Inside a Pro Supercross and Motocross yz250 engine and cylinder.

[@wisecopistoninc]

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!

[@craighills2382]

Well done Wiseco for suporting these riders .Ill buy your products because of that 100%

[@queenofspadz]

Their cranks have/had a spotty reputation over the years. I saw a presser from Wiseco that they've been working on improving reliability of their cranks. Pretty sure Lesher wouldn't run something questionable in a race bike.

[@EarthSurferUSA]

I have a 2019 YZ250 2-stroke with only about 15 hours on it, and I just took off the top end for a rebuild. Bike has stock chain and sprockets that are just starting to show some wear, (to get a better idea of how much use the bike does not have.), and the stock piston has damage it should not have. Yes, I do see a tiny bit of detonation damage (90 octane REC alky free gas is not enough octane for the stock bike), on the intake side of the head/cylinder interface, but the exhaust side has distorted ring grooves, (possibly not letting the rich machine warm up before riding, previous owner had about 4 hours on the machine.). Well, I have never seen a piston is such bad shape with so little time on it, and I expect my new Weisco forged piston to have much more life. As a degree earned quality control engineer myself, I can tell the quality of Yamaha has dropped considerably in the last 2 decades. Can you believe I had to dremel tool some material off the frame head stay area to get the head off, (not enough clearance, head studs possibly too long.). I thought getting the YZ that has not been changed much from 2005/6, would yield top notch quality. I was wrong.

[@1crazypj]

In the 80's (when I had most experience with Wiseco), the machining variation in pistons was a massive problem., usually meant buying at least three sets then sending two back then doing a few modifications to get a fully matched and balanced set. (I trained as a 'precision machinist, 0.003 micron tolerances on production work with a fixed time to 'git r done) Made me avoid 'Wiseco' for a very long time. I didn't see any more Wiseco pistons until early 2000's when you obviously had switched to CNC machining. Guy brought a set in to do re-bore.. Pistons were nice looking and sets were 'matched' out of the box so didn't need to be carved on to get crown height, etc, the same. It was actually very impressive with good QC.

[@erics7712]

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.

[@Jakestarr1723]

Dang 20:1 seems awful rich

[@Ry_Pox]

@@Jakestarr172320:1 would be lean. More oil yes but less fuel. Rich or lean isn’t based off of the oil side of the ratio it’s based off of fuel. (Side note I also don’t agree with running 20:1 but if it’s working for him and making good power running it that fuel lean then I suppose it works lol)

[@waynegarfield6607]

​rejet it for more fuel. I am suprised as well as 20:1 fuel / oil ratio as now almost everyone swears 50 or 60 :1 with these new super super synthetics . I have always run my 2 strokes 32:1 . As long as its jetted good and run on the pipe it will not carbon/ ash up . I even run all my 4 strokes 100:1 with a good synthetic oil and my engines love it.

[@Jakestarr1723]

@@Ry_Pox20:1 will always be considered too “rich” when talking 2 stroke, I see what you are saying but rich vs lean is not always referring to air to fuel ratio. In this case oil to gas ratio. Either way keep rippin 🤟🏻

[@freakyfreerider]

20:1? I'm calling BS that's way too much oil.

[@mikebrown41182]

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

[@bkh5746]

I want to see the rod on a factory 250 and the gearbox.that one crankshaft looked like a stroker with the blueing by crankpin

[@mikebrown41182]

@@bkh5746 Factory 250 fourstroke, or factory 250 two stroke?

[@jasminebebe3455]

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

[@icup7802]

No kick on two sroke is really really not the way to go. It needs to come out of the boxe with a kickstarter even if there is electric starter. I love my enduro ktm exc125 engine with no electricstart. I will buy a bike with both but never will I buy a endurobike without kickstart!

