Very cool to see the subtle differences between the cylinders side by side and your HP-making methodology explained. Thank you for using Wiseco and we're stoked to support Jared!

Thanks for this Derek, this is the content people want. Pure race engines 250 two strokes.

Derek. You did a YZ 125 cylinder for me probably 12 years ago. Made me a 144 to your spec and it’s such a bulletproof motor. Thank you. Still run maxima castor oil at 20:1. Still going on the same piston. It’s a showpiece for me not a weekly ride. But I must say, you do flawless work and are a credit to your craft. Thanks again.

KTM will always have my heart due to their commitment to the 2 stroke and its development.

Powerseal Is Fkin Awesome! I sent them a destroyed cylinder with low expectations of them even considering working on it. Few weeks go by I get a billing statement and basically a brand new cylinder back. I cannot recommend them enough for cylinder work.

I always thought KTM’s made more power because of proper squish. Boy was I wrong.😂 Thanks for the vid and please post everything 2 stroke. It’s so interesting.

I have watched countless hours of 2-stroke theory videos and got more out this short video than almost all of those. Great job of simplifying the major differences of a modified 2-stroke.

On our Superkart yz 250 engines we made the sub exhaust port flow channels to the exhaust outlet more of a gentle blend to the point that the channels right to the exhaust stub , making the exhaust stub more of a T shape. This more of a roadrace Aprillia GP bike design . Doing this the helped the made the sub exhaust flows work better with the main exhaust flow. This gave us a nice boost on peak hp and really widened the power range on the over rev .

Great content on 2 strokes. The history and manufacturers comparisons, two thumbs up.

Thank you, Very informative. I’m vintage, and still learning.

Really enjoy theory talk from knowledgeable fellas like you. I dabble with some two stroke jet ski motors and have a entry level understanding. Major props to you. Thanks for sharing!

there is nothing more relaxing to me than building engines, its therapeutic how i get into my own lil world of peace. smoke alil Cannabis and i literally zone out tell I'm done. it's crazy the tunnel vision i get when I'm building an engine. i know the time it takes to film and edit a video, thank u.

Awesome video. Thanks for sharing. Been rooting for jlesher.

Very cool , ive built a lot of ktm s for off with thin base gaskets and tighten up the squish band with SX heads and a little machine work. Sometimes ill blend the exhaust flange for better flow when the power valve is closed. I haven't really thought about the power valve cooling befor ,thanks.

I opened the sub ports sooner and it seemed to make a good improvement for a local pro's outdoor motor.

Once it is done, run it on your dyno. Would love to see that powerband. Great video.

Thanks for that--very informative. I port my own cylinders and am always looking for information, there is not much printed on the subject. You may know this, but in the 80s Yamaha had a power valve similar to the KTM. It had an hourglass design that changed the whole exhaust port, but I think it was on/off and not gradual.

Brilliant video mate. More content like this would be great! Liked and subscribed 🤙

👍Great explanation. I was picking up what you were putting down

Excited for the changes!

Man… I'm really glad that your advertisement popped up on my Instagram feed so I could immediately X it out and then come over to KZfaq like I always do when I'm interested in something. 😂😂😂 Super glad that I just found this channel right now this minute and I'm gonna be doing some binge watching..... yep. That's what I'm going to do!!!! New sub based on just this video alone… Literally. Excellent job. Thanks.

Priceless info, thank you

Wow one of the best videos on here thanks for explaining

Interesting to get the differences explained 👍🏻

It’s Nice to hear experience 👍

Got to love the yz power valve.i customize my eye ports to open with the main exhaust port for maximum hit .thanks for the idea cheers.

This was awesome, thank you for this.

Thanks for sharing, I learned a lot in 10 minutes.

And, "back in the day" you had Yam, Hon-duh, Suzuki, Kawi.. And a "Bull Taco" (from my youngster years).. I'm happy to see KTM and a few others dug into the mix.. That club got stagnant for a while.. When the big brands (previously) had little slap boxing fights on tech leaps in HP (ETC), it was just.. well, playing games.. Now.. Even at my age now.. I am IMPRESSED..

