Portmap for a 3mb barrel?

  • Hey, this is my first offical thread on this forum, im curious if anyone has a portmap for a 3mb barrel they would like to share, preferbly a digital one or a hand drawn one but with all the lengths and radiuses etc.

    Or if anyone know the radius and area for all the ports, i need them for a software where im trying to figure out the optimal port timings etc for the 3mb barrel, and i have an idea of replicating the triple exhaust port setup found in many other 125s like the ktm exc, im in touch with a guy thats done it on many different barrels alongside the yamaha blaster 200 barrel if im not mistaking and he did it with great results
    Im not after reliability honestly im more on the hunt for power, dumb idea maybe but i wanna give it a try

    Also got a complete 3mb cad model but i honestly dont really know how to use solidworks so i cant really use it to find the radius or areas of ports

    Sorry for such a long thread asking for a portmap

  • Way beyond my technical capabilities.

    You'll need to look towards the Portugual fellas for that I'd suspect 😛

  • Im already following all their stuff religiously, I know they port theyre own triple exhaust port setup on the 170cc athena kit, i need the port areas etc so i can check if it would be necessary for the stock 3mb barrel though and not just destroy the barrel completely

  • @Arild I’m very experienced with Solidworks, been using it for 4 years now, I could take a look at the model if you like? I’d be very interested in the project.

  • @Darty
    sounds good, heres the link to the cad model

    I managed to get the height and width of all the ports, and millimeters from top of port to top of barrel, but im not able to get angles out of the transfers into the cylinder and combustion chamber, nor radius of all the corners of the ports and especially all the areas to the ports

    I dont take credit for the cad model btw, i have no clue how solidworks function, next year ill take my first cad class in school to hopefully learn

  • @Darty said in Portmap for a 3mb barrel?:

    @Arild I’m very experienced with Solidworks, been using it for 4 years now, I could take a look at the model if you like? I’d be very interested in the project.

    Darty, meet my yg I told you about 😂

  • @Arild Firstly do you have access to a 3MB barrel? Why would you not just trace the ports out by hand, if you are a 2stroke guy you'll know this a perfect method.

    Also, trouble you will have here with the model is, that it's an STL file which is only a simplified mesh and actually has no Geometry in CAD.

    I've thought about boost porting before and it has been done by a couple of tuners I know by hand.

    If I was you, I would draw a simplified CAD model of the cylinder and ports using your own measurements with no need to model casting itself. you only need the internal geometry and the YPVS chamber which is very simple indeed.

    Have a look a '2strokestuffing' on Youtube and watch how he models his cylinder in the same method. He's using Fusion360 and I'd say if you can get a copy of Solidworks it be easier to model, but that's my preference.


    This is something I could do nowadays, but I feel it isn't a necessary process unless you really have the understanding to run fluid simulation with the model.

    Then I'd buy a YZ250.

  • @Darty

    Hey, i dont have the barrel at hand currently, its on my bike and its getting ready for inspection so i legally can take it out on the road. So im not gonna tear it apart again before the inspection is done and idk when that will happen yet.
    I did a port map before i put the engine together around 8 months ago when i was thinking about making my exhaust but ive since lost that map sadly.

    I also managed to turn it from a stl file into a solidworks file when you open it up in solidworks, my computer couldnt handle the solid body setting so i had to go with the option in the middle of solidworks, and honestly id rather just wait to tear the bike down again before i try to make my own cad model cause im trash at cad

    heres the video i used to turn it into solid body from stl file

    Also, the tuners you talked about, did they do it to some other cylinder or a dtr like 3mb? Did it make a good difference for them or was it useless. Like i said i know a guy that managed to do it to both a blaster and some other yama cylinder with good results, he used 2 different metal drills to firstly drill from the top of the barrel and then go in through the exhaust port and finish it all up with a 90 degree grinder

  • Even as a Solid, it's low fidelity and I'd prefer to check this model against a real barrel. If it checks out, it's a useful guide to draw from but there isn't any real geometry there as it's a mesh that has been interpolated from origin.

