Porting My YZ250 Project- Part 4

[@onthethrottle7104]

I've noticed that when porting and cutting, you end up losing something but gaining something. The art is to have the gains outweigh the losses. My 250R porting provided amazing top end results, and I mean amazing...but the bottom end suffered a little. The top end benifits were way better than the loss of the bottom end suffer. If someone can show me all around gains I'm all for it. Another great video and excellent explanation from Chuck, great show!

[@lawerncemiller6557]

That was a lot of cutting will be interesting to see the results

[@scottshafer9813]

Love it… I would be scared to do it , can’t wait to see the results. Fantastic content Chuck!

[@mxcollin95]

Please do a video on how well it runs and what differences you feel actually riding the bike. I’d really appreciate that! I have a yz250 too that I’m going to restore at some point but have a few bikes ahead of that one so just doing research on everything at this point. Interesting video! 👍

[@ChuckfromTrueTech]

I posted the first test video a couple days ago.

[@mxcollin95]

@@ChuckfromTrueTech I’ll look for it 🤙

[@BillyWillicker]

The current YZ250 is highly developed for it's intended purpose. It is unlikely that you'll make much, if any improvements at all. Perfecting the combustion chamber for the fuel you are running and the RPM range you'll be using will produce the best gains. The ducting in the crankcase and bottom of cylinder is shaped to push the charge back towards the secondary transfers, it gives the smaller secondaries more velocity while still allowing low velocity charge good access to the primaries. It also is the start of the "loop" of the charge to begin before even entering the transfers, making it more effective at exhaust evacuation. To truly understand 2-stroke porting you must look at the entire loop system. The current YZ250 is flow, loop, AND pulse tuned. Not something you'll easily experiment with without truly in-depth knowledge and tools.

[@ChuckfromTrueTech]

This is why I experiment on my own stuff. I don’t have any intention of doing this for customers, just my own curiosity. The viability of a business based on enhancing performance (besides bolt-ons) is questionable considering the bikes are as good as they are.

[@rickriede2166]

Perhaps it's time for you to build a backyard dynamometer to quantify your testing. Are you familiar with the Two Stroke Stuffing guy? He built on out of a bunch of junkyard parts. Alternately a friend with a stop watch can be helpful in that sense .I've played with port timing on a older GG 250 and at one point in my experimentation the end result yielded a power band about as wide as the edge of a razor blade.

[@ChuckfromTrueTech]

It’s not practical enough for me to put effort into. The fact is that modern engines are excellent for 99.9% of riders. Modifying them increases the risk of failure & gains are minimal even in the best cases.

[@ShawnBlais]

@@ChuckfromTrueTech If you can find a dyno somewhere, would make for some really nice content, especially as you have a stock cylinder ready to go so we could really measure the effects of the porting.

[@user-ww7fv1nw4x]

Yes at BDC the ports are not fully open all round by about 2mm or so. Barrel needs to be lifted and head changed to suit.

[@ChuckfromTrueTech]

The deck height is good though. I’m really not concerned if the piston doesn’t drop to the very bottom of the exhaust port.

[@BillyWillicker]

The bulk of transfer flow volume flows through the top 2/3 of the transfers. Matching the transfer floor to the piston crown edge usually causes vortices 10deg BBDC to 1deg ABDC which --- hampers total transfer flow.

[@muppets_inc]

Keen to see how this goes Chuck! Port timing always seems to set the character for the whole bike and how it performs for different riding styles. I'm a big fan of low-end tractor power, currently on a Beta 300 for this reason.

[@user-rc5fi3kq9y]

This is exciting. Thanks man. I can’t wait to hear the results.

[@yamahakid450f]

Don't forget to do the head... both together is where you see the most benefits.... or just get a head from an 03 YZ250 and the sand or down to get the correct squish you're looking for. The 03 had higher compression... and with all this porting and potential head work, run C-12 at 40:1 and tune it. It's likely you'll get detonation and you'll get the most out of your work.

[@MartinEllisEssex]

Thanks for doing this & filming it.

[@ivnepe]

Great experiment

[@markilleen4027]

that looked really nice

[@lawerncemiller6557]

I'm more of a trail/woods rider I liked where the power was in the older 2 strokes low & mid

[@Motosportz]

Fun. Subscribed Look forward to the reports

[@dcmotive]

Awesome! Cant wait!

[@philipsmith6152]

Great review, be interesting to see what difference it makes ?

[@user-ww7fv1nw4x]

Hi just subscribed looks good and you obviously seen the way the barrel height is way off one standard base gasket and the ports are covered badly at BDC, what do you think of this.

[@ChuckfromTrueTech]

Are you referring to the deck height? I haven’t seen any deck height issues with YZ250s.

[@BillyWillicker]

@@ChuckfromTrueTech He's confused. Having the piston crown above the transfer floors at BDC creates a boundary layer that promotes smoother flow at the upper 2/3 of the transfers.