Wisco has always been my go to piston for rebuilds.. an a good porting an polishing always makes good horsepower, an matching your pipe an silencer, jetting and changing your power valve also make hp.. it just depends on what type of hp an how much hp you want.. an if you match everything you will make massive hp! So you can keep your secrets I already know them😂😂😂😂

Very cool video dude!

That "vapor" blasting is awesome for cleaning parts to look like new. That is one process In have never seen.

Old Yamaha drum power valve was pretty linear bad thing was when it wore the stops out. You make great videos bro very informative. Don’t give away all your secrets.

You should do the same video comparing yz a yz 125 and 125 sx cylinder! Very cool to see the small differences. I have never rode a ktm 250 sx, but love my yz 250!

Man, you're a brilliant teacher! ;D

Great video, the KTM power valve does look far superior, how do Beta and Sherco power valves compare in their design?

I’m real curious how TM stacks up in this category being as small as they are, do they combine both methods of exhaust port design? Super cool, thanks for going deep in this one!

Very cool to know!

MY engine mods for the YZ250 for more low end power. I will not be able to ride it until spring now, but this is what I am doing to it this winter. I will surly write about it after I ride it enough. 1) FMF Gnarly pipe for more low end power. 2) V-force reeds. The stock reed stop plate actually blocks off about 50% of the rear transfer reed port tunnel, and I will open the tunnel to that port window a bit. 3) Lower the cylinder by .024" by removing the cylinder base gasket and sealing the cylinder to the cases with a good gasket sealer, (I use 3M Nitrile rubber and gasket sealer #847 brown, and feed it though a medical syringe with a cut off needle for great bead control.). Your squish will then be about .050" or a tad less (plenty), but with the stock head, you will need about 100 octane fuel, (I will mix 110 with the 90 REC fuel to save money.). Lowering the cylinder will lower the exhaust port time area, in hopes to better match the FMF lower rpm pipe. 4) do a good job jetting the carb. There is probably more than 2hp right there for a stock bike. Mine is so rich, I can't believe I am not fouling plugs, how black, wet it is stock. These simple and reversible mods should shift the power curve down for much more mid range and lower rpm power, and be a much better power delivery for anything but a modern MX track, (which I consider dirty road race courses today basically).

This was so cool

Hi guys it's me again to let you know that one of my ideas (butterfly baffle in the exhaust for shorter tuned length) has been built and tested please search "Two Stroke 3,5 HP to 28 HP in 7 minutes". Bear in mind I and the builder had never had any conversation about the subject so I don't know how he had a similar idea.

Thanks for the info. I run old kdx and a wr450. The old 2t is nice but parts are limited.

Cool stuff man! Question, do you ever use different base gaskets thicknesses to play with the powerband? Ran an athena race gasket (thinner)on my last topend and seemed to give it more bottem end but less up top. Was great for tight tracks.

Nice info 👍

Thank you thank you thank you!

I hope the bearings hold up in that hot rod crank and main bearings

Absolutely shocked to see a powervalve thats either open or closed when Yamaha were using powervalves that opened progressively in the 80s!

Great content, subscribed for shore. Which Oil do you recomend for mix?? I would like the special smell of 2 Strocke racing oil!!?

You know your stuff!👍

Brilliant.

What gains are to be had these days on 2 strokes? Last motor i had ported was a 98 cr125 and it dynod at 37 hp. I thought it was fast lol

I was told that every manufactuter had to have its own powervalve method as each was a propriorty owned patent and each company could not duplicate or even resemble any other. When the all came out each was truly unique. Yamaha on sleds using servo motor and cables seemed overkill ( but linear) and the Rotax with diaphram / guillotine the simpliest but effective and adjustability with preloading spring with rotating threaded disc on cover .