[@ar2043]

I totally agree, although I did buy a brand new Enduro bike without a kickstart. It bothered me and still does but it was the bike I chose based on my needs. I do agree with you though… Every bike should have a kicker. 😢😢😡😡😂😂

[@EarthSurferUSA]

How much do you want the EPA to force development and create costs high enough to damage market share? Not many people riding all these expensive bikes today. With out the 1986 production rule (that nobody in the USA really understands), and the EPA dictatorship forcing the 4-stroke engine on the industry, a new 25 2-stroke today would probably cost between 4-5 thousand dollars. There are land closures too, but that is the reason why bike sales used to be 10 times more than they are today, which is the least in history, especially given the higher population of today. I respect your decision to stay with a 2-stroke as I did with a YZ. But to be frank, nobody making a 2-stroke has really stuck to morality either. Yamaha over charges by about a grand of a new 250 2-stroke to help fund the 4-stroke forced development, and KTM is doing what the dictatorship says, knowing the dictatorship will end them eventually. I have a problem with the entire industry. It is not run by free people anymore. It is not free enterprise anymore.

[@EarthSurferUSA]

250 2-stroke

[@EarthSurferUSA]

Forced by the EPA no matter the cost of a bike, (like the 4-stroke)? We need to reject the force son. Not many can afford it anymore.

[@ncopp4358]

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.

[@agoogleuser7784]

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.

[@spoderacing3910]

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.

[@dalewilliams306]

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 .

[@HPRaceDevelopment]

We have done fairly extensive modifications in this area in R&D. So far as welding the outside of the cylinder so we could grind it the way we really wanted. On our mx pipes it didn't do much. If we keep on this project for next year we might make some pipes.

[@eamh2002]

@@HPRaceDevelopment Is the wiseco piston specifically tailored by wiseco to your bike or some other manufacturer's model? Or is that a big secret? Cheers :)

[@HPRaceDevelopment]

@@eamh2002 We used to sell a custom piston for these bikes years ago - then I found this one for a different bike that did the things we wanted. Saving clients money and allowing them to purchase a piston from any source is something we like to do - which isnt smart for business but i think is morally right

[@craigdavies8099]

@@HPRaceDevelopment So which bike was the piston designed for? I'm building a yz for a mate.

[@HPRaceDevelopment]

@@craigdavies8099 wouldnt be useful for your build without the work we do in our port arrangement

[@charlesgraham9954]

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.

[@EarthSurferUSA]

No, I don't think it is crazy to have that "tunnel vision". Not many people experience it, but I think you focus like that, because you love the work. Possibly?

[@radsdad1]

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

[@ray_s281]

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

[@jcbenson01]

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!

[@adambatchelder4121]

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.

[@vintagetrikesandquads4012]

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.

[@spacejaime]

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

[@HPRaceDevelopment]

Dont have the bike here, but it's already been on the dyno before houston. Our yz250 dyno video is a similar result, jareds is a little better everywhere than the one we published

[@guyroy4857]

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

[@simoncleland704]

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

[@frisk151]

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..

[@EarthSurferUSA]

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).

[@bobhemphut4011]

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

[@EarthSurferUSA]

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

[@ar2043]

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 KZbin 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.

[@skyhawk409]

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.

[@HPRaceDevelopment]

I dont like that arrangment. less mid, no better peak for me

[@shanemoves2567]

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

[@Briggsys_Stuff]

Interesting to get the differences explained 👍🏻

[@Jake-rp9cv]

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!

[@HPRaceDevelopment]

YZ125 and ktm 125 more different than the 250's are but still somewhat similar.

[@bruce3725]

Does the 2022 yz125 still run a split main exhaust port?

[@Jake-rp9cv]

@@bruce3725 The port still has a bridge in the middle.

[@HPRaceDevelopment]

@@bruce3725 Yep.

[@corinnas5186]

My alltime favorit exthause ports, I portet a lot of zylinder. There is so much potential. I think with the exthause and carburetor the most important mod in generating power. Just changing the often seen oval shape to a straight upper edge is enormous, without pushing the timing of the exthauseport upwards. Makes a longevity of the setup compareble to fresh milk, But who cares if it's about power 😅. Put under a 1,5-2mm thicker gasket and take the same amount off from upper part of the zylinder.... Viola you changed the complete port timing some degree upwards. These both mods will make you feel like you got a complete another engine, independent of cubic size.

