Curious about intake windows on piston

[99LRDblaster]

Well I was out in the garage today looking for the stock needle for the carb and couldn't find it, but did find the old piston from the last rebuild.....it's only got like 5 hours of riding on it and is a perfectly good Wiseco piston but since I was a moron and sent it to another guy to get rebuilt when I started out with ATVs, I had the element of surprise of him giving me an out of round bore. 8-|

Anyways......looking at the piston, I noticed the intake windows on the side of the piston and it kind of strikes me as odd that everybody does intake port work.....yet nobody usually does it concurrently with opening up the intake port windows on the side of the piston.......isn't that kind of self defeating? :-/ What's the point of enlarging intake ports if the windows of the piston don't match the ports you just enlarged? Now I do have auxiliary intake ports to the transfers, but had a question about that as well. Wouldn't the high velocity air travel of auxiliary intake ports to the transfers create turbulence in the high velocity flow of the transfer ports?

As a side note....not sure if anybody has it, but does anybody have any pics of the piston at TDC and BDC and the intake port at those locations?

 

[sicivicdude]

Because the piston intake windows are the weakest part of a piston to begin with. Any weakening is a ticking timebomb.

Nate, post your picture!

Also, the piston intake windows are not blocking the cylinder windows the entire stroke. They are completely out of the way at TDC.

 

[DirtDiggler]

Yeah the skirt is a fragile portion of the piston , don't go weakening it , it will grenade your motor

 

[99LRDblaster]

Ok then......but then what's the massive benefit of the porting the intake on the cylinder. Wouldn't the intake window on the piston be the "rate limiting" factor in all the intake air flow?

 

[York Racing]

Yeah just think, when the pistons are completely original and they blow, they can do lots of damage to your engine. Just image when they are weakened. You can use the comparison of snowmobile clutches. When one blows and hits the sheild under the hood, it will blow the sheild apart and rip the hood apart. Without the sheild, it can kill you.

 

[99LRDblaster]

Yeah just think, when the pistons are completely original and they blow, they can do lots of damage to your engine. Just image when they are weakened. You can use the comparison of snowmobile clutches. When one blows and hits the sheild under the hood, it will blow the sheild apart and rip the hood apart. Without the sheild, it can kill you.

I'm well aware of the damage that can occur if a skirt breaks and spits into a crankcase. My point is what's the point of porting the intake on the cylinder if it's ultimately limited by the smaller windows on the piston?

 

[N8tsNastyBlasty]

Well im th geaunie pig for this one. . . On two previous builds i did just that. I opened up the windows to match the ported intake.I had fresh bores and they ran great.Infact the vid on "triple ports and what they are" is one of those builds. This build i did the same but made them too thin on the edges. I should hav bought the bore gauge i have now, used it to see that the jackass i got it from was full of sh*t and pollutant in the tulsa gene pool. He stated it had a fresh top end and just quit running, but he had another spare piston.In all my wisdom i put it together and ran it then after it blew it up i found it was a good bore but the piston was .5mm too small!!!!

 

[99LRDblaster]

Well im th geaunie pig for this one. . . On two previous builds i did just that. I opened up the windows to match the ported intake.I had fresh bores and they ran great.Infact the vid on "triple ports and what they are" is one of those builds. This build i did the same but made them too thin on the edges. I should hav bought the bore gauge i have now, used it to see that the jackass i got it from was full of sh*t and pollutant in the tulsa gene pool. He stated it had a fresh top end and just quit running, but he had another spare piston.In all my wisdom i put it together and ran it then after it blew it up i found it was a good bore but the piston was .5mm too small!!!!

Did you do it with your current piston setup? Hell even Flotek offers it as a service. I know it can weaken the area where the skirt is located....how much is the question and that's more a matter of how you do it.

 

[revin-it02]

Those intake ports are not even really necessary because as said, at TDC, they are completely out of the way thus allowing a completely unobstructed flow to the crank. In fact most modern 2 strokes have pistons with no windows in them, it helps to keep the skirt strength high because as a cylinder wears the more likely the piston begins to "slap" the side of the cylinder wall.

A common practice for DT200 guys is to upgrade to a non windowed piston (available overseas). Idk why yamaha decided to add the windows to the blaster.

Edit: having those ports on the side of the piston acts as a boost port (I believe more so top end oriented)... but the benefit of having them does not out weigh the risk at all.

 

[Surfrjag]

^ i agree, many were concerned on using the wossner piston in the vitos bb topend because the windows dont line up but i dont see that anyone has had a power loss from going to the wossner piston. however due to lack of options its the only forged piston to get for the bbk... also if your intake has worm holes then incoming air with velosity will be forced to your transfers, closer to the combustion than under the piston.

 

[sicivicdude]

The opposite is true as well 99LRD, When the piston is descending, the pressure under the piston pushes the charge through the transfers. If you opened up the windows more, the piston may not have sufficient force to puch the charge up through there. Maybe it's a very well calculated balancing act, windows big enough to allow flow in but also small enough to force flow up.

 

[99LRDblaster]

Those intake ports are not even really necessary because as said, at TDC, they are completely out of the way thus allowing a completely unobstructed flow to the crank. In fact most modern 2 strokes have pistons with no windows in them, it helps to keep the skirt strength high because as a cylinder wears the more likely the piston begins to "slap" the side of the cylinder wall.

A common practice for DT200 guys is to upgrade to a non windowed piston (available overseas). Idk why yamaha decided to add the windows to the blaster.

Edit: having those ports on the side of the piston acts as a boost port (I believe more so top end oriented)... but the benefit of having them does not out weigh the risk at all.

Exactly. This was going to lead to the next question then........Could you run the Blaster with a shorter skirt piston?.......and I guess you already answered that to an extent.

 

[99LRDblaster]

The opposite is true as well 99LRD, When the piston is descending, the pressure under the piston pushes the charge through the transfers. If you opened up the windows more, the piston may not have sufficient force to puch the charge up through there. Maybe it's a very well calculated balancing act, windows big enough to allow flow in but also small enough to force flow up.

I don't know about that. It would only loss like 1cc of material from the piston therefore when the piston is displacing air in the crankcase and the cylinder is also creating a vacuum up from the transfers it wouldn't matter so much. The balancing of the piston if this was done is something to question though, but then again, so is putting the windows in the piston in the first place.

As a side note, do the companies that offer stroker cranks compensate for the space on the piston skirt where the transfer port slots are?