Good job

Ooooooookayyyy I’m subbing 😮‍💨😮‍💨😮‍💨🔥

Have you (or will you) reveal what the two strike launch control was that you almost (or did) get set up before the end of the sx season?

have a look at a Yamaha TZ 250/TZ125 cyl ... mounting looks pretty close and it has a bunch more port ... though it is made for more peek HP at 12k rpm ish my TZ 250 (its a twin ) dyno'ed at 98 hp the 5KE models had a rotary power valve. might not work but just a thought. Cheers Bebop

To YZ 250 owners. I thought running 90 octane "REC fuel" (alky free), would be good enough octane for my stock YZ250 motor, (also knowing Yamaha reduced the compression ration a bit around 2011), but it was wasn't. I just took the top end apart and found a little bit of detonation damage on the intake side of the cylinder/head interface, (I can still use the cylinder thankfully, but am putting on a new head). What I thought was the sound of piston slap at very low rpms when I got on the gas, was probably the detonation that did this bit of damage. I have also never seen a stock piston as weak as the YZ250 stock piston, so get rid of that stock piston ASAP IMO. :)

Can you compare the cylinder from the new yz125 engine wirh the ktm125??? Did Yamaha miss the mark getting ktm like 125 power on their new engine???

Hey, if you have access to a dyno, I have a port roof angle you might want to try. I do port and stroke little 30cc engines for a living, and the engines I work on actually have a negative roof angle on the front transfers (exhaust side). I don't remember the angle degree (under 10 degrees I am sure), but what they are doing is "bouncing" the charge off the piston crown for a more upward stream from the front transfers. The rear transfer roofs are flat. I can't get a YZ250 engine on my dyno. :)

Thanks

Any idea of why that little angled notch/ramp is machined into the KTM cylinder in the bottom edge of the cylinder skirt on the exhaust side?

Great video! Ok so the lower transfer ports you do not polish? I remember back in the day ok I know I’m ancient the factory bikes transfers and exhaust were polished to a mirror finish. They weren’t water cooled so is that why the cylinders aren’t polished? I’m using what I learned in dirt bikes on chainsaws now and you can tell the difference!

It might be because I gained 20-30 lbs, but my 2019 YZ250 is probably the slowest 250cc MX bike I ever owned box stock. My stock 97 KX250 would eat it's lunch. This 2019 YZ runs a lot like my 1986 YZ250 did.

KTM for the win!

My yamaha DT 125R has similar power valve to that ktm, with electronic controll and its an old early 90 model.

What’s the part number for the piston you run ??

There is a progression with the YZ power valve. The main valve opens before the sub exhaust valves, and i bet, by the torque it takes to open the sub exhaust valves may take up to an extra 2000 rpm (I did not measure it), to start opening the sub exhaust port valves.

Class with Professor Harris is in session y’all

Late to the party. Just discovered your channel. How do the modern exhaust port and exhaust valve designs compare in power to say the ancient 1980s and '90s Kawasaki 2-strokes with the KIPS variable exhaust valve timing? Pretty sure Honda and Yamaha had variable exhaust valves too.

I am curious of what kind of fuel/oil and ratio Jared is running in this YZ250 for SX?

Thank you for the info, less comp less cooling ,gee in a sand track 30 minute Moto ? The little extra cooling and less proned to detention look what happened to Hunter today I know its a 4 stroke just saying. Reliable is key

Do you have good experience with PowerSeal coating? I have send them several cylinders and the coating was not hard enough. Two stroke cylinders with only one ring worked for 10 hours of racing. 4 stroke cylinders with three ring applications didn't even survive the starting procedure. I checked ring gaps and everything was mounted correctly.

Hey Derek, will Jared be using the new STIC Super X carb? I keep it under control with the slowest turn G2 throttle cam, for MX!. I immediately started mixing it up with faster riders at the track.

How do they compare to the Sherco

Also notice on the KTM vs. YZ main exhaust port, the roof of the exhaust port on the KTM has a very large arc for a port roof, where the YZ is more flat. You are measuring the width of that KTM exhaust port at a very low spot, just above the transfers, (at the end of the "blow down phase". Have you actually measured the "port time area" of both to see the difference there? Because those shapes can be deceiving.

The KTM valve is much like the original YZ250 power valve from 1982.

My 1983 Yamaha RD 350 YPVS had the same valves like this KTM valves !