[@SreidMX]

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!

[@ericgossard8808]

Also curious about the TM's ability to hang.

[@250race]

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

[@HPRaceDevelopment]

Wiseco, but we hope so too! It's been our experience the OEM bearings and parts are no longer the quality they used to be either...since covid a lot of things have changed.

[@EarthSurferUSA]

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.

[@EarthSurferUSA]

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.

[@jacksargeson1280]

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

[@deanholonics-kz5wr]

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.

[@phatheadracingmx]

Excited for the changes!

[@mbrick]

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

[@1crazypj]

I remember working on those rotary valves in the 1980's. They were used on a bunch of street 125's and 250 twins. That' seems a logical development by KTM, even if it took almost 40 years. (I haven't ridden a KTM since the 80's 300cc one) The guillotine gate valve used to be progressive with a centrifugal governor although it took a bit of tuning to prevent it being on or off. Much better design where it cant fall into cylinder when it breaks I forget if it was Yamaha or Suzuki who went to servomotor control first way back when. Yamaha main market was (is?) 'play bikers', sales were just not high enough to justify a complete redesign for the few hundred bikes they would sell every year to semi-professional racers

[@ibewillow]

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

[@jimduke3]

The power valve that KTM uses is exactly the same as the YPVS that Yamaha used in the 80's. Strange that Yamaha abandoned it and KTM copied it.

[@pc-easy]

it abandoned that design cause there is no need to got a progressive port, reeds do the entire job@@jimduke3

[@Zt3v3]

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.

[@Chris-uh3cm]

Wow one of the best videos on here thanks for explaining

[@EarthSurferUSA]

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. :)

[@vidzofivi]

Man, you're a brilliant teacher! ;D

[@EarthSurferUSA]

Dyno this, my YZ250 set up. I got much better low end power out of it, (still doing some jetting too). They are all reversible. 2019 YZ250 2-stroke. FMF Gnarly pipe, (lower rpm peak hp target). V-force reeds with no stock aluminium spacer, (for tighter primary compression) Drop the cylinder base gasket for more compression, a .048" squish clearance (after 2011 I believe, the compression was lowered by about .0085' more squish from the gasket surface.), and use 100 octane fuel. I forgot to put my induction tach on the bike when it was still stock, but it does not seem like I lost much over-rev. Get the jetting good before testing of course. The low end power is much better, and still pretty smooth, making the bike a joy to ride for me. at 200lbs and stock gearing still (I usually add a couple teeth to the rear), it pulls my body around very well now from lower rpm's, but I still think I will add the 2 teeth on the drive train change anyway. I was trying to mimic my last bike, a 97 KX250, and I think I got pretty close. I also found that the stock reed block, with the metal "stops", blocks off the 5th transfer reed port tunnel, and the engine suffered from donation (90 octane not enough), on the intake side of the head. I think some hot gases were still there for the next cycle, as that port was not flowing as well as it could. to clean it out. I did open up the tunnel only about 1mm, (probably no difference in power.), and the v-force reeds do not have that plate blocking it. If you get time, build that simple build and ride it. I bet you like it. :) Doug in Michigan

[@EarthSurferUSA]

Oh, no cylindr base gasket is a risk. I am using a 3M product called "Nitrilie gasket adhesive, brown, number 847", and so far so good after 5 gallons. That stuff blows Yamabond 4 away IMO. if I can stick to 100 octane gas, I will machine the base for the stock gasket again. Good simple mods, that moved the power down lower very well. Still smooth with the FMF pipe too. Jetting is a pain IMO to get very good, and i think I will get a bit more power,---with the 2nd more lean needle. I have changed every jet on this bike, and it is still pretty rich above the pilot.

