The mixture is entering the crankcase in the crank area, not through these windows. These windows allow for easier transfer of the mixture through the boost port.
Why would windows have effects on intake process when the piston is going down in the crankcase closing the reedvalves? My theory is about the mixture traped under the piston going threw the boost port, it might give you torque at low and mid range rpm.
There is also a secondary reason a windowed piston is used .... as the piston is approaching bottom dead centre and the piston windows are open ... there is a free path where the exhaust port ... transfer ports are open ... this allows the exiting exhaust pulse to drag fresh fuel air mixture into the cylinder ... and as the inlet timing at this time is only controlled by the Reed valve extra fuel air can be scavenged into the crankcase and cylinder ... just another way of wringing every ounce of power out of two strokes ....Reed valves have asymmetrical timing meaning that is there is vacuum on them the will allow fuel air to pass ... but at the cost of being in the way .... I prefer rotary disc valve myself ... lol
Also this engine is a Franco morini s5 engine all 3 engines are air cooled one that is 2 HP the other being 4-6 and the fastest being 6-8 HP mid or late 90’s 50 cc kids dirtbike. Ty for any feedback
You should do more hands on videos like this. Nothing against the white board videos, I've just never really been much for theory(I guess youd call it that?) and lectures even when I enjoy the subject matter.
If I may ask what are your thoughts on having chunks or parts of missing cylinder whether it’s below cylinder window or above cylinder window I was told if it’s below or above cylinder window then it should be fine I can’t remember which one whether it was okay to have missing metal from cylinder below or above just wondering your thought I have 3 if the same engines they all have the same bottom end but the only thing that is different between the 3 of them is the top end and piston I have a top end that has a piston with just a circle whole for the intake and that’s a single reed cylinder and piston while the other one has double reeds with a single oval window on piston siimilar to the piston shown here except your piston has double window and mine base single window that’s oval in shape the top end that’s the fastest has oval window on piston I think it’s 6-8 Hp the second to smallest engine has a circle cutout for single reed intake and the very smallest engine has NO cutout on piston at all and no reeds on intake… what’s your thoughts on the cylinder with missing nika sil above or below the ports I will say the cylinder with the highest HP seem to run fine after a carburetor cleaning but we ended up breaking maine drive shaft sprocket. And the silencer or the stuffing in muffler was saturated with oil and spitting out all over my hand when placing my hand behind it
First time a tried making 2 windows 1 big window i broke off the supporting metal under the window. So it looked like an upside U. But it worked and the piston held. But i was told be a shop owner that my piston was the worst he had seen. So maby i was lucky. =)
Instead of the windows, you can cut off part of the piston skirt which will keep the intake open longer. The windows are easier to screw up where cutting of part of the skirt is relatively simple.
It's crap,the problem is not that the piston is crap the idea is. When you reach the maximum port enhancement you must extend it with welding the casting to enlarge it in some instances. But in my opinion the piston with holes with not draft cleanly at the highest rpm. But anything less it may work well enough.In general the draft or vacuum will be created by the flow the holes disturb that flow as well weaken the piston.
Cheers for the comment- I've been having problems replying to comments but I've fixed it now - The holes in the piston are there during intake through the reed valve. This is to reduce intake pulsing and increase casing filling speeds. Does this work the way it should across all rpm ranges - no - nothing does. thanks again matt
I'm putting on a ported cylinder and while it's apart I was going to add a windowed piston and reed valve. Does it matter if you get a single or double windowed piston? The price is about the same
Matt. Could you tell me why some people even add a third hole above the other 2? I have heard somewhere that it adds power and also helps evacuate hot gasses from underneath the crown especially when desert racing.
The third hole should be under the rings over the exhaust port, which has the effect of adding some fuel to the back pressure wave and help cooling the exhaust port.
I've been looking for some sort of explation about this also. Can't seem to find much about wether windowed piston would work in a none reed valve 2 stroke SOMEONE ADVISE PLEASE?. so.. due to not being able to find any explanation I'm toying with the idea of 'skirting' the piston .. which is shaving off the bottom of the piston when it's at BDC which I'm sure would have the same effect there. Not sure how much lighter it would make the piston though if anything noticeable but sureley would be the same affect as windowed piston?
I have an old jug with one intake hole stripped. I'm porting it now. Will drill/tap and red locktite a new stud. The piston window ? Might do that too. Seems like it would work. Wouldn't it just suck in more fuel/air mix into the crankcase on the pistons way back down ? Even if it was a millisecond?
Will a windowed piston work if the old piston did not have a window? I’m building a 1992 Polaris Trail Boss 250! Any of you have background on 2 stroke performance, let me know!
what is the difference between flat top and crown piston, should i run flat top piston on a standard 2 stroke cylinder kit or i am good with normal crown piston
You've got to remember that this is to allow air to be drawn into the cases when the piston is at BDC. It also helps cool the piston. Does that make sense? thanks for the comment - matt
Pony Power no still makes no sense as then you have fuel going under your piston where it is not supposed to be, never seen a design like this, never seen a carb that would be connected at the bottom of the barrel
@@1stDirtDevil air/fuel mixture is drawn into the crankcase 1st then as piston returns to bdc it forces the mixture into cylinder through transfer ports.
@@dirtygarageguy you missed the ball on this one. Also read Mark Hansons comments below and fess up when a mistake has been made. Your videos are informative and educational and I respect that .. but when something is wrong it's just that
Can I just say that your account of windowed pistons is wrong. For a start the windows are there so at bottom dead centre (which never goes beyond he bottom of the spigot, like you show in this video, unless there is a spacer on the bottom) the mixture can be pushed into the boost ports, nothing more. That's why engines with just side transfers don't need windowed pistons.
LMAO - Look, on the piaggio engine I used in the video this is why the piston is ported/has windows. Its also helps cool the piston and oils the bearings at the small end. Some engines maybe different, but from the 8 ~ 9 engines I've seen with windowed pistons this is how its done. When I align the piston with the cylinder skirt like I did in the video you can see the cut out. What I didn't show was that this was BDC and you can see the transfer ports uncovered if you look from above, down into the bore. Let me ask you this. If the windows in the piston aren't used for this reason, then why have them? The windows in the piston will always be facing the cylinder wall, until thay pass only 2 of the 7 tranfer port (in this engine) and the windows will only give you access to the bottom of the piston. Why would you wanna do that? Weird how the windows are only on one side. Abit like resonance cavities, they're only on the exhaust side? Strange don't you think?
are you swearing at me? they are called boost ports as they usually open fractionally earlier half a mil maybe. I've been tuning engines for 35 years. But I let my engines speak for me . give me your address and I'll come show you how to build a engine be it a R1 or 50 zip. you ingrate
if the cut outs weren't there then the boost ports wouldn't get any charge. It isn't rocket science this. the charge is compressed at BTC to open into the ports. If there wasn't any windows then there would be no need to have a cut out in the spigot. It's 2 stroke tech regardless of piston port or crankcase port. It may be old tech but like others have said bar rotary engines , 2 stroke engines have 90% better power than 4 strokes as some charge has to go down the exhaust , but a good exhaust will push it back in as he inlet timing is longer than exhaust.