If the yz exhaust could be opimized with an electronic motor would it be a noticeable difference? My guess it would because just snapping open is a harsh delivery.

Fitting a thick wall cylinder liner/sleeve would allow repositioning of the exhaust ports and maintain bridges for the rings. It also makes the barrel more serviceable and tuneable. The YZ power valve needs a re-think straight up and would require a re-design due to reduced port timing and increased width when fitting a sleeve.. Bigger isn't always better is demonstrated with crank case and transfer volume differences between the two. Big = slow (low velocity) Small = fast.. Fuel requires velocity in order to stay in suspension. You can not burn what stays on the crankcase walls. More performance could be found through the entire range by reducing the YZ crankcase volume and and reducing the rate of area change. Compression doesn't make power. Releasing the energy from the fuel uniformly and efficiently makes power. Hot spots are the enemy. High octane fuel is actually counter productive to making power. It does however make up for poor thermal efficiency design.

Do you build these setups for other people as well or just this guy? I've been trying to dial in my yz125 for a little bit now and I'd like to do something similar to this

Just put a style KTM sleeve in your cylinder, weld up the ports, and grind them back to match the KTM. LA sleeve, I'm sure can make you a custom sleeve like you want.

If the yz is limited in rpm due to the exhaust port, just maximise it for lower rpm, raise the gearing. Are you always short 5hp against a ktm? You can't get that hp at a lower rpm with the yz?

In your opinion what is the most modern/best stock engine design out there? I like seeing these vids

What engine was that piston for? I just put one in my ktm 250 and it had 2 rings. That one only has one. Do you see any drawbacks with that?

Generally speaking, do all (performance) 2 strokes benefit from a crank stuffer?

New clutch, 20 starts, swap cylinder, new clutch, 20 starts to see best average elapsed time to the “first turn” and compare the cylinders. I chose the cylinder with the better over rev as it felt better on the track in practice, but as we know by the time the motos roll around the national tracks are so rough and rutted that the torquey cylinder may actually help a rider stay on top of things. Hindsight I wish I would’ve done the start comparisons and made my decision on cylinders based solely on that. Get out get clean.

hello! nice video! can you put a ktm cylinder on a yamaha engine?

I gotta get my hands on a ktm

Why is the 2007 250sx such a beast of a engine? 56hp new, while most are high 40s… I’ve heard the cylinder/heads have a role, but also the CDI too… I have one, have kept it for a decade. It SCREAMS. It’s so much faster than other 250s. It smokes a brand new yz250. What about them makes them so good?

My question is why on the 22 yz125 they are using a tpms sensor?

Valve on KTM is similar to 96kx how it changes port timing

do you do repairs on cylinders or just the sweet sweet porting

now i understand why it's harder to ride smooth with a yz250 because ofthe open/close position of the powervalve.

What's the best mod I can do for my 01 cr250 although it's plenty fast. Set squish? Send to you!?

Do y'all have any thoughts on how/why the GasGas two stroke engines are so much more powerful than the Husqvarna and KTM engines even though they're coming out of the same factory in Mattighoffen, Austria ? The testers' shootouts have GasGas power and delivery rated top of the heap against all 7 of the other two strokes in 2023.

KTM has my heart because I can interchange so many parts. I can use an axle from a 2003 125 on 2018 690. Many more examples, but I love parts interchange.

As a privateer riding for fun what is your opinion about reliability of YZ/SX here? Thanks!

How is the wiseco crank working i have heard from several people that they are almost as bad as Chinese crap i almost bought one but decided to just have my old factory one rebuilt trued and balanced the wiseco pistons are great so I had a hard time believing their cranks but so many folks said it but some of those folks might not have been as ocd with rebuilding as i am and I make sure everything is where its supposed to be and everything is moving perfectly and everything is tight and to spec i have seen how some guys just throw everything back together without using a torque wrench and the correct presses and other tools so idk

Yes, the KTM makes more power. But don't put that all on the porting, because we both know the pipe is the other big factor in the equation. It would be interesting to dyno a stock YZ250 with a KTM pipe.

Is the cylinder liner made from cast iron?