[@HPRaceDevelopment]

@@EarthSurferUSA removing reed spacer is less power everywhere. Have published this over 10 years ago. lowering cylinder will sometimes help front side in trade for less power. If you race mx its generally worse. Cutting the head, increasing comp and tightening squish also hurts power, no measurable power improvement. alters power character feels more torquey in trade for rpm loss have owned 5 ys250s, raced them in pro, and built and tested more items on these bikes on the track and dyno than probably anyone still doing work to them.

[@EarthSurferUSA]

@@HPRaceDevelopment I can tell you are very knowledgeable and I respect nothing more. The EXP I had on one bike of the past (I can't remember which one), I made and added a reed block spacer, and that mellowed the power hit for me (seat of the pants evaluation). This bike is set up IMO with higher rpm power, huge brakes, in a feeble effort to race MX against 15 more hp of a 450. That just is not gonna happen IMO, so the bike is not really set up well for anything (I am 60 now and woods riding in Michigan). The mods I did worked very well for more low end grunt and runs pretty smooth into the mid range. I am not sure how my top rpm I lost, (messed up and did not put a tach on it when stock), but it feels like a loss of about 500 rpm maybe. I don't notice it really. But here is something you have not seen before. I port little 30cc Zenoah, (used to be a division of Kamatsu. Now Husky owns the production in Japan still) engines for a living, used in 1/5th scale rc cars/boats and Go-Peds before the 1/5th scale cars came out. They have a 70's single exhaust port with 4 transfers. The interesting part is the front transfers (exhaust side) has a negative roof angle by about 5 degrees, and is bouncing the charge off the piston crown. I know Tom Turner (TSR software I have, and never totally figured out, lol) has never seen that before as I talked with him before he retired. The engines are high revving, up to 21,000 rpm, and can make up to 7hp (I calibrated my water brake dyno by using a new, stock engine, set it up like the manufacture did, no exhaust, no air filter), jetted it the best I could after total ring seal, and adjust my software until I matched the manufactures claim for the stock engine at 2.8hp. It seems to me from my research, there is really no calibration for dyno's, and that is the best way I could come up with. I do have a question about the KTM vs YZ exhaust port for you though. Why would the wider sub-exhaust ports on the Yamaha not make up the difference of the width (time area) of the main exhaust port? Good story too. I think it was 1993 when Kawasaki first went to a semi truck for the factory team. I did a bit of my own porting back then (just getting started) and somehow, a buddy of mine and I got permission to go into the trailer after the fans cleared out for the post race autograph session in the pits. So we come back later, he lets us in, and left us alone. There it was! A cylinder for Mike LaRacco engraved with his name on the bench, so I picked it up to take a lookie. That is when Big daddy Mike LaRacco entered the trailer, saw me with the cylinder in my hands, and kicked us out. :) Good channel sir, I enjoy it. But I could not hear the name of the pro you mentioned, Jeremy something. Buy the way. Since the porting I do is more of a production thing, (like 36 top end kits in a case that takes me a week to do), and I have a ton of machining exp, I may be the first person in the world to port 2-stoke cylinders with a CNC mill, starting in 2007. Doug in Michigan

[@EarthSurferUSA]

Buy the way. Since the porting I do is more of a production thing, (like 36 top end kits in a case that takes me a week to do), and I have a ton of machining exp, I may be the first person in the world to port 2-stoke cylinders with a CNC mill, starting in 2007. Doug in Michigan I see the lack of the spacer for stuffing the crank case volume a bit more, and maybe the results depend on what engine is used. Not sure.

[@minibikemadman]

ah I love nerding out on 2 stroke stuff...have a CPI lynx 380cc top end that's going on some billet cases in my honda trx 250r..I needed torque so I went big bore lol.

[@davidwickboldt712]

My1984 YZ 125 had the roller power valve. Slide valves came out after them.

[@HPRaceDevelopment]

@@davidwickboldt712 quite a bit different in function

[@rcracer641]

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

[@dr.hugog.hackenbush9443]

If your KDX is a 250, regular KX250 parts of the same year will work.

