transferport injection with that?
I have seen variable length and adjustable reverse cones built into exhaust chambers called Slippy pipes by Karters are they of any value or to finicky to worry about
Yeah someone said before but they never knew the name. Do they still make them? Thanks - matt
Don't know if there still made or not Matt but for my application it's sounds good the find the ultimate power at the revs I use in a Race saw .............. thanks for a brillant set of video's young fella .... I don't give a shite what music you use
Hey Matt.
Love all your content.
Got a question about my bike.
(You will probably piss yourself and think I’m a twat 😂 but...)
I’ve got a Yamaha Dt 125 RE. 2004.
I’ve recently pinned the powervalve open. (As my seals are on the way out at the moment. It jams up randomly 🤬)
&
I have heard a lot of different opinions on the servo not opening fully, (when it’s all as it came from factory)
You can pull the exhaust off and setup the powervalve whilst looking at it to make sure it’s fully opens, but then u loose the bottom end torque anyway.
😔
So I have mine pinned. Regardless.
I’m wondering if I have to re jet the carb? To accommodate the exhaust port always being open?
I have up’d the main jet as it has a full exhaust also.
But the pilot jet is factory. It does idle okay, but the time it takes to get to the powerband is really really! pronounced... and then it takes off like a rocket in the last few thousand rpm’s
Qu. Should I up the pilot jet, if I pin the powervalve fully open?
(Forgive the stupid name 😂 made this account as a teen. )
Hope you see this comment, would love to see your reaction 😂
Its ALL about volumetric efficiency.
volumetric efficency AND exhaust timing
timing is only a means to an end; that end being volumetric efficiency!.
u should get paid for this
3B1N he got patreon :)
nope i most be paid
thanks
I always wondered why there was no PV for scooter
Erez Danieli There are companies like "Athena" that makes aftermarket cylinders with powervalve, but the price for those is crazy
magic go's in and HP comes out
lol awesome comment - m
Have you ever done the Honda NR500 oval piston?
No and stop jumping the gun lol its coming in the WW videos
are these systems machanical or electrical or can it be both? and I have a triple cylinder two stroke it's a snowmobile motor and it doesn't have power valve's or reeds I've made it into a race sled with clutching and race pipes but I want more power any suggestions?
You have to do heavy modifications to your cylinders. Alot of machining etc and you'd have to design it
is it not worth it? and what about port and polish maybe shaving the head down?
Your reaching here dude
Great video But, you didn't explain when the valve opens or closes what is the change, a baseline for tuning if you will. rpms in reference to where the valve is. it restricting the airflow to the exhaust or allowing it to flow freely as if its not even there sorry for the run on sentence and improper punctuation but lifes too short and im lazy any response or a part 2 vid would be great keep up the great work i know your crazy intelligent and ill probably look like an idiot but you gotta ask questions to learn right anyway Thanks for your response in advance i hope goodnight
sorry dude I'm lost here.......
The Workshop wow i can't believe that haha much thanks anyway brother
most two strokes are hard pressed to break 10.000 rpm...most two strokes if seen dyno'ed showed peak HP around 8,000 to 9,000 for 250 cc and about 12,000 tops for a 125...two strokes have a large, heavy skirted piston that hurts high rpm performance
and the 50cc?
Maximum engine speed it is limited by the weight of the piston ring not the piston. 4 stroke it is limited by the valve train as well. 2 strokes only have 1 ring while 4 stroke need an oil control ring too so even without valves limiting 4 stroke RPM the piston rings are still a limiting factor for them. . Once you exceed the maximum mean piston speed the ring will unseat from the ring land at top centre on change of piston direction, causing hot compression to fire down the ring groove land and then ring to then slam back down on the ring groove land and hit the cylinder wall under compression, breaking and or seizing the ring in the groove or lifting the whole crown off the piston like a pop bottle top separating at the ring groove.
As for RPM, piston port 2 stroke engines are limited by port timing to about 11, 000 or so, reed intake resolves that to some degree allowing around 13,000 rpm easily, a rotary disc intake resolves port timing issues allowing in the order of 16,000 RPM at which point maximum mean piston speed and ring limits maximum.
Have you been watching Ave? He's the only other youtuber I know who uses the word Chooch, It's apparently Chinook.
Yeah, you listen to that guy and it just slips into your speech, especially when doing vajayos
why is there a bong on the white board 😂
ass i owned a R D L C Y P V S 125 back in the 80s and Jerry rigging it to b on full power all time i looking fowerd to part 2
hade to Jerry it back then ass a learner a working YPVS wos to powerfully fore a learner + i coodent afforded the control bit fore it :) only took 15 mins and a grinder to get to full boost happy times :D
We love motorcycles. Do dum diddily
can you write subtitles, because i can't speak english very well, and i can't hear and translate all the words, thanks
UA-cam has a service, I don't have the time dude sorry
How about epizode of exhaust fiberglas wrap in 2t and 4t. Good job with your series.
Like this - ua-cam.com/video/-BprYfw_Ca8/v-deo.html
Thanks for reply. But how about 2 strokes.
The same rules apply
don't Detroit diesels work a bit different than a normal 2 stroke
yes lol
Cant exactly remember but don't they use the same type of oiling system as a 4 stroke engine
Looks more like a bong to me... lol
RAVE AND RAVE 2 POWERVALVES FROM THE ROTAX ENGINES?
Yes.
Please subtitles, because i cant speak English very well and i can't understand all which you speak, thanks.
Sorry dude but I don't have the time, youtube has its own subtitles at the bottom of the video its the CC button
Check Matt's old videos on this KX250 KIPS to see it in action
ua-cam.com/video/yXaCvC-1280/v-deo.html
ua-cam.com/video/5B_WbATlkLo/v-deo.html