    I've seen it done using a 3MB-P-00 barrel which is the same with a 1mm higher Exhaust port and then the there was a bloke who copied a TZR 4DL-SP cylinder which was very interesting. but I have no information on real performance data from the Boost porting.

    All done by hand like you've said.

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    I have 2 spare 3MB-P-00 barrels lying around so I will have a look and validate some geometry when I get the time. Would be a very interesting thing to model at-least.

  • @Darty
    From what i was able to gather from the cads it all works out, its just scaled down by 50% like the creator says on the website, but i checked the bore and it matched to 56,3mm and i plugged the heights from top of port to top of cylinder into a program and i got the same degrees as i have gotten when checking the port durations manually with a degree wheel, so i think the cad model is scaled and made correctly but u can never be too sure

    Its all just an idea as of now, i need the areas of the ports to see if auxiliery exhausts are actually needed which ill check in the software, and then go from that, everything might end up crap but owell i wanna give it a try, i want to see how much power u possibly can get out of stock bore, i know some guys that managed to get 35hp out of stock bore but they didnt have any dyno papers etc on it and they didnt tell me what they did with the engine so could all just be bs, but seeing as u can get 125s up and over 50hp i dont see why it should be impossible, or maybe it is impossible to push the dtr that far and im just wandering around with my eyes closed and wont get anywhere

    Its all worth a try atleast

  • @Darty
    Also the guy on facebook that did it to his blaster said he got loads of top end after doing this, no dyno papers but he said it made the top end way better, he also says that the transfers are whats holding back the dtr currently, i calculated my barrel to be around 121 degrees in trans duration and he says backed up by software that it should optimally be around 130 degrees

  • Yeah will be interesting to find out if Auxiliary ports can really help this design,

    Just look how tame the DTR is compared to a ROTAX 122

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  • You won't see numbers like that on DTR without serious modification. They are just a different breed. Reliable tame motors.

    Remember those 125s making that sort of power is not on pump fuel. That will be on Avgas. Fueling can make the difference of tens of horsepower on the same engine due to the anti-knock properties. It would be far more effective to simply use a better fuel and advance the ignition than to rework the cylinder.

    I would like to see a BAR Racing DTR in person. Haven spent years around fhe DTR doing a wide variety of tuning, I highly doubt that my DT is more than 20hp...

  • @Darty
    Yeah its such a tame design compared to that rotax cylinder or like other mx bikes like the exc or yz etc, its very held back, maybe mostly for reliability reasons, but if you look at lets say the old aprilia sx125s with that rotax barrel they were still really reliable and didnt need 5-10h oil changes and still pushing around 35hp derestricted im pretty sure

  • @Calum
    I know, the supermoto style bikes are very popular over here in sweden, many guys ride the ktm 125 exc which pushes around 35-40hp depending on like small modifications like reeds pipes etc on normal pump gas, i know you need serious modification to get a dtr even close to that but id atleast like to give it a try even if i wont get anywhere close, it will all be one big lesson and loads of fun to learn how to port and modify the bike, i find stuff like that really fun atleast, and im not really looking for reliability either, ofcourse i dont want my piston seizing or melting every top speed run i do but i wouldnt mind 10h oil changes and piston swaps pretty often aswell

  • @Arild No, a solid de-restricted Rotax 122, pre 2007 stuff, 25hp. Tuned bikes making 28-30hp is impressive.

    I think a brand new KTM SX 125 makes 37.5 peak HP, but you are talking just 30 hours on a set of rings here.

    It's the lack of torque that's the real issue with 2strokes, just gets harder and harder to ride the powercurve.

  • @Darty
    ohh okay i was unsure with the rotax engines, i thought i remember seeing an aprilia sx 125 with 35hp somewhere but it was probably wrong

    Also im not sure on all the different ktms but i know there are loads of supermoto over here pushing 40hp, dont know about theyre torque but theyre going quick and pulling wheelies like its nothing

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