[@bebop502]

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

[@shaynebrown131]

This was awesome, thank you for this.

[@barkeep25]

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.

[@HPRaceDevelopment]

We do this through our port changes for the target goals. Changing gasket heights is noticeable but very small differences.

[@bruce3725]

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???

[@TheStephenspann27]

Priceless info, thank you

[@EarthSurferUSA]

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. :)

[@EarthSurferUSA]

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.

[@EarthSurferUSA]

You can change the timing of the sub exhaust valves with a different ramps on the power valve shaft, that do open the sub exhaust valves later than the main valve.

[@EarthSurferUSA]

Opps, I should listen the the entire vid before I open my mouth. :)

[@hogsbyavgaming9965]

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

[@HPRaceDevelopment]

Not legally for AMA racing

[@hogsbyavgaming9965]

@@HPRaceDevelopment oh ok becouse i thougt that it would b e posible becouse same cc and if the ports just dont match you can just port the crank case. thanks for the awnser!

[@Scissors69]

@@hogsbyavgaming9965 - Also, the carb/reed block are mounted to the cylinder, on the Yam. On the KTM they are mounted the the crank cases, which would make it difficult

[@waynegarfield6607]

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 .

[@DanielTojcic]

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

[@HPRaceDevelopment]

In the mx world on 2 strokes its no contest - ktm - with exception of the EFI system the engines are fantastic. In teh big picture the karting 125's are incredible but not usable power for MX

[@mattcowlard4662]

​@@HPRaceDevelopment how can you say that without comparing it to a tm engine

[@HPRaceDevelopment]

@@mattcowlard4662 I sold tms and built championship winning tms. They are not as good as the ktm - but have some aspects that are better - but more that are worse

[@mattcowlard4662]

@@HPRaceDevelopment what year were those? There latest 250-300 engines are alone better now have you any experience with these ones? Can you tell me what you mean by they do things better and others worse the build quality is very high compared to ktm

[@HPRaceDevelopment]

@@mattcowlard4662 All the way to current. I was/am a tm dealer

[@anomalouswoof2554]

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.

[@HPRaceDevelopment]

The designs improved from the 80s in many ways until last gen engines - this yz or the cr (nearly a ktm level design). The problem is - ktm has the best design by far at this point. The ktm has some flaws - the valve will collect more heat it cant shed than other concepts - but its function is unmatched.

[@skyhawk409]

Yamaha RZ350s in 1983 had a two stage servo motor controld pover valve opened at 6000rpm stage 1,then 8000rpm stage 2 with red line of 10000rpm.the bikes had very good mid range and top end for a 60hp twin 2t.

[@beatluginbuhl3238]

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

[@paulmryglod4802]

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

[@Backwoods145]

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😂😂😂😂

[@EarthSurferUSA]

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.

[@kraftzion]

Very cool video dude!

[@craighills2382]

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

[@HPRaceDevelopment]

We currently make most power at lowest compression setting on the yamaha of all the heads we tested. We will be testing the KTM head profile in the yamaha soon - see what happens. Sucks for hunter - making this title hard for him!

[@TACOMOTOCO]

Class with Professor Harris is in session y’all

[@ni7299]

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.

[@HPRaceDevelopment]

When going against 450s with 8-12 nore hp and 3x the power width, on metal grates that take away rider skill, the start is a non factor. You just wont get a good one, period.

[@bobsbillets8863]

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.

[@HPRaceDevelopment]

Firstly, sleeves loose power vs plating. Quite a lot The bridges between main ex and side exhausts is in the wrong spot. a new sleeve cant fix that - as the bridge is the inner wall of the side ex ports and outer wall of main ex.

[@bobsbillets8863]

I said LA sleeve can make you whatever you want. Whether it be plated or not, they can put the ports anywhere you want as they are the manufacturer. I do CNC machining and If sleeves were my wheel house, it would be easy to make whatever a customer wanted to their specs. @@HPRaceDevelopment

[@HPRaceDevelopment]

@@bobsbillets8863 I dont think you are visualizing the issue. the sleeve isnt going to have enough diameter to correct the issue additionally - the bridges in the oem cyl are there structurally as well. They help carry the combustion force loads the head applies to the cyl. To correct the issues would require a new casting design.

[@EarthSurferUSA]

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

[@EarthSurferUSA]

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?

[@cadillacmoto]

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?

[@bermbuster6]

Thank you thank you thank you!

[@forrestebert5276]

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!

[@dr.hugog.hackenbush9443]

Ive learned that polishing is only benificial for exhaust ports.

[@goinhot9133]

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?

[@goinhot9133]

I know it’s not just mine. Friend had the same model. I’ve completely redone my ‘07. It’s a old, new bike 😅 I’ve rode a lot of 250s and 300s, but the 2 ‘07 250sx I’ve rode are the fastest 250s I’ve ridden..

[@HPRaceDevelopment]

Bring it by and we can dyno it for the channel... if it under performs you can explain why you feel its the fastest 250 but isnt.

[@goinhot9133]

@@HPRaceDevelopment I’d love to, I’m in Ohio. I’m not saying there isn’t faster. But stock? I’d say close. Just based on the numbers from google, the mid 2000s cr250 is pretty close in hp… I’ve rode some newer 250s & 300s & plenty of older ones. Haven’t had it on a dyno. I’m not even talking my bike, but the 07 250sx in general. There’s plenty of talk on forums about that particular model. I’m basically asking if you knew anything about the model, & if so, have you heard similar things? I know my experience, & years of racing. I know a friend bought a yz250 off the show room floor, brought it to the house & we drag raced, swapping back and forth over and over. My particular bike doesn’t have any engine mods. I’ve cleaned the ports up and polished them, but nothing major. If I was going to do anything, I’d drop a 300 kit on it. I’m actually putting a fresh top end in tomorrow. Refreshed the power valve with new bushings and orings, hardware etc. everything willl be new, except the bottom end, radiators, and main frame. I have probably $5k in the full rebuild. Wheels tires suspension carb reeds sub frame on and on.. I’d love to dyno it & get the new OEM carb tuned. Have a jd jetting kit coming with the cylinder head orings tomorrow 😊

[@jdoe9518]

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.

[@HPRaceDevelopment]

Steel sleeves loose significant power from plated cylinders - been there, tested that. Additionally the length of the divider of the aux port becomes prone to cracking is it shortens. The combustion forces are trying to stretch apart the cylinder and a large portion of that load goes through teh bridges.

[@jdoe9518]

@@HPRaceDevelopment Steel is rarely used for sleeves for a variety of reasons. I always thought the combustion forces were pushing the piston down to turn the crank...

[@HPRaceDevelopment]

@@jdoe9518 And equally pushing the head up as a reactionary force… it just doesnt moved

[@jdoe9518]

@@HPRaceDevelopment if you're doing it right peak cylinder pressure will occur 5 - 15 degrees after top dead centre. Because pushing the piston is more efficient than pushing the head

[@HPRaceDevelopment]

@@jdoe9518 I dont think you understand how pressure and forces work. The pressure at any piston position is inside the cylinder - always pushing the head away. this force is trying to lift the head and consequently cylinder away from the cases - at all times.

[@poker8193]

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

[@harryjohnson2]

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

[@HPRaceDevelopment]

Not really.

[@harryjohnson2]

@HPRaceDevelopment thanks for the reply. I have a twin 951 currently rebuilding and was looking at how big the crankcase is. It just got me thinking. Love the videos man! Thanks for posting and sharing knowledge.

[@Lou-eye]

We were stuffing cranks (just the holes) back in the 70's with Epoxy.

[@csongorszoke4527]

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

[@HPRaceDevelopment]

must be a ripper

[@thedirtdigger5990]

Very cool to know!

[@ottokirk2325]

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.

[@HPRaceDevelopment]

We haven't tested with it yet. We have been having some issues with junk getting into his carb/jets late in motos. Not sure why or how, we filter the fuel and have an inline filter. Hope to sort this out soon!

[@Factory928AC]

Ooooooookayyyy I’m subbing 😮‍💨😮‍💨😮‍💨🔥

[@rodneylynn5770]

You know your stuff!👍

[@hannesdobbelaere]

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

[@HPRaceDevelopment]

Only part of it. All 2 strokes have the pipe influence which has a dramatic rise in power as well - the pipe only resonates properly over a small rpm window - aka “getting on the pipe”

[@EarthSurferUSA]

@@HPRaceDevelopment We also learned how to see the clutch to help control the feed of power, especially wide open coming out of corners. Today, I see 2-stroke riders who do not use the clutch much or at all, like smoother power of the 4-stroke technique has become. Especially on a small bore 2-stroke (125 and less cc), we just wicked the throttle open and fed the power to the ground with the clutch. Kent Howerton developed that technique in the 70's when the Jap bikes were getting faster than his Husky. The Jap factory riders could not figure out how he was going as fast as them, and went to the side of the track to watch him. "Clutching it" was born. Howerton got on a Suzuki. :)

[@robtoole1480]

How do they compare to the Sherco

[@danielarney9729]

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

[@seantamke3108]

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?

[@HPRaceDevelopment]

improving torque requires more air trapt into the engine at any rpm You cant just “add torque” by optimizing for “lower rpm” We are already optimizing as much as possible. The optimizations are as I detailed. Aka ktm has advanced their tech and yamaha has not.

[@timmwhite9218]

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.

[@HPRaceDevelopment]

It has a carb vs efi. The efi just isnt there yet the 24 gas gas will be in line with the 23 ktm and husky

[@kyleglenn4893]

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

[@HPRaceDevelopment]

Usually we don't repair anything - cheaper to buy a new one.

[@kyleglenn4893]

@HPRaceDevelopment idk if I can for this 2001 ktm 300 at the moment

[@henrik-josefsson]

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

[@HPRaceDevelopment]

similae but not same

[@henrik-josefsson]

@@HPRaceDevelopment But the shape of the outlet is the same and the system had also an inbetween position, for more torque, at low engine speed!!

[@dsweigart197]

It's kind of crazy to me KTM has used a similar power-valve design since at least 1998(thats the earliest i can confirm) how did yamaha never update

[@HPRaceDevelopment]

two strokes for the japense were dead since 1998. They sold what was already in development, and for yamaha they were lucky enough to have a product people bought far past it's intended design cycle.

[@skyhawk409]

Probly because yamaha were too bizzy winning more mx championships than eny other brand.

[@diesdasa]

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.

[@HPRaceDevelopment]

Sounds like a unique problem to you, we use them all the time and have hundreds of hours of success on their plating.

[@diesdasa]

@HPRaceDevelopment thanks for your answer! I guess its working on Chromed Pistonrings and when it comes to four stroke pistons with sharp chastiron pistonrings, it doesn't match well with the plating material. I tried 4 cylinders in total. Only one survived. Trying monardi Italy now. BTW: thanks for your CDI and Ignition videos! This is how I came here :)

[@HPRaceDevelopment]

@@diesdasa we dont run chromed rings… you probably have other issues

[@EarthSurferUSA]

@@HPRaceDevelopment How would he get chromed rings today? Not from the manufacture. You are right, no chrome rings in plated cylinders.

[@chriseller757]

Wow didn't know that about the 250 ktms

[@klaus5686]

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?

[@HPRaceDevelopment]

Generally 1 ring makes a little more power. Arguments on both sides to benefits for each design.

[@warclownband]

if i had to guess, cr250 gp piston

[@HPRaceDevelopment]

@@warclownband Nope but good guess

[@klaus5686]

@@warclownband Ahhh, the center of a tootsy pop conundrum. The world will never know what kind it is. lol

[@EarthSurferUSA]

Jetting my super stock rich YZ250 2-stroke is a bit new to me with the "Power Jet". I don;'t like the thing. I think it complicates jetting, and does not really add my performance over a well jetted carb. What is your thoughts of them, because I would like to delete mine or go to a 3 jet carb of the past that ran just as good if not better. Definitely easier to jet.

[@HPRaceDevelopment]

@@EarthSurferUSA totally false. it adds repeatable power and overrve

[@EarthSurferUSA]

@@HPRaceDevelopment Well, it sure is not faster than the 3 jet carb bikes I had in the late 80's to the 97 KX250, and I think (man it has been a long time, and I am 20 lbs heaver) my slightly ported 1988 CR 250 would have smoked it from the mid range on up in the YZ stock condition. To be fair though, I did not jet the stock YZ engine at all, and waited until all the engine mods were done. What you you mean by "repeatable" power? (so I understand exactly what you are saying). Ohh, I will put that reed block spacer back on and see how it goes on this Yamaha because of your comment. Thanks man. Doug in Michigan.

[@christower6798]

This was so cool

[@PatrickRiggs33]

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

[@HPRaceDevelopment]

Jared is supported by bludlubricants, and best I remember he runs 32:1

[@Whiskeymike1229]

I gotta get my hands on a ktm

[@HPRaceDevelopment]

lol

[@eaglemx45]

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

[@HPRaceDevelopment]

Not many "bolt ons" will do much. Keeping the engine fresh, and your jetting on the money is the best thing anyone can do, mod or stock.

[@eaglemx45]

@@HPRaceDevelopment thank you!

[@PurpleMonkeyWaffle]

Yamaha had that progressive PV design in the RZ350 and TZR250 in the mid 80's. Not sure why they went guillotine here.

[@AngelRodriguez-eo7wp]

ok so you are using a ktm 250 exc wiseco piston and you are trying to somewhat copy the same port design the ktm cylinder has and yes ktm did copy the power valve off the 97-01 cr250 cylinder word of wisdom use the 808m06640 piston for the yz or rm250 motor also want to make a yz250 wake up use a 2000 wiseco gp cr250 piston cut the wall down just a bit on the intake near the transfer ports you will remember me lol

[@HPRaceDevelopment]

Not trying to copy the ktm - you cant… You cant improve the b ports with your piston selection the way we are, additionally we already modify the intake side - not shown for a reason. We are doing stuff on that side no one has done. Ktm dramatically improved the cr pv design - its not even close in a host of ways. The engine makes fantastic power - some day - we will publish more details.

[@jordanmolinaro6507]

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

[@HPRaceDevelopment]

Full blown race shop that makes a living off selling what we race…If you want our best effort its just time and money

[@jordanmolinaro6507]

@@HPRaceDevelopment good to know, I'm a quality over quantity guy myself so I can appreciate that attitude. I'll be in touch, I'd like to get the most out of a stock bore setup to avoid the big bore headaches

[@ottokirk2325]

The new STIC Super X carb on my stock 200SX...FIRE Derek is a dealer and BTW Lesher runs the STIC metering block version. Might be overkill, if you're only looking for a little more power.

[@64maxpower]

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.

[@HPRaceDevelopment]

No its a guillitine type valve ktm uses one that is the roof - not blocking the roof with a void behind it like the yz It could arguably be slightly better - but not ktm better good question

[@64maxpower]

@HPRaceDevelopment thanks for your response. Your time is appreciated

[@EarthSurferUSA]

@@HPRaceDevelopment Everything can be improved. I see your problem. :)

[@marcschulze3813]

The comparison between the exhaustareatime from ktm and yamaha is not correct. If you have a wider Maine haustport, so you have smaller sideport. For yamaha the opposite. If each done correct, you have the same Exhausttimearea. The smaller mainexhaustport makes a longer pistonlife.